Crab feed(ing)!

Anybody who has visited one of the sandy beaches in California has probably seen kids running around digging up mole crabs (Emerita analoga). These crabs live in the swash zone at around the depth where the waves would be breaking over your ankles, moving up and down with the tide. They are bizarre little creatures, burrowing backwards into the sand with just their eyestalks and first antennae reaching up into the water.

Although it’s called a mole crab, Emerita‘s external anatomy isn’t very similar to that of other crabs. For one thing, it doesn’t have claws. In fact, its legs are quite unlike the legs that you’d see in a typical crab. Check out Emerita‘s appendages:

External anatomy of Emerita analoga

External anatomy of Emerita analoga

The crab’s head faces to the left in this diagram. The real surprise that these little crabs hide is the nature of the second antennae. Usually the crab keeps these long, delicate antennae protected under its outer (third) pair of maxillipeds. This is why you don’t see them when you dig up a mole crab.

You do see them when the crabs are feeding. As a wave washes over the crab, it extends the second antennae and pivots them them around on ball-and-socket joints. The feathery antennae catch particles in the water, then are drawn underneath the maxillipeds so the food can be slurped off and eaten.

Here’s a top-down view of two Emerita feeding. The purple-grayish thing in the field of view is a sand dollar (Dendraster excentricus).

This side view gives a better angle of what’s going on:

I find these little crabs quite captivating. I love how they rise up when I put food into their tank.  Watching them feed always makes me smile.

Posted in Marine biology, Marine invertebrates | 2 Comments

Competence

In the parlance of invertebrate zoologists, competence is the state of development when a larva has all of the structures and energy reserves it needs to undergo metamorphosis into the juvenile form. In the case of my sea urchins, this means that they have four complete pairs of arms, each with its own skeletal rod, and a fully formed juvenile rudiment, which contains the first five tube feet of the water vascular system. A continuous ciliated band runs up and down all eight arms and provides the water current used both for swimming and feeding. The larva will have been eating well and its gut will be full of food. It will have lost the transparency it had when it was younger and will appear to be more solid-looking in the central area.

The first batch of larvae that I began culturing this season are now 42 days old. Some of these are competent, or very nearly so. Last week I isolated about a dozen of these big guys into a small dish, making it easier for me to observe them closely every day. Today they looked decidedly opaque and dumpy, and although some of them were still swimming others were heavy and tended to rest on the bottom of the dish.

Here’s a photo that I took yesterday:

41-day-old pluteus larva of Strongylocentrotus purpuratus, 2 March 2015. ©Allison J. Gong

41-day-old pluteus larva of Strongylocentrotus purpuratus, 2 March 2015.
©Allison J. Gong

General orientation: This is a ventral view. The animal swims with its arms forward, which defines the anterior portion. Thus the bottom of the cup-shaped body is the posterior. This larva measures ~900 microns along the anterior-posterior axis. Plutei have bilateral symmetry that goes all to hell during metamorphosis, from which the urchin crawls away with typical echinoderm pentaradial symmetry. This wholescale change in body organization is one of the truly amazing things about metamorphosis in these animals. It boggles my mind every time I think about it.

You can see that this pluteus has eight arms. The oblong reddish structure in the middle is the stomach, which has taken on the color of the food the animal has been eating. The strange mixed-up looking structure adjacent to the stomach on the animal’s left side is the juvenile rudiment. Focusing up and down through the rudiment shows that it contains five tube feet. After metamorphosis, the juvenile urchin will use those first five tube feet to walk around as a benthic creature, having spent all of its life up to this point as a member of the plankton.

Today I captured about 20 seconds of a larva feeding. This individual is a day older than the one in the photo above and has more of that opacity that I associate with competence.

This is a dorsal view; if you imagine that you’re looking at the animal’s back, you see that the rudiment is indeed on its left side. The larva’s ciliated band is moving a lot of water, and the little specks that you can see flying around are food cells. There wasn’t enough water in this drop for the pluteus to do any actual swimming, but at this point it’s pretty heavy and would tend to sink to the bottom.

Some time in the next several days these guys are going to start metamorphosing. I will be examining them every day; keep your fingers crossed that I catch them in the act!

 

 

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Sea and sky

As a native Californian, I’ve been living with drought my entire life. Well, maybe not so much during the El Niño of 1997-98, but even then the thought “We have water now but might not later…” was always in the back of my mind. This season we had a great few weeks of rain in late November and early December, then January was bone dry and February has been disappointing as well.

This weekend an Arctic storm is moving through the region, bringing rain and cool temperatures to coastal areas and (hopefully) snow in the Sierra Nevada. Here in Santa Cruz it hasn’t rained much yet but we did get a few decent showers this morning. It just so happened that I headed down to the marine lab between showers, and the light was magnificent. The water was that magical color of aquamarine and seaglass green that I associate with the tropics. The sun was shining, casting cloud shadows on the water, which added depth to the color palette when combined with the kelp bed. So pretty!

