Category: Marine invertebrates

Cuteness warning: High alert!

Posted on by Allison J. Gong

This morning I was doing some routine cleaning of animal-containing dishes at the marine lab when I noticed a little blob of snot on the outside of the bowl I was working on. Normally I just wipe off blobs like that, but something about this one caught my attention in a different way and I paused to take a closer look at it. What I saw made me glad I hadn’t given it the old Kim-Wipe™ treatment.

It was this:

Very small juvenile nudibranch (Melibe leonina). 23 September 2015 © Allison J. Gong
Very small juvenile nudibranch (Melibe leonina).
23 September 2015
© Allison J. Gong

This little 3mm blob of cuteness is the tiniest Melibe I’ve ever seen. Melibe is one of my favorite creatures of all time. It’s an entertaining animal that has unfathomable amounts of charm. Unlike most other nudibranchs, which prey on other animals (typically cnidarians, sponges, or bryozoans), Melibe is a filter feeder. It sweeps its large oral hood, visible to the right, through the water to capture plankton. The flat large-ish structures projecting from the animal’s back like wings are cerata, of which there will eventually 4-5 pairs when the slug reaches adult size. The cerata function as gas exchange surfaces; they also contain extensions of the digestive system. When a Melibe is mishandled or stressed, it drops cerata, which can then be regenerated.

Melibe is the most animated of slugs. I dropped a few brine shrimp nauplii on this little guy to see if it would be able to catch them. Unfortunately it looked more like the nauplii were ganging up on the Melibe than the other way around. However, I know from experience that even larger Melibe take a while to figure out how to eat brine shrimp.

But isn’t that the cutest slug you’ve ever seen? It has tiny bright blue dots on its body! Those two little flaps on the top surface of the oral hood are rhinophores. I know they look like ears, but they are chemosensory rather than auditory organs.

And look how fast this little nudibranch can crawl! Remember, it’s only 3mm long, and it’s making pretty good progress getting to the corner of the bowl.

When dislodged from whatever it’s crawling on, Melibe can swim. I thought this one would attach itself to the underside of the surface tension, as they often do, but it thrashed for quite a while before sort of accidentally finding the bottom of the dish again.

And do you know what the best thing about Melibe is? It smells like watermelon. I kid you not. If you touch a Melibe, your finger will smell like watermelon Jolly Ranchers. How could an animal possibly be any cooler than that?

Happy as a . . .

Posted on by Allison J. Gong

. . . clam, right? Yes, except in this case the bivalve is not a clam, but a scallop. I was out at the harbor with Brenna again this morning, looking for molluscs for tomorrow’s molluscan diversity lab. Brenna was hunting for slugs, of course, and had drawn up a rope that had been hanging in the water for god knows how long. Neglected ropes like this are the stuff of dreams for people like Brenna and me, as all sorts of animals recruit to and colonize them. Hauling one up is like going on a treasure hunt.

Two of the animals that had attached to the rope were small kelp scallops, Leptopecten latiauratus. The smaller of the two was about the size of my thumbnail and the larger was about 1.5 times that size. Their shell patterns are very beautiful:

The larger rock scallop (Chlamys hastata) collected at the Santa Cruz Yacht Harbor. 14 September 2015 © Allison J. Gong
The larger kelp scallop (Leptopecten latiauratus) collected at the Santa Cruz Yacht Harbor.
14 September 2015
© Allison J. Gong

The smaller rock scallop (Chlamys hastata) collected at the Santa Cruz Yacht Harbor. 14 September 2015 © Allison J. Gong
The smaller kelp scallop (Leptopecten latiauratus) collected at the Santa Cruz Yacht Harbor.
14 September 2015
© Allison J. Gong

But really, you don’t get a feel for how much fun these animals are until you watch them. Scallops are the most animated of the marine bivalves. They have eyes and sensory tentacles along the ventral edge of the mantle, and react strongly to stimuli. They can clap their valves together so quickly that they actually swim. I wasn’t able to make either of mine swim, but did get to watch them for a while.

The whitish object waving around on the left side of the frame is the scallop’s foot. Rock scallops are not permanently attached to surfaces (if they were, they wouldn’t be able to swim!) but they do use the foot to stick. If they find a spot they like, they try to wedge the dorsal, hinged area of the shell into a crevice.

