This past Tuesday and Wednesday afternoon I took my marine biology students to the rocky intertidal at Natural Bridges State Beach. We completely lucked out with the weather; the storm system that brought some of the rain that we desperately need had cleared out, leaving calm, clear seas and little wind. Perfect weather for taking students out in the field, in fact.
First of all, we didn't see any stars. Not that I was looking for them, particularly, but I was keeping an eye out for them and at this time last year I would have seen many Pisaster ochraceus hanging out in the pools and on the rocks. Here are a couple of pictures I took at Natural Bridges in years past:
The stars, when present, are prominent residents of the mid-intertidal zone, where they feed on mussels. But now, alas, there don't seem to be any. They WILL come back, and it will be interesting to monitor their population recovery.
I enjoy taking students in the field because many of them have never been there before, and it's always fun looking at a familiar scene with fresh eyes. When everything is new, it is very easy to be excited and enthusiastic, which these students are.
Over the Memorial Day weekend I took my students out on the early morning low tides at Natural Bridges State Beach. While they were ooh-ing and ahh-ing and filling out their assignment worksheet, I was playing around with my new camera, taking pictures in the water. Because I am not a photographer and sea anemones just sit there, they quickly became my favorite subjects. Not to mention the fact that they are simply beautiful and photogenic creatures.
At Natural Bridges we have four species of anemones in the genus Anthopleura:
A. xanthogrammica - giant green anemone
A. sola - sunburst anemone
A. elegantissima - aggregating anemone
A. artemisia - moonglow anemone
Of these species, the first two are notable for their large size. At Natural Bridges they can get to be the size of a dinner plate. They live side-by-side in tidepools, and since there are many deep-ish pools at Natural Bridges they are among the most conspicuous animals in the intertidal along the northern California coast.
It's easy to identify these animals when they're sitting right next to each other. The difficulty comes when you see only one in a pool by itself with nothing to compare it to. In a nutshell, here are some things you can use as clues to determine which species you have in front of you.
Let's start with Anthopleura xanthogrammica, the giant green anemone. This animal's oral surface and tentacles are a solid color, varying from bright green to golden brown. There are no conspicuous stripes on the central disc and the tentacles are relatively short and stubby, without any white patches.
Anthopleura sola, on the other hand, usually has distinctive radiating lines on the oral disc. Hence the common name of Sunburst Anemone. Its tentacles are generally longer and more slender than those of A. xanthogrammica, and often have sharp-edged white patches. Sometimes the tips of the tentacles are tinged a pale purple. Anthopleura sola are usually brownish-green in color, and I haven't seen any that are as bright green as the A. xanthogrammica anemones.
That's all well and good, but sometimes you come across an individual that doesn't completely follow the rules. Or rather, it looks like it could belong to both species. Such as this fellow (fella?):
The animals obviously don't read the descriptions. This one has xanthogrammica shape and overall color, but those lines on the disc read as sola-ish. I would call this one a xanthogrammica. What do you think?
As I suspected, the little Dendronotus veligers didn't last very long. On Wednesday the very last survivors had kicked the proverbial bucket. All that was left in the jar was some debris and scum from leftover food. They lasted nine days post-hatching, which is about the norm for me when I've tried to raise nudibranch larvae. Something just happens (or doesn't happen) around Day 10 and they all crash after a week or so of apparently vigorous life. Someday I may figure out what's going on. In the meantime, RIP, little guys.
On the more fun side of marine biology, there's a new exhibit at the Seymour Center that is extremely cool. Someone brought in a buoy that had been out in the ocean for a long time. It's a perfect example of a fouling community.
People who have boats or just spend time in marinas know about fouling communities. They're all the stuff that gets scraped off the bottoms of boats. It's also the same stuff that grows on pilings and the underside of floating docks. In this case the term "fouling" refers to early recruiting animals and algae that grow quickly to monopolize space. Many of the fouling species seen in harbors are invasive non-natives.
A few years ago I hung a box of slides off one of the docks at the Santa Cruz Yacht Harbor and left them there for several months to see what would grow. Here's what recruited and grew on a single slide measuring about 5x7.5 cm:
As you can see, it's a very colorful world down there! The brightest red curly stuff is an introduced species of bryozoan called Watersipora. It is a fast grower and can overtake the other stuff and form large clumps. It grows as an encrusting sheet over surfaces, but when two sheets make contact they grow up each other and form those curly upright bits. To model how this works, hold your hands in front of you, palms down, with the fingers facing each other. Push your hands together until your fingertips meet, then continue to move them towards each other. What happens is that your hands flex and your finger tips get moved upwards until your palms come together in a praying position. If your hands were encrusting sheets of bryozoan colonies, that's how you'd get those curly pieces.
Anyway, the buoy on display at the Seymour Center has a lot of large barnacles. The barnacles have been actively feeding and molting since they arrived last week. They are definitely the most animated critters growing on the buoy, as shown here:
Barnacles are crustaceans that lie on their backs entirely encased in hard shells glued to other surfaces. They feed by extending their thoracic appendages and sweeping them through the water to capture detritus and plankton. It's a strange way to make a living, but it does work.