Posts Tagged ‘soft-sediment benthos’

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.

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

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.

Luidia foliolata

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.

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.

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.

Caprella gracilior on Luidia foliolata.

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

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.

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  

,

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.

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. 

Maroon more pachycerianthis

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 to the hyperiid amphipod captured as food by a different tube anemone (next illustration).

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).

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.

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

 

 

 

 

 

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.

 

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 IIMicroscopic 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…

More on scaphs later….

Until then…

Cheers, Ron