Looking east towards Natural Bridges from Terrace Point, 28 February 2015. ©Allison J. Gong

Looking east towards Natural Bridges from Terrace Point, 28 February 2015.
©Allison J. Gong

See how translucent and green the water is? 28 February 2015. ©Allison J. Gong

See how translucent and green the water is? 28 February 2015.
©Allison J. Gong

Brown pelicans (Pelicanus occidentalis) were one of many bird species whose populations were devastated by widespread use of the pesticide DDT in the mid-20th century; in 1970 it was listed on the federal Endangered Species List. After the general use of DDT was banned in the United States in 1972 the population began to recover, and in 2009 the brown pelican was removed from the Endangered Species List (I believe the bureaucratic jargon for that is “de-listed”). It is now not unusual to see long lines of pelicans skimming the waves as they fly just above the ocean surface.

Today I didn’t see any large groups of pelicans in flight, but I did catch this one flying by right in front of me.

Brown pelican (Pelecanus occidentalis) flying past Terrace Point, 28 February 2015. ©Allison J. Gong

Brown pelican (Pelecanus occidentalis) flying past Terrace Point, 28 February 2015.
©Allison J. Gong

Anyone who knows me personally knows that I’m not a big cheerleader for the marine mammals. However, seeing cetaceans in the wild is always a treat. This morning I was lucky enough to catch this pod of dolphin-type critters as they swam right off the point. There were 6-8 of them, I think. As they swam past the marine lab a couple of them indulged in some tail slapping.

Dolphins swimming past Terrace Point, 28 February 2015. ©Allison J. Gong

Small cetaeans swimming past Terrace Point, 28 February 2015.
©Allison J. Gong

I’m not enough of a cetacean expert to be able to identify the animals from photos. They did have dolphin-like dorsal fins but I couldn’t see a prominent rostrum on any of them. I didn’t have my binoculars with me . . . and I call myself a naturalist??

Since the animals were not traveling very quickly I decided to see if I could catch them on video. I was lucky enough to get this clip:

Can anybody help me identify what these animals are?

Posted in Birds, General natural history | 3 Comments

Perfection! And yet….

Thirty-one days ago, on 20 January 2015, I spawned purple sea urchins (Strongylocentrotus purpuratus) and generated six jars of larvae. I’ve been examining the larvae twice a week ever since. At first they were doing great, developing on schedule with no appreciable abnormalities or warning flags. Then, at about Day 24, the cultures began crashing for no apparent reason. At first I expected to see lots of malformed, shriveled, or underdeveloped larvae, but the thing that I don’t understand is that for the most part they look great. They’re eating, pooping, growing, and (apparently) doing everything that they should be doing.

Case in point:

31-day-old pluteus larva of Strongylocentrotus purpuratus, 20 February 2015. © Allison J. Gong

31-day-old pluteus larva of Strongylocentrotus purpuratus, 20 February 2015.
© Allison J. Gong

This larva is PERFECT. It has all four pairs of arms now, and they are growing symmetrically. The stomach (the inverted-pear-shaped structure in the middle of the cup-shaped region) is pigmented with the red food it has been eating, and there are no skeletal rods protruding beyond the tips of the arms. This individual doesn’t give me any clues as to why the culture it came from took a nosedive this past week. The other larvae that I sampled from this jar today also look good. There aren’t many left in the jars from this spawning, but if they all look as promising as this one then I still have hope that some will be able to metamorphose successfully.

So what gives? I suspect that Day 24 has something to do with it. I’m working on a hypothesis and need to let it percolate inside my brain a bit more. When it’s ready I want to test it, although that will have to wait until next year, as we’ve reached the end of this year’s spawning season.

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Wasting leather (star)

Until recently I hadn’t closely observed what it looks like when a leather star (Dermasterias imbricata) succumbs to wasting syndrome. When I had the outbreak of plague in my table almost 18 months ago now, my only leather star was fine one day and decomposing the next, so I didn’t get to see what actually happened as it was dying.

(Un)fortunately, one of the leather stars at the marine lab started wasting a bit more than two weeks ago, and this time I was able to catch it at the beginning. This animal wasn’t in my care so I didn’t check on it as frequently as I would if it had been living in one of my tables, but one of the aquarists pointed it out to me when it began getting sick.

The first symptom was a lesion on the aboral surface. I say “lesion” but it’s more of an open wound.

