Next week classes for the Fall semester begin, and this will be my fourth term teaching a marine invertebrate zoology class at this particular institution. I have built this class on a foundation of comparative anatomy and functional morphology; lab activities include dissections (to observe how bodies are put together) and diversity labs (to examine the morphological diversity within major taxa). This year I wanted to include a lab with a broader ecological context. So back in April I hung a box of glass slides from one of the boat slips at the harbor. The idea is that the students in the invert zoo class will examine the slides after they’d been marinating in the ocean for several months and have to figure out what’s growing on them.
The organisms that have and will continue to colonize the slides are members of what is rather disparagingly referred to as a “fouling community.” To be fair, they can be nuisances, fouling docks and pilings, boat hulls, water intake and outflow pipes, and pretty much anything that is left in the water for any significant amount of time. In fact, my friend Adam has a job scraping fouling organisms off the bottoms of boats at the harbor; boat owners either pay to have this done or do it themselves every so often. But to me, these animals and algae form a fascinating ecological community that illustrates many of the principles I teach to my students.
Harbors are some of the places where exotic (i.e., non-native) species are first detected. It is not uncommon for many of the species in a fouling community to have evolved elsewhere and been transported (usually, but not always, unintentionally) to a new location, where they grow swiftly and often out-compete the native species. Obviously, not all species introductions “take” and it’s anybody’s guess how many species were dumped in a new site and failed to stick around. The ones that do take, though, tend to become very prominent.
So, back to my slide box. It was still there, hanging from a string about 2.5 meters below the bottom of the dock. As I pulled it up, I was relieved to see different colors and textures:
Up close, it looked even more promising:
Even without knowing what all the differently colored blotches are, you can tell that there’s a lot of stuff growing. I’m not going to dismantle the box until we use it in lab in early November, but I thought it might be worth a closer look. It just so happened that I had both a clean bucket in my car and the foresight to bring it with me onto the dock. This photo shows that the slides themselves are covered with growth:
The red encrusting sheet is the bryozoan Watersipora, probable species subtorquata, an invasive species that is found in harbors all along the California coast. The pale orange blobs are colonies of sea squirts; it is difficult to identify them to species without examination under a microscope. There is also quite a bit of a brown upright branching bryozoan that I think belongs to the genus Bugula.
As an unabashed aficionado of all things hydroid, I’m always very pleased to see certain species of ‘droids at the harbor. They are simply so beautiful that I love looking at them. This is the hydroid Ectopleura crocea. It is common but sporadic and patchy at the harbor, and usually isn’t one of the first species to colonize an area. Its congener, E. marina, occurs in the intertidal; I can find it fairly reliably in a particular pool at Davenport Landing and have occasionally seen it elsewhere.
Having reassured myself that my slide box was doing well I took some time to check out other bits of real estate in that area of the dock. I played around with the super-macro setting on my camera, with mixed results. I do now know, though, that it works underwater:
I found a cooperative barnacle and took some video footage of feeding behavior. Barnacles are strange crustaceans that lie on their backs and kick their modified thoracic appendages through the water to capture small particles. What a weird way to make a living. But the animal is always right, and barnacles can be quite efficient at clearing water.
And, finally, does anybody know the source for the title of this post? Answer in the comments section, please!