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.
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.
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.
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.
Remember that gull we rescued last week? After my husband took it to Native Animal Rescue here in Santa Cruz it was transferred up to International Bird Rescue‘s San Francisco Bay Area center in Fairfield. I e-mailed and asked how the gull was doing and whether I’d be able to witness its release back to the ocean. Yesterday I received this response:
Hi Allison,
This is Cheryl Reynolds, the Volunteer Coordinator for Bird Rescue. Thank you so much for rescuing the juvenile Western Gull and getting him into care at Native Animal Rescue. Hooks and fishing line can cause severe injuries but fortunately this guy is doing okay at this time. He/she had surgery yesterday to repair some of the damage the line caused to his leg and is being treated with antibiotics. He’s not totally out of the woods yet but luckily gulls are pretty tough! I’m giving you his case number here at Bird Rescue #17-1887 but I will be happy to follow up with you on his progress.
To answer your other questions.. We don’t have a timeline yet on release, it depends on how he progresses. We don’t usually send the birds back to Santa Cruz, we have so many young gulls we like to release as a group and in an appropriate location locally.
If you would like to contribute to this birds care please go to our website at https://www.bird-rescue.org/. You can also sign up to receive our Photo of the Week and patient updates and also find us on Facebook.
Thanks again for caring for this birds welfare.
Kind regards,
Cheryl
We hadn’t realized that the fishing line wrapped around the bird’s leg had caused damage that would require surgery. This makes me doubly glad that we were able to rescue it from the surface of Monterey Bay before the injuries became more severe. It sounds like the prognosis is good for this juvenile western gull, and I hope it and several of its cohort can be returned to the skies and sea very soon.
This is the time of year when whales visit Monterey Bay and often come quite close to shore. Humpbacks, in particular, are commonly seen from beaches in the fall. Earlier in the summer they are out over the Monterey Canyon feeding on krill. In the late summer and early fall they switch to feeding on anchovies, which school in shallower water over the continental shelf. Last week they were putting on a show, to the delight of whale watchers who pay for whale watching trips out of Moss Landing and Santa Cruz.
Yesterday evening my husband and I borrowed a friend’s little boat and went out looking for whales. A humpback had been seen from the beach around the cement ship at Seacliff State Beach, lunge-feeding and breaching. Even the Monterey Bay is a big body of water, and I’d rated our chance of finding a whale at about 50%. We did eventually find one swimming parallel to the shore. And I have pictures to prove it!
The Marine Mammal Protection Act of 1972 prohibits humans from approaching any marine mammals, so we kept our distance. The whale undoubtedly knew we were there and it did get a little closer than this, right around the time that we noticed a flock of ~25 pelicans fly overhead and start circling over an area a short distance away. It was starting to get dark and we had to turn around and head back, and on our way we ended up where the pelicans were hanging out.
As we approached we could see a bird flapping about on the surface of the water, but unable to get airborne. It didn’t take long for us to see that it was somehow tied up with a dead common murre and a piece of kelp. We were able to pull the kelp toward the boat and grab the live bird. It appeared to be a juvenile gull.
It had a hook in its right nostril and a hook in each foot. The hook in its beak was attached to line that went around its body, making the bird unable to raise its head. Fortunately Alex was able to cut the line while I held the bird. We didn’t have the tools to try removing the hooks, so we decided to head back in. We wrapped the bird loosely in a towel to keep it from flailing around and held onto it for the long, wet ride back to the harbor.
When we back on land I called the Marine Mammal Center because: (a) I had the number programmed into my phone; and (b) I knew they’d have a live person to answer the phone, who would be able to tell me who to call about this bird. The person I talked to transferred me to Pacific Wildlife Care in Morro Bay. The recorded message told me to place the bird in a box or pet carrier on a towel and leave it in a warm, dark place until we could bring it in the morning. We weren’t about to make a 2.5-hr drive to Morro Bay, but fortunately there is an organization right here in Santa Cruz that we’ve taken animals to before: Native Animal Rescue. We got home, dug out the kitty carrier, and tucked the bird in for the night. The only warm place we could think of that the cats couldn’t get to was the pantry, so the bird spent the night there.
I had a school meeting this morning, so Alex took the bird to Native Animal Rescue. The woman who met him said the bird was a juvenile western gull (Larus occidentalis)–another WEGU. She took the bird out, wrapped it in a towel, and calmed it by simulating a hood on its head.
