Posts Tagged ‘sea pens’

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. 7th Ed.   Brooks/Cole-Thomson Learning. Belmont, CA. xvii +963 pp.+ I1-I 26pp.

Shimek, R. L. Unpublished Observations.

Starting Something New

Tuesday, July 19th, 2011

Nudibranchs

For quite a while I have wanted to post a number of my underwater images which were taken from 1975 through 1994, mostly in a few of the shallow water environs of the Pacific Northwest, a.k.a. the Northeastern Pacific.  Most of these were taken to be illustrative, that is to show the animal or organism, primarily for lectures or in presentations, they were not meant to “artsy” images, although some certainly turned out that way.  I finally have bitten the bullet, and am scanning a lot of these images into high-definition digital form, this being largely facilitated by the purchase of an external hard disk drive (HDD) of terabyte capacity, so that I actually have a convenient place to store the images.  Judging from the size of the scanned images, I may well fill that HDD.  However, I obviously can’t post such high definition images here, nor can I post them all, as I estimate I have well over 5,000 images.  Consequently, I have decided to post a few every few days for the foreseeable future. 

Unfortunately, the posted images are really not the best quality; the images scanned from my slides average about 80 Mbytes each, so, the images posted here are really quite low in resolution.  Sorry about that, but it can’t be helped.  In my scanning, the order is not random, but it is also not taxonomic.  It is “slide holder order.”  I had/have arranged my opisthobranch slides in slide holders in a loose leaf notebook with the nudibranchs first, but within that group they are in more-or-less haphazard order.  If that bothers you, exit now and save yourself the heartburn.  Once I get them all scanned, I will arrange them in some sort of logical order, but that is in the future.  

The very diverse and species-rich array of animals grouped under the name ”Opisthobranchia” were, until recently, thought to be related.  That is no longer the case, and while some subgroupings within the old group, such as the nudibranchs, are good taxonomic groups, the term “opisthobranchia” is now obsolete and used only as an informal term, and one I suspect will die out over the next few decades.  I hope you enjoy the images and the commentary that goes with some of them.  The taxonomic nomenclature (i. e. the names) used in the opisthobranch image postings follows that given in the fine photo reference book:  Beherens, D. W. and A. Hermosillo. 2005. Eastern Pacific Nudibranchs. A Guide to the Opisthobranchs from Alaska to Central America. Sea Challengers Publications. Monterey, California. vi + 137 pp.  If I have made any mistakes in the listing or image names, those are mine and mine alone.

Hermissenda

Hermissenda crassicornis, the opalescent nudibranch.  Photographed at a depth of about 10 m on the 4th of July, 1992 in Barkley Sound, Vancouver Island, British Columbia, Canada.

A pair of Hermissenda crassicornis, the opalescent nudibranchs.  These were photographed at about 10 m on the 14th of October, 1983 near Ohiat Isand in Barkley Sound, Vancouver Island, British Columbia, Canada.

These nudibranchs are not social animals and their appearance together is probably happenstance.  However, they may be getting together to mate.  Unlike many other nudibranchs, particularly the dorid nudibranchs in which copulation may take many hours, mating in Hermissenda is anything but sluggish.  As with all nudibranchs, they are hermaphroditic and mating is reciprocal.  From start to completion, copulation takes but a small fraction of a second.  

Hermissenda crassicornis, the opalescent nudibranch.  Photographed at about 12m depth, on the 2nd of June, 1982 in Barkley Sound, Vancouver Island, British Columbia, Canada.

The above opalescent nudibranch appears to be on a rock with brown algal filaments on its surface, but that is misleading.  The scene is one of a small patch reef created by the annelid worm, Dodecacaeria fewkesi.  What appears to be brown algal filaments on the substrate are actually masses of tentacles arising from the worms whose calcareous tubes are cemented together forming the reef. 

And there is more going on!!!

The tall structures in the background are hydroid colonies; probably the nudibranch would be eating the hydroids if it were on them.  The small white blobs on the hydroids are either individuals of another nudibranch, from the genus Doto, or that species’ eggs.  During the spring, everything in this region grows like crazy, particularly those animals, such as the hydroids, that feed on plankton, which is very abundant.  In this case, the hydroids, of course, feed on small zooplankton. Individuals of Doto species feed on the hydroid polyps and their populations bloom right after they hydroids have their growth spurt.  These small nudibranchs, about 3 or 4 mm long, can have population densities exceeding 5,000 per square meter, and will be featured in an upcoming post.

