Here's another photo, taken from farther away to give you a bigger picture of the scale of things.
Believe it or not, the maker of these trails is the little black turban snail, Tegula funebralis. They are one of my favorite animals in the intertidal, for a number of reasons:
I always root for the underdog and the under-appreciated, and these snails are so numerous in the intertidal that they are practically invisible. People literally do not see them. I know, because I ask.
They are very useful creatures to keep as lab pets. I throw a few of them into each of my seawater tables, except for the table that contains a resident free-ranging sea star, and they do a fantastic job keeping algal growth to a tolerable minimum. They're my little marine lawnmowers!
They come in very handy when I'm teaching invertebrate zoology. Students study them live to observe behavior, and the snails are not shy. They are very tolerant of being picked up and gently prodded, and soon emerge from their shells and carry on their little snail lives. Students also dissect them in lab to learn about gastropod anatomy.
So yes, these tracks in the sand are made by T. funebralis in the high intertidal. In areas where a layer of sand accumulates either at the bottom of a pool or on a flat exposed rock, it is not uncommon to see a turban snail pushing sand out of the way as it crawls along, like a miniature snow plow.
Tegula funebralis and its congeners are called turban snails because their shells are shaped like turbans. Given their small size (a big T. funebralis would have a shell height of 2.5-3 cm), pushing sand around must be a tiresome chore. They do it because they have no choice. Most grazing gastropods, such as turban snails and limpets, can feed only when they are crawling. There may very well be a nice yummy layer of algal scum on the surface of this rock, but the snail has to push the sand out of the way before it can feed on it.
Here's another photo, taken at the snail's level.
This snail is pushing through a wall of sand as tall as itself! I don't know about you, but I sure as heck couldn't do that. Props to these little snails!
A few days ago I was in the intertidal with my friend Brenna. This most recent low tide series followed on the heels of some magnificently large swells and it was iffy whether or not we'd be able to get out to where we wanted to do some collecting. Our first day we went up to Pistachio Beach, just north of Pigeon Point, where the rocky intertidal is bouldery and protected by some large rock outcrops.
So while the swell was indeed really big, we were pretty well protected in the intertidal. The Seymour Center has a standing order for slugs, hermit crabs, and algae. I was easily able to grab my limit (35) of hermit crabs over the course of the afternoon, and while it's too early in the season for the algae to do much I had my sluggy friend with me to take care of finding nudibranchs, which left me free to let my attention wander as it would.
The very first thing to catch my eye as we go out there was the coenocytic green alga Codium setchellii, which I wrote about last time. I've seen and collected C. setchellii from this site before, but don't remember seeing it in such large conspicuous patches. I need to review what I learned about the phenology of various intertidal algae, but here's a thought. Maybe Codium is an early-season species that gets outcompeted by the plethora of fast-growing red algae later in the spring. Red algae were present at Pistachio Beach but not in the lush (and slippery!) abundance that I'll see in, say, June. I'm willing to bet that Codium will be less abundant in the next few months.
In my experience, the six-armed stars of the genus Leptasterias have always been the most abundant sea stars on the stretch of coastline between Franklin Point and Pescadero. Even though they are small--a monstrously ginormous one would be as large as the palm of my hand--they are very numerous in the low-mid intertidal. I've seen them in all sorts of pinks and grays with varying amounts of mottling. Alas, I don't know of any really reliable marks for identifying them to species in the field.
Unlike other familiar stars, such as the various Pisaster species and the common Patiria miniata (bat stars), which reproduce by broadcast spawning their gametes into the water, Leptasterias is a brooder. Males release sperm that is somehow acquired by neighboring females and used to fertilize their eggs. There isn't any space inside a star's body to brood developing embryos, so a Leptasterias female tucks her babies underneath her oral surface and then humps up over them. Leptasterias also humps up when preying on small snails and such, so that particular posture could indicate either feeding or brooding.
Here's a Leptasterias humped up on a rock, photographed last spring:
The only way to tell if a Leptasterias star is feeding or brooding is to pick it up and look at the underside. I did that the other day and saw this:
Those little orange roundish things are developing embryos. While the mother is brooding she cannot feed, and can use only the tips of her arms to hang onto rocks. Don't worry, I replaced this star where I found her and made sure she had attached herself as firmly as possible before I left her. In a few weeks her babies will be big enough to crawl away and she'll be able to feed again.