The woman pulled the hook out of the nostril pretty easily. To remove the hooks from the feet she had to first cut the barbs and then pull them back out. Alex said the whole thing took about 5 minutes. The bird seems otherwise uninjured. The folks at Native Animal Rescue will keep an eye on it for a few days and then release it back to the wild. I think I’ll give them a call tomorrow and see if we can be there when the bird is released.
Update Sunday 20 August: We called Native Animal Rescue this morning and were told that the bird had been transferred to a wildlife care facility up in Fairfield. All of the seabirds that come into Native Animal Rescue get sent up there. So we won’t get to see “our” gull be released back into the wild.
In biology, it is often the exceptions to the rules we teach that are the most interesting organisms. For example, every child knows that the sky is blue and the grass is green. With a few leading questions you can get a child to generalize that all plants are green. We all know this, right? Plants are green because they have chlorophyll, which allows them to perform the magic of photosynthesis. And yes, it really is magic. Harvesting the power of the sun to build complex molecules out of CO2 and H2O? Hell yeah, photoautotrophs are freakin’ amazing!
But what about the plants that aren’t green? How do they make a living?
I’ve already written about dodder, a parasitic plant that is commonly seen growing on pickleweed at Elkhorn Slough. A few weeks ago when I was at Lake Tahoe I encountered another plant that has a parasitic lifestyle: snow plant.
Snow plant (Sarcodes sanguinea) is a non-photosynthetic plant that has zero chlorophyll and thus zero green color, and is instead a rich blood-red color hinted at by its species epithet. It lives on the forest floor in close proximity to coniferous trees. The blood-red inflorescences shoot up from the ground, apparently out of nothing; the rest of the plant lives underground. If you break an angiosperm into its basic anatomical components you have: leaves, stems, roots, and flowers. Snow plant isn’t photosynthetic, so it doesn’t need or have leaves. And since stems are essentially support structures to hold leaves up to the light it doesn’t have those, either. The roots and vegetative parts (rhizomes?) of snow plant are underground and for most of the year there’s no indication that it’s there at all, until it sends up an inflorescence in the late spring as the winter snow is melting.
Since snow plant isn’t autotrophic and doesn’t fix its own carbon, it has to obtain fixed carbon from elsewhere. Snow plant lives under conifers, but is not a parasite on the trees the way that dodder is a parasite on pickleweed. The relationship is much more complex and involves a third player. And all of the action happens underground.
Enter the third player, a mycorrhizal fungus. This fungus’s mycelium spreads through the roots of the conifers with which it has a mutualistic relationship. The tree shares photosynthate (i.e., fixed carbon) to the fungus, which in turn provides minerals to and enhances water uptake for the tree. These mycorrhizal symbioses are very common in Nature, but most often go unnoticed because they occur in the soil.
Sarcodes sanguinea, the third partner in this unusual plant-plant-fungus ménage à trois, takes advantage of the intimacy between the conifer and the fungus. Instead of parasitizing the tree it targets the fungus, siphoning off part of the fungus’s share of photosynthate. I suppose this makes snow plant an indirect parasite of the tree. The tree is doing all the work, as it is the only autotrophic member of the trio. It shares photosynthate with the fungus and gets something vital in return. Snow plant, on the other hand, doesn’t contribute anything to either the fungus or the tree. Rather, it takes directly from the fungus and only secondarily from the tree.
It would be interesting to investigate the energetics of this three-way relationship. How do the fungus and tree react to parasitism by snow plant? On which of the mycorrhizal partners does snow plant have the strongest effect? The fungus, because its share of fixed carbon is being drained directly? Or the tree, which suffers because feeding the snow plant via the fungal intermediary means less photosynthate available to support its own metabolic activities? Does the tree have any way to stop the flow of fixed carbon to an area of the fungal mycelium that is being parasitized by the snow plant?
One last note. Many of the snow plants that we saw on the trail out of Carson Pass to Big Meadow had been surrounded by stones. We never saw any signs so aren’t sure why, but I think hikers want to keep the snow plants from getting trampled. The species isn’t endangered or threatened, although it is restricted to higher altitudes in California’s mountain ranges.
