Tag: natural history

Creepy crawlies

Posted on by Allison J. Gong

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.

The tiniest advantage

Posted on by Allison J. Gong

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 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.

My favorite larva — the actinotroch!

Posted on by Allison J. Gong

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!

A different take on ‘vermiform’

Posted on by Allison J. Gong

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?

Polychaete worms, Phragmatopoma californica, sticking their ‘heads’ out of their tubes at Natural Bridges
26 May 2016
© Allison J. Gong

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.

Phoronids at the Santa Cruz Yacht Harbor
18 September 2017
© Allison J. Gong

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.

The fluidity of sex

Posted on by Allison J. Gong

We humans are accustomed to thinking of sexual function as being both fixed and segregated into bodies that we designate as either Female or Male. And while we, as a species, generally do things this way, in the larger animal kingdom sexual function doesn’t always follow these rules. Many animals are monoecious, or hermaphroditic, having both male and female sex organs in the same body. Not only that, but lots of animals change from one sex to the other. As in so many aspects of biology, the way humans do things may be thought of by us as “normal,” but it isn’t the most interesting way.

Take, for example, the slipper shell Crepidula adunca. This is a small limpet-like creature that lives on the shell of a larger snail. Around here the usual host is a turban snail, either Tegula funebralis or T. brunnea.

Slipper shell (Crepidula adunca) on its host, the turban snail Tegula brunnea, at Pigeon Point
1 May 2017
© Allison J. Gong

There are several species in the genus Crepidula, including C. fornicata, which lives on the Atlantic coast of North America. The species epithet gives an inkling of how reproduction occurs in at least these two species of the genus.

Sometimes C. adunca is found in stacks. I’ve never seen a stack taller than three individuals, but C. fornicata occurs in stacks of about six. The animal at the bottom of the stack is always the largest, and a given turban snail can play host to more than one stack at a time.

Two stacks of Crepidula adunca on the turban snail Tegula funebralis, at Pigeon Point
28 June 2017
© Allison J. Gong

As you might guess, it isn’t mere happenstance that these stacks of C. adunca occur. It turns out that this unusual living arrangement is key to both sexual function and eventual reproduction in this species. The individual on the bottom of the stack (i.e., the oldest) is always a female; those at the top of the stack (i.e., the youngest) are males. However, every stack begins with a single individual, and the default sex in newly settled C. adunca is male. An experiment conducted at Friday Harbor in Washington State1 showed the change from male to female began when the snails reached a size of 7 mm, and all animals larger than 10 mm were female. Animals that begin life as male and transform into females are described as protandrous hermaphrodites. How common is this phenomenon? Not uncommon among fishes, actually. Clownfishes in the genus Amphiprion are protandrous. Remember how in the beginning of the moving Finding Nemo, Nemo’s mom dies? Well, in real life Nemo’s dad would have become his new mom!

In any case, all C. adunca begin adult life as males. If they live long enough to reach about 7 mm in length, they might get to become females. Crepidula adunca‘s unusual living arrangement also facilitates reproduction. Unlike most limpet-like gastropods, C. adunca isn’t a broadcast spawner. Rather, it copulates, as hinted at by the species epithet of its congener C. fornicata. A female slipper shell with a male on her back has a convenient source of sperm with which to fertilize her eggs:  the male reaches into her mantle cavity and transfers sperm to her. Given the constraint of copulation, a female cannot mate until she carries at least one male on her back, and a male cannot reproduce unless he settles atop a female. Once the eggs have been fertilized, they develop within the mother’s mantle cavity until she pushes them out as little miniatures of herself.

Crepidula adunca on the turban snail Tegula brunnea, at Davenport Landing
27 May 2017
© Allison J. Gong

Cool little animals, aren’t they? They remind us not to think of ourselves as The Way Things Are Done. We have a lot to learn from creatures that are not like us, and it’s stories like these that ensure I will never lose my appreciation and love for the marine invertebrates.

1 Collin, R. 2000. Sex Change, Reproduction, and Development of Crepidula adunca and Crepidula lingulata (Gastropoda: Calyptraeidae). The Veliger 43(l):24-33.

