Marine Invertebrate Zoology Class Blog

For the last five weeks I’ve been the TA for Marine Invertebrate Zoology at FHL, taught by Gustav Paulay and Bernadette Holthuis.  One of the students’ assignments was to create a blog post about one animal, interaction, or activity from the course.  Our goal is to begin a record of marine invertebrates from the San Juan Islands that documents specific behaviors and appearances that may not be readily available in other online or text resources.

InvertZoology.wordpress.com

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Red Sea Urchins

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Spines for defense and tube feet for moving, holding on and catching algae.

Strongylocentrotus franciscanus is the name for the red sea urchin, the most common mobile invertebrate we encounter.  Urchins are well known from temperate and tropical habitats around the world to be important herbivores.  In tropical oceans like the Bahamas, urchins help herbivorous fishes keep macroalgae (seaweed) at bay, allowing corals to grow.  In temperate oceans like California, Alaska, New Zealand and the Mediterranean, they are known to form foraging herds that can mow kelp forests down and replace them with “urchin barrens,” regions of coralline algae pavement and encrusting invertebrates.

The urchins of the San Juan Islands violate our preconceptions about urchins as important herbivores.  First, they don’t just eat algae, and second, even when they do, they don’t bother going to search for it.

Robin Elahi, a recent Ph.D. graduate from the Sebens Lab, studied the impact of red sea urchins on rock walls, and found them to consume lots of invertebrates, such as social ascidians.  Robin found that urchins are responsible for creating clearings on the walls by eating away space occupying species, and then chitons maintain these open patches by bulldozing or consuming new recruits.

When the urchins aren’t eating invertebrates, they’re waiting for algae to come to them.  The narrow channels between the San Juan Islands create strong tidal currents, which carrie drift algae back and forth through the channels.  Urchins sit and wait for drift algae to catch in their spines, rather than waste energy foraging for live kelp.  The result of this behavior is that urchins in the San Juans do not form massive herds that wipe out kelp beds.  The transport of this drift algae from the shallow productive zone allows urchins and other herbivores to live in much deeper habitats than they might otherwise be able to.  Several FHL researchers have studied various components of this relationship, including Sarah CarterKevin Britton-Simmons, and Aaron Galloway, a Ph.D. student in the Spatial Subsidy Lab at FHL.

Puget Sound King Crab

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The largest crab we see in the San Juans.  Not edible like the Alaskan king crabs, or at least I’ve never heard of them being harvested and eaten.

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Tim Dwyer, amazed at how large Puget Sound king crabs can get.  Despite the large, heavy claws, these crabs have never pinched us.  When we handle them they tend to tuck all their legs into the body.  This particular crab was scrabbling to find something to crawl away onto, not trying to menace the camera.

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Closeup of the face.  The spiky bits are part of one of the two pairs of the antennae.  You can see the other pair of antennae just above the spiky bit on the left.  The eyes are dead center, on either side of the triangular rostrum (looks like a nose).  The blue rectangular pieces are the 3rd maxillipeds, which help chew up food.  There are five other pairs of mouthparts, including the 2nd and 1st maxillipeds, the 2nd and 1st maxillae, and the mandibles.  All are involved in chewing and shoving food back into the mouth.

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Lopholithodes mandtii is an Anomuran crab, more closely related to the hermit crabs than to shore crabs or Dungeness and red rock crabs.  How to tell if a crab is an Anomuran or a Brachyuran (the group that includes typical crabs)?  Count the number of walking legs, including the pincers.  If it has 4 pairs it’s an Anomuran.  If it has 5 pairs, it’s a Brachyuran.  Another way to tell is to look at the abdomen (the shield on the ventral side of the crab).  If it’s asymmetrical it’s an Anomuran.

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Color in adults tend to be various shades of orange or red, with blue highlights.

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Juveniles are bright orange to red.

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Despite the bright coloration shown in these photos, Puget Sound king crabs are almost perfectly camouflaged.  The bright oranges and red are nearly invisible at the depths these crabs live (we tend to see them at 20m or deeper).  Without the bright colors, they look like all the other rocks they crawl over.  They only pop out when we use flashlights.

Rockfish Recompression

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Images of a bocaccio with severe barotrauma at the surface and in a basket being sent to the bottom for recompression.  Image from NOAA SWFSC

Here is a great PSA put out by NOAA Southwest Fisheries Science Center, all about the effects of barotrauma on rockfish and how to help recompress rockfish once you’ve caught them.  We use the inverted basket method to send our fish back down after we catch them for diet analysis.

The bulging eyes and stomach forced out through the mouth are the result of increased pressure on the internal organs from the swim bladder.

Boyle’s gas law says that as the pressure on a unit of gas decreases, the volume of that gas increases proportionally.  That is, when the pressure is cut in half, the volume doubles.

