Species of the Month: Wait, that white stuff on kelp is an animal?

We’re all familiar with La Jolla’s sea lions, harbor seals, orcas, garibaldi and seabirds. But in this series of stories called Species of the Month, the Light sheds light on other, lesser-known marine creatures in local waters, their role in the ecosystem and more.

The spooky season might not be celebrated in the ocean, but a creature that lives in La Jolla waters somehow manages to bring costumes, coffins and skeletons to the briny deep.

Tiny zooids known as kelp lace bryozoan live in a colony on kelp leaves, or blades, that when combined resemble mold and are sometimes confused as such. In fact, they are sometimes referred to as “moss animals,” said Charlotte Seid, manager of the Benthic Invertebrate Collection at UC San Diego’s Scripps Institution of Oceanography in La Jolla.

Though they’re harmless to humans, other common names are the “lacy crust” or “coffin box” creature because of their appearance.

“Each animal is shaped like a long, thin box,” Seid said. “If you look at them under a microscope, they are small but then they join together and form these mesh grids [similar to coral]. Many people think they are mold when they see them on kelp, but they live on kelp and are not an infection or anything nasty.”

The bryozoan start small, with a colony that initially has a starburst shape, but they grow with the kelp and will take up any available space on a blade, Seid said.

The kelp blades on which the kelp lace bryozoan live do not need to be living themselves, and the bryozoan have been known to live on other forms of algae as well.

Bryozoan are partially opaque and grow on only one side of a blade, so the kelp can still get the sunlight it needs even if they are present.

“The kelp doesn’t necessarily benefit [from the presence of bryozoan], but it is common for them to have many things on them,” Seid said.

While living on kelp leaves, bryozoan “has a little crown-like feature, like a little fan, that it uses to collect plankton as the kelp sways in the water,” she said. “As the kelp moves, it exposes them to other little things to eat.”

Bryozoan, considered a middle player in the food web, also are filter feeders that help clean the water.

Their top predators are nudibranchs sea slugs. Some species of nudibranchs have taken to costuming, or changing their appearance, to look like kelp lace bryozoan so they can get closer and eat them.

“It has the same flat, white mesh pattern, so even I have been fooled,” Seid said.

In addition to sea slugs, other snails have been known to graze on bryozoan.

The zooids start as a single larva floating in the water among the plankton. From there, it finds a kelp leaf to settle on and clones itself to form the colony.

When they are actively feeding, the bryozoan might have a “fuzzy” texture, Seid said. But when not feeding, they can retract to form a thin, rigid crust on the leaf. When the bryozoan are dead or eaten, they can leave an empty grid, or “skeleton,” on the leaf.

So if one washes up on the beach, it might have a different texture depending on whether it is alive or dead, Seid said.

“You would have to look really closely, but it can be seen by the naked eye to tell you if they are alive,” she said. “From far away it might look like paint. But up close it might look like an empty grid. It might be a fun exercise for beach-goers.”