This week I took my Ecology students to the Younger Lagoon Reserve (YLR) on the UC Santa Cruz Coastal Science Campus. The YLR is one of 39 natural reserves in all of the major ecosystems throughout the state of California. The UCSC campus administers five of the reserves: Younger Lagoon, the Campus Reserve, Fort Ord Natural Reserve, Año Nuevo (operated in conjunction with the California State Park system), and the Big Creek Natural Reserve in Big Sur. The UC reserves are lands that have been set aside to use as living laboratories and outdoor classrooms, and are fantastic places to take students to learn about the natural history of California. They provide students with opportunities to gain valuable hands-on experience working in the field, through classes, internships, or volunteering.
The Younger Lagoon Reserve comprises about 70 acres of land, most of which was formerly brussels sprouts fields. The lagoon itself is a Y-shaped body of brackish water that receives input from run-off due to rain. It connects with the water of Monterey Bay only when there is enough freshwater flowing to break through the thick sand berm; this happens once or twice a year during the rainy season. The Lagoon lands were donated to UCSC in the 1970s. East of the actual lagoon are about 47 acres of what are referred to as Terrace Lands, which were incorporated into the YLR in 2009. This is where, for the past three years, I’ve brought students to work on vegetation restoration. The team of reserve stewards, interns, and volunteers has a yearly goal to replant two acres every year.
This year, instead of getting straight to the planting, we began the morning at the bird banding station. Personnel at the YLR have been banding birds for a little over a year now, usually on Fridays and occasionally on Thursdays. The banders, or “bird nerds”, get started at about 07:30, and by the time our class arrived at 09:30 they had caught five birds. It was windy and there was no cloud cover at all, which were not very good conditions for catching birds in either the mist nets or the ground traps.
Notice how both the mist net and the ground trap are empty? That’s the kind of luck we had with the bird banding.
The rest of the morning was very productive. After the bird banding demonstration we joined the UCSC student interns on the Terrace Lands for some planting. The method used for planting has changed since the last time I was here with students in 2016, due to a 5-year study comparing weed control methods. Herbicide was very effective, but obviously toxic to the native plants as well as the weeds. The stewards also tried laying black plastic over the fields and letting the sun bake the weeds to death. This was almost as effective as herbicide; however, the plastic can be used only a few times and then has to be thrown away to end up in the landfill. The result of the study was a compromise between effective weed control and minimal negative environmental impact. The planters now put down a layer of biodegradable paper and cover it with mulch. Holes are punched through the paper and small plants are planted in the holes. The combination of the paper and mulch seems to work pretty well. Plus, there’s no waste!
A large group of about 25 motivated workers can accomplish quite a lot in a few hours. By lunchtime we had lain three long strips of the paper side-by-side, covered them with mulch, and repeated the process twice more, using up the entire roll of paper. The hole-punching and planting go more slowly, but we did place ~200 plants in the ground. It was a busy and productive morning, despite the lack of birds. The students said they learned a lot and had fun doing it. That’s the beauty of field trips!
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.
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!
This week’s field trip for my Ecology class was the first of two visits to the Santa Cruz harbor. The students’ task was to select a site to monitor for a semester-long study of ecological succession. The floating docks at the harbor are the ideal site for this kind of study because I know from experience that the biota changes from season to season throughout the year, on a time scale that can be observed within the confines of a 16-week semester. We will return to the harbor in nine weeks and students will document how their sites have changed in that time.
California is swinging back into the severe drought situation we had before the epic 2016-2017 rainy season. Since the current rainy season began on 1 October 2017, we’ve had hardly any rain at all and very little snow in the Sierra. Fools who thought that one rainy season would get us out of drought are just that–fools. However, one nice thing about drought conditions is that visibility at the harbor is pretty good. Without any significant runoff the water is nice and clear, making it easy for the students to see what’s growing on their section of the docks.
The assignment for this first visit to the harbor was to choose a site, identify what lives on the site, and draw a map of it. I had warned them that all the interesting biology on the docks occurs below the level of their feet, and that they would have to lie or kneel on the dock to get a good look at what’s going on down there. Some of them tried to take a photo of the entire site, but it’s impossible to get far enough away. Unless you’re actually in the water, from where it would be easy. Yeah, you could don a wetsuit and get in the water, but the harbor isn’t the most ideal place to go for a morning swim.
A little back story on the docks at the Santa Cruz harbor
Remember the magnitude 9.0 earthquake and subsequent tsunami that occurred in northern Japan several years ago? That was on 11 March 2011 at 14:46 local time. That morning in Santa Cruz we received a tsunami warning. I didn’t venture down to the harbor (I think I was working at the marine lab that day) but here’s a video shot by a woman who watched the ~0.5 meter tsunami tear through the upper harbor:
Amazing, the destructive power of such a small wave, isn’t it? Boats were wrenched from their moorings and slammed into other boats and harbor infrastructure. I forget the total dollar amount of damage that our harbor sustained, but as a result all of the docks were replaced in the next few years. I did happen to be at the harbor with a group of students on one of the days that the old docks were being removed. It was heartbreaking to see the docks, carrying decades of biological growth on them, dumped in the parking lot to dry out in the afternoon sun. I imagine they were eventually hauled out to the landfill.
