By Birute Skurdenis
If you were strolling on the boardwalk behind Scott’s Restaurant in Jack London Square on September 12th, you might have come across the odd sight of 2 dozen people of all ages, lying on their stomachs on the floating dock below the restaurant, peering into the water. Armed with plastic containers of all sizes and a variety of magnifying lenses, this was the Wild Oakland Marine Biology Tour. Led by Ken-ichi Ueda, founder of iNaturalist, we were going to see what lived under the boat docks of the Oakland Estuary.
Ken-ichi explained that because the estuary is a heavily used international ship channel, the marine biology in Oakland’s ports is a lot more exotic than what you might find in other coastal waters. Biological hitchhikers find their way to San Francisco Bay waters just as many of us humans have. While many of these non-natives are relatively benign, some, like the shipworm, a clam that bores into wood, can cause millions of dollars worth of damage to man-made structures in the Bay. A well-maintained dock requires a regular scraping of the accumulated biological build-up to preserve its integrity.
While some folks had brought their own containers, Ken-ichi supplied us with a photo card and some plastic bowls and challenged us to dip into the water under the docks to find the 9 creatures on our card: skeleton shrimp, bryozoan, sea squirts, yellow sponge, scale worms, feather duster worms, brittle star, sea slugs and Bay pipefish. Soon words like ‘nudibranch’ (the “ch” is pronounced like a “k”,) ‘tunicate’ and ‘stylidae’ were flying around. There were a few people who were familiar with what we were looking at and helped the rest of us identify what we were pulling up from the Bay.
We dipped our containers and started looking. My personal favorites were the brittle stars (Ophiuroids), which are related to starfish. As we found them in the Oakland Estuary, they were small (1/4 “ – 1/2 ”) organisms with a tiny round center and 5 stick figure “arms” that moved like those of an octopus. If you were lucky enough to pull them up from the water, you could watch them use their arms to swing around your container like miniscule monkeys.
Some folks brought up big clumps of seaweed, algae, mussels and sponge and picked it all apart to see what it contained. The chains holding the floating dock in place were a good place to start a search. One of the more elusive creatures on our “to find” list, was the sea slug, or nudibranch. Those we found in the water that day were very small, 1/8” to1/4” in size and, to the untrained eye, looked like a piece of algae debris. With a hand lens, however, you could make out the antennae and slug body. Fortunately, the sea slugs were often found together with bryozoa, an easily identified organism (or more correctly, a colony of organisms) with a distinctive branch-like structure that looked like fine blood veins or plant roots.
Another creature we looked for was the pipefish and were excited to find tiny juveniles, no more than 1” long until someone pulled a 6” pipefish out of the water. It’s a relative of the sea horse, with a long, eel-like body and sea horse-like head, and. like the sea horse, the males raise the eggs in a pouch on their belly.
Collectively, we found everything on our photo cards. Everyone, young and old, got a big kick out of discovering this unknown, aquatic world in our own back yard. So find a public dock, get down on your belly and take a look.
For more photos and information about marine biology of the Oakland Estuary, see the Wild Oakland blog from last year!
Here are a few pictures of what we found: