How El Nino and a persistent marine heat wave are affecting West Coast wildlife
The marine heat wave contributed to a significant seabird die-off in California.
The combined effects of a potentially historic El Nino and a persistent marine heat wave off the California coast, amplified by climate change, are having far-reaching impacts on West Coast wildlife, experts say.
El Nino events and marine heat waves can mean unexpected visitors along the California coast as warm-water marine life, such as sharks, begin showing up in areas they don’t normally visit, according to the National Oceanic and Atmospheric Administration (NOAA), making their appearance one of the more visible signs of a shift in ocean temperatures.
Researchers say changing ocean conditions can affect species in different ways. But El Nino often weakens coastal upwelling in the eastern Pacific, reducing the supply of nutrients that support plankton at the base of the marine food chain. As food sources shift, some species move to find prey, while others follow warmer waters into new areas.
“The warmer waters off the coast of North America can also lead to an influx of subtropical and tropical species of plankton and fish,” said Mark Ohman, distinguished professor at UC San Diego's Scripps Institution of Oceanography.
Fish species, such as yellowfin tuna, dorado, and striped marlin, have already extended their ranges north along the West Coast as marine heat waves have warmed coastal waters without El Nino, NOAA says.
Warmer waters can make it harder for young salmon to find the nutrient-rich food they need to grow once they enter the ocean. NOAA says the lack of quality food reduces their chances of survival and the likelihood that they will return to rivers as adults.
Marine mammals are also affected by shifting ocean conditions; however, the degree of impact depends on the species. Ocean upwelling and circulation changes can displace the food that whales, dolphins, seals and sea lions depend on.
“Marine mammals may consequently shift their distribution, migration timing or foraging behavior,” said Simone Baumann-Pickering, a biological oceanographer at Scripps Institution of Oceanography.
While whales and dolphins can easily travel long distances to find food, nursing sea lions are more constrained because mothers must repeatedly return to their pups.
“During previous warm-water events, mothers traveled farther to find food, and many pups became undernourished or stranded,” Baumann-Pickering added.
Seabirds could provide some of the clearest signs of changing ocean conditions, as shifts in their populations, distribution and mortality can reflect disruptions in the marine food chain.
The warmer waters can increase ocean stratification, making it harder for nutrient-rich water from deeper layers to reach the surface. This can reduce productivity at the base of the food chain, triggering a chain reaction throughout the marine ecosystem.
“Due to less food availability, marine predators, like seabirds, can’t find enough food, which leads to decreased body condition, reproductive success, and increased mortality,” said Tammy Russell, a marine ecologist at Scripps Institution of Oceanography. “The longer these warm periods persist, the more mortality we see."
Earlier this year, the marine heat wave contributed to a significant seabird die-off along the California coast. Scientists worry that ongoing El Nino conditions could further stress seabird populations.
“Our fear is that with El Nino comes continued warm water, less productive conditions that will continue to challenge seabirds and other marine predators, and their ability to find food, survive, and reproduce,” Russell added.
Common murres, black-and-white seabirds with a penguin-like appearance, have been particularly hard hit.
Pacific Wildlife Care, a wildlife rehabilitation center in San Luis Obispo County, says it has responded to an unprecedented influx of common murres washing ashore along California’s Central Coast since early September. The clinic had received more than 800 murres by mid-October, most in critical condition from starvation.
While some wildlife may struggle, others could benefit from the changing ocean conditions, researchers say. For example, anchovy increased from record lows to record highs during the prolonged ocean-warming event a decade ago, an abundant food source for many species that eat them, including sea lions, tuna and seabirds.
“There will always be different species that thrive in different conditions,” said Rasmus Swalethorp, director of ship operations for CalCOFI.
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