Human Presence Takes A Toll On Galapagos Sea Lions

sea_lionWhen you think about the Galapagos Islands, there are a few things that come to mind. There’s Charles Darwin, of course, and the studies he made there that contributed to his development of the idea of evolution. And the amazing wildlife, including tortoises and iguanas and a whole host of birds. What you don’t think of are things like pollution and invasive species, but these are growing problems, especially in the areas inhabited by humans.

Some islands are still pristine, though, and that gave a group of biologists, led by the Zoological Society of London, a chance to see how one species, the Galapagos sea lion, is affected by the presence of humans. The researchers compared immune activity and body condition of two populations, one in Bahia Paraiso on the undeveloped island of Santa Fe and another that lives in the center of the rapidly growing town of Puerto Bazquierizo Moreno on San Cristobal. The study was published last week in PLOS One.

None of the animals appeared to have signs that they were sick, but those that lived in town had more active immune systems. And among the pups in that colony, those that had higher levels of antibodies had thinner skinfolds and were skinnier.

“A tell-tale sign of an unhealthy sea lion is a thinner than normal layer of blubber, which is what we saw in the sea lions on San Cristobal,” study coauthor Paddy Brock of the ZSL said in a statement. The more active immune systems could indicate “a threat of infectious disease, which could mean human activity is increasing the chance of potentially dangerous diseases emerging in the Galapagos sea lion,” Brock said.

Puerto Bazquierizo Moreno does not seem like it would be a great place to be a sea lion. The bay is home to more than 200 boats and filled with fecal contamination from the vessels and sewage from the town. And the land has a bunch of animal threats, including people’s pets, feral cats and rats. If these factors are impairing the immune systems of the sea lions that live in the area, the impaired immunity could reduce the marine mammals’ ability to hunt, the researchers say.

And the Galapagos sea lions don’t need anything else to hamper their survival. The species was listed as endangered by the IUCN after its already-small population declined by more than 50 percent in the last three decades. The sea lions, which are a bit smaller than the more familiar California species, are not afraid of humans and like to hang out on rocky shorelines and sandy beaches (above). That can put them in direct contact with the human population and make them vulnerable to threats like uncontrolled dogs that will kill sea lion pups.

These sea lions have figured out ways to deal with some threats — they’ve been known to mob Galapagos sharks that approach their rookeries — but they haven’t yet evolved to deal with the ones humans have brought to them. Their immune systems didn’t evolve to exist in a sewage-filled, pet-dominated environment. And it appears that’s put them at even more risk of disappearing from the planet.

Image credit: ZSL_Paddy Brock, via EurekAlert


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