Just like you and me, scallops have bilateral symmetry, complete with left and right sides. Unlike you and me, however, their bodies are laterally flattened and entirely enclosed between the left and right shells. The only parts of the body that extend from between the shells are the foot and the sensory structures on the mantle edge. Leptopecten has many long filament-like sensory tentacles, and brilliant blue eyes.

I thought I’d provoke a reaction by passing my finger over the animal and casting a shadow over it. Nada. But then it closed its shells a couple of times for no reason that I could discern. However, as my graduate advisor Todd Newberry used to say, The Animal Is Always Right™, and what doesn’t seem like anything to me could very well be a threat to a scallop.

And by the way, I did also collect a few slugs and a chiton for tomorrow’s lab. The highlight for me, though, was the scallops. I hope my students are as captivated by these little bivalves as I was!

Off with the old, into the new

Posted on by Allison J. Gong

The Seymour Marine Discovery Center, where I spend some time hanging out several days a week, has a spiny lobster (Panulirus interruptus) on exhibit. While the lobster doesn’t have an official name, for obvious reasons the aquarists call it Fluffy. We don’t know if Fluffy is male or female, but for convenience sake we’ve been referring to it as ‘he’ which may or may not be sexist, depending on one’s point of view. Fluffy came to the Seymour Center as a full-grown adult in September (I think) of 2012 and has molted every year close to the anniversary of his arrival.

Fluffy, the spiny lobster (Panulirus interruptus) on exhibit at the Seymour Marine Discovery Center. 7 September 2015 © Allison J. Gong
Fluffy, the spiny lobster (Panulirus interruptus) on exhibit at the Seymour Marine Discovery Center.
7 September 2015
© Allison J. Gong

Fluffy’s latest molt occurred some time between Saturday afternoon and this morning, probably in the dark of night. The molt remains in the tank, to show visitors what happened.

Spiny lobster (Panulirus interruptus) on the right and its molt. 7 September 2015 © Allison J. Gong
Spiny lobster (Panulirus interruptus) on the right and its molt on the left.
7 September 2015
© Allison J. Gong

Being encased in a rigid exoskeleton, all arthropods grow in stepwise fashion, increasing in size only during that brief period between when the old exoskeleton has been shed and the new one has hardened. Once they reach full adult size they may continue to molt yearly, but no longer grow. Fluffy’s exoskeleton may be hard by now, and to the naked eye he doesn’t look any larger than he was before. Then again, if he was already full-grown when he came here, I wouldn’t expect him to grow much, if at all.

When crabs and lobsters molt, the old exoskeleton splits apart at the junction between the carapace and abdomen. The animal slips out backwards through the split, leaving the entire covering of its body behind. Before molting the lobster’s epidermis would have resorbed some of the minerals from the old cuticle, and what is left behind is much thinner and more fragile than it was when the animal was wearing it.

Molted exoskeleton of a spiny lobster (Panulirus interruptus). 7 September 2015 © Allison J. Gong
Molted exoskeleton of a spiny lobster (Panulirus interruptus).
7 September 2015
© Allison J. Gong

In the photo above you can see the split between the carapace and abdomen. I think it’s amazing how the legs, eye stalks, and antennae can slip out of the old cuticle without being broken or damaged. However, until the new exoskeleton has fully hardened the animal is vulnerable and usually hides out for a few days. Fluffy may not eat until tomorrow or the next day. One interesting note. A lobster’s gills, being external structures, are covered by a thin layer of cuticle and are molted along with everything else. If you come across a recent crab molt, lift up the carapace and you might be able to see where the gills are located. How cool is that?

A series of unfortunate events

Posted on by Allison J. Gong

Now is not a good time to be a sea star in my care. Although to be honest, I doubt these animals would be better off in anybody else’s care, either. And what’s going on today isn’t so much a series of unfortunate events as a trio of additional episodes in the two-year serial catastrophe that we call sea star wasting syndrome (SSWS).

Episode 1: My third Leptasterias star finally bit the dust today, a full week after the first one tore itself into pieces. Yesterday I was teaching all day and didn’t have time to take pictures when I checked on things at the lab, but the star was intact. Today, not so much:

Leptasterias sp. star exploded due to SSWS. 4 September 2015 © Allison J. Gong
Leptasterias sp. star exploded due to SSWS.
4 September 2015
© Allison J. Gong

On Monday, four days ago, the star had a small lesion on the aboral surface of its central disc. It was crawling around and aside from the lesion appeared healthy. While this individual survived longer than the other two, the progression of SSWS from small lesion to total dismemberment is surprisingly rapid. I shouldn’t be surprised, as I’ve watched SSWS take apparently healthy Pisaster ochraceus stars and turn them into piles of rotting disembodied arms in a single day. That was almost exactly two years ago. Maybe it’s something about the Labor Day holiday.

