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There are certain creatures that, for whatever reason, give me the creeps. I imagine everyone has them. Some people have arachnophobia, I have caterpillarphobia. While fear of some animals makes a certain amount of evolutionary sense--spiders and snakes, for example, can have deadly bites--my own personal phobia can be traced back to a traumatic childhood event involving an older cousin and a slew of very large tomato hornworms. Even typing the words decades later makes me want to rub my hands on my jeans.

But enough about caterpillars. This Halloween I want to share something that isn't nearly as disgusting, but can still creep me out sometimes. Commonly called skeleton shrimps, caprellid amphipods are a type of small crustacean very common in certain marine habitats. They are bizarre creatures, but a close look reveals their crustacean nature. For example, they possess the jointed appendages and compound eyes that only arthropods have.

Female caprellid amphipod (Caprella sp.)
22 October 2017
© Allison J. Gong

Around here the easiest place to find caprellids is at the harbor, where they can be extremely abundant. The last time I went to the harbor to collect hydroids for my class, the caprellids were swarming all over everything. When I brought things back to the lab I had to spend an hour or so picking the caprellids off the hydroids. I don't think they eat the 'droids, but they gallop around and keep messing up the field of view, making observation difficult. They're essentially just a PITA to deal with, and everything is easier after they've been removed.

Caprellid amphipods (Caprella sp.) at the Santa Cruz Yacht Harbor
23 June 2017
© Allison J. Gong

Caprellids are amphipods, members of a group of crustaceans called the Peracarida (I'll come back to the significance of the name in a bit). They have the requisite two pairs of antennae that crustaceans have, and seven pairs of thoracic appendages of varying morphology. Some of these thoracic legs are claws or hooked feet that like to grab onto things. A caprellid removed from whatever it's attached to and placed by itself in a bowl of seawater thrashes around spastically. Only when it finds something to grab does it calm down. Even then, they attach with their posterior appendages and wave around the front half of the body in what I call the caprellid dance: they extend up and forward, and sort of jerk front to back or side to side. It isn't pretty.

A bunch of caprellids removed from their substrate and dumped into a bowl together will use each other as something to grab. This forms the sort of writhing mass that makes my skin crawl. I was nice enough to give them a piece of bryozoan colony to hang onto, but even so they ended up glomming together.

Now, back to the thing about caprellids being peracarids. The name Peracarida means "pouch shrimp" and refers to a ventral structure called a marsupium, in which females brood their young. Males don't have a marsupium, so adult caprellids are sexually dimorphic. When carrying young, a female caprellid looks like she's pregnant. See that caprellid in the top photo? She's a brooding female. That's all fine, until her marsupium itself starts writhing. This ups the creepiness factor again. Here's that same brooding female, in live action:

Crustaceans obviously don't get pregnant the way that mammals do, but many of them spend considerable energy caring for their young. Well, females do, at least. A female caprellid doesn't just carry her babies around inside a pouch on her belly. Although she isn't nourishing them from her own body in the way of mammals (each of the youngsters in the marsupium is living off energy stores provisioned in its egg), the mother does aerate the developing young by opening and closing the flaps to the marsupium. This flushes away any metabolic wastes and keeps the juveniles surrounded by clean water. As the young caprellids get bigger, they begin to crawl around inside the pouch, and eventually leave it. They don't depart from their mother right away, though; rather they cling to her back for a while, doing the caprellid dance in place as she galumphs along herself.

Until the juveniles strike out on their own they form a small writhing mass on top of a female who can herself be part of a larger writhing mass. And the sight through the microscope of all these long skinny bodies jerking around spasmodically can indeed be very creepy. Fortunately not as creepy as caterpillars, or I wouldn't be able to teach my class or go docking with my friend Brenna. And it's a good thing caprellids are small, 'cause if they were any bigger. . . just, no.

 

Although the world's oceans cover approximately 70% of the Earth's surface, most humans interact with only the narrow strip that runs up onto the land. This bit of real estate experiences terrestrial conditions on a once- or twice-daily basis. None of these abiotic factors, including drying air, the heat of the sun, and UV radiation, greatly affects any but the uppermost few meters of the ocean's surface so most marine organisms don't need to worry about them. Despite the apparent paradox of where they live, intertidal organisms are also entirely marine--they cannot survive prolonged exposure to in air or freshwater. So how do they manage to live here?

