Sea anemone native to Southern Hemiphere found in Tomales Bay

A Monterey County man’s internet post about tiny, tentacled organisms in the mudflats at the edge of Tomales Bay has spurred new research into how a species from the Southern Hemisphere got so far north and what effect it may have on the local ecosystem.

Native to the waters off Chile, New Zealand and Australia, the small brown sea anemone — Anthopleura hermaphroditica — appears never to have been reported north of the equator, until last year.

But already the tiny creatures can be found in dense patches at several sites along the middle reaches of the 15-mile-long inlet, primarily along the eastern shore, between Nick’s Cove and Marshall.

Since last summer, a few areas of high concentrations have appeared on the opposite, Point Reyes National Seashore side, as well, according to one researcher at the UC Davis Bodega Marine Laboratory, where several people are studying the newly arrived organism.

“It’s kind of funny,” Keira Monuki, a fourth-year Ph.D. candidate at the marine lab, said as she surveyed small brown sea anemones at Blakes Landing earlier this week. “Last year, I went to the west side, and I hardly saw any. I went again yesterday, and they were all over the place.”

Light brown with light-colored mottling, the small brown sea anemone is, like it’s name suggests, very small: about a centimeter across at full size. In most cases, only the disc-like mouth area and tentacles are visible at the water’s edge — the column that supports it mostly nestled in the mud.

But it can reproduce through self-cloning, without the need of a mating partner, and thus can proliferate quickly, producing crowded areas of sea anemones among the rocks, eel grass and scattered sea shells along Tomales Bay’s rugged beaches.

The sea anemones also belong to a family of anemones that host symbiotic algae — photosynthetic organisms that create energy from the sun that leaches into the host. It’s possible that feature is a factor in the sea anemone’s successful occupation of Tomales Bay.

But sea anemones, whose species number more than 1,000, also are generally hearty and highly adaptable, though their chosen environment at Tomales Bay is similar to their native context, Monuki said.

Scientists say it’s too early to know the ramifications of their presence, though the findings of one marine lab student indicate they can out-compete native sea anemones for food resources in their midst, Monuki said.

Anything that crowds out or starves native species would threaten local biodiversity, Bodega Marine Lab Professor Eric Sanford said.

But the experts also say there’s no immediate cause for alarm.

Those consulted were unaware of any obvious ecological or economic threat from the southern anemones, unlike known invasives long ago introduced to Tomales Bay — such as the Atlantic oyster drill, a predatory sea snail that feeds on oysters, or the European green crab, which also eats oysters and native invertebrates, like clams.

But much is still unknown.

James Carlton, professor emeritus of marine sciences and director emeritus of the Williams-Mystic Coastal & Ocean Studies Program of Williams College in Connecticut, is a world expert on invasive species. He described a kind of “ecological roulette” as to whether a non-native species introduced somewhere new may herald “first order human impacts.”

“You do not know which one is going to be the next marine zebra mussel,” Carlton said, referring to a highly invasive, Eurasian freshwater bivalve that has threatened waterways and water supply equipment in many areas of the United States, including California and local reservoirs.

But for an Asian species from the western Pacific to make it all the way into Tomales Bay is pretty remarkable, he said.

The new arrival in Tomales Bay was brought to light when a teacher visiting during a family vacation in June 2022 saw some intertidal critters near Marconi State Historic Park that he didn’t recognize, despite a background in biology. He posted photos on iNaturalist.org, and the online community of experts and citizen scientists went to work to identify it.

Carlton was alerted to the post by a site contributor — a research associate affiliated with the UC Santa Barbara Marine Science Institute and the California Academy of Sciences — and informed others in California, including Sanford.

He and his wife, Jackie Sones, the lab’s Bodega Marine Reserve research coordinator, went to Tomales to check for themselves, and “within about 10 seconds of getting out of the car, we found one, because they’re all over the place,” Sanford said.

Though they resemble some other species, under a microscope, they appeared to be Anthopleura hermaphroditica. But there was no record of them in the Northern Hemisphere, Sanford said, so Monuki, his student, arranged for genetic sequencing of the tissue against known samples and got a match.

“As far as we know, it’s the first record of it anywhere in the Northern Hemisphere, which is unusual and interesting,” Sanford said.

(An earlier iNaturalist post from Tomales Bay on March 13, 2022, has since been identified by contributors as small brown anemone, based on the ID of the June observation. An August sighting on the coast of Wales may be, as well.)

Like many estuaries, Tomales Bay has its share of non-natives, including several species of mudsnail and mussel, a tunicate, the Atlantic oyster drill and the green crab.

But introductions commonly occur at shipping ports, where organisms have taken up residence after falling off vessels, arriving in bilge water or even coming in with seed stock for aquaculture.

Yet no sighting for San Francisco Bay or even Bodega Harbor has been reported, though it doesn’t necessarily mean the sea anemone hasn’t arrived there. It could be it’s just not been reported.

Debris that crossed the Pacific after a massive March 2011 earthquake and tsunami in Japan transported non-native organisms, too. Almost 400 Japanese species have been found on the coasts of Hawaii and the mainland since 2012, Carlton said, one of them believed to be related to Anthopleura hermaphroditica, though it’s not yet been subject to genetic testing.

“We’ve been moving a lot of marine species in the oceans and seas around the world since the 1600s, so its been a busy game for 400 years,” he said.

Climate change and the habitat alterations it fosters also is pushing wildlife into new spaces.

Climate-related range shifts are the focus of Monuki’s studies, but she’s embraced the inquiry into the small brown sea organism, conducting much of the field work under Sanford’s oversight. The Tomales Bay Foundation is funding some of her work.

She’s just done her second round of annual surveys, collecting data on densities at selected sites, and is interested to know how the sea anemone spreads or recedes from different areas, both within Tomales Bay and nearby areas.

“I think it will be kind of interesting to see over the next few years if it shows up somewhere, like in San Francisco Bay,” Monuki said. “We haven’t seen them there yet, so maybe they did try to establish there and didn’t do well.”

They also may have a brief residence in some area but not found conditions favorable, she said.

A key focus will include the anemone’s interaction with and impact on other aquatic organisms and communities in the mud.

“I think that we just don’t know a lot,” she said, “so it’s a pretty exciting project to be involved with.”

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or mary.callahan@pressdemocrat.com. On X/Twitter @MaryCallahanB.