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A Star of The Cowlitz Cacophony

Monday, March 25th, 2013

The First Star Of The Cowlitz Cacophony…

Luidia foliolata

The winter in the Cowlitz Bay subtidal habitats is a time when nothing much appears to be happening, at least down to around a depth of 18m (60 ft) or so. If large is bigger than a golf ball, then a lot of such large critters are visible; however, most of them, such as Pachycerianthus fimbriatus, the large cerianthid tube anemone, and the weathervane scallop, Patinopecten caurinus, while quite attractive and morphologically interesting, are sessile, and observing their behavioral array takes special skills or goals.

A Weathervane scallop, Patinopecten caurinus. photographed in the ealry winter.

While both species do play noteworthy roles in the natural history drama of Cowlitz Bay, their version of a one dive’s act needs some serious augmentation to keep someone’s interest. Individuals of neither species do much – at least overtly. The anemone can … wait for it … retract down into its tube; … rapidly. Wow!! Golly gee, be still, my beating heart! Woo… Woo… Impressive!!

Tube anemones or cerianthids are commonly found in Cowlitz Bay. Here an individual of Pachycerianthus fimbriatus is blowing in the current at about 20 m. The currents in this bay can common reach about 2km/hr. This individual was on the top of the relatively steep slope leading to much deeper water.

These are the "mucus" and "ptychocysts" which are specialized nematocysts tubes which may extend into the sediment for a meter or more. The animal can retract rapidly into them..

These tubes comprised of “mucus” and “ptychocysts”, specialized nematocysts, may extend into the sediment for a meter or more. The animal can retract rapidly into them when startled.

And the scallop… well, now. It may close its shells, an event truly worth a negative number on the excitement scale. However, if one has been blessed by the fates, a scallop may actually swim (!) by rapidly clapping its valves together a few times. This actually IS exciting. Of course, probably the main reason for any excitement is that the behavior happens so rarely and it is compared to all of the other apparently non-interesting things happening in the vacinity. Normally, Patinopecten scallops are the epitome of dull. An individual spends its life in its little mud depression filtering water to obtain the phytoplankton it eats. Of course, a fair-sized clam such as fully-grown weathervane scallop contains a large mass of delicious muscles along with other nutritious innards. Consequently, the scallop is desirable prey item for any number of predators, including sea stars. Presumably as a result, natural selection has given the scallop its rather spectacular swimming escape response. If its mantle edge is contacted by a single tube foot from a sunflower sea star (Pycnopodia helianthoides), the scallop will usually start to clap its valves together rapidly and repeatedly, forcefully blowing water from between the closing valves forcing the clam up into the overlying water where it is blown away by the current. In a way, calling this “swimming” is overstating the activity, it has no direction and a very limited extent. However, currents in the area are often relatively strong, and the behavior can work to move the scallop away from the star. And that is truly worth the show. And then, after the scallop is done, it can be collected and become dinner for an altogether more lethal predator.

Normally, though, to see some interesting action in this habitat in the winter – and actually, through the rest of the year, as well – it is necessary to look for other predators at work. Fortunately, the array of active predators on the surface, in the sediments and in the waters above the soft-sediment areas of Cowlitz Bay is rich, diverse, and impressive resulting in a lot of opportunities to see “ecology in action”. The variety of predators ranges from diving ducks to dogfish and various other fishes from sculpins to flatfishes to sepiolid squids, nudibranchs, moon snails, and crabs. However, perhaps the most commonly seen, abundant, and continuously active predators in the region are sea stars.

The most commonly seen stars are Pycnopodia helianthoides, the sunflower star, and Luidia foliolata, the snakeskin star, both of which may attain large sizes. Sunflower star individuals have reportedly been measured at 1.5 m (5 feet) in diameter, while I have measured the average size in some Vancouver Island populations to be about 81 cm (32 inches) in diameter. While Luidia foliolata individuals don’t commonly exceed 1 m (39 inches), they are often around 80 cm (31.5 inches) in diameter. Pycnopodia helianthoides has been the object of a lot research, undoubtedly because of their large size and ubiquitous nature. They are probably the most frequently encountered, relatively large, subtidal sea star in the region, and given the demonstrated importance of asteroids in ecologically controlling marine communities, they justifiably have attracted a lot of interest. Luidia foliolata, hasn’t been investigated anywhere nearly as much, and as I spent more than a bit of time watching Cowlitz Bay’s L. foliolata, I thought this post would be a good place to introduce them.

The Mouth That Roared, Wetly

Asteroids are one of the most common educational poster children for invertebrates. Back in those ancient days when I was in high school, some time in a biology class was spent dissecting and examining a poor, rather pathetic, pickled Asterias individual shipped in from the New England coast to Montana where it spent the last of its cohesive existence boring some kids who had never seen a body of water much larger than a small farm pond and who didn’t really care for any animals without fur, fins or feathers. For those few of us who had a bit more on the ball (or so we thought), the asteroid’s pentaradiality along with its implied strangeness was really a pretty good introduction to invertebrate weirdness.

To even the most literate of us, a sea star was a pretty exotic critter; most of us had never seen a living one. Had the specimen been remotely like a living animal, it really would have been a neat thing to examine, I think. Unfortunately, the specimens reeked of formalin, and had a semi-slushy consistency resulting from much of the ossicular skeleton having dissolved in the acidic formaldehyde solution in which they had been stored. Finally, to top everything else off, their normal purplish color had turned to a gawd-awful pale diarrhea brown. Although the dissection wasn’t too hard, determining one tan glob from another was uninspiring to say the least. Still… the effort was made to show us sea stars, and point out some pertinent typical features of their anatomy and biology, such as their complete gut, part of which, the so-called “cardiac stomach” could be extended into the clams that they ate, and the suckered tube feet which used suction to hang on to anything.

Long years later, I was trying to teach many of the same things to my students. Fortunately, we were using specimens more freshly murdered “for the cause”, which weren’t a pasty mess. I hoped the students were able to more carefully examine and “understand” what they were seeing in their specimens than I had been in mine so many years before. Remembering my travails, I tried a number of different ways to make the important points. One of these was that they got to examine other sea stars, to become aware of a bit of the diversity in this awesome group. I always tried to have a live Luidia foliolata available in this exercise, as this was the first of a number of examples I used in my survey course to show the students that the “typical” animals they were learning about were, perhaps, not that “typical” after all.

This specimen of the snakeskin sea star, Luidia foliolata was about 50 cm across the arms.

This close-up image, of the Luidia shown above, shows a patch of green (arrow) due to the presence of a species of endoparasitic green alga. These infections are certainly lethal in some stars, but the outcome of such an infection is unknown in this species.

To a careful observer, even one unfamiliar with sea stars, Luidia specimens are a bit weird. When first observed, there is just something about them that seems “odd”; perhaps it is the spines on edges of the rays, or the odd “scale-like” pattern of plates on the top of the arms, or the non-descript brownish-grey color of the aboral surface, but they leave the impression that they are somehow “different”. And, of course, they are (otherwise the “wily” instructor, aka “the old fart”, would not have put it out for them to examine).

Close examination shows that these animals lack the “suckers” or, more correctly, the “adhesive pads”, on their tube feet. Nonetheless, they are still able to stick to surfaces and hang on to prey. As is now known, sea stars attach themselves to substrata by a duo-gland adhesive system, not suction. Duo-gland adhesive systems were first discovered using Luidia, in part because the stars were seen crawling up the sides of aquaria by some students who flashed on the fact that this is a star that lacks “suckers” on its tube feet, and it shouldn’t be able to climb up a vertical aquarium wall. And if that weren’t odd enough, Luidia do not have a complete gut and do not (actually, cannot) extend their stomach into any clams that they eat. In Cowlitz bay their primary prey are sea cucumbers, although small clams are also on the menu. And all of the prey items are ingested.

A Luidia individual burying as it is feeding. This image was taken in Cowlitz Bay in mid May.

A Luidia individual about 60 cm in diameter is burying as it is feeding. This image was taken in Cowlitz Bay in mid May.

Individuals of Luidia foliolata move over the substrate in Cowlitz Bay at a fairly good pace. Although a big one can move along at about a meter per minute when it is, for some reason, in a hurry, normally their pace is more leisurely. When they decide to feed, they stop, and start to burrow into the substrate. The tube feet move sediments from beneath the arms and central disk out to beside the animal and the whole critter just slowly descends into the substrate, taking a day or so to disappear completely. This activity leaves a large Luidia-sized star-shaped pattern on the sediment surface. Presumably, as it descends, any potential prey items, such as individuals of sea cucumbers in the genus Pentamera, or small bivalves such as Macoma carlottensis are transported to the mouth and ingested. I suspect they stop descending into the sediments when the tube feet have not encountered sufficient numbers of appropriate sea cucumbers for a while. They spend some time, probably no more than a couple of days below the surface, feeding and digesting their meal. When they are done, they rise up, emerge from the sand, regurgitate the indigestible remains of their meal, and mosey off looking for another place to feed.

This is depression left after the departure of a Luidia foliolata that had been feeding. Some of the regurgitated indigestible remains of its meal are in the center area, the remainder were probably scavenged by some other animal such a large hermit crab.

In Cowlitz Bay, the aboral surface of Luidia foliolata individuals is sometimes covered with a layer of the large caprellid amphipods, Caprella gracilior. More than several hundred may be found on the back of a large star. When the star buries in the sediment, these amphipods will be seen filling the star‑shaped pattern with a layer of pink skeleton shrimp. The amphipods remain in place and when the asteroid rises from the sediments, they climb on their host and continue their ride. What these are doing on the back of the asteroid is unclear. This relationship has not been commonly reported, and I have never seen it elsewhere, although it was fairly commonly seen on my dives in Cowlitz Bay. It was just one more thing about this place that made it a worthwhile place to work.

Caprella gracilior on Luidia foliolata.

Caprellids waiting on the sediment for their submerged sea star to emerge.

A mass of Caprella gracilior on the substrate over a buried Luidia foliolata.

The tale of Cowlitz Bay will continue in the future…

Until later,

Cheers, Ron

Tags:Caprella, Cowlitz Bay, foliolata, gracilior, helianthoides, Luidia, natural history, NE Pacific, northeast pacific ocean, pacific northwest, Pycnopodia, San Juan Islands, Shimek, soft-sediment benthos, soft-sediment ecology, Waldron Island, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | Comments Closed

Benthic Natural History In Cowlitz Bay, Waldron Island.