Episode 2: Since I lost two of my bat stars (Patiria miniata) to SSWS back in July, I’ve been keeping an eye on the five that remain. They seemed to be doing fine until this week, when I noticed that one of them had developed a lesion. It was a very small superficial lesion on Monday but now it has grown both larger and deeper.

Patiria miniata (bat star) with small lesion. 4 September 2015 © Allison J. Gong
Patiria miniata (bat star) with aboral small lesion.
4 September 2015
© Allison J. Gong

Here’s a brief note about sea star anatomy. The small inter-radial clean-edged pale orange structure located at 6 o’clock is not a lesion. That is the animal’s madreporite, the ossicle through which water passes in and out of the water vascular system. The madreporite of Patiria tends to be pretty conspicuous; in other species it can be more difficult to find.

The lesion is the larger, paler, fluffier bit that doesn’t have clean edges. It’s an open wound, and the white fluffy stuff is the star’s soft tissue. Today the wound measures about 1 cm across its widest dimension:

Lesion on aboral surface of Patiria miniata. 4 September 2015 © Allison J. Gong
Lesion on aboral surface of Patiria miniata.
4 September 2015
© Allison J. Gong

I’ll keep checking on this star and see how quickly the lesion grows.

Episode 3: Scott and I have had to accept that we aren’t having much luck growing up our tiny Pisaster stars. This afternoon we counted 16 of the 0.5mm orange dots that are juvenile stars. We consolidated 12 of them into a single jar and kept the other four in a bowl with a piece of mussel shell. We have failed to determine what it is they eat when they’re this small, unless it’s more than sheer luck that the four with the mussel shell haven’t experienced any mortality in two weeks. And yes, we will continue to change the water in the jar and the bowl twice a week.

For broadcast spawners such as Pisaster ochraceus, which shed gametes into the water, reproductive success is all about numbers–numbers of spawning individuals in a population as well as numbers of gametes produced. In our experiment the numbers just weren’t working in our favor: (1) we got usable quantities of gametes from only two females and two males; (2) fertilization success was pretty low for both crosses (Purple x Purple and Orange x Orange); (3) all embryos for the Orange x Orange cross died in the early developmental stages; and (4) settlement and metamorphosis success was low for the Purple x Purple cross survivors. And now we’re down to 16 stars. By this time next week we may be down to zero stars, although those four on the mussel shell might still be hanging on.

We knew going in that the crux of the problem would be feeding the juveniles; I was reasonably certain that we’d be able to get through the larval stages successfully. And this is indeed what has been the case. Right now I feel more than a little disheartened even though the result we got (i.e., we can’t get the damn things to eat once they metamorphose) is far from unexpected. Fortunately it will be months before our brood stock can be spawned again so I have lots of time to decide if it would be worthwhile to try the experiment again. I will need to come up with some new ideas of what to feed the juveniles.

You are what you eat, part the third

Posted on by Allison J. Gong

To recap:  Way back in January I spawned some sea urchins. The resulting progeny are now almost 7.5 months old, counting from the day that they were zygotes. Once they metamorphosed and became established as post-larval urchins in June, I divided them into three feeding treatments:  the kelp Macrocystis pyrifera, the green alga Ulva sp., and a red coralline alga. Since then I’ve been counting and measuring them monthly, and today I completed the fourth data collection.

I could tell by looking at the bowls that the Macrocystis and Ulva urchins continue to grow much more quickly than the poor urchins stuck on the coralline diet. The Macrocystis urchins are, overall, bigger than the Ulva urchins, despite the qualitative observation that the Ulva urchins appear to be eating more. However, I am not monitoring the amount of food that is eaten by any of the urchins.

Test diameter of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 2 September 2015. © Allison J. Gong
Test diameter of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet.
2 September 2015.
© Allison J. Gong

In the past month I lost almost half of the coralline urchins; I’m down to six. Mortality for the other groups remains low. I think the Macrocystis and Ulva urchins have for the most part gotten big enough that, barring any unexpected disastrophe (yes, I made up that word), they shouldn’t experience much mortality.