Gulls

Posted on by Allison J. Gong

Earlier this week I accidentally came upon a baby bird. I was on my way out to the cliff at the marine lab to dispose of a corpse (a fish that died of natural causes) when I noticed a western gull perched on the fence railing and allowing me to get unusually close. It was wary, though, and very alert. When I stopped to listen and watch for a while I heard a high-pitched “cheep-cheep-cheep” coming from beyond the shrubs on the other side of the fence. To get to the point where I could throw the dead fish off the cliff I had to pass closer than I wanted to the chick, which I could then see standing among the ground cover.

Western gull (Larus occidentalis) adult and chick at Terrace Point
2 August 2017
© Allison J. Gong

The western gull (Larus occidentalis), or WEGU in birders’ parlance, is a California Current endemic species. It is a bird of the Pacific coast of North America, and is rarely found more than a few miles inland. So if you don’t live right on the coast and have problems with gulls in landfills or parks, you cannot pin the blame on a WEGU. Western gulls are present year-round, feeding on whatever they can get. Like many gulls they are quite efficient scavengers and have a varied diet that often includes human refuse. They have become quite adapted to human presence, and have taken advantage of the fact that we tend to leave our garbage all over the place.

Western gull (Larus occidentalis) adult and chick at Terrace Point
5 August 2017
© Allison J. Gong

Yesterday the chick was in the same area, only a little more visible from directly above. I’d seen as many as five adults hanging around the chick, with no idea who the actual parents are. The chick is big and feathered enough to thermoregulate on its own but is still entirely dependent on its parents (and other cooperative adults) for food.

Being a gull, it is very vocal. It doesn’t sound like a gull, though. The calls sound like they’re coming from a much smaller bird. It cheeped continuously during the 20 minutes or so I was watching it, even with its parents standing right next to it. When this chick fledges, the only direction it can go is out over the water. Unless it can steer its flight well enough to land on one of the intertidal benches to the left of its present location, it’ll end up in the water. I imagine it will be able to swim just fine, but the next thing it will have to learn is how to get up in the air from the water.

Western gulls do not migrate and, garbage notwithstanding, depend on the California Current for most of their food. And while it may seem that there are gulls all over the place with plenty to burn, the WEGU’s restricted range makes this species vulnerable to perturbations in the ecology of the coastal ocean. Not only might their food supply be interrupted as prey species’ distributions change, but their nesting sites on cliffs may be inundated as sea level rises due to climate change.

Western gull (L. occidentalis) in adult breeding plumage
5 August 2017
© Allison J. Gong

Gulls have a reputation as trash birds, but the adult WEGU really is beautiful. Their large-ish body size, pure white head and front, and pink legs/feet are pretty distinctive. WEGUs are the only gulls that I feel at all comfortable IDing in the field, and that’s only when the birds are in adult plumage. This species, and many other gull species, takes four years to attain the adult coloration. The juveniles of many species all look very similar, which makes field identification a hazardous exercise. To make things even more complicated, western gulls are known to hybridize with the glaucous-winged gull (Larus glaucescens); fortunately for California birders, the hybridization zone is further north in Washington State.

Seabirds of all types depend on their feathers for insulation. Small-bodied endotherms like birds have an unfavorable surface area:volume ratio and would be unable to maintain their body temperature in cold water if they didn’t have insulation. One of the adaptations that enables a life in cold water is a preen gland near the base of the tail. This gland secretes an oily substance that the bird spreads over its feathers as a waterproof coating, very effectively shielding the body from the cold water. Feathers themselves have water-shedding properties of their own, but augmenting this feature with oil is sheer genius. You’ve heard the phrase “like water off a duck’s back”? We can say that because ducks and other water fowl have preen glands.

Feathers must be clean and lie properly for a bird to fly and thermoregulate, and birds at rest spend a lot of time grooming. All birds preen, but for aquatic birds this activity is especially crucial. Watching a bird preen is like watching a cat take a bath: the sequence of actions appears to be haphazard, but eventually the whole body gets attention.

