Unusually rapid warming of ocean temperatures is affecting marine ecosystems and the people who depend on them much more frequently than scientists expected, even accounting for recent climate warming trends.
Examining data from 65 large marine ecosystems around the world for the period 1854-2018 the researchers found an average of 12 "surprising warming events" each year over the past seven years, including a high of 23 in 2016. They expected about six or seven. That was the case in the Arctic, North Atlantic, eastern Pacific and waters off Australia.
"Based on historical and lived experience, people expect certain conditions to prevail in the ecosystems they depend upon. Climate change is now introducing strong trends that push conditions beyond historic levels," the researchers write in the abstract for, "Challenges to natural and human communities from surprising ocean temperatures."
The effects of surprising ocean warming events
The researchers used the data to develop a theory regarding how temperature trends and events will impact natural and human communities. It suggests that the abundance and diversity of natural marine communities will decrease and that we need to change the way we make decisions regarding marine resources.
Different species occupying the same niche in the marine food web will be affected differently depending primarily on how fast they reproduce. "The decline will be less strongly felt by fast-reproducing species," according to the researchers. "This creates the potential for decoupling between different components of the food web," predator and prey species, for example, they point out.
The result would be that while the composition of the species in marine ecosystems changes, the abundance of fast-reproducing species will be higher than that for slow-reproducing species. "While the species composition in a region will change, the fast-reproducing component of the ecosystem is more likely to maintain high biomass levels than slower-reproducing species such as fish," according to the report.
"If they are trophically coupled, reducing the slower-growing predators will further increase the abundance of the faster-growing prey. Adding additional processes such as immigration and dispersal could alter these effects, potentially providing a way for the dynamics in the slow-reproducing community to get closer to those in the faster community."
Parallels in real-world marine ecosystems
The researchers' model was developed to represent a generalized, ideal community of marine species. The way they responded to the higher frequency of surprising warming events and general climate warming has parallels in coral reef ecosystems, however, according to the researchers.
They point out that corals with the narrowest tolerance in terms of temperature range tend to have higher growth rates. "The long-term warming in the tropics is contributing to a decline in coral cover, consistent with our prediction of reduced abundance," the researchers elaborate. "The shifts toward lower coral cover and less complex reefs has important ramifications for the ecosystem services reefs provide, including fisheries and shoreline protection."
The implications of the research results for humans are clear, according to the research team. "Historical experience is becoming less relevant. To be successful, human institutions including businesses, communities, management agencies, and governments will need to adopt strategies that look forward rather than backward.
"For example, when the Gulf of Maine experienced a rapid increase in temperature, the backward-facing fishery management process was not able to act quickly enough to reduce fishing on cod and avoid a collapse of the fishery."
Climate models, for example, offer a long-term view and incorporate contingencies associated with global carbon emissions. In addition, the use of seasonal and multiyear forecasts are becoming more accurate and more common. The timescale at which they are considered reliable varies from region to region, however, the researchers note.
"Our results strongly suggest that betting on the status quo will be an increasingly risky strategy. Financial tools such as insurance or derivatives can provide a way for individuals or companies to buffer loses," they write.