Rockfish live in deep water, typically 20m or deeper, and often several hundred meters deep.  Standing at sea level, you have all the weight of the gaseous atmosphere pressing down on you.  When you dive into the water, the weight of the water is added to that, at a rate of the equivalent of one atmosphere every 10m you descend.  The pressure at 20m is 3atm.  If a rockfish is brought from 20m to the surface, the pressure on it decreases to 1/3 the original pressure, which means the volume of its swim bladder increases 3-fold.

Unlike salmon and other surface-oriented fishes, the swim bladder of rockfish is not connected to the esophagus.  Salmon add gas to their swim bladder by swallowing gulps of air from the surface.  This limits them to staying near the surface.  Rockfish use a capillary system like that surrounding our lungs to deliver gas to the swim bladder.  The benefit of this system is that rockfish are not tied to the surface, and can colonize deeper habitats.  However, it also prevents them from being able to quickly vent gas as the surrounding pressure decreases.

Since rockfish can’t burp, when they are brought to the surface the swim bladder swells and causes the stomach and eyes to bulge out.

Year of the Serpent

Today marks the beginning of the Chinese New Year – the Year of the Snake.

A few snakey photos from my research were featured in a post about snakes and serpents on the UW Biology Department graduate students’ blog, Science Positive.

Serpula columbiana tube worms are sessile invertebrates that secrete a calcareous tube (Serpula means “serpent”).  There are also brittle star arms snaking out from the crack in the rock (brittle stars are in a group called the ophiuroids, which means “snake-like”).

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The scientific name for lingcod is Ophiodon elongatus (Ophiodon means “snake-tooth”).

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Greenling Eggs

In the fall we frequently see small clutches of fish eggs.  We typically see them laid inside empty giant barnacle shells, and sometimes even in the holes in the bricks we use in our clod card work.This egg mass is different for two reasons.  First, it’s not laid inside any protective shell or brick, and second, the developing fish can be seen inside their eggs – usually the eggs we see are either opaque or don’t have any clear differentiation inside them.

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If you look close you can see eyes and even the coiled body of the embryos.

We think these are the eggs of a greenling, mostly because they don’t look like lingcod or red irish lord egg masses.  If they are greenling, they’re likely kelp greenling, the most common species of greenling.

Greenling are relatives of lingcod (note the “ling”).  However, greenling don’t get nearly as large as lingcod, and are much more active.  Greenling are commonly seen by divers, and even seem to follow us around on our dives.  Here are some photos of adults (not my photos):

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This is a female.  Key characteristics to look for: gold fins and lots of small dark spots on a light background.

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This is a male.  Note the blue-grey fins and few large light spots concentrated near the head on a dark background.

I remember the two genders with the color of their fins: boys are blue and girls are gold.

Split Arms

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This Pisaster brevispinus has a pretty dramatic split arm.  I wonder how they control the regrowth of limbs to reach the same length as the others.  This photo is from Neck Point in October 2010.

Seastars can drop their arms if they feel threatened, a process called autotomy (“self-sever”), and regrow the arm later on.  But sometimes things go screwy and they don’t regrow quite right.  Seeing six arms on a star that should have only 5 is fairly common.  These photos are from one of the more unique examples I’ve encountered.

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Can you see the little nub on the Pycnopodia helianthoides arm?

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And yes, there are tube feet on the bottom, just like any proper seastar arm.

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Pycnopodia helianthoides is my favorite example to use when students complain about having to learn the scientific names for organisms.  As long as the describer didn’t name the organism after a person or a place, the scientific name can be very descriptive.  “Dense-feet sun-flower-ish” is a very accurate description of this star.

Octopus

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Enteroctopus dofleini arm sliding out of its den.  We typically find octopus by looking for midden heaps, piles of shells leftover from the octopus’ meals.

Octopus sightings seem to be getting more and more common.  This one hangs out under a boulder at Neck Point.  Megan Cook, the 2012 North American Rolex Scholar, joined us for a few days of diving and snapped these photos.

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The giant pacific octopus feeds on all kinds of prey, from the red rock crabs and clams seen in these photos, to dogfish sharks and seagulls.

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Octopus are well known for their ability to change colors.  This one is showing a lot of white, which may mean that it’s scared or upset at our presence or the flash of the camera.

This octopus (or at least the den) has been here for some time.  Tim Dwyer got this excellent video in September 2011.  Near the end of the video watch for a rapid skin color and texture change as it leaps into its den.

For as large as they are, giant pacific octopus do not live very long – only 3-5 years.  After mating, females lay a cluster of eggs in their den and stop feeding.  They spend all of their time guarding the eggs and pumping water through them to keep the developing larvae oxygenated.  By the time the larvae hatch the female has used up all of her energy reserves, and dies.