As oceans warm around the world, marine predators are poised to become increasingly aggressive, according to new research, potentially leaving countless species and marine ecosystems on the brink of imbalance.
Researchers conducted experiments ranging from enclosing prey species in cages to placing “squid protrusions” to measure how many predators came to feed, depending on the water temperature they lived at.
Marine predators have long been thought to be more vicious in tropical waters, but with climate change leading to global warming, researchers at the Smithsonian’s Environmental Research Center (SERC) wanted to see what the consequences might be. to have this for the future.
Usually, temperature changes, which cause major changes in marine ecosystems, occur over millennia, not decades.
“It took thousands of years for us to reach this state, and then we suddenly raise the temperature at a much higher rate,” said Gail Ashton, lead author of the new report and a marine biologist at SERC, in a press release. “And we don’t really know the consequences of this rise in temperature.”
An international team of researchers, led by SERC, conducted experiments on marine predators and prey in 36 locations on America’s Atlantic and Pacific coasts to study how these species respond to different temperatures, hoping to predict what a warmer ocean will bring.
The results, published Friday in the journal Science, found that predation would increase in intensity as the oceans warmed, with unknown – but certainly extensive – effects on other species and the ocean as a whole.
“Warmer waters tend to favor animals high in the food chain, who are becoming more active and in need of more food, and their prey is the one that pays for this increased activity,” said Emmett Duffy, director of the Global Marine Observatory Network. of Earth (MarineGEO) by the Smithsonian and co-author of the study, the statement said. “This suggests that warming seas could lead to major changes in the lives of sensitive seabed habitats.”
To get their results, the researchers conducted three specific experiments at each site to test how strong the predator’s response was in different waters.
The places reach Alaska to the north and Tierra del Fuego to the south, an archipelago at the very bottom of South America.
First, researchers confirmed that warmer waters correlate with greater predation.
In this experiment, researchers created an attractive delicacy for predators, invented “squid pop” because of its resemblance to dessert “cake pops”. These balls of dried squid on a stick were left underwater to attract fish, and then the researchers checked again in an hour to see how much of the “protruding squid” remained. The results were clear: in warmer waters, many more predators went out to eat, while in waters below 20 degrees Celsius, there was almost zero registered predation.
“This temperature threshold is an ecological turning point in these coastal marine ecosystems, above which the intensity of predation is increasing,” said Amy Freestone, co-author and associate professor of biology at Temple University. “With climate change, more coastal waters will exceed this turning point or become even warmer, fundamentally changing the way these ecosystems function.
Once this is established, researchers place prey creatures in different positions of accessibility for predators to see how predation affects their growth and numbers in different waters.
In one experiment, they left prey such as underwater invertebrates, membranes and bryozoans to grow on plastic panels for three months, some protected from predators with cages and others left exposed to any potential fish that wants a snack.
In the latest experiment, researchers placed protective cells around all their victims for 10 weeks and then released half of them for another two weeks to test what happened when they grew up safe and then exposed to predators.
These experiments were performed in waters with drastically varying temperatures, and the results confirmed what the researchers suspected would happen: the levels of prey species fell into hotter waters if left uncaged and unprotected. But in colder waters, it didn’t matter if the prey was protected or not – predation levels remained very low, which reinforced that predation was less active in colder waters.
But what does this really mean for the whole ecosystem, as more and more water gets warmer?
Researchers say common marine ecosystems can become more “top-down” as water warms, with predators controlling the oceans instead of balancing them.
“Such large-scale changes in top-down control could have far-reaching implications, given the key role of species interactions in maintaining ecosystem structure, diversity, biogeochemical processes and the provision of critical ecosystem services to human communities,” the statement said. the study. .
For example, some species of prey that have been consumed more in areas of higher predation, such as membranes, play significant roles in the overall ecosystem. The tunics filter the water and provide “places” for other sea creatures to live, the press release explains.
“With the change in predation, some species will be winners and others losers,” said Greg Ruiz, head of SERC’s Marine Invasion Research Laboratory and co-author of the study. “Some will be protected; others will be vulnerable. But we don’t know exactly how that will develop. “
Although these problems have been measured in smaller studies before, this is one of the biggest to look at the bigger picture of how temperature affects these levels of predation.
The researchers noted that due to different levels of marine species in different regions of the ocean, some of the results may have been affected by these different levels of biomass.
“More broadly, the differences between the sites underscore the need for high replication and broad coverage in order to thoroughly assess both regional and global models,” the study said.
“Our results suggest that climate change may have foreseeable effects on the regulation of coastal communities along the world’s coastline.
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