CO₂ Benefits the “Rats and Cockroaches” of Marine World

Beneath the waves, swelling levels of carbon dioxide could be boosting some species to ecological dominance while dooming others.

A study published yesterday in Current Biology suggests ocean acidification is driving a cascading set of behavioral and environmental changes that drains oceans’ biodiversity. Niche species and intermediate predators suffer at the expense of a handful of aggressive species.

Sea-level rise and coral bleaching often dominate discussions about how climate change affects the ocean, but a host of more subtle—and harder to research—trends also play a role in reshaping the world’s marine ecosystems. Among the most pressing questions is how fish react to rising levels of CO₂, said Tom Bigford, policy director at the American Fisheries Society.

“The hurdles for behavioral changes are far lower than the hurdles for life and death,” said Bigford, who worked with fish habitats at NOAA for more than three decades.

Now, for the first time, researchers from the University of Adelaide in South Australia have cataloged the changing ways marine species interact with each other.

For three years, they observed marine environments near undersea volcanic vents where CO₂ levels are high—providing a window into the future acidity of ocean water—along with adjacent areas of normal acidity. They also conducted behavioral experiments on fish from the different zones to test their responses to food and habitat competition.

Receding kelp means less habitat for intermediate predators, with about half as many near the volcanic vents.

But the acidified conditions proved to be a boon to what the researchers called “the marine equivalent to rats and cockroaches”—small fish with low commercial or culinary value.

Snails and small crustaceans can flourish in high-CO₂ conditions, providing plenty of prey for those small fish. And their high risk-taking behavior and competitive strength, coupled with the collapse of predator populations, allowed them to more than double their population.

In water with higher CO₂, the dominant species were willing to adapt to riskier habitats, preferring bare surfaces instead of turf while subordinate species were nearby.

Mimicked predator attacks also showed the dominant species adopted riskier behavior in higher-acidity water, fleeing shorter distances than the fish in water with normal acidity. Subordinate species showed no change.

Rare and specialist species are the most vulnerable to climate change, even though they “contribute disproportionately to [ecosystems’] functional diversity,” the researchers wrote.

To counter that diversity loss, the researchers suggested stronger fishing protections for predators.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.