In 2023, biologists Lauren Stefaniak and Marie Nydam had time to kill before their university workshop on marine invertebrates began, so they drove to a marina not far from Los Angeles to gather organisms for their students to study. They strolled along floating docks, pausing periodically to sit down or to lie on their stomachs and pluck an assortment of small creatures from the water. Stefaniak, a marine scientist at Coastal Carolina University in South Carolina, and Nydam, a marine evolutionary geneticist at Soka University of America, in California, are experts at identifying the myriad animals — shelled or squishy, scurrying or stuck in place — that festoon docks, buoys, pilings and ropes at the water’s edge. But that day, one finding surprised them: reddish blobs about 2.5 centimeters (1 inch) long that they didn’t recognize.
As it turned out, they had collected the first specimens of the ascidian Corella japonica from North America. Scientists don’t yet know whether this new member of California’s marine fauna will have ecological impacts, but its arrival highlights the massive, largely uncontrolled movement of marine species via ships that travel the world.
Ascidians, which are a type of tunicate also known as a sea squirt, are part of the ocean’s seafloor ecosystems, or benthic zone. Like many benthic organisms, they are sessile, meaning once they settle down as adults, they don’t move again. Some ascidians, including C. japonica, resemble small fleshy balloons; others spread out as rubbery colonial mats. Adult sea squirts filter feed, sucking seawater in through one siphon, capturing any tiny food particles — bacteria, algae and the like — and squirting the filtered water out through another. Only a few of the approximately 3,000 ascidian species in the world are well studied, and ascidians’ roles in ecosystems and potential for becoming a nuisance outside their home ranges aren’t always clear.
C. japonica is native to the Northwest Pacific Ocean, including Japan, where its common name is doro boya. Encountering it in California was exciting because “it had previously been known from the western Pacific, and now it’s in the eastern Pacific,” Stefaniak said. She, Nydam and a colleague reported the finding in a paper published in April in the Journal of the Marine Biological Association of the United Kingdom.
C. japonica most likely arrived in California by hitchhiking on a ship. For as long as humans have traveled by boat, Stefaniak said, we’ve carried other organisms around with us, some intentionally, others not. Ships suck ballast water up near coastlines to help with stability; in the process, they capture tiny organisms that they later release, along with the water, in a new location. Marine species including ascidians sometimes settle on the submerged surfaces of a vessel and come along for the voyage. While people generally keep ship hulls clean to reduce drag and save on fuel costs, creatures can squirrel away in harder-to-clean areas, such as on rudders.
According to a January report by California’s State Lands Commission, shipping is “the major pathway” by which nonnative aquatic species move globally, including almost 80% of the nonnative aquatic species that have become established in North America. “Shipping has historically been the primary way for aquatic, non-indigenous species to be introduced, everywhere,” Chris Scianni, an environmental program manager with the commission’s Marine Invasive Species Program who worked on the report, told Mongabay. Scianni, who was not involved with the new research, agreed that C. japonica appeared to be new to the West Coast.
While some marine organisms can populate new areas with minimal impacts, a few cause economic or ecological chaos in new locations, including some tunicate species. For example, the colonial Didemnum vexillum, or carpet sea squirt, which scientists think originated in the same region as C. japonica, has spread to many parts of the world, sometimes carpeting the underwater parts of docks and the seafloor — along with other sessile creatures living there — in large mats. In New Zealand, carpet sea squirt has spread from shipping ports to overgrow commercial mussel beds.
California, with its approximately 1,350-kilometer (840-mile) coastline, has taken note. According to Scianni, about 6,000 commercial ships arrive at the Los Angeles and Long Beach port complex each year. For a quarter-century, the state has tried to curb the movement of marine stowaways through regulations of large boats and commercial ports. But as CalMatters has reported, those regulations can lack teeth. To date, few ships have their ballast water sampled in California ports, and there are no hull cleanliness standards that state officials can enforce. Plus, new regulations this year will require California to comply with less-stringent federal biofouling and ballast-water standards. Those new regulations also limit how much money California can collect in fees from ships arriving from ports outside the state, which it uses to fund the Marine Invasive Species Control Fund, putting the state’s regulatory process as a whole in danger.
In any event, existing regulations don’t include smaller recreational vessels of the kind that likely brought C. japonica to the marina where Stefaniak and Nydam collected it. According to Scianni, there are at least 7,000 recreational boats and yachts in the Los Angeles area each year. “The yachts and the recreational boats don’t really have any requirements to manage biofouling,” Scianni said. “So the concern is, now it’s there and it’s in and around where those boats and yachts are, that it likely will spread.”
So far the C. japonica population at the marina has not been quantified. Nydam surveyed 35 locations throughout Southern California in 2024 and found no other populations, but Stefaniak expressed confidence that it will eventually spread.
Stefaniak said regulating introductions by smaller vessels, such as those that dock at the marina where she found C. japonica, is hard. “With smaller vessels, it’s really a matter of public education — making sure that people are aware that these things can be present and that cleaning off your boat is a good idea, especially if you’re moving it from one area to another,” she said. To that end, Scianni’s department has produced educational materials advising recreational and fishing boat owners on how to voluntarily avoid moving aquatic life along with their vessels.
Scientists don’t know what, if any, impact C. japonica will have upon coastal life in California. Eric Laughlin, a communications manager at the California Department of Fish and Wildlife, told Mongabay in an email that “non-indigenous tunicates are relatively common; our data indicate there are already over 20 non-indigenous tunicate species established in California.” The department has not confirmed this new species.
He added the department is directing its resources toward managing invasions of Caulerpa prolifera, a nonnative seaweed that managers worry will replace native eelgrass and be inedible to native fish and invertebrates, and golden mussel (Limnoperna fortunei), a nonnative bivalve that can alter aquatic ecosystems and clog pipes. Compared with C. japonica, these “present considerably greater threats due to their ability to rapidly spread,” Laughlin said.
When Stefaniak and her colleagues realized they had found a new-to-the-region species, they preserved some of the ascidians so their genetic material could be used to confirm their identity via DNA barcoding. DNA collections can also serve as a reference for environmental sampling — efforts to quickly quantify local biodiversity by identifying stray DNA. But while these DNA techniques can be useful, they are expensive and out of reach for some people, including citizen scientists, Stefaniak said.
To her, the most exciting part of this new finding may be the old truth it revealed: the value of “just going to a dock and poking around,” as she put it. “Even if someone is not an expert taxonomist, they can still notice when there’s something new,” she said.
This article was first published at Mongabay.
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