Since then, the biota on the new floating docks seems finally to be stabilizing. If I had been teaching Ecology back in 2013, we would have had pristine habitat in which to observe honest-to-goodness primary succession. As things are, however, I’m giving students the option of scraping all or part of their plot clear, to simulate primary succession. Their other option is to leave the plot as-is, and pick up the succession process somewhere in the middle and see what happens from this point forward.
So, what did they see down there?
Well, even though the water was relatively clear, a lot of the photos looked like this:
I can identify much of the stuff in this photo, but this isn’t the best shot to showcase the biodiversity on the docks. I decided that the camera would do a better job if I used it to photograph individual organisms instead. Here are some of my favorites.
This shot is looking straight down along the edge of one of the docks. The macroscopic life begins 2-3 cm below the waterline, and even above that the dock surface is covered with microscopic scuzzes.
I had shown the students pictures of organisms they would be likely to see at the harbor. One of the critters that shows up sporadically is the introduced hydroid Ectopleura crocea. Later in the semester we will discuss species introductions and invasions in more detail. Harbors generally tend to be heavily populated by non-native species, and our local harbor is no exception. The species of Ectopleura found in harbors has hydranths that can be 8-10 cm long, and when it occurs it tends to be quite conspicuous. The congeneric species, E. marina, lives in intertidal in some areas on the open coast; I’ve seen it in a few tidepools at Davenport Landing, for example. The intertidal species is much smaller, about 2-3 cm tall and doesn’t form the dense clumps that typifies E. crocea.
The ubiquitous caprellid amphipods were crawling all over everything, as usual. Some of the students really didn’t like these guys and one of them had the same reaction to them that I do, which is a general shudder. They’re sort of cute in still photos, but when they start inchworming around they look sort of creepy. And when there’s a bunch of them writhing around in an oozy mass, they’re REALLY creepy.
One of the most conspicuous worms at the harbor is Eudistylia polymorphora, the so-called feather duster worm. They come in oranges, purples, and yellows. This one was pure white. Lovely animal!
Tube-dwelling polychaete worms, such as Eudistylia, don’t have much in the way of a head but they do have many light-sensitive eyespots on the tentacles. They react very quickly to many stimuli, and even a shadow passing over a worm causes it to yank its tentacles into its tube in the blink of an eye. Usually they’re not too shy, though, and will extend their tentacles soon to resume feeding.
All told we were on the docks for about 2.5 hours. Not a bad way to spend a glorious morning, is it?
I like to venture out of my comfort zone every once in a while, as that’s the only way to keep learning. Even though my particular area of interest is the marine invertebrates, there are a lot of other aspects of marine biology that are almost as interesting. And if I’m going to call myself a naturalist I should extend my knowledge in as many directions as I can, right? Besides, going out and learning new stuff is a lot of fun!
Shortly after the new year I went up to Año Nuevo State Park to see the northern elephant seals (Mirounga angustirostris) at their winter breeding rookery. Of course, I’ve known about the rookery ever since I came to Santa Cruz and have had friends in the Ph.D. program doing their dissertation out there, yet for whatever reason I never managed to get out there during the breeding season. The park is open all year, but while seals are on the beach for breeding the trail out to the rookery is accessible only via docent-led tour. This year I remembered to buy tickets ahead of time, to ensure that we’d be able to see the seals on a day we had time to do so.
The day we went, a Thursday, was threatening to be stormy, so we took our rain jackets just in case. We met up with our docent, a woman named Trevlyn, and hiked out to the beaches. Before we got there, though, we saw a mother bobcat (Lynx rufus) and her two kittens. This particular mom is well known to the folks at the park, who see her frequently. Because of the overcast skies, these normally crepuscular wild cats were active in the middle of the day.
Both of the kittens looked healthy, alert, and well fed. It looks like the heavy rains of the 2016-2017 season resulted in an abundance of prey–everything from insects to rodents to rabbits to birds–for carnivores, including bobcats. Given the bobcat’s variable and adaptable diet, the future looks bright for these kittens who were lucky enough to be born in a state park. They (and their prey) will not be poisoned by pesticides or herbicides or hunted by humans, although it is likely that mountain lions (Felis concolor) prowl these trails as well.
