Fishing in surge channels

This weekend we have some of the loveliest morning low tides of the year, and fortunately the local beaches have been opened up again for locals. The beaches in San Mateo County had been closed for two months, to keep people from gathering during the pandemic. For the first time in over a year I was able to get out to Franklin Point to check on the staurozoans. These are the elusive and camera shy animals that we don’t know much about, except that they are patchy in both space and time.

Yesterday the beach at Franklin Point was quite tall, as a good meter or so of sand had accumulated. This is a normal part of the seasonal cycle of sand movement along the coast–sand piles up in the summer and gets washed away during the winter storms. The rocks that you can see only the tops of in this photo would be much more exposed in the winter.

It took a while to find the staurozoans. Every time I visit Franklin Point it takes my search image a while to kick into gear, but each time I find the staurozoans my intuition gets a teensy bit better calibrated. As usual, the staurozoans were very patchy. I’d not see any in the immediate vicinity, then I’d move a meter or so away and see them all over. Part of that is due to usual honing of the search image, but part of it is that the staurozoans really are that patchy.

They are always attached to red algae, often the most diaphanous, wispy filamentous reds out there. And they don’t seem to like pools, where the water becomes still for a few moments between save surges. No, they like areas where the water sloshes back and forth constantly.

You can see why it’s so difficult getting a decent photo of these animals! They’re never still for more than a split-second. Staurozoans may have a delicate appearance, but they’re very tough critters. Their bodies are entirely flexible, being made out of jelly, and offer zero resistance to the force of the waves. It’s a very low-energy way of thriving in a very high energy environment. Who says you need a brain to be smart?

And, of course, they are predators. Being cnidarians they have cnidocytes that they use to catch prey. The cnidocytes are concentrated in the eight pompon-shaped tentacle clusters at the ends of the arms. To humans the tentacles feel sticky rather than stingy, similar to how our local anemones’ tentacles feel. Still, I wouldn’t want to put my tongue on one of them. The tentacles catch food, and then the arms curl inward to bring the food to the mouth, which is located in the center of the calyx.

The natural assumption to make is that animals tend feed on smaller and simpler animals. Somehow the predator is always considered to be “better” or at least more complex than the prey. I’m delighted to report that cnidarians turn that assumption upside-down. In terms of morphology, at least, cnidarians are the simplest of the true animals. Their bodies consist of two tissue layers with a layer of snot sandwiched between them. They have only the most rudimentary nervous system, and a simple network of fluid-filled canals that function as both digestive and circulatory system. That said, they have the most sophisticated and fastest-acting cell in the animal kingdom–the cnidocyte–which can inject prey with the most toxic venoms in the world.

They don’t look like deadly predators, do they?

Cnidarians use cnidocytes to catch prey and defend against their own predators. The cnidocytes of Haliclystus are strong enough to catch and subdue fish. Anything that can be shoved even partway into a cnidarian’s gullet will be digested, even if it isn’t quite dead yet. This fish was long dead when we saw it, but its tail is still sticking out of the staurozoan’s mouth.

Imagine being shoved head-first into a chamber lined with stinging cells. Death, inevitable but perhaps slow to arrive, would be a blessing. Although perhaps less horrific than being digested slowly feet-first.

Speaking of fishing, I caught one of my own yesterday. I saw it fairly high in the intertidal, above the reach of the surging waves. At first I saw only the pale blotchy tail, and even though I recognized it I didn’t think it was alive.

I poked it with my toe. No reaction. Then Alex found a kelp stipe, and I poked it again. It seemed to move a little bit. I’m a lot less squeamish about live things than dead things, so I picked it up to see how alive it was.

It was a monkeyface prickleback (Cebidichthyes violaceus)!

Monkeyface pricklebacks are common enough around here that people fish for them. They (the pricklebacks) hide in crevices in the intertidal. Like other intertidal fishes, they can breathe air and are well suited to hang out where the water drains away twice daily. I put this one in a deeper pool and watched it slither away into the algae.

Staurozoans found always mean a successful day in the intertidal. Day after tomorrow I’m going to look for them at a different spot. iNaturalist says they’re there, and I want to see for myself. I’m not sure exactly where to look, but I know the habitat they like. And even if I don’t find them, it’ll be a nice chance to explore a new site. Finger crossed!