Monday, February 4th, 2013

Passing into deeper water from the eelgrass beds found in the shallow nearshore environments of many embayments of the American San Juan Islands, the highly organic muddy sand substrate is typically replaced by a less organic or “cleaner” mixture of sand and silt. Such a transition is certainly the case in Cowlitz Bay of Waldron Island. I can verify that the silty-sand substrate continues to, at least, a depth of 50 m (165 feet). Except for emergent rocky outcrops, this habitat type is likely characteristic of all the deeper water of Cowlitz Bay and the nearby San Juan Channel and Boundary Passages.

The tidal ranges that distinguish this region, coupled with its geography, mean that high tidal currents are the norm, and the volume of tidal water movement is immense. All of this, added to the dense, rich plankton found in those waters creates a habitat that is probably nearly optimal for suspension feeders. As a result, virtually all of the hard subtidal real estate is occupied some sort of organism specialized to grab food or nutrients from the water moving past them. Subtidal rocky substrates are often characterized by dense populations of suspension-feeding epifaunal sea cucumbers. And, although it may seem unlikely, some of the unconsolidated, silty-sand, habitats are also dominated by dendrochirote holothurians, albeit in this case these cases they are infaunal, not epifaunal. Infaunal sea cucumbers dominate the subtidal Cowlitz Bay benthic environment below 10 m.

0 - Pentamera cf populifera 11vii77 6m Cowlitz Bay, Waldron Id. 01 Juveniles

Pentamera individuals extending from the bottom of Cowlitz Bay, 11 July, 1977. The abundance of the adult animals exceeds 20,000/m2 (about 0.2 m2) is visible.

Pentamera sp. indivdiual with some of the many juveniles in the sediment circled. Taken 11 July, 1977.

Pentamera sp. adult indivdiual with some of the many juveniles in the sediment circled. Taken 11 July, 1977. The juveniles become evident in the sediments in early summer, indicating spawning likely occurs in the spring.

Although a few other species are rarely found, the vast majority of these suspension-feeding, infaunal cukes belong to a few species of Pentamera. The individuals belonging to the different species are relatively similar in size, shape, and coloration making them effectively indistinguishable in the field by non-specialists, so I will refer to them all as Pentamera. Living buried in the sediments they feed by extending a small portion of the oral end of the body above the sediments. This exposes just a bit of the animal, primarily the mouth, and its surrounding crown of highly-branched feeding tentacles.

White, and only about 2 or 3 cm long, these relatively small sea cucumbers are often found in beds so very dense that in the summer, the benthic sediment appears snow-covered due to the many tentacles visible. In the clear water of the late autumn and winter plankton-free periods, these holothuroids do not feed. Presumably quiescent, they remain buried under the sediment surface. During these seasons, the habitat looks relatively barren; with only scattered larger animals, such as individuals of tube anemones, Pachycerianthus fimbriatus, orange sea pens, Ptilosarcus gurneyi, snake-skin stars, Luidia foliolata, sunflower stars, Pycnopodia helianthoides, or weather-vane scallops, Patinopecten caurinus being evident to the casual observer.

Patinopecten caurinus, the Weather Vane Scallop, about 15 cm (6" in) in diameter. Photographed in the Summer (June, 1977). Note the visible Pentamera cukes.

Patinopecten caurinus, the Weather Vane Scallop, about 15 cm (6″ in) in diameter. Photographed in the Summer (June, 1977) on the benthic subtrate of Cowlitz Bay; note the abundant Pentamera cukes.

Patinopecten caurinus. Area as before, except it was photographed in the ealry winter (December, 1976). Note the lack of visible cukes.

With beginning of the diatom bloom starting in February, smaller life “returns to”, or more correctly, becomes evident again on the benthos. The sediment becomes covered completely with a thick and rather ugly, dense dark brown film, consisting of several species of microalgae, primarily diatoms and dinoflagellates.

Unidentified Polyclad Turbellarian, photographed in April, 1983. The "black material" is the diatom film that is found in this area in the spring.

Unidentified Polyclad Turbellarian, anterior end to the left, photographed on April, 1983 on the substrate in Cowlitz Bay. The “black material” is the diatom film that is found in this area in the spring.

By early March, many turbellarian flatworms of several visually distinctive types are commonly found gliding over the brown algal film and sediments. These small worms, each only a few millimeters long, may be distinguished by their differing shapes and color patterns. Although common, at least in the spring, virtually nothing is known of their natural history. Shortly after the worms become common, small caprellid amphipods, otherwise known as “skeleton shrimp”, seem to appear out of nowhere and are soon found covering the diatom film. These small, about a centimeter (0.4 inch) long, animals reproduce rapidly and soon reach abundances around 1 animal per square centimeter, or a density of 10,000 animals per square meter. As they become common, pelagic predators, such as ctenophores and chaetognaths, may be observed grabbing copepods off the bottom and swimming back up into the overlying water.

A Sagitta (planktonic chaetognath carnivore) photograph near the bottom, hunting for caprellids.

A Sagitta (an almost completely transparent planktonic chaetognath and a predator normally on zooplankton) photographed near the bottom, where I have seen other individuals grab caprellids.

By the middle of March, the spring plankton are in full bloom and the Pentamera are beginning to feed. By moving up and down in the sediment, the resulting bioturbation soon destroys the diatom film, and the sediment becomes relatively clean again. Snake-skin stars, Luidia foliolata, are common in this habitat where these sea cucumbers are their principal prey. Caprellid amphipods, Caprella gracilior, and small hermit crabs are often seen on the aboral surface of the stars. The Luidia-sized, star‑shaped, feeding depressions, along with the small piles of regurgitated remains attest to the star’s feeding habits. Pycnopodia helianthoides is also commonly found in these beds and may also feed on the sea cucumbers. Some aspects of the natural history of Luidia in this habitat will be discussed in subsequent post.

Individuals of the large, up to 15 cm (6 inches) in diameter, weathervane scallops, Patinopecten caurinus, rather rare elsewhere in the San Juans, are found not uncommonly in these cucumber beds. They are found lying in shallow, somewhat bowl-shaped, depressions probably created over time by the scallops’ feeding currents which might gently displace and excavate the sediments. Eaten by the sunflower star, the scallops will swim in response to being touched by the predator. They are not particularly vigorous swimmers, however, nor do they seem to start swimming immediately, thus they could be captured relatively easily. Their shells are a common feature in this habitat, so presumably some predators are capturing them. These large shells, either living or dead, provide about the only hard substrate in these habitats, and are often covered with barnacles, algae, or occasionally attached bryozoans or hydroids.

Both color varieties or “morphs” of Pachycerianthus fimbriatus found in the benthos of Cowlitz Bay.

The tube-dwelling anemone, Pachycerianthus fimbriatus, is particularly common in this habitat, and becomes very abundant just below the dense Pentamera beds in the more silty habitats of the steeply sloping areas. Pachycerianthus individuals may be colored either gray or a dark brown to maroon. These do not appear to represent separate species, and the different colors have no known significance. Close examination of the anemones will show some very small epifaunal, possibly stenothoid, amphipods visible as small dots moving over the anemone’s body and tentacles. During the spring and early summer periods of dense plankton, it is possible to watch the Pachycerianthus catch copepods, and other small crustacean zooplankton, with their long tapering, thin, tentacles.

An ectoparasitic, or commensal, stenothoid amphipod on a Pachycerianthus tentacle. Assuming the tentacles are about the same size (and they are) compare this amphipod’s size to that of the hyperiid amphipod captured as food by a different tube anemone (next illustration).

A small Pachycerianthus fimbriatus with a captured planktonic hyperiid amphipod (arrow).

These slightly deeper habitats where Pachycerianthus is most common, ranging downward from about 10m (33 feet) in depth, have a silty sand substrate. Pentamera are found in these regions, they are just not as abundant as they are in the dense assemblages in shallower water. Individuals of the orange sea pen, Ptilosarcus gurneyi, are well represented in these deeper habitats, and although they are not as abundant here as they are in the dense sea pen beds of the lower Puget Sound region, they are nonetheless found relatively frequently. Occasionally, a different type of pennatulacean, a sea whip, may be found. In the genus Virgularia, these whips are narrow pennatulaceans, with short “leaves”. At least two species within this genus found in our waters and they are not terribly difficult to distinguish in the field. The species found in Cowlitz bay is small, tan to whitish, with small “leaves” and is seldom over 15 cm (6 inches) in height. The feeding zooids often appear to arise from directly from the central stalk. The other species, found in other areas, such as Lopez Sound, is larger and more robust, pink to orange, and often reaches heights of 50 or more centimeters. This species has larger relatively distinct “leaves” with the gastrozooids on them.

A small, about 8 cm (3.5 in) high, pennatulacean, probably a species of Virgularia.

Several nudibranch species are also found in these areas, most of which are probably preying on the cnidarians. The largest and most evident of these are individuals of Dendronotus iris. These are amongst the largest local snails; in this area they often reach lengths exceeding 25 cm (10 inches) which is probably due to the high abundances of their preferred prey, the Pachycerianthus anemones. They approach the anemones by slowly crawling under the tentacle crown, to where the anemones extend from their tube. They, then, reach up rapidly, bite, and hang on to either a mass of tentacles or even the anemone’s column. Generally, the Pachycerianthus rapidly withdraws into its tube when it is bitten, and in these cases, it often pulls the predator in with it. Sometime later, the Dendronotus iris often crawls out of the now empty tube, and may set off in search of another anemone. The nudibranch may, at times, lay its loosely coiled egg masses attached to the Pachycerianthus tube, bits of shell, or just bits of the sediment.

0 - Dendronotus iris Cowlitz Bay, Waldron Id. -7m 11vii77 WA 01

A 10 cm (4 inch) long Dendronotus iris in Cowlitz Bay. Photographed at a depth about 7 m. This large nudibranch reaches over 30 cm (12 inches) in length, and eats Pachycerianthus.

Other nudibranch specimens are found in the area, and they can be relatively common at certain times of the year. Dendronotus albus specimens will be found occasionally, preying on those few hydroids that are found attached to the shell fragments or other hard substrata present on the sediment surface. These nudibranchs are slender and may reach lengths of about 10 cm. The basic ground color is white, but the tips of the branched cerata are tipped in orange. Individuals of another dendronotid, Dendronotus albopunctatus, are often abundant in the spring. These animals are brown to pink and freckled with small light dots. They only reaches lengths of 2 to 3 cm (up to about 1.5 inches), but they are recognizable by their somewhat “oversized”, relatively large, “front” cerata, which are often about a centimeter in length. Little is known of the natural history of this species, although it is likely a predator on small cnidarians.