Snow in July

Posted on by Allison J. Gong

The Sierra snowpack is California’s largest single reservoir of fresh water, accounting for 1/3 of the state’s water supply1. A state with a mediterranean climate, such as California, receives precipitation only during the short rain/snow season. During years of drought, when the average Californian frets about how little rain is falling, state water managers are keeping a worried eye on the amount of snow falling in the Sierra. Snow surveyors use remote sensing and field measurements to estimate the water content of the snowpack. The snow water equivalent on 1 April is used to compare snowpack water content across years.

The 2016-2017 snow year was a productive one, dumping near-record amounts of ‘Sierra cement’ on the mountains. (Skiers accustomed to the powder snows of Utah and Colorado often disparage the heavy snow in the Sierra, but Sierra cement carries a lot more water than powder so is much more beneficial to the state’s water supply). Most of that snow eventually melts, births streams and rivers, and flows from the mountains to lower elevations. After a good snow year, though, snow fields remain at high altitudes even during high summer. That definitely is the case around Lake Tahoe.

A few days ago my husband and I hiked from Carson Pass to Big Meadow, a through hike about 8 miles long. The hike goes through some gorgeous alpine meadow, with an absolutely stunning display of wildflowers. Even in late July we had to cross several streams and saw lots of snow.

Round Top Mountain, viewed from meadow above Carson Pass
25 July 2017
© Allison J. Gong
Snow field in the high Sierra
25 July 2017
© Allison J. Gong

If you look closely at the bottom photo, you may notice some faint pink streaks on the face of the snow field. This pink snow is called ‘watermelon snow’ because of the color. It is a phenomenon that occurs only at high altitudes or polar regions in the summer. Here’s a closer look, taken with a 70-200 mm lens that I rented for the week.

Watermelon snow
25 July 2017
© Allison J. Gong

Given the color of those streaks, you’d think the organism producing it would be a red alga of some sort, wouldn’t you? I did, too, until I did some research and learned that it is a green alga! Chlamydomonas is a genus of unicellular green algae, most of which are indeed green in color because the only photosynthetic pigments they contain are chlorophylls. However, Chlamydomonas nivalis also contains reddish carotenoid pigments that serve to shield the cell’s photosynthetic pigments from excess radiation, which is intense at the high altitudes where the algae live. The pigments absorb heat, which increases the melting of snow in the immediate vicinity and provides liquid water that the algae require. Watermelon snow is found in alpine regions across the globe, although it isn’t known whether or not the same species of alga is responsible in all cases.

Cross-country skiers and snowshoers pass through these areas in the winter, and never report seeing watermelon snow. What happens to the cells in the winter? Do they die?

It turns out that the alga persists year-round, although in different life history stages. Given the inhospitality of their habitat, most of the life cycle involves waiting in a dormant stage, with a short burst of activity in the spring. The red form that we see in the summer is a dormant resting stage, having lost the pair of flagella possessed by swimming unicellular green algae. These spores, former zygotes resulting from fertilization, are non-motile and cannot escape to deeper snow to avoid UV radiation, so they use carotenoids to serve as sunscreens. They are not dead, though, and continue to photosynthesize all summer. They rest through the winter and germinate in the spring, stimulated into activity by increased light and nutrients, and flowing water. Germination involves the release of biflagellated cells that swim to the surface of the snow, where at least some of them function as gametes. Fertilization occurs, with the resulting zygotes soon after forming the resting spores that result in watermelon snow.

It may seem strange that this organism spends most of its time in a dormant stage, but this is not at all uncommon for things that live in hostile habitats. When conditions for life are difficult, the best strategy can be to hang out and wait until things get better. Chlamydomonas nivalis does this on a yearly basis, as do many of the marine unicellular algae. And some animals, namely tardigrades, can dry out and live for decades or perhaps even centuries in a state of suspended animation, returning to life when returned to water. As with many natural phenomena, this kind of lifestyle seems bizarre to us because it is so unlike how we do things. But if C. nivalis could observe and think about how we live, it would no doubt consider us inconceivably wasteful, expending enormous amounts of energy to remain active at times when, clearly, it would much more sensible (from C. nivalis‘s point of view) to sleep until better conditions return.