Population sizes of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 2 September 2015. © Allison J. Gong
Population sizes of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet.
2 September 2015.
© Allison J. Gong

In terms of color, I think the differences between the Macrocystis and Ulva diets have become more pronounced in the last month. Today I tried to photograph the two groups of urchins under the same lighting conditions, with mixed success. There’s some variation within groups, of course, but overall the Macrocystis urchins have a more golden color on both the test and the spines. . .

Juvenile sea urchins (Strongylocentrotus purpuratus) eating the kelp Macrocystis pyrifera. 2 September 2015. © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus) eating the kelp Macrocystis pyrifera.
2 September 2015
© Allison J. Gong

. . . whereas the Ulva urchins have more purple coloration:

Juvenile sea urchins (Strongylocentrotus purpuratus) eating the green alga Ulva sp. 2 September 2015 © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus) eating the green alga Ulva sp.
2 September 2015
© Allison J. Gong

And, just to make sure that I hadn’t inadvertently biased the light in favor of one group at the expense of the other, I manhandled all of the urchins to one side of their respective bowls and took a picture of the two bowls side by side. Let me tell you, it was like herding cats. I’d get one group all bunched together then start working on the other, and the first ones would immediately begin wandering away from where I’d put them. This is the best shot I managed to get. Without reading the caption, you can still figure out which group is which, right?

Juvenile sea urchins (Strongylocentrotus purpuratus) feeding on Macrocystis (left) and Ulva (right). 2 September 2015 © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus) feeding on Macrocystis (left) and Ulva (right).
2 September 2015
© Allison J. Gong

We’re coming into the time of year when it might be difficult obtaining food for these urchins on a regular basis. Everybody may have to go on a diet for a few months. As long as I can get my hands on both Ulva and Macrocystis I’ll keep feeding them, and when I run out of one food the other group will have to fast also. I think they’re well enough established by now that not having unlimited food won’t do much harm.

I just had another thought. I could put the Ulva and Macrocystis urchins back on coralline rocks and see how they do over the winter. Something to think about.

Spying on filter-feeders

Posted on by Allison J. Gong

Late yesterday afternoon I met my friend Brenna at the harbor to go on a slug hunt. Brenna is working on the taxonomy of a group of nudibranchs for her dissertation, and we’ve gone collecting out in the intertidal together a few times. I knew I’d need some harbor therapy after teaching a microscope class in the afternoon so when she suggested a slug hunt I didn’t have to think twice about saying “Yes!”

I arrived at the harbor before Brenna did, and spent some time lying on the docks taking pictures of the fouling community that lives there. The late summer afternoon light was perfect for picture taking, and I got some great shots.

Mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

This is one of my favorites. It’s a view into the posterior end of a live mussel (Mytilus sp.). Mussels live inside a pair of shells and open up only the posterior end to suck in water for respiration and filter feeding. They shut the shells very quickly when disturbed, so I had to sneak up on this individual and take a picture before it knew I was there. Looking through the opening you can see a blurry pale structure running from left to right; I think this is the mussel’s gill. The elaborately fringed dark structure that looks like a pair of curtains extending towards each other is the edge of the mantle. Because most of the mussel’s body is enclosed within the shells, the mantle edge contains most of the animal’s sensory organs. Mantles are exquisitely sensitive to touch, light, and certain chemicals; scallops, another type of bivalve mollusk, often have actual eyes on the mantle edge.

In addition to spying on mussels, I also tried to catch polychaete worms off-guard. There are several different types of tube-dwelling polychaetes living at the harbor. Most of the ones I saw yesterday were serpulids living in meandering calcareous tubes. Like these:

Serpulid polychaete worm at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Two examples of Serpula columbiana, a tube-dwelling polychaete worm, at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Polychaete worm tubes come in many different materials and morphologies. These serpulids live in calcareous tubes that snake over surfaces. Because the tubes are mineralized, they can extend upwards from a surface, too. The worm spends its entire post-larval life in the tube that it secretes, extending only its “head”, visible as a tentacular crown, for filter-feeding. Like the mussels, serpulid polychaetes are very quick to respond to anything they perceive as a threat. Even a mere shadow passing over them can cause a rapid retreat into the tube finalized by sealing off the tube with the trumpet-shaped operculum.