Dendronotus albus.

Dendronotus albus is a not uncommon, small, about 3 cm, (1.2 inches) long, nudibranch in habitats such as those found in Cowlitz Bay. It eats hydroids, as this individual was doing when photographed

0 - Dendronotus albopunctatus Cowlitz Bay, Waldron Id. -9m 28iv83 WA 01

Dendronotus albopunctatus, about 3 cm (1.2 inches) long on the sediment of Cowlitz Bay. It also has been seen to eat hydroids.

0 - Acanthodoris brunnea, Cowlitz Bay, Waldron Id., -9m, 13v86 WA 01

Acanthodoris brunnea, about 2 cm (0.8 inch) long, photographed on the sediment of Cowlitz Bay. Reported to eat bryozoans, this dorid species is found on muddy-sand, a habitat notably lacking in bryozoans. In this region and habitat, it is likely eating something other than bryozans.

Acanthodoris brunnea is another nudibranch species that is somewhat common at times in this habitat; little is known of its natural history. These animals are small dorids, roughly the same size as Dentdronotus albopunctatus, reaching lengths of 2 to 3 cm (up to about 1.5 inches). Their basic coloration is brown; the individuals are covered with distinctive relatively large papillae on the back. This species is considered to be predatory on bryozoans, but that is unlikely in this region as bryozoans are exceedingly rare in this habitat.

Also found in these areas are pennatulid-eating nudibranchs in the genus Tritonia. The most abundant of these are individuals of the small white Tritonia festiva, described in the earlier post on sea pen beds. Here, as well, T. festiva individuals seem to prey on Ptilosarcus. Individuals of the larger, orange nudibranch, Tritonia diomedea, are also occasionally seen in these areas. They seem to prefer the larger Virgularia as prey.

Large shelled gastropods are relatively rare in this particular habitat, although several smaller species can be very abundant. Perhaps the largest commonly found gastropod, and certainly one of the most beautiful, is the wentletrap, Epitonium indianorum. These animals are often found buried near to the bases of the tube anemones upon which they feed. As with most snails, wentletraps have a feeding organ called a radula; unlike the “classic” gastropodan radula which functions something like a rasp, filing off pieces of tissue, the wentletraps’ radulae are highly modified and look like an inverted thimble lined on the inside with sharp teeth. A wentletrap crawls up to the anemone and pokes the anemone with its radula everting the “thimble” in the process. This turns the radula inside out, which in turn, carves a circular hole in the tissues on the side of the anemone. The lacerated tissues are eaten, and the snail extends its proboscis which has the radula on its tip through the hole and proceeds to use the radula to cut up and eat other internal anemone tissues. These snails reach lengths of 3 cm or more, and don’t seem to move much once they have found an anemone to feed on. It is recognized by the distinct axial ribs, the rounded aperture, and the relatively high spire.

One cephalopod can be relatively common in the lower slope areas, the Pacific Bob‑Tailed Squid, Rossia pacifica. This small benthic squid lives buried in the bottom during the day. If a diver is careful, they can sometimes see the slight depression that the Rossia occupies, and then can make out the eyes watching him. The hole for the siphon is generally visible and if approached carefully, one can see the regular breathing movements of the mantle. Rossia pacifica reaches lengths of about 10 cm, and seems to live about a year or eighteen months. They have an interesting, stereotyped, escape response which I have described, briefly, in a previous post. This small squid preys on small shrimps, crabs, and fishes, and is a nocturnal hunter.

Well, that’s enough for now… 🙂

More later,

Cheers, Ron

Tags:Acanthodoris brunnea, behavior, benthos, chaetognatha, Cowlitz Bay, Dendronotus, Dendronotus albopunctatus, Dendronotus albus, Dendronotus iris, diving, ecology, epitonium, indianorum, invertebrates, marine biology, mollusca, NE Pacific, northeast pacific ocean, Pachycerianthus fimbriatus, pacific northwest, Patinopecten, Pentamera, predator-prey interactions, Ptilosarcus gurneyi, Sagitta, Salish Sea, San Juan Islands, seasonality, Shimek, soft-sediment benthos, stenothoid amphipod, Tritonia diomedia, Tritonia festiva, turbellaria, Virgularia, Waldron Island, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | 2 Comments »

A Pentamera-Dominated Sandy Environment

Wednesday, August 29th, 2012

The Place – Where, When, Why.

The American San Juan Islands in the Northern Puget Sound. Waldron Island is at the top (North), CB = Cowlitz Bay. The Friday Harbor Laboratories location is indicated by the colored star on San Juan Island.

Cowlitz Bay, Waldron Island, Washinton. Viewed from the north, July, 1976. The primary study area is indicated in blue, the rocky reef used for orientatioin is indicated in yellow.

Cowlitz Bay of Waldron Island, Washington initially attracted my attention in the early 1970s as the result of a collecting trip undertaken out of the University of Washington Friday Harbor Laboratories (FHL) as part of my doctoral dissertation research. These trips used a converted fishing boat which was configured to pull a “biological dredge”, which is effectively a metal frame with some sort of netting attached to retain the catch.

M/V HYDAH
Operated under contract to the University of Washington’s Friday Harbor Laboratories, this was the boat I used for dredging in the 1970s. Photographed in San Juan Channel, July, 1976.

This dredge is lowered to the sea floor and pulled along it for some, supposedly, known distance. Depending on vessel’s velocity, the configuration of the dredge frame, and the substrate, the apparatus will – optimally – dig into the bottom and collect a sample of that bottom along with what is in it. The dredge is returned to the surface, emptied on to a “sorting table”, typically, a large box-like apparatus which contains the sample. The sample is rinsed and organisms of interest are collected.

Samples collected in this manner by oceanographic vessels using well-designed dredges can be taken in a reasonably precise manner. For example, if the apparatus is pulled at a given speed, it will dig into the bottom of a certain type to a known depth. Our samples were nowhere near as well-controlled! In shallow waters, 60 to 200 feet, we could be reasonably sure of getting something. At other times, it was quite feasible to have the dredge hang up on an underwater obstacle no sample would be obtained. Very occasionally the apparatus could be lost, along with all of the cable pulling it. This latter proposition is, at the very least, expensive and, at least to the person in charge, embarrassing. Consequently, one had to choose one’s dredging sites with care, and hope that the boat driver knew what he/she was doing.

To help pay for my studies, I applied for and was awarded what at the time was referred to as an National Science Foundation doctoral dissertation grant. As part of the grant, I requested funding to explore habitats in the region for various of the turrid gastropods I was studying. I used these funds to pay for dredging trips to the soft sediment habitats that nobody else was really interested in investigating. I would sort through the materials obtained by the various dredges and if I found some of my “target” snails, and if the area seemed otherwise interesting and diveable, I would try to do some diving in the area and ascertain the habitat first hand.

I chose to dredge in Cowlitz Bay because it was off of the beaten track. Most of the dredging trips out of the FHL went to the same places over and over, ignoring other areas both near and far from the labs. As I could readily get information from the commonly dredged places, I decided to spend my grant’s money to go elsewhere. I didn’t find much in the way of turrids in the dredging results from Cowlitz Bay, but I did find some live scaphopods, Rhabdus rectius, to be exact.

Scaphopods, 3 species commonly found in the Pacific Northwest. Gadila aberrans is not found in Cowlitz Bay, the sediment is unsuitable, and the salinity is likely too low.

As I had an abiding interest in scaphopods predating my interest in turrids, I later spent some relatively intensive field work looking at the scaphopods and other critters found in the bay. I did over 30 dives in Cowlitz Bay, most of them with my friend, Dr. F. Scott McEuen, as my diving partner. Our objectives, on many of these dives, were doing various types of quantitative sampling, either doing transect surveys or collect samples for later laboratory analyses. On other dives, we simply took pictures. Scott was investigating the sea cucumbers in the genus Pentamera which are found there in absolutely mind-boggling numbers, and I was looking at the scaphopods whose abundances, while significantly less than boggling, were still high enough to make sampling worthwhile. Additionally, there were a lot of other interesting things of one sort or another, either in the bottom, on the bottom, or swimming above the bottom of the bay that served to tweak our collective or individual fancies bringing us back to the bay time and time again.

Sea cucumbers in the genus Pentamera in the substate in 20 feet (6 m) of water in Cowlitz Bay in July, 1977. Juveniles of the year have just settled, but are too small to see in this image; all the cukes that are visible are adults. The cucumber population density is in excess of 50,000 animals per square meter.

The Place

This large west-facing embayment opens toward the west. Most of my diving was done in the northern half of the bay. There is an underwater ridge running more or less east-west located in the middle to eastern portion of the bay, about one third of the distance from the bluffs forming the southern edge of the bay to the spit of land forming the northern edge. The ridge has a kelp bed growing from it, so to orient ourselves when we arrived, we would find the kelp bed and go north in our boat until we had covered about half the distance to the northern shore. There we’d anchor, typically in about 60 feet (18 m) of water. When we anchored we were a long way from any shoreline, easily a half mile (700 to 800 m), and on cold, drizzly, gray winter days, it seemed a lot further. This meant that when we hit the bottom after following the anchor line down, we took careful compass bearings so that when we needed to surface we could find our way back to the vicinity of the boat. Or at least that was the plan.

The substrate in the area was sand or sandy-mud and was generally gently sloping to the west or south. The deepest we normally swam to was about 90 feet (27 m), and most of our dives were between 20 to 60 feet (6m to 18m). Occasionally, we did a dive in the shallower eastern reaches of the bay. Over the course of several years, I made dives in this region in every season, and what I will discuss in this sequence of blog articles is a summary and compilation of my diving logs from all of the dives.

