Here's another photo, taken from farther away to give you a bigger picture of the scale of things.
Believe it or not, the maker of these trails is the little black turban snail, Tegula funebralis. They are one of my favorite animals in the intertidal, for a number of reasons:
I always root for the underdog and the under-appreciated, and these snails are so numerous in the intertidal that they are practically invisible. People literally do not see them. I know, because I ask.
They are very useful creatures to keep as lab pets. I throw a few of them into each of my seawater tables, except for the table that contains a resident free-ranging sea star, and they do a fantastic job keeping algal growth to a tolerable minimum. They're my little marine lawnmowers!
They come in very handy when I'm teaching invertebrate zoology. Students study them live to observe behavior, and the snails are not shy. They are very tolerant of being picked up and gently prodded, and soon emerge from their shells and carry on their little snail lives. Students also dissect them in lab to learn about gastropod anatomy.
So yes, these tracks in the sand are made by T. funebralis in the high intertidal. In areas where a layer of sand accumulates either at the bottom of a pool or on a flat exposed rock, it is not uncommon to see a turban snail pushing sand out of the way as it crawls along, like a miniature snow plow.
Tegula funebralis and its congeners are called turban snails because their shells are shaped like turbans. Given their small size (a big T. funebralis would have a shell height of 2.5-3 cm), pushing sand around must be a tiresome chore. They do it because they have no choice. Most grazing gastropods, such as turban snails and limpets, can feed only when they are crawling. There may very well be a nice yummy layer of algal scum on the surface of this rock, but the snail has to push the sand out of the way before it can feed on it.
Here's another photo, taken at the snail's level.
This snail is pushing through a wall of sand as tall as itself! I don't know about you, but I sure as heck couldn't do that. Props to these little snails!
Although the world's oceans cover approximately 70% of the Earth's surface, most humans interact with only the narrow strip that runs up onto the land. This bit of real estate experiences terrestrial conditions on a once- or twice-daily basis. None of these abiotic factors, including drying air, the heat of the sun, and UV radiation, greatly affects any but the uppermost few meters of the ocean's surface so most marine organisms don't need to worry about them. Despite the apparent paradox of where they live, intertidal organisms are also entirely marine--they cannot survive prolonged exposure to in air or freshwater. So how do they manage to live here?
Some organisms have a physiological tolerance for difficult conditions. These tidepool copepods and periwinkle snails, for example, are able to survive in the highest pools in the splash zone, where salinity can be either very high (due to evaporation) or very low (due to rain or freshwater runoff), dissolved oxygen is often depleted due to high temperature, and temperature itself can be quite warm. Sculpins and other tidepool fishes cope with low oxygen levels by gulping air and/or retreating to deep corners of their home pools.
Of course, animals that can locomote have the option of moving to a more favorable location. Other creatures, living permanently attached to their chosen site, aren't quite so lucky. Let's take barnacles as an example.
Barnacles have two planktonic larval stages: the nauplius and the cyprid. The nauplius is the first larval stage and hatches out of the egg with three pairs of appendages. It can be distinguished from the nauplius of other crustaceans by the presence of two lateral "horns" on the anterior edge of the carapace. The nauplius's job is to feed and accumulate energy reserves. It swims around in the plankton for several days or perhaps a couple of weeks, getting blown about by the currents and feeding on phytoplankton.
After sufficient time feeding in the plankton, a barnacle nauplius metamorphoses into the second larval stage, the cyprid. A cyprid is a bivalved creature, with the body enclosed between a pair of transparent shells. It has more appendages than the nauplius, and these are more differentiated. If the nauplius has done its job well, then the cyprid also contains a number of oil droplets under its shell. These droplets are of crucial importance, because the cyprid itself does not feed. For as long as it remains in the plankton it survives on the calories stored in those droplets. The cyprid's job is to return to the shore and find a suitable place on which to settle. Somehow, a creature about 1 mm long, being tossed about by waves crashing onto rocks, has to find a place to live and then stick to it.
Returning to the topic of the challenges that marine organisms face when they live under terrestrial conditions, let's see how these barnacles manage. Along the northern California coast we have a handful of barnacle species living in the intertidal. In the higher mid-tidal regions at some sites, small acorn barnacles of the genera Balanus and Chthamalus may be the most abundant animals.
However, nowhere is a particular pattern of barnacle distribution more evident than at Natural Bridges. Here, the barnacles in the high-mid intertidal are small, and concentrated in little fissures and cracks in the rock.
I think most of these small (~5 mm) barnacles are Balanus glandula:
And here's a closer look:
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.
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.
See what I mean?
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.
Okay, now for some more 'forest' pictures.
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.
Here's another nice clump of Phragmatopoma:
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.
This is the second year that the California Academy of Sciences has sponsored Snapshot Cal Coast, a major effort to document and characterize the biodiversity of the California coast. To this end the Academy has organized several Bioblitzes at various sites in northern California, and solicited volunteers to lead their own Blitzes, either as individuals or with groups. A Bioblitz is a citizen science activity in which people take photographs of organisms or traces of organisms (shells, scat, tracks, etc.), then upload their observations into iNaturalist. Experts then identify the organisms in the observations, and the data are publicly available to anyone who wants to use them.