Some organisms have a physiological tolerance for difficult conditions. These tidepool copepods and periwinkle snails, for example, are able to survive in the highest pools in the splash zone, where salinity can be either very high (due to evaporation) or very low (due to rain or freshwater runoff), dissolved oxygen is often depleted due to high temperature, and temperature itself can be quite warm. Sculpins and other tidepool fishes cope with low oxygen levels by gulping air and/or retreating to deep corners of their home pools.

Of course, animals that can locomote have the option of moving to a more favorable location. Other creatures, living permanently attached to their chosen site, aren't quite so lucky. Let's take barnacles as an example.

Nauplius larva of the barnacle Elminius modestus
© Wikimedia Commons

Barnacles have two planktonic larval stages: the nauplius and the cyprid. The nauplius is the first larval stage and hatches out of the egg with three pairs of appendages. It can be distinguished from the nauplius of other crustaceans by the presence of two lateral "horns" on the anterior edge of the carapace. The nauplius's job is to feed and accumulate energy reserves. It swims around in the plankton for several days or perhaps a couple of weeks, getting blown about by the currents and feeding on phytoplankton.

Cyprid larva of a barnacle

After sufficient time feeding in the plankton, a barnacle nauplius metamorphoses into the second larval stage, the cyprid. A cyprid is a bivalved creature, with the body enclosed between a pair of transparent shells. It has more appendages than the nauplius, and these are more differentiated. If the nauplius has done its  job well, then the cyprid also contains a number of oil droplets under its shell. These droplets are of crucial importance, because the cyprid itself does not feed. For as long as it remains in the plankton it survives on the calories stored in those droplets. The cyprid's job is to return to the shore and find a suitable place on which to settle. Somehow, a creature about 1 mm long, being tossed about by waves crashing onto rocks, has to find a place to live and then stick to it.

Returning to the topic of the challenges that marine organisms face when they live under terrestrial conditions, let's see how these barnacles manage. Along the northern California coast we have a handful of barnacle species living in the intertidal. In the higher mid-tidal regions at some sites, small acorn barnacles of the genera Balanus and Chthamalus may be the most abundant animals.

Mixed population of the acorn barnacles Balanus glandula and Chthamalus dalli/fissus at Davenport Landing
27 June 2017
© Allison J. Gong

However, nowhere is a particular pattern of barnacle distribution more evident than at Natural Bridges. Here, the barnacles in the high-mid intertidal are small, and concentrated in little fissures and cracks in the rock.

I think most of these small (~5 mm) barnacles are Balanus glandula:

Small acorn barnacles (Balanus glandula) at Natural Bridges
11 October 2017
© Allison J. Gong

And here's a closer look:

Small acorn barnacles (Balanus glandula) at Natural Bridges
11 October 2017
© Allison J. Gong

If all of the rock surfaces were equally suitable habitat, the barnacles would be distributed more randomly over the entire area. Instead, they are clearly segregated to the cracks in the rock. Each of these barnacles metamorphosed from a cyprid into a juvenile exactly where it is currently located. The cyprid may be able to move around to fine-tune its final location, but once the decision has been made that X marks the spot and the cyprid has glued its anterior to the rock, the commitment is real and lifelong. The barnacle will live its entire life in that spot and eventually die there. It is quite probable that cyprids landed in those empty areas on the rock, but they didn't survive to adulthood.

How did this distribution of adult barnacles come to be?

There is one very important biological reason for barnacles to live in close groups, and that is reproduction. They are obligate copulators, which I touched on in this post, and as such need to live in close proximity to potential mates. But today I'm thinking more about abiotic factors. In a habitat like the hid-mid rocky intertidal, desiccation is a real and daily threat. Even a minute crack or shallow depression will hold water a bit longer than an exposed flat surface, giving the creatures living there a tiny advantage in the struggle for survival. No doubt cyprid larvae can and do settle on those empty areas of the rock. However, they likely die from desiccation when the tide recedes, leaving only the cyprids that landed in one of the low areas to survive and metamorphose successfully. There are other factors as well, such as the presence of adult individuals, that make a location preferable for a home-hunting cyprid. In addition to facilitating copulation, hanging out in a cluster slows down the rate of water evaporation, giving another teensy edge to animals living at the upper limit of their thermal tolerance.