Near-shore shallow waters of the NE Pacific are tremendously influenced by the local climate. The annual cycle is worth mentioning here, as I will discuss details of it in passing. It is not too much of a stretch to say, “Everything depends on the weather”. Undoubtedly, climate change is affecting the subtidal communities of this region; while I can guess some of the changes due to global alterations, I don’t think that is a profitable course of action. These images were taken in the period from about 1976 through 1986, and I will use the observations I made at the time

The Seasons

The seasons of the marine shallow subtidal habitats in this part of the Pacific Northwest region, basically the shallow waters of Northern Washington, British Columbia, and Southeastern Alaska, bear only a passing resemblance to the seasons likely to be encountered above the waterline (Table 1). As with the terrestrial environment, the primary driver of seasonality is sunlight, but sunlight’s effects come in pure and modified forms. Pure solar illumination is really pretty uncommon in this region, and typically is found mostly in the summer; generally these bursts of sunlight result in phytoplankton blooms that degrade visibility significantly. The blooms tend to alternate, in textbook fashion, with periods of very clear water, probably due to zooplankton blooms. When we were diving in this area, the visibility we would expect was predictable most of the year, but in the later summer, as the old carnie saying goes, “You pays your money and you takes your chances.”

The rest of the time, sunlight is filtered and muted through clouds. While solar illumination is, of course, the ultimate driver for the region’s weather both illumination and weather events working together results in the overall marine environment of the entire region exhibiting remarkably stable physical conditions. Temperature variations below 16.5 feet (5 m) are minor, seldom varying by more than a couple of Celsius degrees, and generally no more than about 6 or 7 Fahrenheit degrees. Salinity fluctuates much more drastically due to the rainfall and runoff from snowmelt, but even so, deeper areas, below 10 m (33 feet) remain reasonably stable. Freshwater layers due to major runoff events such as floods tend to flow out over the more stable underlying areas. This is not to say there are no effects due to these factors, but major salinity and temperature effects are abnormal, variable in extent and degree, and relatively unpredictable.

Table 1. Subtidal Seasons Of Cowlitz Bay, And The Northern San Juan Islands, Washington.
Season	Starts	Ends	Cause	Manifestation
Dark	Mid-October	Mid-February	Low Illumination, Cool Temperatures	“Everything is shut down” Clear water, no plankton
Diatom	Mid-February	Early-March	Increasing illumination and temperature, Nutrients from spriing runoff increase	Substrate becomes covered with a thick diatom coat. There is clear water with scarce plankton. Filter-feeders start emergence
First Plankton	Early-March	Late-March	As Above	Phytoplankton blooms; Water becomes greenish and visibility drops; Substrate diatom layer becomes thinner; Some benthic herbivores present; Filter-feeders emerged.
Second Plankton	Late-March	Late – May	As Above	Zooplankton bloom becomes noticeable; Phytoplankton presence is less, Water visibility increases slightly, Water color changes from green to gray-green/aquamarine; Spawning is occurring with some benthos, Diatom cover is largely gone, Benthic herbivores are common.
Settlement	Late – May	August	Nutrients from runoff become less, Illumination and temperature still increasing	Small animals and settled juveniles become very common. Plankton pulses, going from phytoplankton dominated to zooplankton dominated to no plankton (clear water) in short (week long) sequences; Water often cloudy, greenish white.
Growth	August	Early- October	Runoff absent, Illumination begins to drop, Temperature peaks.	Filter-feeders evident; Benthic predators very active. Diatom cover almost gone. Small predators disappearing.
Shutdown	Early October	Mid to LateOctober	Temperature drops, Illumination drops, Rains begin.	Plankton disappears; Filter-feeders shut down. Water clears up, becomes dark green. Diatoms on benthos gone.

The Current Conditions Are….

Cowlitz Bay, as in the rest of the San Juan Islands, has semidiurnal tides which generally have a pattern of two unequal high tides interspersed with two unequal low tides. The tidal cycle is primarily driven by the lunar cycle, and the relative magnitudes of the highs and lows fluctuate through the year following the lunar calendar. The most extreme tides, the largest difference between the higher high and the lower low tides, are found near the solstices, while the least extreme tides are found near the equinoxes. The differences between the most extreme tides is reflected in the velocity of water currents, and the unconsolidated substrate in the bay belies the rather strong currents that may occur there.

Coming up next… the animals and interactions.

Tags:benthic ecology, Cowlitz Bay, currents, ecology, habitat, marine biology, natural history, NE Pacific, northeast pacific ocean, pacific northwest, San Juan Islands, scaphopoda, soft-sediment benthos, soft-sediment ecology, Waldron Island, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | Comments Closed

To Pen A Tale Of Pens…

Wednesday, September 28th, 2011

Life History

The term “life history” is really a misnomer. What the term really means is the generalized “story” of an average individual’s life. Probably the animal whose life history is best known is the human. Broken down by geographical region, and other demographics, it is possible to predict with surprising accuracy the life span, as well as the major life experiences, such as the number of offspring, and when they occur, for the average individual of many human populations. In the case of humans, the driving force for the accumulation of such knowledge is not the desire for “abstract knowledge,” but rather the desire to make a profit. On such knowledge is the insurance industry built, and it is based to a great extent on studies of human life history profiles extended to the greatest precision possible. We also know the life histories of a large number of other, mostly terrestrial, organisms. In these cases, biologists have spent a great deal of time studying populations of these animals and have noted when the animals are born, when they die, how long they live, when they mate, and so on. All of these data can be massaged and manipulated statistically to provide a good understanding of the essential experiences of an average member of those species.

However, once we pass out of the terrestrial realm and into the oceanic environment, our ability to see all of the relevant aspects of any given organism’s life is significantly obscured by a wall of water. To accumulate the data and the observational knowledge to flesh out a “life history” takes good, down to earth (or ocean bottom), tedious, long-term, expensive and dedicated research. Because of the effort involved, such work has been completed for precious few animals, most of which are temperate, due primarily to the prevalence of marine laboratories in temperate regions.

The Story

In this essay, I summarize the results of a series of research projects concerning a temperate octocoral, the sea pen, Ptilosarcus gurneyi. This species has also been known as Ptilosarcus quadrangulare, Leioptilus quadrangulare, Leioptilus guerneyi, and Ptilosarcus quadrangularis, but these names have long been considered to be junior synonyms. Nonetheless, they still turn up from time to time, particularly in comments on the internet. The basic research on which this article is based was reported in two papers (Chia and Crawford, 1973; Birkeland, 1974), but in addition, there is a significant amount of my own hitherto unpublished research. For ease of readability, I will not cite either main reference again. If the reader is interested in more detail, please read these articles or contact me directly. In total, this information represents several thousand person-hours of observational time. As far as I know, no similar body of knowledge exists for any tropical octocoral, although there are similar accumulations of information regarding some Mediterranean gorgonians. I hope, however, that this example will give some appreciation for the life history of, at least, one type of octocoral. Perhaps, as well, this essay will present the types of data needed to discuss the biology of these animals.

Figure 1. A mature Ptilosarcus gurneyi individual extended about 50 cm out of the sediment. The primary polyp consists of the base which extends into the sediment, and the rachis or stalk extending from the base up between the “leaves.” The gastrozooids or feeding polyps are found on the outside of the leaf edges, while the siphonozooids, or pumping individuals, are found in the orange regions on the sides of the rachis. The “warts” on a few of the leaves are caused by a parasitic isopod living inside the pen’s tissues.

Figure 2. A portion of a sea pen bed in the central Puget Sound region, the depth was about 15 m. Water flow was from the left, and the foreground field of view is about 1.5 meters (5 feet) across.

Sea pens are octocorals. Taxonomically, they are placed in the Order Pennatulacea of the Subclass Octocorallia (= Alcyonaria), in the Class Anthozoa of the Phylum Cnidaria. All of this jargon means they are animals whose major body parts consist of modified polyps. Being octocorallians, their polyps show an octamerous or eight-fold symmetry most obviously manifested by the presence of eight tentacles around the mouth of the feeding polyps, or gastrozooids. These eight tentacles each have a series of small side branches, a condition referred to as “pinnate branching.” Unlike other octocorals, sea pens are mobile. While they are sessile, living in unconsolidated ocean bottom sediments, they are not fastened to the substrate and at least some sea pens are capable of significant locomotion.

The adult sea pen is body considered to be comprised by the fused modifications of three types of polyps. The base and central stalk region, or rachis, is considered to be the modified original polyp. The feeding polyps possess tentacles are called gastrozooids and typically found either extending from the surface of the rachis much like the spokes of an umbrella, or on lateral extensions from the rachis, the “leaves”. Depending on the sea pen species and the adult size, there may be from about ten to many thousand gastrozooids. Embedded in the rachis surface are the siphonozooids; modified polyps lacking tentacles. These structures consist of a “mouth” which is lined with microscopically sized, beating, hair-like projections called “cilia.” Siphonozooids pump water into the body of the colony. The colony has quite an intricate system of channels which allow the movement of water and nutrients throughout the body. The forces necessary for the water movement comes from muscular contraction of the body and the beating of the cilia lining the water channels.

Figure 3. The “leaf” edges of a mature sea pen showing many gastrozooids. The leaves are oriented into the current, and can generate hydrodynamic lift. When the animals are disturbed, they may orient into the current, inflate, climb out of the sediment, and drift away in the current.

Figure 4. The siphonozooid region of a sea pen rachis; siphonozooids, basically polyps without tentacles, pump water into the pen. Small stenothoid amphipods are commonly found on the pen’s surface.

Sea pens are like the late comic, Rodney Dangerfield, in that they “don’t get no respect.” They are often largely ignored in invertebrate zoology classes, and hardly discussed at all in many marine biology classes. Nonetheless, they are surprisingly abundant and, in fact, may be the dominant cnidarians over large regions of the earth’s surface; areas where stony corals, other octocorals, and most sea anemones are essentially absent, the deep sea soft-sediment bottom. The largest of Earth’s ecosystems, much of this area is characterized by the presence of sea pens. I doubt anybody has made the calculations, but I suspect that it would a sure bet to say that the biomass of sea pen living tissue exceeds that of all other benthic cnidarians combined.

Figure 5. A small sea pen that had been drifting across the bottom.

