Thousands of small, self-cloning sea anemones native to the Southern Hemisphere are rapidly spreading in Tomales Bay, an event researchers say could be the first recorded sighting of the species above the equator.
After the anemone was reported last year through a citizen science app, iNature, researchers at the University of California at Davis’ Bodega Marine Laboratory confirmed the species to be Anthopleura hermaphroditica, known as the small brown sea anemone. The striped anemone, which is less than an inch, is native to New Zealand, Australia and Chile.
UC Davis researchers, led by doctoral student Keira Monuki, are contemplating how the species could affect the bay’s ecosystems.
One of the reasons the anemones have spread so successfully in Tomales Bay is that they can reproduce asexually, said Eric Sanford, a UC Davis biology professor. A single sea anemone could make thousands of clones of itself.
“They can proliferate rapidly because they don’t need another individual to reproduce. They can just spit out these genetically identical clones of themselves,” Sanford said. “So in a lot of ways, it’s something out of a science fiction movie if you’re thinking of what would be the perfect invader from outer space.”
Sanford said genome sequencing will allow researchers to estimate how many anemones first colonized Tomales Bay. It is possible, he said, that the thousands of anemones matting the intertidal areas in eastern Tomales Bay came from just one or two individuals.
The anemones also host a symbiotic algae that will be researched to determine if it influenced the species’ successful proliferation in Tomales Bay.
Another question researchers are looking to answer is whether the anemone will compete with native species in the bay, including one known as the aggregating sea anemone. Using a club-shaped organ hidden under their tentacles that contains stinging cells, the anemones battle each other for territory.
“Anemones will have these aggressive interactions and one will give up and close up or drift away,” Sanford said. “What we want to know is if this introduced anemone from far off is it out-competing the native anemone.”
There is also the question of how the anemones could impact Tomales Bay’s renowned oyster farms. Sanford said he does not believe the anemones will be a threat. While oysters filter algae in the water for their meals, anemones use their tentacles to grab small marine critters or zooplankton.
“There shouldn’t be direct competition for food or anything like that,” Sanford said.
Hog Island Oyster Co. co-owner Terry Sawyer said he has not seen any impacts on oysters so far.
“That’s the good news,” Sawyer said. “The bad news is that we still are concerned because it’s an ecosystem out of balance and all of us need to be paying attention to that, what niche they’re occupying and displacing. Now that they’re here, we have to watch what’s going on.”
Tomales Bay and the California coast are no strangers to non-native or invasive species. Species have long hitched rides on the bottoms of ships or in ballast water, eventually detaching or being dumped into new territories in which they flourish. They can also be introduced through aquaculture or people dumping their aquarium pets into a body of water.
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For the past 15 years, the state has provided funding to San Francisco State University’s Smithsonian Environmental Research Center in Tiburon and the Moss Landing Marine Lab to survey state waters for introduced species. Andrew Chang, an ecologist at the Tiburon center, said a number of species have been found, including potentially non-native sea anemones, in the region.
“But that work is ongoing to determine whether and where/when we may have detected this particular species in those surveys, including of Tomales Bay,” Chang wrote in an email. “I’d say, too, that the intertidal habitat in Tomales is one area we have not yet surveyed systematically.”
Sanford said the Anthopleura hermaphroditica could have already been established in other areas, such as San Francisco Bay.
“We don’t know but we’re potentially interested,” Sanford said.
The study is being funded by a grant from the Tomales Bay Foundation.
Zoe Richardson, a UC Davis doctorate student, looks for non-native sea anemones along the shore of Tomales Bay in Marshall early Friday morning, Aug. 4, 2023. (Alan Dep/Marin Independent Journal)