Research shows how climate shifts can play out in local ecosystems
FRISCO — Rare Galápagos penguins may be benefiting from shifts in trade winds and ocean currents, researchers said after tracking subtle climate shifts that have enlarged a cold pool of water the penguins rely on for food and breeding.
The trend could continue during the coming decades, helping to bolster northern hemisphere’s only penguin population, which has doubled from just a few hundred to about 1,000 in the last 30 years, the scientists said in paper to be published in Geophysical Research Letters, an American Geophysical Union journal.
“The penguins are the innocent bystanders experiencing feast or famine depending on what the Equatorial Undercurrent is doing from year to year,” said Kristopher Karnauskas, a climate scientist who performed the research while at Woods Hole Oceanographic Institution in Cape Cod, Massachusetts.
Galápagos penguins landed on the endangered species list in 2000 after the population plummeted to only a few hundred individuals and are now considered the rarest penguins in the world. The birds feed on fish that live in a cold pool of water along the southwester coast of the archipelago’s westernmost islands. The pool is fed by the Equatorial Undercurrent, which flows toward the islands from the west. When the current runs into Isabela and Fernandina, water surges upward, bringing cold, nutrient-rich water to the surface.
The study suggests that long-term shifts in wind currents have nudged the current north, expanding the pool nutrient-rich, cold water. Climate change could further shift wind patterns and ocean currents, expanding cold water further north along the coasts of Isabela and Fernandina and driving fish populations higher, according to the new study.
The new findings could help inform conservation efforts to save the endangered penguins, said the study’s authors. Increasing efforts on the northern coasts of the islands and expanding marine-protected areas north to where the penguins are now feeding and breeding could support population growth, the study’s authors said.
But Karnauskas said the vast majority of marine organisms will be negatively affected by the rise in ocean temperatures and acidification that are expected to occur across the globe as a result of climate change.
“With climate change, there are a lot of new and increasing stresses on ecosystems, but biology sometimes surprises us,” said Karnauskas. “There might be places, little outposts, where ecosystems might thrive just by coincidence.”
The Galápagos penguin population has never been huge, once numbering about 2,000 by some estimates, but one of the strongest El Niños on record in the early 1980s, along with predation and disturbance by non-native dogs, cats and rats pushed that number down to about 500.
When the population subsequently started rebounding, scientists noticed that birds stayed near the coldest stretches of water. To determine if the population growth was related to local changes in ocean temperature, they combined previously-collected penguin population data from 1982 to 2014 with sea surface temperature data from satellites, ships and buoys for the same time period.
The results showed that, by 2014, the the cold water pocket extended across the entire western coasts of the archipelago’s westernmost islands and concluded the change was driven by a shift in trade winds and underwater ocean currents.
Trade winds are a key driver of heat exchange around the equator, pushing ocean waters from the southern side of the equator to the northern side. As surface waters pile up in the north, the water at the bottom of the pile is squished south, nudging the Equatorial Undercurrent – a cold current that flows roughly 50 meters (160 feet) under the ocean surface – south of the equator.
Those winds slackened during the 30-year period covered by the study, which increased the amount of cold water coming to the Galápagos Islands. Satellite images showed that this expanded pool of cold water likely encouraged the growth of phytoplankton, which in turn attracted more fish, which are the main source of food for the penguins. And the strongest pulses of cold water reached the islands from July through December, coinciding with the penguins’ breeding season.
Models indicate trade winds will continue to abate in the future as the climate warms, Karnauskas said. Other animal populations like the endangered Galápagos fur seal and the marine iguana also may profit from the prolific amount of food in the Galápagos cold pool, according to the study’s authors.
Wind and ocean currents could also possibly return to where they were in the 1980s, compressing the cold pool and possibly leading to a decline in penguins, Karnauskas added.
The new study shows how large-scale changes in the climate can act locally, said Michelle L’Heureux, a climate scientist with the National Oceanic and Atmospheric Administration’s Climate Prediction Center in College Park, Maryland, and not an author on the new paper.
“While it is important that we focus on the big picture with climate change, it’s really the small scale that matters to the animals and plants that are impacted,” she said.