Ptilosarcus guneyi, the subject of this article is found throughout the Northeastern Pacific from Alaska to Southern California. Fully expanded, large, adult individuals may extend for about 60 cm (2 feet) out of the sediments, with the base extending into the sediments another 15 to 30 cm (6 to 12 inches). Fully contracted, these same large adults will be about 15 to 20 cm (6 to 8 inches) long. The body color ranges from a pale cream to deep orange red. The body morphology may remind one of a fat, carrot-colored quill pen; hence, “sea pens”; alternatively, when contracted, they may remind one more, simply, of carrots. Internally, they contain a single large calcareous and proteinaceous style. The size of the style is related to the age of the sea pens, and measurements of it may be used to obtain ages of individuals in a population. Ptilosarcus gurneyi are found in shallow waters, ranging from the lowest intertidal zone to depths of about 500 feet, but are most abundant in shallow waters. And, the animals in this species may be amazingly abundant. In the Puget Sound areas studied by Birkland, the number of sea pens averaged about 23 pens per square meter, with about 8 of these being three or more years in age. Sea pen beds typically reach depths in excess of 50 m, and extend laterally for dozens of kilometers, interrupted only physical features such as scouring by river currents, dredged harbors and the like. Although these beds are discontinuous, because of the currents in the area, they are not isolated from adjacent beds. Larvae are dispersed throughout the region, and even adult pens may move laterally great distances. The adults can crawl up out of the sediment, inflate with water, and drift along in the currents, much like an underwater balloon.

Figure 6. A sea pen photographed in the field, shortly after the spring equinox, a day or two prior to spawning, showing the eggs in the gastrozooids. The extended nature of the gastrozooids is visible in the image. Their guts extend through the leaves into the rachis where they meet and fuse with a large internal canal system that extends throughout the animal. The eggs are about 0.6 mm in diameter.

The sea pens have a cyclic behavior pattern of inflation, feeding, and then deflation. They may do this several times a day, and the rhythm appears more-or-less unrelated to feeding or available foods. At any one time, Birkeland found that only about a fourth of the pens were exposed, with the rest being completely buried in the sediments, often to a depth of 30 cm (1 foot) or more. The sea pens totally dominate and structure these communities. Very few other macroscopic animals live in the sediments of sea pen beds, possibly because the continuous bioturbation resulting from the movement of the sea pens.

As one might expect, the shear mass of sea pen flesh in these areas is a resource that has not “gone unnoticed” by predators. In fact, there is an amazing variety of predators that have become adapted and, in some cases, totally dependent upon the sea pen populations. In many respects, Ptilosarcus gurneyi in sea pen beds fills an ecological position similar to the huge herds of bison that used to occupy the American Great Plains or the grazing animals of the Serengeti. In each of these cases, whole food webs were built upon the basic primary resource species. Sea pens are suspension-feeders eating small organic particulate material, larvae, and other small zooplankton. In turn, they are the food of a wide variety of benthic predators. When small, they are eaten by several, mostly small, nudibranch species. As they grow they become too large for some of the nudibranchs, although others may still eat them. However, as the pens grow to maturity, they become the prey of several sea star species. At the apex of this food web is yet another sea star, which preys on those stars.

In The Water

Ptilosarcus gurneyi generally spawns in the first week following the spring equinox. In the laboratory during that time, sunlight hitting a tank of gravid sea pens that has been shaded will induce spawning. The eggs are large, about 600 μm across, and a mature female colony will produce upwards of 200,000 of them. Fertilization occurs in water column. Embryonic development occurs over about 3 days at 12º C, and results in a foot-ball shaped, mobile, non-feeding, planula larva about 1 mm long. After about five days, planulae raised in the laboratory begin to swim to the bottom of their containers. By inference, the same behavior in nature would move them toward the ocean bottom. In laboratory containers, they repeatedly swim vertically downward and touch their anterior end to the sediments. If the sediments are coarse sand, with particle diameters in the 0.250 to 0.500 μm range, they will stick to, and “settle” into that sediment and begin to metamorphose into a small sea pen. If appropriate sediments are not available, settlement and metamorphosis may be delayed for as much as a month. Without appropriate sediment, the animal will die. These pens are found in an areas dominated by vigorous tidal flows and offshore currents. In a month, the larvae could disperse over great distances.

Figure 7. Drawings done from life of developing Ptilosarcus gurneyi embryos. Top. The newly released ovum. Center. Embryo at about the beginning of the 4-cell stage; about 4 hours old. Cleavage is incomplete and doesn’t extend through the embryo. Bottom: Embryo between the 4 and 8 cell stages, about 6 hours after fertilization.

Figure 8. Drawings done from life of developing Ptilosarcus gurneyi. Top. The 8-celled stage is about the same diameter as a newly spawned egg; about 7 hours after fertilization. Center. The embryo is at the 16-celled stage; about 8 hours old. Bottom: This embryo is at the blastula stage, about 12 hours old.

Figure 9. Drawings done from life of developing Ptilosarcus gurneyi. Gastrula stages; individual cells no longer visible. Left. Early gastrula, irregularly shaped, about 24 hours old. Center. Gastrula, about 36 hours old. Right: Late Gastrula, the embryo has become ciliated and is swimming; 2 days old.

Figure 10. Drawings done from life of developing Ptilosarcus gurneyi. Top. Early planula, about 3 days old. Bottom: Planula larva at 4 days old.

Figure 11. Drawings, done from life, of developing Ptilosarcus gurneyi. Top. Planula at 5 days. Center. Planula, settling, about 6 days. Bottom: Settled larva undergoing metamorphosis into a juvenile sea pen; about 8 days of age. The animal is capable of contraction and elongation.

Once metamorphosis begins development to a feeding individual is rapid, with the first polyp having functional tentacles within 2 weeks of spawning. Active feeding begins soon thereafter and given sufficient food, growth is relatively rapid. Once the sea pens have settled, they become potential prey for many predators. Birkeland found that small sea pens are eaten at the rate of about 200 per year per square meter by small nudibranchs. If they can survive this period, they get large enough to avoid becoming prey for the smallest of the nudibranchs, but they graduate into become food for sea stars. Sea pens grow at a relatively constant rate, reaching sexual maturity when they are about 24 cm (9. 4 inches) tall and five years old.

Both growth and predation rates are continuous; there is no cessation of growth upon reaching an “adult size.” As with many cnidarians, no old age or senescence is demonstrable in these animals. Nonetheless, they don’t live forever. In essence, Ptilosarcus life is an exercise in “beating the odds,” and as in all such cases, the “odds,” – in this case, the odds of being eaten by a predator – are too great for indefinite success. The life expectancy of an individual sea pen in the Puget Sound areas appears to be about 14 to 15 years. Older animals may be occasionally found but, if so, they are very rare. Predators aren’t the only source of mortality in sea pens, nor are sea pens immune from parasites which may influence their growth and survival; however, these factors remain unstudied.

Figure 12. Drawings, done from life, of developing Ptilosarcus gurneyi. Larva undergoing metamorphosis. Top. 11 days. Center. 13 days old; tentacles clearly evident; bumps on body surface are of unknown function, spicules were not present; mouth is open and a gullet or gut is evident. Botom: 15 days old; note the development of the first pinnae on the tentacles.

Figure 13. Drawings, done from life, of developing Ptilosarcus gurneyi. Two individuals about 3 weeks old; spicules are visible in the body wall. They have one complete feeding polyp, the primary polyp, and siphonozooids on the stalk. The animals were actively feeding at this time and were about 3.5 mm long. The extent of the visible gut is shown in the right individual. The individuals were settled and growing in coarse sand. At this point, I terminated this growth series and transplanted the juveniles to a sea pen bed in one of my benthic research study sites.

Figure 14. A juvenile sea pen, photographed in nature; depth about 15 m. The animal is an estimated one year old. It was between one and two centimeters (about 0.4 to 0.8 inches) high. Note gastrozooids, and the internal calcareous style (visible as a white band).

Figure 15. Juvenile sea pen, photographed in nature; depth about 15 m. This animal is about two years old. It was about 5 centimeters (about 2 inches) high. Note: the gastrozooids, the siphonozooids (visible as bumps on the stalk), and the developing leaves.

Figure 16. Older juvenile sea pen, probably about 4 years old, about 15 cm (6 inches) high. The internal style that can be used to age the animals is clearly visible as a white internal stripe.

Figure 17. Evidence of incomplete, or attempted, predation; in both cases these partially eaten sea pens probably were attacked by nudibranchs.

Figure 18. The Predators. These nudibranchs primarily eat the smallest pens and become common in sea pen beds shortly after the juveniles settle and metamorphose out of the plankton. Top. Hermissenda crassicornis. Bottom. Flabellina trophina. Both nudibranchs are small, reaching lengths that do not exceed about 4 cm (1.6 inches). These species are responsible for the deaths, on the average, of upwards of 200 sea pens per square meter, per year.

Figure 19. The Predators. This nudibranch, Tritonia festiva, reaches lengths of about 10 cm (4 inches) and primarily eats small to medium-sized sea pens, but will not hesitate to take a chunk out of a larger one, as the above individual is about to do.

Figure 20. The Predators. These two large nudibranchs, Tritonia diomedia (top) reaching lengths of 15 cm (6 inches) and Tokuina tetraquetra (bottom) reaching lengths in excess of 30 cm (12 inches) also eat sea pens. Tritonia is common in sea pen beds, Tokuina are uncommon in those areas, and tends to eat isolated sea pens growing in sediment pockets in rocks. Individuals of these two species can eat the largest of sea pens without any difficulty whatsoever.

Figure 21. The Predators. These images show Armina californica, (top) probably the most abundant nudibranch predator that eats Ptilosarcus in the Puget Sound region. Although solitary individuals are capable of eating a pen, these animals are gregarious and are often seen clustered over the remains of their prey (bottom). Armina californica are reach lengths of about 10 cm (4 inches) long, and will eat all size categories of pens.

Figure 22. The Predators. In the areas of the sea pen beds, about 50% of the food items eaten by the rosy sunstar, Crossaster papposus, are sea pens.

Figure 23. The predators. In the areas of the sea pen beds, about 98% of the food items eaten by leather star, Dermasterias imbricata are sea pens.

Figure 24. The Predators. The vermillion seastar, Mediaster aequalis, preys on sea pens, among many other things. Here a sea star is hanging on to a previously buried sea pen that is expanding and trying to dislodge it. Pens bury into the sediments and, if stimulated, the pen will sometimes inflate, and expand in an apparent attempt dislodge the predator. Note that the pen has lifted the sea star totally off the substrate.

Figure 25. The Predators. The spiny sea star, Hippasteria spinosa, eats only sea pens. It takes a full grown star about 4 to 5 days eaten a fully grown sea pen.

Figure 26. The end result of the effects of all of the predators is the style.