1 California Department of Water Resources

Puzzling

Posted on by Allison J. Gong

The marine macroalgae are, as a group, the most conspicuous organisms in the intertidal. Yet, most tidepool explorers dismiss them as “seaweeds” and move on to the next thing, which they hope is somehow more interesting. This is akin to visiting the jungles of Brazil and not paying attention to the lush foliage that defines that particular biome. I will admit that, as a zoologist whose primary interest is the marine invertebrates, I have been guilty of this offense. I’ve also felt guilty about the oversight and thought to myself, “I really should know the algae better.” I have no formal training in phycology beyond auditing marine botany labs after I finished graduate school, but I’ve got the basics down and really have no excuse for the continuation of this gap in my knowledge.

So a couple of years ago I decided to start filling in that gap. I dragged out my marine botany notebook and have slowly been adding to it, building up my herbarium collection at the same time.

The red algae (Rhodophyta) are the arguably the most beautiful of the seaweeds, and inarguably are the most diverse on our coast. Some of them are easy to identify because nothing else looks like them, but many share enough morphological similarity that field IDs can be tricky if not downright impossible. For example, to ID a specimen and distinguish it from a close relative you may need to examine the number, size, and arrangement of cells in a cross-section of a blade. Some species are impossible to identify beyond genus (or even family, in some cases) unless you can look at their reproductive structures, which they might not have at the time they’re collected.

One of the most ubiquitous red seaweeds, and one that is easily identified to genus, is Mazzaella. The genus name for this group of species used to be Iridea, which gives a hint as to the appearance of the thalli–many of them are iridescent, especially when wet. The species that I see most often are M. flaccida in the mid intertidal and M. splendens lower down. These species are usually not difficult to tell apart once you get used to looking at them and their respective habitats.

Mazzaella splendens at Whaler’s Cove at Pigeon Point
28 June 2017
© Allison J. Gong
Mazzaella flaccida at Natural Bridges
9 July 2017
© Allison J. Gong

Mazzaella splendens is generally a solid brown with sometimes a green or purple cast. It is soft and floppy, and the blades are long (up to 50 cm) and taper to a point. The Marine Algae of California, which we call the MAC, uses the term “lanceolate” to describe this shape. Mazzaella flaccida is green or greenish-purple, sometimes more brownish along the edges; its blades are flexible but a teensy bit crisper than those of M. splendens, and its blades are described as cordate (heart-shaped) or broadly lanceolate.

Got it. That’s not too bad, right?

But then you see something like this, and a whole other set of questions comes to mind.

Thalli of Mazzaella flaccida at Natural Bridges
9 July 2017
© Allison J. Gong

Based on habitat alone these are both M. flaccida. The greenish thallus on top looks like textbook M. flaccida, but the lower thallus looks more ambiguous. It has the right size and shape but is the wrong color, and what’s up with all those bumps? I brought these thalli back to the lab to examine them more closely. Here are the entries from my lab notebook:

Now is the time to bring up the subject of life cycles in red algae. Algae such as Mazzaella alternate through three generations: male and female gametophytes, both of which are haploid; a diploid sporophyte; and a diploid carposporophyte. Here’s a diagram that shows how this alternation of three generations works:

Life cycle of some red algae, showing alternation of three generations
© McGraw-Hill

It was easy to see that the bumpy thallus I collected was sexy, while the smooth green thallus was probably not reproductive. Having both thalli in hand, along with the MAC and phycology texts in the lab, I was able to determine that the bumpy brown thallus is actually two generations in one body. So cool! But how does this work? The bumps on the thallus are called cystocarps. In Mazzaella a cystocarp contains the diploid tissue of the carposporophyte surrounded by the haploid tissue of the female gametophyte. Et voilà! Two generations in a single thallus.

