March 2, 2021 — In the waters around the Aleutian Islands, the 1,200-mile chain that arcs across the southern edge of the Bering Sea from Alaska to Kamchatka, modern climate change has layered atop a centuries-old legacy of human assaults to send combined impacts cascading through the marine ecosystem.
Evidence is in the once-colorful corals that have nurtured schools of fish supporting some of the world’s largest commercial seafood harvests. Under the clear waters is a pale world that signals a habitat in a tailspin.
The pale-pink scene shows the slow death of cold-water coral reefs that used to be buffered by the kelp, said Doug Rasher, a marine ecologist with the Maine-based Bigelow Laboratory for Ocean Science. “We’re passing the tipping point where these reefs have persisted and been able to survive,” said Rasher, who led a study of the coral ecosystem’s downward spiral.
The reefs are dying because they are being attacked by an exploding population of sea urchins. Having mowed down the surrounding kelp forest, the urchins are consuming the algae that the reefs produce to build their structures. The urchin population is booming because the sea otters that used to eat them have disappeared.
Climate change also weakens the corals. Warmer waters make the urchins grow faster, requiring them to eat more. Rasher’s study examined the algae’s microscopic growth layers and found that urchin foraging increased by up to 60 percent since preindustrial times.
Adding to the assault is ocean acidification, to which the Bering Sea is especially vulnerable. The shallow Bering, with its relatively cold waters, abundant sea life and wide seasonal fluctuations, is naturally primed to hold carbon. And carbon emitted by fossil-fuel burning is absorbed from the atmosphere into the water, lowering pH levels and threatening calcium-building life forms — not just the coral reefs, but shellfish such as crabs, as well the tiny creatures such as pteropods that make up the diet of fish like salmon.