Lower in the intertidal, where terrestrial conditions are mitigated by more time immersed, barnacles and other organisms do indeed live on flat rock spaces. But at the high-mid tide level and above, macroscopic life exists mostly in areas that hang onto water the longest. Pools are refuges, of course, but so are the tiniest cracks that most of us overlook. Next time you venture into the intertidal, take time on your way down to stop and salute the barnacles for their tenacity.

Five days ago I collected the phoronid worms that I wrote about earlier this week, and today I'm really glad I did. I noticed when I first looked at them under the scope that several of them were brooding eggs among the tentacles of the lophophore. My attempts to photograph this phenomenon were not entirely successful, but see that clump of white stuff in the center of the lophophore? Those are eggs! Oh, and in case you're wondering what that tannish brown tube is, it's a fecal pellet. Everyone poops, even worms!

Lophophore of a phoronid worm (Phonoris ijimai)
18 Septenber 2017
© Allison J. Gong

Based on species records where I found these adult worms, I think they are Phoronis ijimai, which I originally learned as Phoronis vancouverensis. The location fits and the lophophore is the right shape. Besides, there are only two genera and fewer than 15 described species of phoronids worldwide.

Two days after I first collected the worms, I was watching them feed when I noticed some tiny approximately spherical white ciliated blobs swimming around. Closer examination under the compound scope showed them to be the phoronids' larvae--actinotrochs! Actinotrochs have been my favorite marine invertebrate larvae--and that's saying quite a lot, given my overall infatuation with such life forms--since I first encountered them in a course in comparative invertebrate embryology at the Friday Harbor Labs when I was in graduate school.

2-day-old actinotroch larva of Phoronis ijimai
22 September 2017
© Allison J. Gong

The above is a mostly top-down view on an actinotroch, which measured about 70 µm long. They swim incredibly fast, and trying to photograph them was an exercise in futility. They are small enough to swim freely in a drop of water on a depression slide, so I tried observing them in a big drop of water under a coverslip on a flat glass slide. At first they were a bit squashed, but as soon as I gave them enough water to wiggle themselves back into shape they took off swimming out of view.

Here's the same photo, with parts of the body labelled:

2-day-old actinotroch larva of Phoronis ijimai
22 September 2017
© Allison J. Gong

The hood indicates the anterior end of the larva and the telotroch is the band of cilia around the posterior end. The hood hangs down in front of the mouth and is very flexible. At this stage the larva possesses four tentacles, which are ciliated and will get longer as the larva grows. These are not the same as the tentacles of the adult worm's lophophore, which will be formed from a different structure when the larva undergoes metamorphosis.

As usual, a photograph doesn't give a very satisfactory impression of the larva's three-dimensional structure. There's a lot going on in this little body! The entire surface is ciliated, and this actinotroch's gut is full of phytoplankton cells. You can see a lot more in the video, although this larva is also a little squished.

I've been offering a cocktail of Dunaliella tertiolecta and Isochrysis galbana to the adult phoronids, and these are the green and golden cells churning around in the larva's gut. However, good eaten is not necessarily food digested, and the poops that I saw the larvae excrete looked a lot like the food cells themselves. Today I collected more larvae from the parents' bowl and offered them a few drops of Rhodomonas sp., a cryptonomad with red cells. This is the food that we fed actinotrochs in my class at Friday Harbor. We didn't have enough time then to observe their long-term success or failure, but I did note that they appeared to eat the red cells.

I don't know if phoronids reproduce year-round. It would be a simple task to run down and collect a few every month or so and see if any worms are brooding. Now that I know where they are, it would also be a good idea to keep an eye on the size of the patch. Some species of phoronid can clone themselves, although I don't know if P. ijimai is one of them. In any case, even allowing for the possibility of clonal division, an increase in the size of the adult population would be at least partially due to recruitment of new individuals. If recruitment happens throughout the year, it follows logically that sexual reproduction is likewise a year-round activity. Doesn't that sound like a nifty little project?

Besides, it's never a bad idea to spend time at the harbor!

For several centuries now, Earth's only natural satellite has been associated with odd or unusual behavior. Lunatics were people we would describe today as mentally ill, who behaved in ways that couldn't be predicted and might be dangerous. The erratic behaviors were attributed to the vague condition of lunacy. These words are derived from the Latin luna, which means 'moon'. The cycles of the moon have long been thought to influence human behavior as well; hence such legends as the werewolf.

