Predator Loss & Climate Change – A Lethal Combination

“It’s well documented that humans are changing Earth’s ecosystems by altering the climate and by removing large predators, but scientists rarely study those processes together.” Douglas Rasher, senior research scientist

Living reefs in the kelp forests on the coasts of Alaska are being destroyed by predator loss and climate change.

Douglas Rasher, a senior research scientist at Bigelow Laboratory for Ocean Sciences  in a research team studying the reefs said:

” These long-lived reefs are now disappearing before our eyes, and we’re looking at a collapse likely on the order of decades rather than centuries.”

The coral-like reefs, built by the red alga Clathromorphum nereostratum, are being ground down by sea urchins. Sea urchins exploded in number after their predator, the Aleutian sea otter, became functionally extinct in the 1990’s. Without the urchins’ natural predator to keep them in check, urchins have transformed the seascape – first by mowing down the dense kelp forests, and now by turning their attention to the coralline algae that form the reef.

The massive reefs built by Clathromorphum have long played a vital role in the Aleutian Islands’ marine ecosystem, including during past urchin booms. Sea otters were hunted to near extinction during the maritime fur trade of the 1700s and 1800s. When urchin populations spiked in response, the reefs held their ground.

The international team of scientists have concluded that due to climate change the grazing of sea urchins has become devastating with grazing rates accelerating with rising seawater temperatures.

Douglas Rasher said:

“Restoring sea otter populations would bring many ecological benefits, and would also buy us time to get our act together on curbing carbon emissions, before this foundational reef builder is lost.”

Sea otters, the “keystone predator” of Aleutian kelp forests, experienced dramatic population declines in the 1990’s. In the wake of this event, herbivorous sea urchins proliferated, de-forested the region, and in recent years – with the help of climate change – triggered the widespread collapse of living reefs that have underpinned Alaskan kelp forests for centuries. Credit: J. Tomoleoni

The research was published in the journal Science and funded by the US National Science Foundation (PLR-1316141 and MGG-1459706) and the National Sciences and Engineering Council of Canada (Discovery Grants).

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