Now, what’s inside the cystocarp? What does the carposporophyte tissue actually look like? To find out I had to do some microsurgery, first to remove a carpospore (1-1.5 mm in diameter) from the female gametophyte and then to cut it open to see what’s inside. What’s inside were microscopic diploid carpospores, which grow into the macroscopic sporophyte generation. Forcibly dissected out as they were, they don’t look like much, just tiny round cells about 2 µm in diameter.

Carpospores of Mazzaella flaccida
12 July 2017
© Allison J. Gong

The next logical step would be to isolate some of the carpospores and try to grow them up. I wasn’t thinking about that at the time and pressed both thalli. However, I do have another female gametophyte with cystocarps that I can investigate further tomorrow. It’s probably a fool’s errand, as I am not going to bother with sterile media and whatnot. Oh well. Nothing ventured, nothing gained, right?

Now you see it, now you don’t

Posted on by Allison J. Gong

This morning in the intertidal I was reminded of how often I encounter animals I wasn’t looking for and almost missed seeing at all. That got me thinking about color and pattern in the intertidal, and how they can be used either to be seen or to avoid being seen. Some critters–the nudibranchs immediately come to mind–are so brightly colored that they are impossible to miss, while others are camouflaged to the point that it takes a trained eye to see them.

Truth be told, however, most of the animals in the intertidal don’t have eyes, or at least eyes that can form images the way ours do. While just about any animal might be preyed upon by birds at low tide, most of the predators a creature of the tidepools might face would not be visual predators. This in turn begs the question of just how adaptive or not a species’ crypticness is. The way I see it, there are three options, or hypotheses about the potential benefit of an animal’s coloration and patterning:

  1. Colors and patterns that make an animal conspicuous are advantageous.
  2. Colors and patterns that make an animal cryptic or camouflaged are advantageous.
  3. Colors and patterns are neither advantageous or disadvantageous.

Today I’m going to consider hypothesis #2, as it is the most interesting one. Let’s put aside for now the question of how an animal’s color comes to be and consider only its effect on visibility to Homo sapiens (specifically, me).

Example #1 (obvious): Tonicella chitons

These are the pink chitons that I find on exposed coasts. They eat encrusting coralline algae, and I suspect their color derives at least in part from their diet. Here’s one that perfectly matches its food:

The chiton Tonicella lokii at Pistachio Beach
29 May 2017
© Allison J. Gong

On the other hand, Tonicella isn’t always this entirely pink, nor is it always seen on coralline algae:

The chiton Tonicella lokii at Pistachio Beach
29 May 2017
© Allison J. Gong
The chiton Tonicella lokii at Monastery Beach
27 October 2015
© Allison J. Gong

The chiton I saw at Monastery Beach wasn’t anywhere near coralline algae. It has obviously been eating something, probably algal films of whatever sort it comes across. Correlation is not causation, but it may not be mere coincidence that this pale version of Tonicella lokii lives on rock devoid of coralline algae.

Example #2 (obvious): Decorator crabs

Tonicella doesn’t intentionally alter its appearance by eating pink food. Given the extremely rudimentary nature of a chiton’s nervous system, it likely can’t intentionally do much of anything. It doesn’t have eyes so it cannot see, although there are light-sensing organs called aesthetes in the dorsal shell plates and light-sensitive cells in the lateral girdle. Chitons make their way through the world largely by following chemical gradients, either in the water current or on the substrate.

Crabs, on the other hand, have very complex compound eyes and can, to some extent, see what’s going on around them. The compound eyes of arthropods are highly effective motion sensors, certainly much more sensitive than our eyes are, which is why it’s so hard to sneak up on a fly even if you’re extending your reach by using a fly swatter. Crabs certainly are aware of the visual aspects of their surroundings. They can see potential threats and typically respond in one of three ways: (1) scuttling away; (2) coming out fighting; and (3) remaining still and trying not to be noticed.