For Snapshot Cal Coast 2017 I have four Bioblitzes planned for the intertidal. Here are some of my observations made in the first two.
Day 1: Natural Bridges, Sunday 25 June 2017, low tide -1.7 ft at 06:27
My friend Brenna joined me on an early low tide at Natural Bridges. The intertidal topography at Natural Bridges consists of a series of gently sloping benches that are riddled with potholes of various sizes and depths. For the purposes of this Bioblitz I decided to confine my observations to the geological structure that I call the peninsula, which sticks out farther into the ocean than the edges of the benches.
The peninsula is most easily accessible when the tide is at least as low as -1 ft, although large swell can make it entirely unsafe to do so at even very low tides. Fortunately the swell wasn't big enough to keep me from the peninsula yesterday, and I confined most of my observations to this location. I've found that making observations for Bioblitzes requires a different kind of attention and focus than either collecting or observing for more general purposes. In the spectrum of forest-to-trees levels of observation, Bioblitzes are all about individual trees. When left to my own devices I tend to move quite fluidly between forest-level observations (e.g., broadscale ecological patterns) and tree-level observations (e.g., what organism is that?), and confining myself to only tree-level observations was, well, confining. It's undoubtedly a good discipline, but one that I find a little stifling.
Here are some of the "trees" I saw at Natural Bridges.
I've been keeping an eye on this abalone for a couple of years now. It has gotten bigger and in the last year has become heavily encrusted with other animals and algae. Right now it is sporting lots of acorn barnacles (both large and small), at least one tube of Phragmatopoma californica, limpets, encrusting and upright coralline algae, and other red algae.
Smithora naiadum is a red alga whose thallus consists of small flat blades. It grows only as an epiphyte on seagrasses, in this case the surfgrass Phyllospadix scouleri. Later in the summer many surfgrass leaves will be almost entirely covered with Smithora.
My favorite observation of the morning was this little hermit crab.
I love how this hermit is clinging to a piece of giant kelp. It lives in a shell of the olive snail Olivella biplicata, as many of its conspecifics do. These shells get to a bit over 2 cm in length, and their narrow diameter means there isn't much empty space inside. Fortunately, P. hirsutiusculus is one of the smaller hermit crabs and doesn't need much space.
An extreme low tide like yesterday's has two benefits. The most obvious is that more real estate is exposed, thus more area to explore. The second benefit of a really low tide is time. Much of the biodiversity of the intertidal is in the low-mid and low zones; the lower the tide, the longer it takes for the ocean to return and reclaim its property. I was able to spend the better part of two hours out on the peninsula, which doesn't happen every year. Lucky me!
Day 2: Franklin Point, Monday 26 June 2017, low tide -1.5 ft at 07:15
To get to the beach at Franklin Point you have to hike ~10 minutes over the dunes along a maintained trail. The views along the way are often quite spectacular, even when it's foggy. This morning it was unusually clear, and I wished I had brought along my big camera. For example, looking north towards Pigeon Point I saw this:
I mean, come on. How much more beautiful can a vista be?
The intertidal at Franklin Point has changed dramatically over the past year. Heavy storms over the 2016-2017 winter removed about two vertical meters of sand from the beach, exposing rocks that had been buried for years. Even today, months after the peak of the storm season, you can see bare rock that has yet to be heavily colonized by living things.
Primary succession is the sequence of species' arrival and eventual replacement in an area that has never hosted life before. These rocks may very well have served as habitat for organisms years ago, but in my memory they had been buried in sand until the recent storms. Their exposure provides an opportunity to observe primary succession in this very dynamic habitat.
The first organisms to arrive and take hold in any newly available habitat are primary producers. Makes sense, as there is no food for heterotrophs yet. In the case of the intertidal the first visible organisms are algae. The algae at Franklin Point have been going like gangbusters all spring and into the summer. Faunal diversity, on the other hand, has been rather low. I spent quite a while looking at and photographing algae, many of which I couldn't identify in the field.
Some things were entirely unfamiliar to me. For example, I'd never seen coralline algae encrusting on the tips of another red alga. And yet, here it is:
As I mentioned above, animal life at Franklin Point has been rather depauperate this year. HOWEVER, I did get to let out a few whoops of triumph when I found this:
These animals, staurozoans, are incredibly difficult to photograph. Not only are they the same color as many of the algae they live with and attach to, but they like areas where the water is constantly moving back and forth. Plus, the pools and channels where I found them were cloudy with Ulva spooge. I took a lot of pictures of backscatter and blurry staurozoans.
Here's another shot:
Staurozoans are the strangest and by far the coolest cnidarians. Their common name 'stalked jellyfish' harkens back to when they were considered scyphozoans, close kin to moon jellies (Aurelia) and the like. They are now known to be in their own group, the Staurozoa, related to but not part of the Scyphozoa.