One of the most conspicuous animals at the harbor is an invasive encrusting bryozoan, Watersipora subtorquata. This animal is one of the first to colonize new real estate. Nothing else looks like it, so it is easy to identify.

Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Watersipora grows as a crust on surfaces such as mussel shells and floating docks, but when two colonies meet they use each other as surfaces, forming these curling sheets. The faint fuzziness that you see sort of hovering above the surface of the sheets is due to the lophophores extending from the zooids. Here’s a closer shot:

Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Another of the common introduced species at the harbor is the colonial sea squirt Botrylloides violaceus. This animal comes in a wide range of oranges and even purple. Here’s a colony that seems to understand the visual impact of pairing high-contrast colors:

Colony of the colonial sea squirt Botrylloides violaceus growing over mussel shells at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Colony of the colonial sea squirt Botrylloides violaceus growing over mussel shells at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

What looks like a mass of pale orange doughnuts is actually a strictly organized colony. Each of the doughnuts is a zooid, and the hole of the doughnut is the incurrent siphon through which the zooid draws water in. Each zooid has its own incurrent siphon. In this photo you can see several larger holes; these are excurrent siphons, shared by several zooids, through which waste water is expelled. It’s difficult to see in the photo, but the excurrent siphons are raised up above the level of the colony, so water that has already been filtered doesn’t get sucked in again. This is exactly the reason that human structures such as smokestacks and chimneys are tall.

Oh, and since you asked, Brenna did indeed find slugs! And she taught me some field characteristics to help me ID slugs that I find. We both got what we needed on our little jaunt to the harbor.

Hanging on

Posted on by Allison J. Gong

Day 3 of wasting in Leptasterias

The saga continues. When I checked on my ailing stars yesterday I saw, as expected, that most of what I had called Leptasterias #1 (the pink star that had ripped itself into pieces the day before) had disintegrated into small piles of mush. There was no sign of life in any of the small fragments so I threw them away. The largest piece, consisting of two adjacent arms attached to what looks like most of the central disc, was still walking around so I kept it. Today I was surprised to see that it hasn’t died yet. In fact, it looks a little better, with both of the arms active and the central disc appearing to be somewhat more contracted and less sloppy.

Remnant of wasting Leptasterias star, 30 August 2015. © Allison J. Gong
Remnant of wasting Leptasterias star, 30 August 2015.
© Allison J. Gong

The two arms appear to be working together, rather than trying to walk away from each other. I think this is a good sign, although it’s too early tell how much longer this fragment of a star will survive.

The star I had designated Leptasterias #2, which had the very large lesion on Friday, had died and dissolved into a mass of amorphous tissue and skeletal ossicles when I looked at it yesterday.

On the other hand, Leptasterias #3, the larger of the two gray stars, seems to be holding its own, or at least not getting any worse. On Day 1 of the outbreak this star had a small fluffy lesion on its aboral surface. Today the wound appears to have grown a bit but its edges look a little cleaner:

Leptasterias star affected by wasting syndrome, 30 August 2015. © Allison J. Gong
Leptasterias star affected by wasting syndrome, 30 August 2015.
© Allison J. Gong

This star was particularly active this morning. I didn’t want to disturb it or give it any incentive to autotomize its arms, so I left it in its screened container to take pictures and video. It was zooming around and acting, for all intents and purposes, like a normal healthy star.

Fingers crossed that this one makes it!

Whiskey Tango Foxtrot

Posted on by Allison J. Gong

Sometimes the only word that will do is a bad word. I generally try not to use a lot of bad language because on the occasions when I do swear I want my f-bombs to really mean something. Late this afternoon I was on my way out of the lab when I made a quick last trip through the wet lab just to make sure everybody would be okay for the night, when out of the corner of my eye I saw a few odd pink bits in one of my screened containers.

This container held three small six-armed stars of the genus Leptasterias. I had collected them earlier this summer with the goal of showing them to my students when we do the echinoderm diversity lab at the end of the semester. Stars in this genus are interesting because their normal arm number is six and they brood their babies instead of broadcasting gametes into the sea to meet, fertilize, and develop on their own. Plus, like all their echinoderm kin, they are pretty animals. Lastly, enamored as I am of oddballs and out-of-the-ordinary things, I am charmed by Leptasterias‘s six arms because most stars have only five.

So when I opened up the screened container and saw that one of my Leptasterias stars had torn itself into pieces, I let fly with a few f-bombs and other choice expletives. I removed the star pieces into a bowl for a better view.

