Tuesday May 27, 2025
Mongabay —
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.