Bryazoans!

Sometime in February of 2019, I went on a trip to the Bodega Marine Lab (BML) with the Marine Ecology class taught by Dr. Jay Stachowics. This was the first time I was visiting the lab (which was soon to become a place I now call home). On this trip, we visited Spud Point Marina. We weren’t there to see the boats but rather the life that lived underneath and alongside the docks. At this point in time, I was unfamiliar with the kinds of animals that we know as suspension feeding invertebrates. I remember my TA reaching over the side of the dock and pulling out a rope from the water and along with it came clumps of orange, brown, and maroon colors. I was startled by the water that began squirting in all directions. My TA pointed out that this was covered in sea squirts. I looked carefully at the clusters and noticed a dark burgundy color that was arranged into ribbons which reminded me of a complex arrangement of rose petals. I left that trip thinking it was some kind of plant.

So what is a Bryazoan?

Bryozoans, also known as Moss animals, are some of the most common and abundant phyla (the primary categorization of a group of animals based off body plan). There are approximately 4,000 known living species of Bryozoans and are known to exist all around the globe including the cold waters of the Antarctic and as deep as 8200 meters below the surface of the ocean! These species are found mostly in coastal waters attached to rocks, algae, and on the shells of living animals.

Bryozoans use their lophophores to be effective suspension feeders. Within each zoid there is a lophophore which is the defining characteristics of the individual members of the colony. They look like small flowers but, instead of petals, they have tentacles that curve radially outward. These tentacles are covered in cilia (hair like vibrating structures) that create a current that directs water between their tentacles. Small phytoplankton are driven into their funnels along with the water current. When food touches their vibrating cilia, it bounces the particle upstream and then rolls it down into the mouth with the flicking motions. When non-food particles (like sand) come into contact with lophophores, the cilia bounce it out and away from the individual. The particle is then bounced to one of the neighboring individuals which does the same and so on. The result is that you get a bunch of lophophores bouncing around a grain of sand the same way that a crowd may bounce around a ball at a concert or a sports event (Basically, they know how to party).

These sessile invertebrates may seem vulnerable to predation, but research has discovered one species of bryozoans has inducible defenses. A study by Harvell (1984) found that predation by nudibranchs triggers defensive spines in the bryozoan Membranipora membranacea. Previously this kind of inducible defense was only observed in plants, rotifers (microscopic aquatic invertebrates), and cladocerans (small crustaceans also known as water fleas). Photos taken by California naturalist Jackie Sones, show that spines were protruded from the edges where zoids connect. A video taken at BML by Dr. Eric Sanford shows how the attack from the nudibranch can induce these nasty spines (well, nasty for the nudibranch).