Before arriving at the rookery we stopped so that Trevlyn could go over some elephant seal biology and give us the rules for visiting the beaches. The rules were: (1) stay behind Trevlyn at all times; and (2) do whatever she says without question. These animals are BIG and can move surprisingly fast over short distances. We were there at the early part of the season and there were only a few hundred animals at the rookery. But later, after all the adult animals have returned to land and the pups are born, it gets very crowded and stinky.
Elephant seal biology
The northern elephant seal is a highly pelagic animal, coming to land for two purposes at different times of the year: to breed in the winter and to molt. While they are hauled out for either purpose they do not feed, and survive on blubber reserves accumulated during the months foraging at sea. The different demographic groups (pups, juveniles, adult females, and adult males) haul out at different times of year.
The breeding season begins in mid-November, with the adult males arriving first. As they are staking out beach territory the females start arriving about three weeks later. They are pregnant and usually give birth a few or several days after their arrival.
A female who has given birth spends all of her time resting and nursing her pup. See how the pup in the photo above is sort of skinny, with wrinkled skin? This tells us that it is only a couple of days old. As it continues to nurse that loose skin gets filled out and the pup gets nice and fat. In the meantime, its mother is fasting while she nurses, and loses a significant portion of her bodyweight.
Sometimes the juvenile males, who have not yet proven their worth against an established bull male, get a little overexcited and try to mate with a female who has just given birth. These females are not receptive because, well, they’ve just given birth and have not yet gone into estrus. Watch this female above rebuff the attention of a juvenile male. Trevlyn told us that females try to rest near the larger bull males, whose presence will keep the juvenile males in line. Oh, and those markings on the young male? Those are made with ordinary hair dye, to identify the animals being studied.
Pups nurse for 28 days, then are abruptly weaned when their mothers mate and return to the sea. At this point the pups are called weaners. Weaners can’t follow their mothers to the sea until they molt their pup fur and learn how to swim. They usually head out around early May, when they become fodder for white sharks lurking just offshore. The sharks ain’t stupid.
The spectacular showdowns between adult male seals fighting for mating rights should be starting up about now.
Adult males are by far the largest animals on the beach. They also have a much larger proboscis. And see that pinkish stuff on the neck? That is thickened, callused skin that forms when the animals are fighting. As two bull males charge into each other they rear back and then slam forward, trying to gouge each other’s neck with their teeth. The fights are not deadly but can become quite bloody before the loser decides to give in to the dominant male. While they aren’t fighting or mating the males are resting to conserve their energy. This early in the season there is plenty of space on the beach and things are pretty serene, although as animals continue to arrive and pups are born, the fighting and mating will begin in earnest and there will be a lot more activity.
But at least as of early January, youngsters like these yearlings can relax on the beach without having to worry about being run over by males weighing up to 2500 kg.
Año Nuevo Island lies just offshore. When northern elephant seals began to return to this part of California they established their first breeding colony on the Island. Many pinnipeds, as well as seabirds, breed on islands because they are protected from land predators. In the case of the northern elephant seal, the major land predator was the grizzly bear.
Problem is, Año Nuevo Island has limited beach real estate. Elephant seals can’t climb up even short cliffs, so can come ashore only on sandy beaches. The last wild grizzly bear in California was spotted in 1924, and since then the elephant seals have began taking over the coastal beaches near the island. All told, some couple thousand elephant seals will be on the beach at Año Nuevo this winter. This is a small rookery; the rookery south at Piedras Blancas is much larger. The northern elephant seal population in California seems pretty robust, with the animals having recovered nicely after being hunted to near extinction at the end of the 19th century. In these days when all news about the environment seems to be doom and gloom, it’s nice to hear of a wildlife species doing so well.
The other day I was walking along Pescadero Beach about an hour north of where I live. My husband and I had gone on a short afternoon hike in Pescadero Marsh and decided to return to the car via the beach. It was a windy afternoon, making photography difficult, but I did enjoy the chance to get out, stretch my legs, and observe some nature. The ocean was quite lively, and as always it was fun watching surf scoters playing in the waves crashing on the beach. These ducks breed in freshwater lakes in northern Canada and Alaska, but spend their winters along the Pacific and Atlantic coasts of North America, where they forage on small invertebrates.
High on the beach well above the high-tide line we spotted some little brown puff balls, perfectly colored to match the sand and tiny enough to disappear completely in the divots formed by the footsteps of previous beach combers. They would run along the sand and duck behind a small hillock of sand, where they would be protected from the wind and from visual predators. See how well they disappear?
These are the delightful snowy plovers in their winter plumage. The field guides describe them as inconspicuous, pale little birds, which they certainly are. Unlike the sanderlings and other ‘peeps’ that frequent our beaches, which gather in large flocks and run away from both waves and people, snowy plovers react to human presence by hunkering down in small depressions and relying on their cryptic coloration for protection. Snowies live in California year-round, but I see them usually in the winter and spring. They nest in the sand, laying eggs in small depressions lined with shells, pebbles, and other like debris. Both parents incubate the clutch of 3-4 speckled eggs, which hatch into speckled nestlings.