Looks like the reproductive season for Leptasterias has begun.
The next day Brenna and I went to Davenport, again hoping to get lucky despite another not-so-low tide and big swell.
Davenport Landing Beach is a popular sandy beach, with rocky areas to the north and south. The topography of the north end is quite variable, with some large shallow pools and lots of vertical real estate to make the biota very diverse and interesting. The big rocks also provide shelter from the wind, a big plus for the intrepid marine biologist who insists on going out even when it's crazy windy. The southern rocky area is very different, consisting of flat benches that slope gently towards the ocean, with comparatively little vertical terrain. The southern end of the beach is always more easily accessible, which is why I almost always go to the north. But this day the north wasn't going to happen. The winter storms had washed away at least a vertical meter of sand between the rock outcrops. That and the not-so-low tide combined for conditions that made even getting out to the intended collecting site a pretty dodgy affair. So Brenna and I trudged across the beach to the south.
Along the way we saw lots of these thumb-sized objects on the beach. At first glance they look like pieces of plastic, but after you see a few of them you realize that they are clearly (ha!) gelatinous things of biological origin. They are slipper-shaped and you can stick them over the ends of your fingers. They have a bumpy texture on the outside and are smooth on the inside.
Any guesses as to what they are?
These funny little things are the pseudoconchs of a pelagic gastropod named Corolla spectabilis. What is a pseudoconch, you ask? If we break down the word into its Greek roots we have 'pseudo-' which means 'false' and 'conch' which means shell. Thus a pseudoconch is a false shell. In this case, 'false' refers to the fact that this shell is both internal (as opposed to external) and uncalcified.
The animal that made these pseudoconchs, Corolla spectabilis, is a type of gastropod called a pteropod (Gk: 'wing-foot'). Pteropods are pelagic relatives of nudibranchs, sea hares, and other marine slugs. They are indeed entirely pelagic, swimming with the elongated lateral edges of their foot. Like almost all pelagic animals, Corolla has a transparent gelatinous body. Even their shell is gelatinous, rather flimsier than most shells, but it serves to provide support for the animal's body as it swims.
You can read more about Corolla spectabilis and see pictures and video here.
Why, you may be wondering, do the pseudoconchs of C. spectabilis end up on the beach, and where is the rest of the animal? The body of Corolla and other pteropods is soft and fragile. When strong storms and heavy swells seep through the area, the water gets churned up and pteropods (and other pelagic animals) get tossed about and shredded. This leaves their pseudoconchs to float on currents until they are either themselves demolished by turbulence or cast upon the beach. Corolla is commonly seen in Monterey Bay, and it is not unusual to find their pseudoconchs on the beaches after a series of severe storms.
Brenna and I were wondering if we could preserve the pseudoconchs somehow. I took several back to the lab and tried to dry them, thinking that they might behave like Velella velella does when dried. Unfortunately, the next day they had shriveled into unrecognizable little blobs of dried snot, and the day after that they had disintegrated completely into piles of dust. Maybe drying them more slowly would work. Something to consider the next time I run across pseudoconchs in the sand.
Before Christmas I was invited to speak at one of the monthly public talks hosted by the Seymour Marine Discovery Center. I'm always happy to be asked to speak to students or the public, so my default answer to these requests is "Yes!" Usually for this kind of presentation I get to choose the topic, but this time my name came up because one of the Seymour Center staffers came up with "bees, banana slugs, and bat stars" so that's what I was given to work with. When my brain took hold of this topic and these very disparate animals, the common theme that came to mind was . . . wait for it . . . reproduction. So yes, this is going to be another sex talk.
What this means is that I need to provide some information on the talk and photos so that the Seymour Center can start publicizing the event, which is in March. Banana slugs are still in the mix, and I don't have any pictures of them, so this afternoon I took advantage of a break between storms to go hiking in the forest and look for slugs. I'd been feeling a little cabin fever for the past few days because of the rain and my own recovery from bronchitis which sapped all of my energy, so I was grateful for an excuse to leave my desk and get outside for a bit.