It takes energy to scuttle back and forth, and the little shore crabs (Pachygrapsus crassipes) are always on the move. They are quick to run for cover when approached, but will come out and resume their explorations if you sit still for about a minute. They are really fast and difficult to catch, perhaps not quite as challenging as the Sally Lightfoot crabs that so enraged the crew of the Western Flyer during Ed Ricketts’ and John Steinbeck’s excursion to the Sea of Cortez, but hard enough to be not worth my effort. Fighting is an option only for those equipped to fight. Rock crabs (for example, Romaleon antennarium) remain hidden under algae or partially buried in sand, but when exposed they come out with big claws open and ready to pinch the hell out of anything that comes close. These are the only animals that I really worry could hurt me in the intertidal.

Which leaves the hold-still-and-hope-not-to-be-seen option. This is what decorator crabs do. In terms of temperament, decorator crabs (of which there are several species) are placid and unaggressive: they will pinch when provoked and it can hurt, but they won’t do the kind of damage that a rock crab would happily inflict. Decorator crabs hide in plain sight by covering their carapace and legs with little bits of the environment, usually algae. A well-decorated crab can be sporting several species of algae on its back.

This morning I saw and collected this small crab:

A small decorator crab, Pugettia richii, on a bed of Egregia menziesii at Davenport Landing
11 July 2017
© Allison J. Gong

I actually didn’t see it at first. I was pawing through the thick algal growth and felt its little feet scratching my hand. I peeked under the algae and there was the crab. Its carapace is about 2.5 cm across, and its claws probably wouldn’t be able to pinch human skin even if the crab tried to. Which it certainly didn’t. I wanted to observe the crab more closely in and keep it for use when I teach the crustacean diversity lab this fall, so I brought it back to be examined under the dissecting scope.

A decorated Pugettia richii, observed in the lab
11 July 201
© Allison J. Gong

The crab’s own color is a dark brownish red, which helps it hide amongst the red algae. It adds to the environment-as-appearance effect by attaching at least three species of red algae to its carapace. The crab does this by grabbing a piece of algae with one of its claws, then reaching up and behind its head to put it on the carapace, which has has tiny hooks that hang onto the decoration. It’s a very nifty scheme, but there’s one big problem. Each time the crab molts it loses its decoration and has to acquire its accessories all over again.

Example #3 (not obvious at all): Lottia digitalis

We have about a gazillion species of limpets on the California coast. Well, not really but it certainly does feel like it. To make things even more difficult I can’t seem to keep the current scientific names straight. I know that many of the commonly encountered intertidal limpets have been consolidated into the genus Lottia (this includes species that I learned by another name way back when) and I’m slowly getting used to recognizing the Lottia “look”. However, aside from the owl limpet (L. gigantea), which is much bigger and more conspicuous than any others, the other species are difficult to distinguish and I can never remember if species x has the deep ridges or if that’s species y. Ugh.

Earlier this spring I was in the field with my friend Brenna, and she was showing me the differences between Lottia scabra and L. digitalis. Brenna studies molluscs so I know she knows what she’s talking about. Lottia scabra is now easy for me to recognize, but L. digitalis is both trickier and more interesting.

Limpets Lottia scabra (upper right) and L. digitalis (left and lower right) among barnacles at Natural Bridges
25 June 2017
© Allison J. Gong

See how those all look like limpets? Now look at this:

Davenport Landing
11 July 2017
© Allison J. Gong

Do you even see the limpets?

The large animals in the photo are gooseneck barnacles, Pollicipes polymerus. They live on and amongst mussels in the mid-intertidal. This spring Brenna told me that Lottia digitalis comes in a morph that lives on and looks like Pollicipes. I’d never seen it until today. Look at the photo again. Can you see the limpets now?

Here are some more photos.

Lottia digitalis (“Pollicipes morph”) at Natural Bridges
11 July 2017
© Allison J. Gong
Lottia digitalis (“Pollicipes morph”) at Natural Bridges
11 July 2017
© Allison J. Gong

Isn’t it remarkable how these limpets have exactly the colors and pattern as the plates of Pollicipes? And I didn’t even know about them six months ago. I love having new things to learn and more reasons to pay closer attention to creatures I tend to take for granted. I think it’s time for me to tackle the challenge of identifying limpets in the field. Next season, that is. Today was probably my last day in the intertidal for a few months. We won’t have decent low tides during daylight hours until November.