Dermasterias imbricata with aboral lesion, 2 February 2015. ©Allison J. Gong

Dermasterias imbricata with aboral lesion, 2 February 2015.
©Allison J. Gong

You can see that the animal’s insides are exposed to the external environment. In the photo above the whitish milky-looking stuff is gonad (I’m pretty sure this animal was a male) and the beige ribbon bits are pyloric caeca, essentially branches of the stomach that extend into the arms. What typically happens along with the development of lesions like this is an overall deflating of the star as the water vascular system and other coelomic systems become increasingly compromised, and the tendency for the animal to start tearing off its arms.

Which results in this, a week later:

Wasting Dermasterias imbricata, autotomizing its arm, 9 February 2015. ©Allison J. Gong

Wasting Dermasterias imbricata, autotomizing its arm, 9 February 2015.
©Allison J. Gong

This poor animal had torn its arm off, and continued to live for a while. I find it fascinating that the lack of a centralized nervous system means that this animal literally didn’t know it was dead. It was finally declared officially dead two days later. Compared to how quickly wasting syndrome kills the forcipulates that I’ve seen (Pisaster, Pycnopodia, and Orthasterias), the leather stars take a long time to die–several days from start to finish, opposed to a matter of hours as I saw with my stars. The leathers didn’t seem to be hit as hard by the first wave of the disease outbreak, either. Is Dermasterias somehow able to fight off the infection a bit longer? It would be interesting to know, wouldn’t it?

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In all her glory

This afternoon I was enjoying the sunshine and watching the small finchy birds flitting about in the big coffeeberry bush off our back deck. I call this bush the “conference bush” because every spring the birds congregate in it and chatter to each other like conventioneers. When the bush blooms it becomes populated with foraging honeybees, which add their own buzz to the cacaphony. I had identified lesser goldfinches, juncos, chestnut-backed chickadees, and the impossible-to-distinguish purple/house finches and was watching a male Anna’s hummingbird making his diving displays. I was looking for the female he was displaying to when out of the corner of my eye I saw a brown bird, about the size of a scrub jay, crash into the bush.

All of the little finchy birds fled the bush instantly and the bush became silent. Training my binocs on the locus of the commotion I saw a sharp-shinned hawk perching in the tree.

Juvenile sharp-shinned hawk (Accipiter striatus).

Juvenile sharp-shinned hawk (Accipiter striatus). © John Rowe, October 2010

It was a very handsome bird. It perched and looked around for a few seconds then did a bit of preening. Directly above the hawk’s right shoulder I saw a female finch, perched desperately frozen to her twig. I don’t know why she hadn’t escaped with the others. She was obviously trying her hardest not to be seen, but the writing was on the wall. While I was watching through the binocs the sharpie exploded up and grabbed the finch, then busted out of the bush, carrying its prey out of view. I heard the poor finch squawking for about half a minute before she finally died.

This is definitely the most amazing thing I’ve seen so far this week. Nature, in all her glory, is every bit as unsentimental as she is spectacular. Wow!

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Off to the races!

Yesterday I drove up the coast to Pigeon Point to do a little poking around. I had originally planned to search for little stars, survivors that had made it through the most recent outbreak of wasting syndrome. But I got distracted by other things and gave up on the stars, for now. I need to do some thinking about the best way to find tiny animals in a very complex 3-dimensional habitat.

I did spend quite a bit of time turning over rocks in tidepools. The most common critters I found were the usual suspects–porcelain crabs, limpets, snails, the odd sculpin or two, and chitons. One rock yielded a gold mine: five chitons of a species I didn’t recognize (which doesn’t mean I haven’t seen it before, just that I didn’t immediately know its name) that demonstrated a most interesting behavior.

Stenoplax heathiana, on underside of rock, 31 January 2015. Photo credit:  Allison J. Gong

Stenoplax heathiana, on underside of rock, 31 January 2015.
Photo credit: Allison J. Gong

I turned the rock over and watched as the chitons ran away from the exposed surface onto the other side. Yes, RAN. I’ve never seen a chiton do anything this fast. Chitons, for the most part, lead apparently inactive lives. When we do get to see them in their natural setting, at low tide, they are usually scrunched down hard on the rock waiting for the water to come back. Obviously they are much more active when covered with water, but we don’t get to see them then. In the lab, where they can be immersed all the time unless they crawl up the walls, they do wander around a bit; however, to see a chiton do much of anything requires time-lapse photography.

Don’t believe that a chiton can run? Well, get a load of this:

This is in real-time, not sped up. Watch the chiton push a limpet and the snail out of the way. Okay, I’ll grant that a limpet and a snail are not the strongest obstacles one could face when trying to flee from the light. But you can’t deny that this chiton seems to be feeling a sense of urgency.

This species, Stenoplax heathiana, spends its days buried in sand on the underside of rocks. It comes out to feed at night, not on algal scums as most chitons do, but on bits of algae that drift by and get caught between rocks. Apparently the chiton can be found exposed in the very early morning. I’m going to have to try finding some this spring when we get our morning low tides back.  Anybody want to come with me?

 

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