Dodecaceria fewkesi, the “reef building” cirratulid worms.  Photographed on the 28th of April, 1984 inDodger Channel, Barkley Sound, Vancouver Island, British Columbia, Canada.

These worms secrete the calcareous tubes that they live in.  Dodecaceria individuals aggregate together, probably due to asexual reproduction as well as larval recruitment.  In doing so, their calcaeous tubes fuse forming, first, what appear to be small rocks with worm holes in them.  Later, as time goes on, these rocks grow by the addition of more worms.  In doing so, they create one of the few types of reefs, other than those made by corals, that are biogenic, or made by living organisms.  These worm reefs are never very large, but they can be as much at 20 to 30 (6 to 9 m) feet long and 6 to 10 feet (2 to 3m) high, or as big as some coral patch reefs.

A portion of a small reef built byDodecaceria fewkesi, the calcareous-tubed hair worm.  Photographed on the 29th of April, 1983 in Pole Pass, between Crane Island and Orcas Island, in northern Puget Sound, Washington, USA.  The slightly “foggy” appearance to this image is due to small plankton in the water reflecting my strobes’ light. 

This image shows the small “rocky reef” made by the hair worms.  This area in the San Juan Islands of Washington, was one of my primary research study sites in the early 1980s.  In addition to the small patch reefs made by this worm species, there are other, much larger, reefs at this site that are made by a different type of worm, the sabellariids, and I will probably post images of them in the future.  Most biologists don’t realize that corals are not the only reef forming animals, and when told of these worm-built reefs, often respond with disbelief and incredulity.  Nonetheless, such structures are reasonably well-known and described in the scientific literature. 

As with coral reefs, these worm reefs are “hot spots” of local species diversity.  However, there small size and lack of much 3-D heterogeneity, limits the number of other animals that live with them.  Nonetheless, opalescent nudibranchs, and the hydroids they feed on are often common on these reefs.   Due to the distance from the reef, not much other life is recognizable in this image, though.  The large white blob is probably a contracted plumose sea anemone (Metridium sp.), which when inflated fully would be a couple of feet high.  The golden crescent near the bottom, is the aperture of a large scallop (Hinnites sp.) that is found in the area.  These animals cement their shells to rocks, and unlike most scallops are immobile when they are adult.  That individual is probably about four inches (10 cm) across.  

Flabellina

 There are lot of small aeolid nudibranchs found on, and eating, hydroid colonies or other cnidarians in the spring in this region.  Here are a couple of shots relating to, and of, Flabellina trilineata.

The orange structure is a colonial hydroid, Garveia annulata, that was occasionally common in some areas that I dove in.  The hydroid colony in this image is a couple of centimeters long. Notice the large orange “balls”  (reproductive polyps), they are about 1/4 mm in diameter.

The three-lined nudibranch, Fabellina trilineata.  This little nudi reaches lengths of about 1.5 inches (36 mm) or so, and is commonly found in the spring in rocky areas in the Pacific NW subtidal regions.  It,  like many aeolid nudibranchs eats hydroids, including Garveia.

This image shows a baby F. trilineata (notice the rows of tiny cerata growing on its back) eating Garveia.  The nudi is about 2 to 3 mm (about 1/8th inch) long.  You can get an idea of size by noting the reproductive polyps and comparing this image with the images of Garveia, above.

One of the activities I tried to do at times during my diving career was to take “extreme” macro shots of various invertebrates in the field.  I had an apparatus that allowed me to get an image magnified up to about 12x on the slide; so, if the animal was 2 mm long, the image would be about an inch long on a 35 mm slide.  In this case, the nudibranch in the last image above was magnified about 8 times.  There were a lot of technical problems with taking these images, not the least of which was that the object to lens distance was very small, and that it had to be accommodated within my camera’s underwater housing.  Given the water currents in the areas where these images were taken, even holding one’s position during the water flow, euphemistically referred to as slack water, could be difficult.  The large camera and strobe housing caused an immense amount of drag, and severely limited my mobility.  Other problems included looking through the viewfinder of the camera with a scuba mask on, and so on…  Suffice it to say getting any sort of image was a problem.

The major difficulty, however, was getting enough light hitting the very small object to reflect back, passing through the underwater housing plastic, then the lens, and then the bellows that was on the front of the camera, and into the camera to properly expose the film.  I began to feel like I needed a tactical nuke to take the picture.  If I was able to successfully expose the object so that the slide was properly exposed, it sometimes felt like I need to produce so much light that it would vaporize the object I was taking photographing.

In the above image of the baby Flabellina on Garveia, the digital software ”pushed” the exposure quite a lot, but doing so increased noise, and that noise is particularly apparent at the low resolution I must use here.  That is why the image is a bit blurred.  It can’t be helpped, sorry.