I headed out to the Forest of Nisene Marks State Park, knowing that where there are redwood trees there should also be banana slugs, especially after all the rain we've had recently. You know how when you're looking for something you can't find it, and when you're not looking for it you see them all over the place? That's how this hike began. It turns out that looking for banana slugs under a deadline makes them very hard to find. And I did have a deadline, as I'd promised to have the blurb and photos for my talk ready today.
After about half an hour of slowly meandering along the trails and getting distracted by all the fungi that popped up after the rains, I did see a banana slug:
That is such a gastropod face! Banana slugs are really cool (and ectothermic, too) animals. One of my buddies in grad school kept one for a pet in our office bullpen; we called it Terry, because slugs are hermaphrodites and deserve androgynous names. Terry really liked eating mushrooms and lettuce.
Banana slugs, and all of the terrestrial snails and slugs, are pulmonate ("lung") gastropods. Most of their marine relatives, with whom I spend so much quality time in the lab and in the field, are prosobranch ("gill in front") gastropods. The nudibranchs and sea hares, which are so photogenic and conspicuous, are opisthobranch ("gill on back") gastropods. As these names imply, the prosobranchs and opisthobranchs possess gills (although they are very different kinds of gills) and thus live in water. The pulmonates don't have gills; they live on land and breathe air. [There are aquatic pulmonates, too. Only a few are marine, and most live in fresh water. They have to come to the surface to breathe.]
So, what is the lung of a banana slug? It's actually the mantle cavity, that oh-so-molluscan feature, that in prosobranchs contains the gill(s). In the pulmonates, the mantle cavity is highly vascularized, as you'd expect from any gas-exchange surface, and opens to the outside by a hole called a pneumostome.
Here's the pneumostome of my first banana slug of the afternoon:
The pneumostome is always on the right side of the animal's mantle. You can actually watch it open and close as the slug breathes.
I found a second slug about an hour into the hike.
See? No pneumostome on the left side.
If I'd had the time, I would have put the slugs together to see if they'd mate. It is a sex talk I'm prepping for, after all. Heck, what would be even better would be to find two slugs already in copulo. No such luck today, though. What's good about not finding everything that I was looking for today is that it gives me incentive to keep going out to search for it. And in the meantime, I've got to start studying up on local fungi. I saw so many different kinds of mushrooms today that now I'm motivated to fill in this particular gap in my knowledge. Might as well take advantage of the El Niño rains, right?
The Dendronotus veligers are still alive. I've been running into the same difficulties I've always had when trying to rear nudibranch larvae: hydrophobic shells that tend to get stuck in the surface tension of the water. Larvae that are trapped at the surface can neither swim nor feed.
We can pretty easily rear sea urchin larvae in culture by stirring jars on a paddle table. The stirring keeps the larvae and their food in suspension; without stirring the larvae would settle on the bottom and die. Nudibranch veligers are stronger and faster swimmers than sea urchin larvae and I thought I could get away with not stirring them, as I worried that the paddles might break the larval shells.
Two jars of larvae are being stirred on the paddle table, along with several jars of sea urchin juveniles that resulted from a spawning I did back in late February. The paddles move back and forth and keep the water moving, ensuring that the larvae have pretty consistent access to food.
It's a little early to tell, but it seems that there may be fewer larvae trapped at the surface in these jars. And I didn't see more smashed or broken larvae in these jars compared to the others. I'll look at them again tomorrow to reassess.
One jar of larvae is being gently bubbled, to see if this helps break the surface tension. I started with bubbling that was too gentle, and the other day upped the airflow a bit. There is a slow circular current in the jar that might be helping.
The two beakers in the front of this table have no agitation at all. These larvae are dependent on oxygen dissolving into the water from the surface, and I'm a little worried that they might be a little oxygen-stressed. They are definitely getting stuck at the surface, so I doubt this will be a long-term solution to that particular problem.
Tomorrow I will change the water in all the jars and beakers, and try to assess the amount of stuckage in each. Hopefully either stirring or bubbling will be the way to maximize survival of my larvae.