Distribution of Sarcodes sanguinea in California
I think the stone rings were put there both to point out and protect the S. sanguinea inflorescences, although it would be hard to miss them. Nothing else is that bloody shade of red, and it really does stand out. Even small plants are very conspicuous.
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.
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.
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.
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.
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.
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.
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.
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 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.
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:
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.
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?
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:
Colors and patterns that make an animal conspicuous are advantageous.
Colors and patterns that make an animal cryptic or camouflaged are advantageous.
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 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.
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.
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.
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?
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.
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.
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.
The intertidal portion of my participation in Snapshot Cal Coast 2017 is complete. I organized four Bioblitzes, two of which consisted of myself and Brenna and the other two for docents of the Seymour Marine Discovery Center (Tuesday) and the docents of Año Nuevo and Pigeon Point State Parks (Wednesday). The four consecutive days of early morning low tides have been exhausting for a concussed brain and a body dealing with bronchitis for the past several weeks. Good thing the low tide arrives 40-50 minutes later, or I’d probably be dead by now. And even so, I tried to take advantage of the later tides to venture a bit farther afield, so I still ended up getting up at the butt-crack of dawn.
But oh, so totally worth it!
Day 3: Davenport Landing with docents from the Seymour Marine Discovery Center, Tuesday 27 June 2017, low tide -1.1 ft at 08:03
Davenport Landing Beach is a sandy beach with rock outcrops and a fair amount of vertical terrain to the north, and a series of flat benches (similar to those at Natural Bridges) to the south. To get to the good spots at the north end you have to do some cliff scrambling, unless the tide is low enough that you can walk around the rock, which happens maybe once or twice a year. Because it’s easier to get around on the benches to the south, that’s where I took my group for the Bioblitz. The difference in topography also results in some differences in biota and distribution/abundance of organisms; overall biodiversity is probably equivalent at both sites, but certain species are more abundant at one site versus the other.
The morning we went to Davenport was sunny and (almost) warm. This makes for plenty of light for photography, but also lots of glare of the surface of pools and the wet surfaces of organisms themselves. My most successful photos are the ones I took with the camera underwater. Wanting to improve my skills at identifying algae, I concentrated most of my efforts on them while not ignoring my beloved invertebrates.
Coralline algae are red algae whose cells are impregnated with CaCO3. This gives them a crunch texture that is unusual for algae. Corallines come in two forms, encrusting and upright, and can be one of the most abundant organisms in the high and mid intertidal. There are several species of both encrusting and upright corallines on our coast, and most of the time they aren’t identifiable to species by the naked eye. Sometimes I can distinguish between genera for the upright branching species. However, the encrusting species require microscopic examination of cell size, crust thickness, and reproductive structures, none of which can be observed in the field.
Some algae are so distinctive that a quick glance is all it takes to know exactly who they are. With its tiny holdfast, long elastic stipe, and single large pneumatocyst, bullwhip kelp doesn’t look anything like the other kelps in California. Like most kelps, N. luetkeana lives mostly in the very low intertidal or subtidal, where under certain conditions it can be a canopy-forming kelp. About a month ago I noted a big recruitment of baby Nereocystis kelps in the intertidal on the north side of Davenport Landing Beach. I speculated then that they probably wouldn’t persist into the summer. I’ll have to take a morning soon to go up and check on them. Anyway, on our Tuesday Bioblitz we found this big N. luetkeana growing in the intertidal. The stipe was about 1.5 meters long and the pneumatocyst was a little smaller than my closed fist. Given that this individual recruited to that spot and has persisted for a few months, probably, it has a good chance of continuing to survive into the fall. Winter storms, especially if they’re anything like the ones we had this past year, will most likely tear it off, though.
Coralline algae aren’t the only pink things in tidepools. There are pink fish!
Sculpins are notoriously difficult to ID if you don’t have the animal in hand to count things like fin rays and spines. Someone on iNaturalist may be able to ID this fish, but I don’t think the photo is very helpful.
And, just because they’re my favorite photographic subjects in the intertidal, here’s a shot of Anthopleura sola:
As of this writing, 10 participants in this Bioblitz have submitted 204 observations to iNaturalist, with 70 species identified. I know that some people haven’t upload their observations yet, and expect more to come in the next couple of weeks. The docents enjoyed themselves, to the extent that two of them accompanied Brenna and me to our fourth Bioblitz at Pigeon Point.