It’s this habit of nesting on sand that imperils the snowy plover. They are not as a species considered endangered, but some populations are declining. Human activities and the presence of dogs on beaches disrupt breeding birds and destroy eggs. Such tiny birds have a high metabolism and need to feed constantly. Every time they are disturbed into running away from humans they expend precious energy that they cannot spare. This is why some beaches where snowies are known to be nesting are closed to humans during the nesting season.
So if you see one of these signs on the beach, stay out of the fenced areas and keep your eyes open for tiny sand-colored puff balls. Even when the birds are not breeding they should be left alone and watched from a distance. Use your binoculars to get a close-up view of them.
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.
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.
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.
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.
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:
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 mid-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!
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.
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:
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!
If I asked you to draw a worm and designate the front and back ends, you’d most likely come up with something that looks like this:
And you would be entirely correct. A worm, or any creature described as ‘vermiform’ for that matter, has an elongated, wormlike body. Some worms have actual heads with eyes and sensory tentacles, but many don’t. The great many polychaete worms that live in tubes don’t have much of a head at all: usually all you can see sticking out of the tube is a crown of tentacles used for feeding. Although even the use of the word ‘crown’ more than suggests the presence of a head, doesn’t it? After all, where else does one wear a crown?
Most worms, including the worm that we imagined above, are bilaterally symmetrical, with bodies elongated along the Anterior-Posterior axis. This means the head is at the anterior end and the rear is the posterior end. For animals that don’t have a prominent head, the Anterior can also be defined by the direction of locomotion. Worms crawl with their bellies against the ground, which sets up a second axis of symmetry, the Dorsal-Ventral axis. The third axis of symmetry is the Left-Right axis. These axes should sound familiar, because they apply to our own bodies, as well of those of all other vertebrates and many invertebrates. Because of our upright stance we actually walk with our ventral surface forward, which is a little confusing, but if you don’t trust me you can see for yourself by crawling around on hands and knees for a while.
Now back to our worms, hypothetical and otherwise. Consider a worm that is elongated not along its Anterior-Posterior axis, but along its Dorsal-Ventral axis. It sounds strange, but such worms do exist. They are called phoronid worms, and are classified within their own phylum, the Phoronida. They all live in tubes, and the few times I’ve seen them they have been in pretty dense aggregations. As with most tube-dwelling worms the only part of the body that you can usually see is the crown of feeding tentacles, which in these animals (as well as in the Bryozoa and Brachiopoda) is called a lophophore.
The other day I was at the harbor looking for slugs with my friend Brenna, and spotted these pale tentacles swaying in the current.
These are the lophophores of an aggregation of phoronids! I’d never seen them at the harbor before, so I was pretty excited about it. They were on the side of a floating walkway, down almost beyond the reach of my outstretched arm. The current caused the lophophores to sway continuously and I was barely able to snap some blurry photos without falling in (I couldn’t really see what I was doing and just hoped for the best) when I accidentally caught this one shot. I wanted to have at least one clear-ish shot to submit to iNaturalist. I did manage to scrape off some bits of stuff that I hoped contained intact phoronids, so I could observe them under the dissecting scope at the lab.
And these are some lovely little worms!
The tubes that these phoronids inhabit are more like burrows of slime to which the surrounding sediments adhere. The tube itself isn’t anything particularly interesting, but the bodies of the worms are beautifully transparent. One of the coolest things you can see in a living phoronid is its circulatory system. They have red blood that, like ours, contains hemoglobin, so it’s easy to see the vessels that run along the length of the worm (which is the Dorsal-Ventral axis, remember) and the two blood rings around the base of the lophophore. If you get the lighting right you can even see the vessels that extend into each tentacle of the lophophore.
Single phoronid worm extending its lophophore 18 September 2017
I was disappointed to see that none of the video clips I took really do justice to these worms. They are so pretty when I look at them through the microscope, and I wish I could capture their beauty. You may at least be able to see blood moving through the larger vessels of the body in this short video.
Seems I need to upgrade my photomicroscopy set-up. Anybody have a few thousand bucks they want to donate to the cause?
I’m keeping the phoronids for as long as I can, although I don’t know what to feed them. I had time to take just a quick look at them this morning, and they look fine. Just for kicks I offered them a little phytoplankton to see what they’d do with it and couldn’t see if they were reacting at all. Still, they are filter feeders, and if I can adjust the lighting and get a good view of those ciliated tentacles I should be able to see if they are creating a water current that is bringing food to the mouth. Friday is the next day I have time to spend with these animals that I don’t get to see very often. Maybe then I’ll have something else to report.
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.
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. . .
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.
