Quirks & Quarks

Sea otters have been saving Pacific kelp forests from rapacious sea urchins

Pacific kelp forests took a big hit after a record die-off of starfish and an unprecedented marine heat wave

Pacific kelp forests took a big hit after a record die-off of starfish and an unprecedented marine heat wave

Sea otter is foraging on a purple sea urchin in Monterey Bay, California, USA. (Morgan Rector)

Marine kelp forests along the Pacific coast took quite a beating a few years ago. 

These dense underwater coastal forests are one of the most productive ecosystems on our planet, that's also hugely important for regulating climate change. But since 2013, they've faced unprecedented challenges from a destructive environmental double whammy.

In a new study, Joshua Smith, a PhD candidate in marine biology at the University of California in Santa Cruz, found that sea otters are playing an important role in helping preserve these vital ecosystems.

Kelp forests provide a critical habitat for many species. ( Michael Langhans)

In 2013, starfish along the Pacific coast were struck with sea-star wasting syndrome that caused their massive die-off from Alaska all the way down to Mexico.

The crash in the sea star population meant their prey, sea urchins, were free to come out of hiding and attack the kelp forests.

Then, in 2014 and 2015, an unprecedented marine heat wave raised coastal ocean temperatures by up to 4 degrees Celsius.

A record marine heat wave and sea star wasting disease that killed many sea stars have taken a toll on kelp forests up and down the Pacific Coast. ( Michael Langhans)

Kelp forests do much better in cooler waters, so the unusually warm ocean temperatures further decimated kelp forests along the coast.

The California marine coast consists of interspersed "sea urchin barrens" with patches of kelp forests. (Michael Langhans)

Overgrazing by urchins and inhibition of growth in warm water resulted in a patchy mosaic of healthy kelp forests interspersed with bare, denuded seafloor that scientists have dubbed "sea urchin barrens."

Smith found sea otters have stepped up their predation on sea urchins, particularly in the remaining patches of kelp forest. As long as conditions don't worsen, these healthy kelp patches should eventually help re-seed the barrens and help the kelp forests recover.

Sea otters prefer eating healthy sea urchins found in remaining patches of kelp forests (above) rather than their starved, but still surviving, counterparts in the "sea urchin barrens" (below.) (Joshua Smith / University of California in Santa Cruz)

Produced and written by Sonya Buyting