Warmer Ocean Temperature Leads to Explosion of Hot Pink Sea Slug Population Off Northern California Coast

Sea slugs are populating waters near San Francisco in an unexpected boom of sea slugs. What triggered this growth?

These animals are rarely seen in the environment where they are now being found, leaving some investigators to question the effect warming temperatures could be exerting on wildlife.

Monterey Bay, located south of San Jose and San Francisco, is now being populated by the hot pink, inch-long sea slugs. These creatures are commonly found in waters near Los Angeles and San Diego.
The Hopkins' Rose nudibranch sea slug may be beautiful, but their effect on the environment could be harmful to local ecosystems. Researchers investigating the unusual growths have recorded dozens of sea slugs in each square yard of coastal regions.

"We haven't seen anything like it in years. These nudibranchs are mainly southern species, and they have been all but absent for more than a decade," John Pearse of the University of California, Santa Cruz, said.

El Niño seasons in 1983 and 1998 resulted in population blooms of the slugs similar to the one seen this season. However, the weather system is not present this year.

A similar occurrence was seen in 1977, during a season featuring a weak El Niño season.
"I remembered 1977 and decided to sample my old study sites on either side of Monterey Bay. Both also had exceptionally abundant Okenia, plus other southern nudibranchs not typically present, including at one site the stunning purple and orange Spanish Shawl," Jeff Goddard from the California Academy of Sciences and the Marine Science Institute stated in a university press release.
Unusual wind patterns over the last 12 months have warmed waters off the coast of North America, raising water temperatures as much as five degrees over normal.

Warmer ocean temperatures are resulting in the observation of animals outside their natural habitats. In addition to the southern sea slugs, dolphins and whales are spending more times than normal in San Francisco Bay. One person, fishing in waters near the City by the Bay, caught a sea turtle that normal lives exclusively near Mexico and the Galapagos Islands.

Bryozoan are microorganisms much like moss and are a favorite food source of Hopkins' Rose sea slugs. It is consumption of these creatures that provide the nudibranch with its distinctive pink color.

"There are some detrimental impacts to the ecosystem. Higher temperature often means the water is less productive," Goddard said.