Leptasterias star dismembered due to wasting syndrome, 28 August 2015. © Allison J. Gong
Leptasterias star dismembered due to wasting syndrome, 28 August 2015.
© Allison J. Gong

Seeing a star that had ripped its own arms off is every bit as horrifying when the star has six arms as when it has five. This act of self-mutilation had probably occurred today, as the star looked fine when I checked on it yesterday. All of the pieces were still alive and crawling around:

Actually, if you examined each of the pieces independently and didn’t know that it was only part of a greater whole, you’d think that they were entirely viable. I put these pieces aside in a separate bowl, although honestly I don’t know why. I’m almost certain they’ll be dead when I check on things at the lab tomorrow morning, and even if they aren’t they’ll be decomposing while still sort of alive, which is even worse. I must be a glutton for punishment.

For a while I held out a teensy glimmer of hope that the other two stars might be okay, but that didn’t last long. It took only a glance to see a big aboral lesion on the center of one of them:

Leptasterias star with large aboral lesion, 28 August 2015. © Allison J. Gong
Leptasterias star with large aboral lesion, 28 August 2015.
© Allison J. Gong

Examination under higher magnification shows just how deep and intrusive these lesions are. The body wall is entirely compromised, resulting in the exposure of internal organs to the outside environment.

Lesion on aboral surface of Leptasterias star, 28 August 2015. © Allison J. Gong
Large lesion on aboral surface of Leptasterias star, 28 August 2015.
© Allison J. Gong

It turns out that none of these Leptasterias is unaffected. The third star in my container has a small aboral lesion:

Small aboral lesion on Leptasterias, 28 August 2015. © Allison J. Gong
Small aboral lesion on Leptasterias star, 28 August 2015.
© Allison J. Gong

Whether or not this third individual will survive is up for grabs, but I wouldn’t bet on it. From my experience with wasting syndrome in Pisaster and Pycnopodia, the disorder progresses extremely rapidly once the animal starts showing signs of illness. And all of these animals appeared just fine yesterday. The small pink star is essentially dead already, it just hasn’t realized it yet. The gray star with the large lesion may very well be dead tomorrow, too. The star with the small lesion might still be alive tomorrow, and this is the only one for which I have a bit of hope for survival.

About a week ago the seawater temperature dropped to 16°C for a few days, but then started creeping back up; today it topped out at 19°C. Correlation is not causation, but I do wonder if another spike in the 19-20° range, on top of stress caused by the ongoing period of warm water, is the proverbial straw that broke the camel’s back. These poor stars have gone through hell lately, and there’s no indication that the water will cool off any time soon. I’d throw up my hands and ask, “What’s next?” but I have a sneaking suspicion that I’ll find out soon enough.

Falling in love

Posted on by Allison J. Gong

Today Scott and I gathered all of our tiny Pisaster stars and assigned them to food treatments. We’re not doing a feeding experiment per se but have the goal of getting these juveniles to grow, and to do that we need to figure out what they eat when they’re this small. Nobody knows, or at least we haven’t been able to find any literature on the subject, so we’re trying a shotgun approach and offering them several different items.

One of the food items is the bryozoan Membranipora membranacea, which I wrote about yesterday. Scott picked up some fresh kelp yesterday afternoon and several of the blades were encrusted with Membranipora. We thought these new colonies might be a more appetizing meal for the stars. We knew we’d have to remove any of the Corambe slugs that might be feasting on the bryozoan, so I put a piece under the scope. And. . . whoa. . .

So lively! The bryozoan colony was unbelievably gorgeous. All of the zooids were active and reactive, with lophophores extended and tentacles flicking. This video is taken in real-time. Note how the zooids act independently, but REact as a group. They share enough neural apparatus that stimuli are perceived almost instantaneously by all the zooids in a region.

One of the things I love about colonial and clonal animals is that they upend our preconceived notions of what an individual is. In an animal like a bryozoan, what is the individual? Is it the zooid, possessing its own feeding apparatus that it employs independently from the other zooids to which it is genetically identical? Or is it the colony, consisting of many zooids? And what role does genetic identity play in the definition of individual? How much integration among units is required before they collectively form what we call a body? So many fascinating questions to ponder!

