Posts Tagged ‘soft-sediment ecology’

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  


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.

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,


The Northern San Juan Islands, Washington. 









Low Illumination, Cool Temperatures

“Everything is shut down”

Clear water, no plankton




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



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 – 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.


Late – May


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.



Early- October

Runoff absent,  Illumination begins to drop, Temperature peaks.

Filter-feeders evident;

Benthic predators very active. 

Diatom cover almost gone. 

Small predators disappearing.


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.



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,