Figure 27. The Green Disease. As if predation wasn’t enough, the sea pens are subject to other maladies. The green coloration in the pens above is caused by an endoparasitic green alga, which appears to kill the pens, albeit it takes several years to do so.

Figure 28. Not all Ptilsosarcus gurneyi in the Northeastern Pacific are found in dense beds. They may be found in many other habitats where sand pockets of the appropriate type occur. The anemones to the left are Urticina piscivora, and are about 30 cm (12 inches) across the oral disk.

During their lifetime, these pens probably reproduce about ten times. If the average number of eggs produced by one pen is 200,000, then each female will produce about 2,000,000 eggs over her life span. If the populations are assumed to be constant, neither shrinking nor growing, then over the life span of the female she must spawn the eggs to replace herself and her mate, indicating the odds of survival to successful reproduction by any given Ptilosarcus gurneyi individual in the Puget Sound region is about 1,000,000 to 1. Although those odds seem pretty slim, they are significantly greater than many other marine animals such as pelagic fishes.

Figure 29. Juvenile Ptilosarcus settle in dense assemblages; they have to, to be able to withstand the predation pressure of the array of predators that feed upon them.

Finishing Thoughts…

There are some things that may be taken to heart from my tale of sea pen life and, mostly, death. First, despite their apparent simplicity, these are hardy animals capable of surviving much environmental perturbation and unless they are eaten, they have the potential of living a long time. Second, they are mobile and capable of movement, and will leave areas that are not to their liking. Third, although P. gurneyi lack zooxanthellae, they have a rapid growth rate. The Puget Sound region, the so-called “Emerald Sea,” is exceedingly rich in plankton. One reason sea pens are so abundant in the region is all of the potential food. They eat small zooplankton. They probably will not eat much phytoplankton unless it is a suspension of clumped cells. Finally, these are very neat and strikingly beautiful animals, I haven’t even touched on their bioluminescence, but suffice it to say, in a dense sea pen bed at night the blue green glow from the pens is bright enough to take notes by. This species is as typical of the Pacific Northwest as apples and sasquatch, and yet it is almost as unknown as the giant Palouse earthworm. And that is a pity!

References:

Birkeland, C. 1974. Interactions between a sea pen and seven of its predators. Ecological Monographs. 44: 211-232.

Chia, F. S. and B. J. Crawford. 1973. Some observations on gametogenesis, larval development and substratum selection of the sea pen Ptilosarcus gurneyi. Marine Biology. 23: 73-82.

Kozloff, E. N. 1990. Invertebrates. SaundersCollege Publishing. Philadelphia. 866 pp.

Ruppert, E. E, R. S. Fox, and R. D. Barnes. 2003. Invertebrate Zoology, A Functional Evolutionary Approach. 7^th Ed. Brooks/Cole-Thomson Learning. Belmont, CA. xvii +963 pp.+ I1-I 26pp.

Shimek, R. L. Unpublished Observations.

Tags:anthozoa, Armina californica, azooxanthellate, corals, Dermasterias imbricata, ecology, Emerald Sea., feeding, Flabellina trophina, Hermissenda crassicornis, Hippasteria spinosa, invertebrates, marine biology, Mediaster aequalis, NE Pacific, octocorallia, pacific northwest, pennatulacea, pennatulacean, predator-prey interactions, ptilosarcus, Ptilosarcus gurneyi, puget sound, sea pens, Seattle, Shimek, soft coral, soft corals, Tokuina tetraquetra, Tritonia diomedia, Tritonia festiva, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | Comments Closed

Predators In The Sand, Or…

Monday, September 5th, 2011

Thoughts On The Evolution And Natural History Of Scaphopods.

Why Here And Why Now?

This post is, obvously, the continuation of a series dealing with scaphopods and some of the data I will be posting subsequently are also to be found on one or another of my website’s scaphopod pages. However, these blog entries are not strictly duplicative; I have added a number of new data and I have altered some of the information to reflect my present thoughts. Some of the ideas and data to be presented here are somewhat iconoclastic, and contrary to what some authorities have proposed. It is unlikely I will get the opportunity to publish these ideas in more formal, peer-reviewed, jounals, and as a result I thought this is an appropriate place to let the ideas see some glimmer of the light of day, albeit dimly and through some wet mud. To the questions of “Why Here and Why Now?” I think the reasonable answers are, “Because I think this is an appropriate place and it is time.” Or phrased another way, “Why Not?”

One of Three Groups…

The scaphopods are the last of the classical molluscan classes to show up in the fossil record, with arguably the first unequivocal scaphopod being Rhytiodentalium kentuckyesnis Pojeta & Runnegar, 1979. However, this unequivocality is not likely the case; the specimens of Rhytiodentalium are all significantly altered fossils, and from personal examination, it is impossible to tell exactly what they are. Although some of them match the general shape of modern – and presumably – highly derived scaphopod shells, these “shells” appear to be comprised of small pelletized material. It is unclear if these pellets are the result of significant or minor diagenesis. In the first case, the shells could considered as scaphopods. In the second, they would have to be something else, perhaps, some sort of worm tube. I think the latter is much more likely than the former.

The term “armchair quarterback” has been coined to describe those individuals who after watching a football game at home on the “aptly-named” boob tube, dissect a quarterback’s performance and describe, a posteriori, what he should have done. Of course, such a critique, if that’s what it may be called, is done without the experience of being under the tremendous pressure of the momnet on the field of play, without the sport’s equivalent of the “fog of war” clouding information input and, most importantly, it is done with the precision vision of hindsight. Of course, in the armchair experience, errors made on the field become glaringly obvious. One of the prime theories of scaphopod evolution is that scaphopods arose from an ancestor that either was in the extinct class, Rostrochonchia, or pehaps in its ancestral group, is the malacological equivalent of such airchair quarterbacking, however, with one glaring exception. It is undoubtedly wrong, most likely as a result of being proposed by individuals who have had no experience examining or studying live scaphopods or, indeed, live animals of any sort..

There are a number of very serious problems with the Scaphopods from Rostroconchs derivation, not the least of which is that the scaphopod shell is univalved and tubular, while the rostroconch shell is bivalved of various non-cylindrical shapes. Additioanally, the scaphopods are all predators or scavenger/predators; as a result, they must move; no predator on infauna waits for the prey to come to it. Then, the scaphopod radula, the structure used to macerate, break, crush or smash prey is the largest radula relative to the adult body size in all the mollusca. On the scale of the organisms, it is a truly massive structure. This massive radula is presumed to have been derived from an ancestor in the same group that is supposed to have given rise to the bivalves. However, not only do the bivalves lack the radua, but also any remnant of the head it is found in. While the scaphopod head is reduced and kept within the shell, it is present, and has a relatively large brain, also a structure missing in the bivalves – and presumably their rostroconch ancestor. The rostroconch shapes vary quite a bit, but one thing that is evident in all of them is that they are not streamlined and capable of easy movement through sediments. Indeed, with the shapes typically found in rostroconchs, it is quite likely, that like some oddly shaped infaunal bivalves today, they did not move at all as adults. Scaphopods, on the other hand, are all mobile and many of them, given the appropriate stimulus, are capable of bursts of relatively rapid motion, after which they often stop, construct a feeding cavity and feed. Given the sizes of the adult scaphopods, the number of body lengths that they are able to move in any given amount of time, and the media that they move through, it is quite reasonable to consider many of them to be “high speed” predators. Finally, recent molecular genetic work shows them to be grouped with the cephalopods, not the bivalves.

I think it is likely that one of the first branchings of the ancestral molluscan stock gave rise to a predatory organism that had a tendency to develop or elongate in a dorso-ventral direction. In turn, this ancestor, over time, gave rise to three successful clades, eventually leading to the crown groups of the cephalopods, gastropods, and scaphopods. All of these groups are all characterized by dorso-vental flexing in the visceral region, a well-developed radula, and elaborations of the cephalic tentacles.

Each of the three dorso-ventrally flexed groups shows particular adaptations and modifications for its primary habitat. The cephalopods are highly successful predators in the pelagic enviroment. Gastropods have radiated into virtually every possible niche except aerial flight, and are found in all terrestrial, fresh-water, and marine environments, although their ancestral habitat was the marine benthic epifaunal environment. Scaphopods have become highly adapted for predation on organisms living in unconsolidated marine benthic sediments.

Cadulus tolmiei in situ, modified from Poon, 1987.

The above image shows Cadulus tolmiei feeding in sediment, cb= captacular bulb, dd= digestive diverticula, fc = foot cavity, g = gonad, m= mantle, pa = posterior aperture, s = shell,

References:

Pojeta Jr., J. et. al. 1972. Rostroconchia: A New Class of Bivalved Mollusks. Science. 177: 264-267.

Poon, Perry A. 1987. The diet and feeding behavior of Cadulus tolmiei Dall, 1897 (Scaphopoda: Siphonodentalioida). The Nautilus: 101: 88-92.

Steiner, G. and H. Dreyer. 2003. Molecular phylogeny of Scaphopoda (Mollusca) inferred from 18S rDNA sequences: support for a Scaphopoda–Cephalopoda clade. Zoologica Scripta. 32:343-356.

More to come…

Until then,

Cheers!!!

Tags:adaptation, antalis, cadulus, dentalium, ecology, evolution, gadila, invertebrates, marine biology, mollusca, NE Pacific, pacific northwest, Paleontology, predation, predator-prey interactions, pretiosum, pulsellum, rhabdus, rostroconchia, scaphopoda, Vancouver Island, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | 5 Comments »

Scaphopods

Thursday, August 18th, 2011

Where

Recently I started scanning my images of scaphopods, an animal group from which very few people have seen living animals. I did a lot of research on them actually starting about 1975, and becoming intensely active in 1983 and finally winding down about 1997. I still have a paper or two to write but I haven’t done any field work in a long time. I described two deep-sea species (1, 2) from specimens sent to me, but most of my work has been done on the scaphopods found in the shallow waters of the Northeastern Pacific. Scaphopods are particularly common in many of the fjord environments north of the Strait of Juan de Fuca. I spent some small amount of time examining their distribution in the waters of Northern Puget Sound, particularly in the northern American San Juan Islands. In this area, two species of scaphopods, Rhabdus rectius and Pulsellum salishorum are found, and may be reasonably common in a few areas. There a couple of marine research laboratories/field stations in that region, but as far as I know, I am the only person in the last half century who has worked at one of those labs and done any kind of research on scaphopods.