Anyway, Scott had the brilliant idea of gut-loading the bryozoans before feeding them to the stars, so I fetched a couple mL of the green alga Dunaliella tertiolecta that we have growing in pure culture and gave them a few drops, just to see what the zooids would do.

Wow.

This video is also shot in real-time. The zooids are kind of just doing their thing, but when I add the drop of algae about halfway through the video they kick into high gear and go hyper. I didn’t expect such an energetic response.

It is difficult to convey just how mesmerizing these bryozoans are. They are a fantastic example of animals that are completely overlooked even by many biologists because to understand and appreciate them you need to look at them under a microscope. Without magnification they really don’t look like much, just whitish gray crusts growing on kelp blades. But the microscope opens up a view into their lives and shows us how complex and beautiful they are. Sometimes the most amazing and gorgeous things are the ones you can’t see with the naked eye. And that is exactly what I love about them.

The Enemy of the State

Posted on by Allison J. Gong

I came of age, in an academic sense, working as a technician in a lab where the research focused on colonial hydroids. The other tech in the lab, Brenda, and I would get sent out to collect hydroids, then spend another day or so picking the predatory nudibranchs off the colonies. The PI of the lab called nudibranchs “the enemies of the state” and they really did have a way of showing up out of nowhere and then eating a hydroid colony down to nothing. It was rather amazing, actually. Brenda and I would swear we’d picked off all the nudibranchs, and more would show up the next day. This same PI had another saying:  “For every hydroid there’s a nudibranch that lives on it, eats it, and looks just like it.”

Case in point. Today Scott and I were examining not hydroids, but bryozoans, which are a completely unrelated type of colonial animal. We want to see if our tiny juvenile Pisaster stars will eat the bryozoan. It didn’t take long to see this:

The nudibranch Corambe sp. on the encrusting bryozoan Membranipora membranacea. 13 August 2015. © Allison J. Gong
The nudibranch Corambe sp. on the encrusting bryozoan Membranipora membranacea. 13 August 2015.
© Allison J. Gong

A bryozoan colony consists of many units, called zooids, that are connected in some way to form a functioning larger body. The brick-like white structures in the above photo are the zooecia, or “houses” of the bryozoan zooids. The round object near the center of the photo with wavy white lines is the nudibranch Corambe. The white lines on the back of the slug make it blend in very nicely with the bryozoan on which it feeds, and break up the outline of the body to disguise its size; how can you determine how big something is if you can’t see its edges? This slug is probably 2-3 mm long. As with most creatures this size and so effectively cryptic, it is very easy to overlook the slugs and never see them; however, once you have a good search image they become much more conspicuous and you find them everywhere. Search images are great things.

It’s also easier to see something if it’s moving, and it turns out that this slug can move pretty fast:

The voice that you hear is Scott’s.

Corambe lives primarily on Membranipora and eats it. Membranipora responds to this predation by forming spines along the edges of the colony; the spines make it more difficult for the nudibranch to crawl around. This kind of response is called an inducible defense. The same thing occurs when plants begin to produce noxious chemicals after being munched on by an insect herbivore. Scott and I will set up some feeding treatments for our juvenile stars and Membranipora will be one of the courses served, so we were both glad to see that despite all the slugs we picked off there were still lots of viable zooids remaining.

Here’s what a bryozoan is all about. Each zooecium forms the outer casing of one zooid. The zooecium itself is non-living but contains the living part. In Membranipora all of the zooids in the colony are the same, and each one possesses a ciliated tentacular crown called a lophophore. The cilia on the tentacles produce a current that directs food particles to the mouth, which is located at the base of the lophophore. In this video you can see particles moving in the current, and one zooid accidentally sucks in a glom of stuff that is too big. Watch how it tries to get rid of the piece it doesn’t want.

See how the individual tentacles sort of bend and then straighten up? I call that tentacle flicking.

If you spend a couple of hours looking at something through a microscope it’s inevitable that you’ll see something different and new. In one of the bryozoan pieces I saw two little pink blobs in an otherwise empty zooecium. It looked like they were moving, so I zoomed in and saw that they looked like shmoos. “Shmoo” has become my term for any undifferentiated, unsegmented, worm-like thing that I can’t identify. These pink shmoos were definitely moving, and here’s the video to prove it:

That little squeal at the end of the video? That’s me. I was delighted to see that the shmoos have two eyes and turn somersaults. I still have no idea what they are, and I’m totally okay with that. It’s enough to know that they exist.