We do know that the moon indeed has a very strong influence on aspects of many organisms, primarily through the tides. For example, reproduction in many marine animals is timed to coincide with a particular point in the tidal cycle. Grunion (Leuresthes tenuis, small, silver, finger-shaped fishes) run themselves up onto California beaches at night to spawn following the full and new moon high tides in the early summer months. Corals in the Great Barrier Reef spawn together in the handful of nights after the full moon in November. Animals such as these, which reproduce via broadcast spawning, are the ones most likely to benefit from synchronized spawning; after all, there is no point in spawning if you're the only one doing it. Invertebrates don't have watches or calendars; they keep time by sensing the natural cycles of sun and moon. The moon's strong effect on the tides is a signal that all marine creatures can sense and use to coordinate spawning, increasing the probability of successful fertilization for all.

Last night, Wednesday 6 September 2017, the moon was full. Yesterday at the lab, I noticed that  the large Anthopleura sola anemones living in the corner of my table had spawned.

A male Anthopleura sola anemone that had spawned
6 September 2017
© Allison J. Gong

That diffuse grayish stuff in the right-hand side of the photo is a pile of sperm. I looked at a sample under the microscope, just to be sure. By this time they had been sitting at the bottom of the table for several hours and most of them were dead. But they were definitely sperm:

Whenever I see something unusual like this my first impulse is to see if it's happening anywhere else at the lab. So I started poking around. The aquarists at the Seymour Center told me that some of their big anemones had spawned in the past couple of days; however, since they clean and vacuum the tanks every day all evidence was long gone.

Fortunately there are several A. sola anemones in other labs that aren't cleaned as regularly as the public viewing areas. One of the animals in the lab next door to where I have my table had also spawned. . .

Female Anthopleura sola
6 September 2017
© Allison J. Gong

. . . and this one is a female! What looks like a pile of fine dust is actually a pile of eggs.

Eggs of Anthopleura sola
6 September 2017
© Allison J. Gong

And the eggs are really cool. See those spines? They are called cytospines and apparently deter predation. Other species in the genus Anthopleura (A. elegantissima and A. xanthogrammica) are known to have spiny eggs, so it appears that this is a shared feature. Now, if only I could get my hands on eggs of the fourth congeneric species--A. artemisia, the moonglow anemone--that occurs in our area, I'd know for certain, at least for California species. I examined the eggs under higher magnification, but due to their opacity I couldn't tell if the had been fertilized. Most appeared to be solid single undivided cells; they could, however, be multicellular embryos.

All told, of the anemones that had obviously spawned, 1 was female and 4 were male. I sucked up some of the eggs and put them in a beaker of filtered seawater. I doubt that anything will happen, but I may be in for a pleasant surprise when I check on them tomorrow.

Remember that gull we rescued last week? After my husband took it to Native Animal Rescue here in Santa Cruz it was transferred up to International Bird Rescue's San Francisco Bay Area center in Fairfield. I e-mailed and asked how the gull was doing and whether I'd be able to witness its release back to the ocean. Yesterday I received this response:

Hi Allison,

This is Cheryl Reynolds, the Volunteer Coordinator for Bird Rescue. Thank you so much for rescuing the juvenile Western Gull and getting him into care at Native Animal Rescue. Hooks and fishing line can cause severe injuries but fortunately this guy is doing okay at this time. He/she had surgery yesterday to repair some of the damage the line caused to his leg and is being treated with antibiotics. He's not totally out of the woods yet but luckily gulls are pretty tough! I'm giving you his case number here at Bird Rescue #17-1887 but I will be happy to follow up with you on his progress. 
To answer your other questions.. We don't have a timeline yet on release, it depends on how he progresses. We don't usually send the birds back to Santa Cruz, we have so many young gulls we like to release as a group and in an appropriate location locally. 
If you would like to contribute to this birds care please go to our website at https://www.bird-rescue.org/. You can also sign up to receive our Photo of the Week and patient updates and also find us on Facebook. 
Thanks again for caring for this birds welfare. 
Kind regards,
Cheryl
We hadn't realized that the fishing line wrapped around the bird's leg had caused damage that would require surgery. This makes me doubly glad that we were able to rescue it from the surface of Monterey Bay before the injuries became more severe. It sounds like the prognosis is good for this juvenile western gull, and I hope it and several of its cohort can be returned to the skies and sea very soon.
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