During the period from 1981 until 2003, I taught at various times at a Canadian marine station located in Bamfield, British Columbia, situated on a small inlet on the southeast side of Barkley Sound, a large fjord system on the west side of Vancouver Island. This marine laboratory, known as the Bamfield Marine Station from its beginning in the 1970s until it morphed into the Bamfield Marine Sciences Centre in the early 2003, offers easy access to some of the scaphopod habitats of the Barkley Sound region. For the two-year period from September of 1983 until September of 1985, I was the Assistant Director of the marine station, and actively carried out an intensive project on scaphopod ecology and natural history. Subsequent to that time, I worked up data collected during that period, as well as initiating other scaphopod work, mostly with specimens sent to me by various researchers. As a result, I have published about a half dozen research papers on scaphopods, and have a couple of more in the works… if I can only get my act together enough to finish them.

The Critters

Scaphopods, or “tusk” or “tooth” shells are mollusks that live as subsurface predators in the marine sandy or muddy sea bottom. Covering an estimated 60% of the planetary surface, this is THE largest habitat in on the planet’s surface. As the scaphopods are either abundant or dominant predators in this habitat, that makes them some of the most ecologically important animals.

By last count there are about 8 to 10 people living today who have published papers on scaphopods, which may make them the most understudied of all important marine animals. Given that a number of those people are museum workers whose entire conception of the Molluscan Class Scaphopoda is that it is a collection of oddly shaped shells, it is evident that the world-wide scientific interest in the group is probably so close to nil as to be statistically indistinguishable from it.

This means that to a very real extent, that anybody who works on scaphopods as a full, or even part-, time venture is on their way to committing, or has committed, scientific/academic suicide. While it is true, to paraphrase one of my old profs, “If only five people work on your group, you can’t be ranked any lower than the fifth most prestigious worker on the group.”

However, if only five people work on your group of interest, it means nobody will care what you write. So, the good side is that everybody working on the group knows who you are. On the other hand, nobody else in the world – or known universe – cares who you are or anything about the animals… If there is so little interest in group worldwide, no matter how good your publications are, they will simply disappear into the large black cesspool of unread papers as nobody will care about you write.

Well, who am I to argue? I will state, however, in my defense, after that statement that I am the senior author of the definitive reference about the animals published to date: Shimek, R. L., and G. Steiner. 1997. Scaphopoda. In: Harrison F., and A. J. Kohn, Eds. Mollusca II. Microscopic Anatomy of the Invertebrates. Volume 6B: 719-781. Wiley-Liss Inc. New York, NY. ISBN 0-471-15441-5. Whooopty-doooo…

Five species of Scaphopods found in the Barkley Sound region of Vancouver Island, British Columbia, Canada. The scale bar is in millimeter.

From top to bottom, Pulsellum salishorum, upper two rows, females on the left, males on the right, next single row, Cadulus tolmiei, female left, male right, below that species is a single row of two Gadila aberrans, female left, males right, The next two individuals are Rhabdus rectius, female on the top, male on the bottom, and the lower-most individual is a single specimen of Antalis pretiosum (formerly Dentalium pretiosum), the “Indian Money Shell.” These individuals were alive at the time, and in the high definition of the moment, the top four species have shells that are thin enough to be translucent, and the gonads from each gender are differently colored, so I could discrimate the sexes. It is hard to see in the low res image here, but if you look at the top animals on the left, you can see a hint of pink in the shell, and that is the color of the ovaries of Pulsellum salishorum.

Heretofore…

Scaphopods were very economically important animals in the North American native cultures. Given the common name of the “Indian Money Shell,” one species, at one time called “Dentalium pretiosum,” was collected and traded throughout large parts of Northern North America. Here is an image from a National Geographic Magazine article about the trade; I was a technical advisor to the NGM for that article. The scaphopods were harvested in by some of the tribes from the Pacific Northwest, both in what would become Canada and the U.S. There are numerous “tales” about how the shells were collected, and at least two different and likely ways of collecting them. Knowing what I found out about the habits of that species (now called Antalis pretiosum), it appears that very few of the actual living animals were collected, but rather shells containing small hermit crabs the primary source of “scaphopods.” There is a hermit crab in the region were the scaphopods are found that is not coiled to fit into a snail shell as are most hermit crabs, rather this one, Orthopagurus mimumus, has a straight body and lives preferentially in the large “dentalium” shells. The crabs crawl around on the surface of the habitat, while the living animals are generally deeply under the surface, at least a foot (30 cm) below the water/sediment interface. In fact, the living scaphopods all have a rapid burrowing response – an exposed scaph is a dead scaph – as crabs and fish eat them. In text books and references, they are often illustrated as having their pointed ends exposed from the sediments, and some are found this way, between1 in 60, to 1 in about 10,000 depending on the species I have looked are exposed at any one time. So much for the standard references… More about why this should be so in my next issue of this blog.

Anyway, one of the more recent “proofs” of the hypothesis that it was mostly dead scaphopod shells inhabitated by hermit crabs that were collected actually comes from one of the National Geographic Magazine sites. They have a series of images purported to be Antalis pretiosum, all of dead scaphopod shells taken by David Doubilet, and all showing hermit crabs showing hermit crabs in the shells. Doubilet was apparently in search of the wily dentalium and, by golly, he got some pictures of it… or at least of its shell. Interestingly enough, there is an image also on their site showing Antalis pretiosum feeding below the sediment surface. This wonderful image is a painting by Gregory A. Harlin, and it clearly shows that scaphopods don’t have legs… Of course, Doubilet didn’t look at the painted image. One further note that adds even more humor to this bit of fubardom (fubar = fucked up beyond all recognition) is that Harlin’s painting was done for the previously mentioned earlier article in NGM about the dentalium trade for which I was a technical advisor. Harlin based his painting on my drawing of Rhabdus rectius feeding below the sediment surface that was used in Shimek and Steiner, 1997.

A diagram of Rhabdus rectius shown in its feeding posture below the sediment surface, drawn in life from animals in aquaria. Compare with the painting by Gregory A. Harlin,

The dentalium shells collected on the coast were traded through out North America, at least as far east as the Great Lakes and were quite valuable. They were used in the construction of jewelry and as ornamentation on clothing. I have read, with no real estimate of the validity of the statement, that one or two of them could be exchanged for a tanned buffalo hide. Consider that when you look at the image I have imbedded below.

Plains Indian neck ring jewelry in the collection of the Burke Museum,University of Washington, Seattle, Washington.

It has been reported, that given that the shells of the animals were quite valuable, it stands to reason that the one of the first things the Europeans did (in the guise of the Hudson’s Bay Company) was to “devalue the currency” by flooding the market with “counterfeit” shells. When the HBC traders began to realize how valuable the shells were, they sent word back up the communications chain, and European shells were harvested in some relatively great numbers. The European species, Dentalium entale, is/was essentially identical to Dentalium pretiosum and easily collected (and remember, both are now in the genus Antalis). These were sent to HBC traders throughoutNorth America and used to purchase all sorts of trade goods. So many shells became available that this sufficiently brought the value of the shells down so low as to make them worthless as trade goods for the coastal tribes as they could not harvest enough to get the traditional materials (such as buffalo robes, and they became dependent upon the HBC to sell them blankets). If this is true, it is a great (?) lesson in market economics…

Gastropteron

Monday, August 8th, 2011

Although they look like they are nudibranchs, the two snail species featured in today’s posting are surely not nudibranchs, even if one is kind of sluggish in form and fashion. The larger of the two, Gastropteron pacificum, is a bubble shell, meaning it has a shell that looks quite like a soap bubble and it is about as durable. When sitting on the bottom, the animal is about the size of a grape. The sides of the animal’s foot are expanded into two long lateral lobes that are normally folded up over the animal, but virtually nothing of the animal is normally visible as it is generally covered in a mucous sheet which, in turn, is covered by sediment particles. The animal looks like a lump of mud on a bottom that is covered in lumps of mud, and so this is pretty good camouflage.

Gastropteron pacificum, a stationary lump of pseudo-mud. The pink structure is a fleshy, tubular, siphon that brings in breathing water.

Gastopteron pacificum individuals are found frequently in the spring in waters of the North American “Pacific Northwest” and if a diver ventures into its gorpy, mucky, muddy habitat – otherwise known when I was working in these areas, as a “Shimek study site” – one can often see the trails left by these little guys as they move around, presumably in search of food or a mate.

Gastropteron pacificum, leaving a trail in the mud as it crawls from there to here.

They are probably detritivores, as they are reported to eat detritus and diatoms in the laboratory, but I am not sure what they eat in nature, and neither, to the best of my knowledge, is anybody else. I don’t think they have been studied in any detail which, if true, is quite a pity as they are neat little critters. When something startles them – a diver (me) in my case for the photograph, or the presence of a bottom-feeding fish, such as the ratfish, Hydrolagus colliei, the little snail unfolds its foot flaps and flaps away. They are quite strong swimmers and this appears to often be an effective escape response.

Hydrolagus colliei

This “rat fish,” or “chimerid,” is a cartilaginous-skeletoned fish but obviously not a shark. Individuals in this particular species can reach about 70 cm (28 inches) in length. Rat fishes are some of the most common predators in the soft-sediment ecosystems of the NE Pacific, and some of my unpublished data indicate they feed on mollusks, annelids, and echinoderms.

A Gastropteron pacificum individual.

This little animal is swimming away from the most fearsome and horrific predator of all, a diver – in this case, of course, me. I was sensed, probably by my water disturbances, and it then took off, and stayed waterborne for about 2 minutes. Although Gastropteron swimming appears to be undirected, given the currents in the region, it will likely cover some distance before it quits swimming and falls back to the bottom.

If the Gastropteron is successful in its life, it find a good friend and they will do the snaily version of the “wild thing” resulting some time later in the deposition of some jelly-like “egg masses” attached to the bottom. These are filled with small fertilized eggs (zygotes) that develop within the misnamed egg mass, which eventually dissolves releasing the larvae into the plankton.

A group of Gastropteron “egg,” actually embryo, masses. I don’t know if all of these are deposited by one individual or if they aggregate during spawning to deposit the jelly-like masses (many snails in this region do form spawning aggregatations).

However, they don’t get a break! There is a small sacoglossan slug, Olea hansinensis, in the area that searches out and eats the eggs of Gastropteron and its relatives.

Olea hansinensis.

