Climate change is totally reshaping ocean communities

"Given the complexity of the oceans and ocean life, it is really remarkable that a single factor—ocean temperature—is such a powerful predictor of change," says Ben Halpern. (Credit: Joachim S. Müller/Flickr)

Climate change is reshaping communities of fish and other sea life, according to a new study.

As waters warm, cold-loving species, from plankton to fish, leave the area and warm water species become more successful, the researchers say.

The scientists compiled the most comprehensive assessment of how ocean warming is affecting the mix of species in our oceans. They looked at fishes, invertebrates such as crabs and other crustaceans, and plankton in the North Atlantic and North Pacific, across two continents and two oceans. They analyzed three million records of thousands of species from 200 ecological communities across the globe from 1985 to 2014.

“We’ve known for a while that marine species tend to track ocean temperature, but this is the first time we’ve seen how entire communities respond, and that the redistribution of species is so predictable by temperature alone,” says coauthor Ben Halpern, a professor in the Bren School of Environmental Science & Management at the University of California, Santa Barbara who directs the National Center for Ecological Analysis and Synthesis. “The implications are very large for the ecology of the oceans and for the benefits—like food from fishing—people get from the oceans.”

The global view of climate change

“The changes we’re observing ripple throughout local and global economies all the way to our dinner plates,” says coauthor Malin Pinsky, an associate professor in the ecology, evolution, and natural resources department in the School of Environmental and Biological Sciences at Rutgers University–New Brunswick.

“We found dramatic evidence that changing temperatures are already reshaping communities of ocean organisms,” Pinsky says. “We found that warm-water species are rapidly increasing and cold-water marine species are decreasing as the global temperature rises. Changes like this are often disrupting our fisheries and ocean food chains.”

The team showed how subtle changes in the movement of species that prefer cold water or warm water, in response to rising temperatures, had a big effect on the global picture.

“For the period from 1985-2014 we created the equivalent of an electoral poll in the ocean, showing swings between types of fish and plankton normally associated with either cold or warm habitats,” Burrows says. “As species increase in number and move into, or decline and leave a particular ecological community, the make-up of that community will change in a predictable way.”

A small shift with large effects

The study looked at data from the North Atlantic, Western Europe, Newfoundland and the Labrador Sea, the US east coast, the Gulf of Mexico, and the North Pacific from California to Alaska. Regions with stable temperatures (the Northeast Pacific and Gulf of Mexico, for example) show little change in species dominance, while warming areas (the North Atlantic, for example) are experiencing strong shifts toward the dominance of warm-water species, the study says.

While researchers observed the global warming trend widely, the North Atlantic showed the largest rise in average temperature during the time period. However, for fish communities in the Labrador Sea, where the temperature at 100 meters [328 feet] deep can be as much as five degrees Celsius [nine degrees Fahrenheit] cooler than the surface, moving deeper in the water column allowed the cold-water species to remain successful.

These species’ avoiding declines by seeking refuge in cooler, deeper water is a bit like plants on land that move to higher elevations to avoid heat, Pinsky says.

“Most of the data collected were targeted surveys of commercial fish stocks, so the changes seen reflect those likely to be seen in fish markets as cold-water fish like cod and haddock decline, while warm-water species like red mullet increase with warming,” says marine ecologist Michael Burrows of the Scottish Association for Marine Science (SAMS) in Oban, adding that there has been a temperature rise of almost one degree Celsius [1.8 degrees Fahrenheit] in some parts of the ocean since 1985.

While one degree Celsius may not seem like a big change, for those fish and other marine organisms already at their maximum temperature tolerance the shift is enough to alter their chances of success in a given area and impact the global ocean food web, according to the researchers.

“Given the complexity of the oceans and ocean life, it is really remarkable that a single factor—ocean temperature—is such a powerful predictor of change,” Halpern says. “Few things in life can be explained by a single factor.”

The research appears in the journal Nature Climate Change.

Additional researchers contributed from the University of Southampton and Memorial University of Newfoundland; the University of Auckland; Sir Alister Hardy Foundation for Ocean Science; Plymouth University; the University of Tasmania; SAMS; Bangor University; Rutgers University; Hokkaido University; the University of the Sunshine Coast and Nelson Mandela University; and the Alfred Wegener Institute and the University of Queensland.

Source: UC Santa Barbara