How The Clean Water Act Helped A Sea Slug’s Return

seaslugThis striking sea slug, Felimare californiensis (a.k.a. the California chromodorid), used to be a common find along the California coast, from Point Conception to San Diego, and along the Channel Islands. One early 20th-century guidebook, for example, described the invertebrate as “fairly abundant in the tide pools from Monterey to San Diego.”

But by 1983, this species had disappeared from California. Researchers and amateurs searched for the nudibranch, but it could no longer be found outside Mexican waters.

Until 2003, when it again turned up in small numbers around Santa Catalina Island. And in 2011, it reappeared off of Santa Cruz Island and near San Diego. Researchers now say that the sea slug is poised for a comeback.

So what happened? According to a study led by the University of California Santa Barbara and published in Marine Biology, the decline of the sea slug can be traced to water pollution. But the pollution didn’t affect F. californiensis directly; the researchers conclude that because similar sea slug species were unaffected. Instead, the pollution somehow affected the quality or abundance of the sea slug’s main prey, the sponge Dysidea amblia, possibly by having some sort of effect on symbiotic cyanobacteria that could serve as sources of defensive metabolites or provide chemical cues used in the sea slug’s reproductive cycle.

Pollution along the California coast reached its peak around the time that F. californiensis was on the decline. But water quality turned around in the years following the passage of the Clean Water Act in 1972. And when El Niño events brought the sea slugs up from Mexico, they were able to reestablish themselves in the cleaner water.

“Since the passage of the Clean Water Act in 1972, big strides have been made in reducing pollutants in the Southern California Bight, especially from large wastewater outfalls, and these improvements may have allowed Felimare californiensis to regain a foothold in the region,” study coauthor Jeff Goddard of UCSB said in a statement.

Whether this sea slug can make a full return to its previous range can’t be known. But no one should assume that its recovery is guaranteed. As the researchers point out in their paper, though the Clean Water Act did have a profound impact on water quality, there are still plenty of other pollutants to worry about. They write, “a vast array of chemicals unregulated, illegally used, or not previously considered as contaminants (e.g., pharmaceuticals, hormones, and antibiotics) flow increasingly into [the water] through multiple pathways, presenting daunting environmental challenges.”

Those are challenges faced by many species across the country. Whether we do anything about it, well, that remains to be seen.

Image credit: Kenneth Kopp, via EurekAlert