This is a small sacoglossan slug that eats eggs of cephalaspidean snails, such as Gastropteron. This one was about 3 mm (1/8th inch) long, but larger individuals are said to reach about 13 mm, or half an inch in length.

More later,

Until then,

Cheers,

Tags:barkley sound, behavior, benthos, bubble shell, cephalaspidean, chimerid, feeding, gastropod, Gastropteron, gastropteron pacificum, Hydrolagus colliei, marine biology, mollusk, NE Pacific, pacificum, predator-prey interactions, puget sound, rat fish, ratfish, snail, soft-sediment ecology, Vancouver Island, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | Comments Closed

Rossia

Saturday, February 12th, 2011

One of my favorite animals is the little sepiolid squid found in the Pacific Northwest, Rossia pacifica. So…

I thought I would just post a few images of this wonderful small squid. The next two images were taken sequentially as rapidly as my strobes would recycle. The color change occurring in response to the strobe’s flash was impressive and “instantaneous.”

Rossia pacifica, in one of my research localities.

A Rossia that has changed color in response to my strobes. This is the same individual shown in the preceding image.

The animal below saw me coming and watched me. It moved a bit but not too much as I approached, presumably a predator, such as a dog fish (Squalus) would try to catch a swimming squid, and . When I got about a meter away, it turned “white;” at the ambient light at that depth it really just matched to bottom color.

A Rossia that "went white" when it saw me approaching. NOT a happy critter!

Individuals of Rossia have a very stereotyped escape response. It appears to be a response to slow patrolling predators on the bottom fauna, particularly dogfish sharks. The sepiolid lauches from the bottom and swims about 30 to 40 cm above the bottom more-or-less in a straight line inking every few meters. When it should ink the last time, it doesn’t, but it turns dark, throws its arms up in a “scatter” posture and drifts like an ink blot until it hits the bottom, whereupon it bleaches (which makes it effectively disappear) and rapidly covers itself with sediments.

Rossia in its "drifting" posture. This posture will occur prior to the animal dropping to the bottom and covering itself with sediment.

This is an ink blot made a swimming "escaping" Rossia. Unfortunately, the sediment in the water obscures it somewhat, but it mantains a coherent shape roughly that of a swimming squidlet.

Rossia drifting and mimicking an ink blot. It has already inked a couple of times, and is not actively swimming, but is just drifting in the current.

After the successful escapes, eventually eggs are laid and after several months they hatch. The first image is of an egg clutch. The next two are of a newly-hatched, itsy-bitsy, baby Rossia.

Rossia pacifica egg capsules on an old discarded coffee mug. The capsules are about a centimeter long.

A newly-hatched Rossia. Less than a 1 cm long, this animal is probably only a few days post hatching..

A baby Rossia swimming. When this color pattern occurs as the animal is swimming, it effectively "disappears" and becomes very cryptic as it swims or drifts over the substrate.

This last image is of a Rossia watching me as I took its picture. Who could resist those eyes?

A Rossia watching me; it was about 2.5 centimeters (1 inch) long.

Until next time,

Cheers,

Tags:behavior, ecology, egg capsules, escape response, hatching, invertebrates, marine biology, natural history, Rossia, sepiolid, Washington
Posted in Ecological Observations From Northeastern Pacific Subtidal Habitats | Comments Closed

Sky Sharks And SCUBA

Sunday, December 19th, 2010

Hi Folks,

My wife and I got treated to quite a show yesterday. For several hours, a male prairie falcon was cruising around our yard hunting doves. These latter birds are Eurasian collared doves, one of several introduced pest birds (think large white/gray/tan pigeons) found locally – thesea are probably descended from birds released by some non-thinking idiot who decided it would be cool to release doves symbolizing something or other at a ceremony somewhere near here. Anyway, said skyrats appeared about four years ago, and have been doing well here.

Eurasian Collared Dove

Periodically, though, a truly native sky shark comes by to thin the herd a bit, and that is what happened yesterday. It was great entertainment to watch the falcon, though I doubt the doves thought so. 🙂 I saw him miss his target by inches on one pass; the dove was surprisingly agile in the air when the situation warranted! The falcon was around for a while, and then vanished. I hope he finally got dinner and settled down near by to enjoy his repast.

Almost exactly a year ago, we had a similar opportunity to watch a goshawk for a few days, and the second picture, below, shows the final outcome. The first picture was taken a few days before the second one, and it appeared to be the same animal. In the second image, the hawk is standing over his plucked prey that he has been eating.

Sharp-shinned Hawk in the poplar outside my office window.

Sharp-Shinned Hawk and Dinner

It was an amazing show.

Of such events, are the sciences of behavioral biology, or ethology, and ecology, made. And people who study these things in terrestrial environments truly lose out. I used to tell my students that one of the very neat things about being an ecologist who worked subtidally using SCUBA was that one got to see a lot more interactions than one’s terresterially-bound counterparts.

If you think about it, how many times have you seen a predatory animal in nature around you (excluding those events caused by humanity or human pets ) actually kill and eat a prey organism? I would wager that the total sum of those events witnessed by anybody is pretty small; I know it is with me, and I look for them. It is possible to calculate some sort estimat of the odds of seeing such an interaction at any given moment. For example, if a person is 35 years old, that person has been alive about 1 billion seconds. If each second is a discrete a moment of observation, the rough, back-of-the-envelope odds of having seen such an event through that person’s lifetime are easy to work out. First, assume that about of the third of the time has been spent sleeping, so subtract a third of the billion away, phffftt!, and now there 667,000,000 million potential moments of observations. Then assume that for the first third of the persons’s life she or he was effectively unaware of the world (childhood, teen-aged years, and so forth), so subtract a third of the previous remains and now there about 444,700,000 million potential observational moments. Now, drop out a another third for meals, and other daily mindless activities, and now there about 296,400,000 million observational times. Being generous, let’s say our victim subject was outside observing nature 1/10 of each day (and I think that will be a vast over estimate for most folks, but, what the hey, let’s go with it), so now there are 29,640,000 potential moments of observation. And if that person witnessed 10 natural events wherein one animal killed and ate another (and I suspect that would an overestimate), that means our subject’s odds of seeing such an event were 10 in 29,640,000, or 1/2,964,000, or (very roughly) 0.0000003.

Pretty slim odds (!) of seeing some interesting natural event such as predation.

Back to my point about working underwater in the marine world, I could see animals kill and eat other animals many times during a hour’s dive, and often did so. Below are a couple of images recording some of those times (and be sure to click on the sculpin image to see the shrimp’s antenna). Obviously, the moral of the story, of course, is that one must dive to really observe and understand nature.

A Buffalo Sculpin, Enophrys bison, that has just eaten a shrimp, note the antenna visible protruding from the mouth.

A red rock crab, Cancer productus, eating a scallop.

Yeah, sure!!!

But the point that visible large animal to animal interactions are more evident in the marine environment is, I think, a valid one.

Behavior and Marine Aquariums

Thinking about the point made above, and making a not-so-tortuous connection to marine aquaria, those boxes of water full of critters may be (depending, of course, on how the boxes are set up, and what’s in them) quite reasonable analogues to a natural environment. And that means, any aquarist with such a tank should expect to see predatory (and other “natural” ecological or behavioral) events occurring with some reasonable frequency in their systems.

And, of course, all of us aquarists (or at least of us who observe our systems) do see these events. Everytime we feed some live animal to our livestock, we see predation, albeit those are staged events, but with suspension-feeding animals, corals for example, within the staged event, the actual feeding behavior on the part of the coral, is likely essentially the same as when the “real thing” occurs in nature. But even if those “wo/man-made” events are factored out, all aquarists have seen unintened predation occur in our systems, and sometimes rather frequently, as when when a newly-observed acoel flatworm on the aquarium wall is seen to capture and eat a copepod. In fact, by observing some of these types of events any aquarist worth their artificial (sea)-salt can – for some animals, at least – see interactions that have never been seen in nature, and depending on the interaction – such as with the flatworm and copepod example – such events may be exactly what occurs in the real world, or a mimic so close that the difference is immaterial.

So, folks, on this cold winter, while the snow outside blankets the northern hemisphere, those of you with coral reef aquaria kick back and relax and enjoy the tropical world in your living room.

It’s a world of your making and if you have done your job, properly, it is a VERY real world.

For the rest of you, it is time to shovel snow!

Until later,

Cheers,

Tags:aquarium, buffalo sculpin, Cancer productus, diving, dove, ecology, Enophrys bison, feeding, husbandry, marine biology, Montana, predation, red-rock crab, SCUBA, sharp-shinned hawk, Washington
Posted in Off The Wall | Comments Closed

Posts Tagged ‘Washington’

Table 1. Subtidal Seasons Of Cowlitz Bay,

And

The Northern San Juan Islands, Washington.

Season

Starts

Ends

Cause

Manifestation

Dark

Mid-October

Mid-February

Low Illumination, Cool Temperatures

“Everything is shut down”

Clear water, no plankton

Diatom

Mid-February

Early-March

Increasing illumination and temperature, Nutrients from spriing runoff increase

Substrate becomes covered with a thick diatom coat.

There is clear water with scarce plankton.

Filter-feeders start emergence

First Plankton

Early-March

Late-March

As Above

Phytoplankton blooms;

Water becomes greenish and visibility drops;

Substrate diatom layer becomes thinner;

Some benthic herbivores present;

Filter-feeders emerged.

Second Plankton

Late-March

Late – May

As Above

Zooplankton bloom becomes noticeable;

Phytoplankton presence is less, Water visibility increases slightly,

Water color changes from green to gray-green/aquamarine;

Spawning is occurring with some benthos,

Diatom cover is largely gone,

Benthic herbivores are common.

Settlement

Late – May

August

Nutrients from runoff become less, Illumination and temperature still increasing

Small animals and settled juveniles become very common.

Plankton pulses, going from phytoplankton dominated to zooplankton dominated to no plankton (clear water) in short (week long) sequences;

Water often cloudy, greenish white.

Growth

August

Early- October

Runoff absent, Illumination begins to drop, Temperature peaks.

Filter-feeders evident;

Benthic predators very active.

Diatom cover almost gone.

Small predators disappearing.

Shutdown

Early October

Mid to LateOctober

Temperature drops, Illumination drops, Rains begin.

Plankton disappears;

Filter-feeders shut down.

Water clears up, becomes dark green.

Diatoms on benthos gone.

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