When big is small, and small is big

Posted on by Allison J. Gong

As far as animal sizes go, we Homo sapiens are rather on the large side of things. While it’s true that many animals are larger than us (we can conveniently lump these animals in the category of ‘charismatic megafuauna’), the truth of the matter is that most animals are much smaller than us. We tend not to think about them much because, well, they’re small and easily escape notice. Numerically, about 98% of scientifically described animal species (~1,324,402 out of ~1,382,402) are invertebrates*, the vast majority of which are arthropods. Think insects, crabs, and spiders, and you get the idea: these animals are vastly numerous, but small. We are certainly more aware of big animals because we can see them and intentionally interact with them, but my casual observation is that the average person can’t see anything smaller than about 5 mm. For all intents and purposes, objects smaller than that are essentially invisible.

There is nothing good or bad about this bias towards large(r) animals; it simply is. If you think about our evolutionary history as hominids, it was much more adaptive for our ancestors to notice the large predator chasing them (or the large potential prey animal foraging in the field in front of them) than the inevitable and unescapable tiny parasites lurking in their guts or crawling on their skin.

Part of what defines an animal is multicellularity–animal bodies are made of different types of cells. The number and type of cell varies from species to species, and in some species the number of cells in the adult body is fixed, a phenomenon called ‘eutely’. Given the multicellularity of animals, it is understandable to assume that we are bigger than unicellular organisms, such as bacteria and protozoans. And for the most part, this is true.

Of course, it’s the exceptions to the rule that are most interesting. Yesterday I completed my contribution to Snapshot Cal Coast 2017 by collecting a plankton sample from the Santa Cruz Municipal Wharf and adding a couple dozen observations to iNaturalist. The plankton was surprisingly. . . boring. There was hardly any phytoplankton at all, and not much in the way of animal diversity. I expected more.

I did, however, see these two organisms:

They are about the same size, approximately 3 mm in diameter. But one is an animal and the other is a protozoan. Can you guess which is which?

The organism on the left is a protozoan, a predatory marine amoeba-like creature called an acantharian. As such an acantharian consists of a single cell, the protoplasm of which you can see as the darkish matter from which the skeletal spines protrude. Like all amoebae, acantharians feed by engulfing and digesting other cells. The spines, composed of strontium sulfate, are thought both to deter predation and retard sinking. For an organism that has no propulsive capability of its own, the possession of spines to increase drag is a handy way to remain in the warmer surface waters where food is more abundant. Acantharians are usually most abundant in local coastal plankton during the spring and summer. I do occasionally see them in the winter, but they are always smaller than the ones I see in the summer.

The organism on the right is an animal, the medusa of the hydrozoan Obelia. The hydroid form of this animal is very common on pilings and docks, and its medusae are present in the plankton year-round.

Life cycle of the hydroid Obelia sp.
© McGraw-Hill

These two vastly different organisms demonstrate very nicely that what’s big for one group can be quite small for another. The acantharian above, measuring a whopping 3 mm in diameter (a size that would be invisible to most people), is much bigger than several multicellular animals–tardigrades, rotifers, and the larvae of many marine invertebrates come to mind. In fact, newly settled juveniles of the sea star Pisaster ochraceus are about 500 µm in diameter, or 1/6 the size of that acantharian. Of course, bigness and smallness are both relative, are they not?

Ultimate body size, whether singular or multicellular, has ramifications for physiology and ecology. Small organisms are much more strongly affected by the external environment than large ones and thus generally have more difficulty maintaining homeostasis. On the other hand, small organisms take less time to reach adulthood, have shorter generation times, and can respond more quickly to changing environmental conditions. Big organisms require more resources–space, food, etc.–and at a population level are less quick to adapt when the environment changes.

Maybe there’s a lesson for us, no?

Reference: Brusca et al, 2016. Invertebrates, 3rd edition. Sinauer Associates, Inc.