I don't really know why I'm so enamored of the staurozoans. Maybe it's because they are rare and poorly understood. I know them only from Franklin Point and one sighting at Carmel Point. The systematics of the staurozoans is in flux; I'm not brave enough to assign a species epithet to this critter, but a colleague who is one of the people working on this group suggests that it is H. sanjuanensis, a species that has not yet been formally described. All of the staurozoans I saw today were this brownish-red color, but in previous years I've also seen them in a brilliant bottle green. Those would probably be easier to see among all the red algae, but with my luck the green ones would all be hanging out with Ulva.
The very last part of the hike to the intertidal is a steep decline down the dune to the beach. Getting down is easy, you just sort of ski down. Getting up is much more of a challenge. Ever try to climb a sand dune? Each step gets you about a quarter of a step above the last one, so it's hard work, especially when the dune is steep. There have been times that I've hiked all the way out to the beach, only to turn around and go back because I didn't think I'd be able to climb back up the dune in my hip boots. And since I have bronchitis right now by the time I got back to the top today it felt as though I had climbed Mt. Everest.
All told, I added about 150 observations to iNaturalist these first two Bioblitzes. I'm not really into making observations just to make observations, so for me that 150 is a good two days' production. Now I need to rest up for tomorrow's low tide.
It seems that most years, the Memorial Day weekend brings some of the lowest spring tides of the year, and 2017 certainly fits the bill. I've been out for the past two days, heading out just as the sun is starting to rise, and already I've seen enough to whet my appetite for more. And with plans for the next few days, I'm pleased to say that my dance card is completely full for this tide series. There are a lot of stories building out there!
At this time of year everything is growing and reproducing. Many of the larvae I've seen in the plankton have parents that live in the intertidal; makes sense that those parents should be having sex now. Barnacles, for example, copulate when the tide is high. I've seen them go at it in the lab, but never in the field, as they don't mate while emersed. This morning I interrupted a pair of isopods locked in a mating embrace, and they swam off, still coupled together, when I disturbed them. Other animals were much less shy. Lifting up a curtain of Mazzaella to see what was underneath, I spotted a small group of dogwhelks (small, predatory snails). I can't be certain, but suspect they were having an orgy.
A short distance away I found the inevitable result of the dogwhelk orgies.
Each of those urn-shaped objects is an egg capsule, containing a few dozen developing embryos. After the snails copulate the mating individuals go their separate ways. The females lay these egg capsules in patches in the mid-intertidal, usually on a vertical surface under the cover of algae to minimize the risk of desiccation.
For many years now, some of my favorite animals have been hydroids. I worked in a hydroid lab as an undergraduate, and this is when I fell in love with the magic of a good dissecting microscope. A whole new world became visible, and I found it easier than I ever imagined to fall under the spell of critters so small they can't be seen with the naked eye. I still do.
Hydroid colonies come in a variety of forms, shapes, and colors. Most of them are small and cryptic, resembling plants more than any 'typical' animal, and aren't easily seen unless you're looking for them. One intertidal species, however, is pretty conspicuous even to the casual tidepool visitor or beachcomber. It often gets torn off its mooring and washes up on the beach.
A hydroid colony is the benthic polyp stage of the standard cnidarian life cycle. The polyp represents the clonal phase of the life cycle and reproduces by dividing to make several copies of itself. In a colony such as a hydroid, the polyps remain connected to each other and even share a common digestive system. The polyps don't reproduce sexually. That function is reserved for the medusa stage of the life cycle. Some hydroid colonies produce free-swimming medusae, and others hang onto reduced medusa buds or structures so un-medusa-like that they're called gonangia. Aglaophenia is a hydroid that houses its sexual structures in gonangia that are located on the side-branches of the fronds.
Here's a closer view of a single frond of the Aglaophenia colony. I had to bring it back to the lab to look at it under the scope.
The gonangia look like leaves, or pages of a book, don't they? After working a low tide I'm always hungry, and when the lows are early in the morning I'm often cold and sleep-deprived as well. That's my excuse for not dissecting open one of the gonangia to see what's inside.
Even the algae are getting into the act of reproducing and recruiting. This spring I've noticed a lot of baby bullwhip kelps (Nereocystis luetkeana). Nereocystis is one of the canopy-forming kelps in subtidal kelp forests along our coast, but every year some recruit to the low intertidal. However I don't remember seeing so many baby Nereocystis thalli in the tidepools. The smallest one I saw this morning had a pneumatocyst (float) the size of a pea! In mature thalli, the float might get as big as a cantaloupe.
Nereocystis doesn't usually persist or get very large in the intertidal. It is more common to see detached thalli washed up on the beach than to see a living bullwhip kelp longer than about 2 meters in the intertidal. Whether or not this particular nursery area results in an established population remains to be seen. I'm betting 'No' but could very well be proved wrong. Only time will tell.