Today a lot of my Dendronotus eggs had hatched on their own, swimming through the water as bona fide veliger larvae. Nudibranch larval culture has officially started!
These bad boys are much more spherical now--whew!-- which makes me think that pointy-shell thing I saw last week was an artifact of their premature hatching. Now they look like little swimming bubbles. Interestingly, their shells are mostly empty. My invertebrate larval culture guide says that planktotrophic larvae (those that feed while in the plankton) such as these hatch with relatively tiny bodies that grow as the larvae feed. We'll see if that holds for these guys.
I captured some video of the little veligers zooming around. Here they are at 10X magnification:
Here's another short video clip of some veligers that were conveniently squished under the coverslip. This kept them from swimming away and I was able to film them at higher magnification. You can see the little velum whirling away and then being retracted. See also how most of the shell space is empty?
So, now that these guys have hatched and have all that empty space inside their shells to fill up, they need to eat. What do I feed them, you ask? Well, because I was in a hurry to get them something, anything, to eat this morning, I fed them a bit of Isochrysis galbana, which is a haptophyte. Algal taxonomy is not well established yet, and there are many ways of classifying both micro- and macroalgae. I hesitate to wade into those murky waters, so suffice it to say that Isochrysis is a unicellular alga, golden-brown in color but neither a diatom nor a dinoflagellate.
This is what Isochrysis galbana looks like in culture. We grow it in 1000-mL flasks of sterilized seawater and nutrients.
According to the literature, veligers of Dendronotus frondosus can be raised on a mixture of Isochrysis galbana and a red alga called Rhodomonas salina. And it just so happens that we also have R. salina in culture, so starting tomorrow the veligers will get a mixture of algae for their breakfast.
The marine gastropods and bivalves go through a larval stage called a veliger. This larva gets its name from the ciliated structure, called a velum, that the animal uses for swimming. Veligers have shells--1 for gastropods and 2 for bivalves--and can withdraw the velum into the shell. Even gastropods that lack shells as adults, such as nudibranchs, have shells as larvae.
The egg mass from Dendronotus is still intact and the embryos are developing nicely. This morning when I looked at it through the microscope I could see the little larvae swimming around inside their egg capsules. I wanted to take a closer look under the compound scope, and when I teased apart the egg mass some of the larvae were forced to "hatch" prematurely. They're not yet ready for life on their own but now they're out in the real world swimming, for better or for worse.
Not being one to let an opportunity like this go to waste, I took some video of the almost-veligers.
You can see the cilia on their little velums whirling around. The larvae aren't as spherical as I had expected, based on what I've seen in other nudibranchs, and I think it'll be fun seeing how they develop. More as things unfold!
What better way to start a new blog than to talk about sex?
This morning at the Seymour Center I noticed a blob of what looked like nudibranch eggs on the wall of one of the tanks. Looking around for the likely culprit I saw three big nudibranchs on the tank. Ooh, cool!
This is Dendronotus iris, a large nudibranch, or sea slug. This bad boy/girl had a foot (the flat white bit that you see reflected in the aquarium glass) that was about 15 cm long. The brownish branched structures on the slug's back are its cerata, which function as gills. These animals do not have the ctenidium, or gill, that is typical of marine snails. Other nudibranchs carry their gills in a single plume that surrounds the anus.
There is one other big slug in this tank. It has a paler body color and cerata that are banded with orange and tipped with white.
Nudibranchs are among the rock stars of marine invertebrates--they are flamboyantly colored, have short adult lives with lots of sex, and leave beautiful corpses when they die. After a planktonic larval life of a few weeks, adult nudibranchs spend their time eating, copulating, and laying eggs. Each slug is a simultaneous hermaphrodite, capable of functioning as both male and female, and mating involves an exchange of sperm. In some other species of nudibranch the act of love can be followed by an act of cannibalism.
Nudibranchs lay egg masses in ribbons or strings that are characteristic of the species. It turns out that Dendronotus egg masses look like Top Ramen noodles:
Each of those individual little white blobs is an egg capsule that contains 10-30 developing embryos. These eggs were deposited yesterday (3 June) and the embryos have been developing but are not yet at any distinct stage. With water temperature at about 13C, I think they'll develop pretty quickly.