Day 4: Whaler’s Cove at Pigeon Point with rangers (and one docent) from Pigeon Point and Año Nuevo state parks, Wednesday 28 June 2017, low tide -0.6 ft at 08:53
Usually when I go to Pigeon Point I go to the north side of the point, either scrambling down the cliff next to the lighthouse or about half a mile north to Pistachio Beach. When the park rangers and I were organizing this Bioblitz they suggested going to Whaler’s Cove, as the access is very easy due to a staircase and would be much easier for docents who aren’t used to climbing down cliffs. It ended up being a good decision, as there was much to be seen.
Bioblitzes and iNaturalist are all about photographing individual organisms (as much as possible) so that they can be ID’d by experts in particular fields. This is the ‘tree’ level of observation I mentioned in my previous post. I find that when I’m taking photos with the intent to upload them to iNaturalist the photos themselves tend to be rather boring. The intertidal is such a dynamic and complex habitat that photos of single species tend to lack the visual interest of the real thing. I’ve learned that one of my favorite things to see is organisms living on other organisms.
Four of this chiton’s eight shell plates are completely covered with encrusting coralline algae. It is also wearing some upright corallines and at least two other red algae, one of which is Mastocarpus papillatus. This photo produced six observations for iNaturalist.
Which is not to say that single-subject photos are always boring. When the subject is as weighty as this gumboot chiton (Cryptochiton stelleri), it deserves its own photo or two.
The largest chiton in the world, Cryptochiton typically lives in the subtidal or the very low intertidal. Unlike other chitons, it doesn’t stick very firmly to the substrate. I was able to reach down and pick up this one with very little effort. In the subtidal this lack of suction isn’t a handicap, as water movement there is less energetic compared to the intertidal, and Cryptochiton does quite well. But it doesn’t really look like a chiton at all, does it? That’s because its eight dorsal shell plates are covered by a thick, tough layer of skin called the mantle. In most chiton species the mantle is restricted to the lateral edges of the dorsal surface. The girdle, as it’s called, exposes the shell plates to some degree. We don’t see Cryptochiton‘s shell plates, but if you run your finger down the middle of the dorsum you can sort of feel them underneath the mantle.
I love this one. There’s a lot going on in this small area. The greenish-brown algae are actually a red alga, Mazzaella flaccida. There are two large clumps of stuff in the photo. The clump on the left, consisting of round lumps, is a clone of the aggregating anemone Anthopleura elegantissima. The other clump is a mass of tubes of the polychaete worm Phragmatopoma californica. These two clumps were formed in very different ways, reflecting the vastly different biology of the animals that made them.
Anthopleura elegantissima is one of four species of Anthopleura anemones we have in California and is the only one to grow by cloning. It does so via longitudinal fission, in which an anemone literally rips itself in half. I wrote about them last year. Note that in this aggregation, all of the anemones are about the same size. That’s because they’re all clones of each other and share the exact same genetic makeup.
Whereas a clone of A. elegantissima represents a single genotype formed by cloning, clumps of Phragmatopoma arise by gregarious settlement. Each of the tubes in a clump is occupied by a single worm, which recruited to that spot as a larva and settled down to live its life. When it comes time to look for a permanent home, the planktonic larvae of Phragmatopoma are attracted by the scent of adult conspecifics. The larvae settle on the tubes of existing adults and undergo metamorphosis. Each worm builds its tube as it grows, using some kind of miraculous cement that sticks sand grains together, much as a mason stacks bricks to build a wall. One of the remarkable things about this construction is that the cement is secreted by the animal’s body and starts out sticky and then hardens, all in seawater. It’s a likely candidate for Best Underwater Epoxy around. Interestingly, Phragmatopoma can build its tube only as a growing juvenile. Adult worms that are removed from their tubes do not build new ones, and soon die.
See that pile of rocks out there? That’s where we were blitzing. Given the not-so-lowness of the tide I didn’t know if we would be able to make it out there. We were lucky, though, and were able to spend ~30 minutes out on that little point.
So far, the Pigeon Point Bioblitz has yielded 204 observations for iNaturalist, with three participants (so far!) identifying 77 species. Several of my observations were of red algae that I did not recognize; hopefully an expert will come along to ID those for me. Snapshot Cal Coast 2017 continues through this weekend. My intertidal Bioblitzes are over, but I hope to contribute one last set of observations by collecting and examining plankton on Sunday.