The next species of choice is Flabellina trophina, one of the more blah of the these normally spectacular wee beasties.  Nonetheless, I have a fair number of images of it, as the species was common in some habitats I was investigating, and there were often not a lot of other animals visible there, so rather than return to shore with only half a roll of film shot off, I would take images of individuals of this species of nudi, and sometimes a few other critters.

Flabellina trophina.  Photographed near Seattle in central Puget Sound, WA. in 10 m of water in 1982.

A head-on view, this image shows to advantage the extensions of the brown or tan digestive gland up into the cerata on the animal’s dorsum.  “Cnidosacs,” specialized structures containing undischarged nematocysts from the animal’s previous dinners are located at the tips of each ceras and their presence is emphasized by the bright white coloration.  This is probably aposematic or “warning” coloration for any visual predator, in these cases either a fish or crab that might consider this nudi a tasty snack.

Flabellina trophina.  Photographed near Seward, AK in 10 m of water, in 1982.

This shows the animal in a side or lateral view; F. trophina can reach lengths of about 50 mm, or 2 inches.  The structure visible on the animal’s right shoulder is the combined anal and genital apertures.  All nudibranchs have their genital openings in this region, but the anus may vary in position, and that is – as one might guess – one of the characteristics defining each different subgrouping within the nudibranchs.  The aeolidacea all have these apertures in position as shown in this individual. 

Flabellina trophina.  Photographed south of Seattle in central Puget Sound, WA. in 12 m of water in 1988.

I have no quantitative data, but my notes list several observations of this species feeding on sea pens (Ptilosarcus gurneyi).  I was working on photodocumenting the events occurring in sea pen aggregations (called sea pen “beds,” for no logical reason known to human cogitation).  Over some 20 plus years, I made, maybe, 150 dives in this habitat and took several hundred images. There will be slides of many other different animals posted during these excursions through my slides that were taken in the sea pen aggregations.  Starting with some nice research by Chuck Birkeland the natural history and “ecology” of the sea pens in the Puget Sound region are probably the most well known of all pennatulaceans.  In any case, I was photographing F. trophina in the beds not because it was documented to feed on the sea pens (it was not, even though I found that it is a common predator on them – or at least it was when I was actively diving in those areas), but rather because it was common and somewhat attractive, and sometimes, I just wanted to take its picture. :-) .  I took the above image because it shows a lateral view of the animal with its snout elevated which is a common posture.

Flabellina trophina.  Same images as above. 

While I was preparing the scanned image for this post to the forum, which involved making lower (much lower) resolution images, I noticed what I thought might be artifacts due to fine hairs that got on the slide prior to it being scanned.  And, gee, living in a house with a large hair factory, one that specializes in producing very thin, fine hairs (a.k.a. – my true buddy, Casper = “A Maine Coon Cat” = giant fur ball).  I figured that if these were, indeed, fine Casper hairs, I would have to reclean the slides and try scanning them again.   The “hair” images/artifacts are circled, and if one examines the image above this one, it is quite possible to see them without the circles.  There are a lot more faint “hair-artifacts” visible than are circled.  

My buddy, Casper, a generator of loose, fine hair, but not guilty of being the source of “hair-like” images on my nudibranch slides. 

Flabellina trophina.  Same images as above. 

When I examined the fine “hairs,” I found that Casper was off the hook, they were not artifacts at all, but were actually part of the original image.  They were microscopic phytoplankton floating by in the water as I took the images.  As I described above, I could photograph microscopic subjects.  Well, here is the inadvertent proof of that statement!  And, it is something that I had never seen on the image before this scan! 

I further enlarged the portions of the images in the red circles and included them in the original image.  They are shown outlined in red and are indicated by the arrows.  Note the “zig-zag” structures.  Well, those structures are not 2-D zig-zags, but rather 3-D helices of chained diatoms.  Here is a link to a photomicrograph showing similar diatoms in a better view.  

WOW!!!  I think this is REALLY neat, because it shows how what appears to be the relatively clear water in a photograph of an underwater scene may, in fact, be filled with plankton that are just below the resolution capabilities of either the camera or the printer or scanner to show.  I have often heard a comment to the effect that a given tropical coral reef image shows water so clear that it is ”obvious” that there is no plankton in it.  I wonder how many of those images would show microscopic plankton of one sort or another if they had been taken with a better camera or printed in better manner.  

No plankton present…  LOL!!!  Obvious, INDEED!!!

More images soon.

Until then,

Cheers, Ron