Kelp loss

What caused Kelp Loss?

Kelp Loss | Sea Urchin Barrens | The Process

The loss of kelp forests in California is a story of why predators are so important for regulating herbivores and how decreasing biodiversity can weaken ecosystems leaving them vulnerable to disaster.

Sea otters, a key predator of purple sea urchins, were extensively hunted in the early 1800s for their soft, valuable fur. At Fort Ross, 9366 sea otters were caught over just 11 years (1809 – 1823) until few remained [1]. The substantial reduction in catch over just a few years reflects the immense hunting pressure and lack of population recovery. Globally, the sea otter population dwindled because of the fur trade. Sea otters declined from an estimated 300,000 to just ~2,000.

Video: Dione Deaker, FRC, Monterey Bay

Today, sea otters are endangered and are rarely seen along California, Oregon and Washington with the exception of two populations. One is near Monterey Bay, CA, where 50 sea otters that escaped the hunt were discovered in 1938. The other is between Destruction Island and Cape Flattery, WA, where otters were successfully reintroduced in 1969. Reintroducing sea otters is complex and an attempt in Oregon in the 1960s was unsuccessful.

Removing sea otters weakened the food web in the kelp forest ecosystem. The now critically endangered sunflower sea star became the purple sea urchin’s only predator on the North West Coast. When the sea star wasting syndrome caused ~5.75 billion sunflower sea stars to perish in 2013, the purple sea urchin was freed from predator control. Finally, a marine heatwave brought increased ocean temperatures to the region from 2014-2016. Together, these three stressors created the perfect storm for a surge in sea urchins and the loss of kelp.

Sources:
[1] De Roquefeuil, 1823, I, pp.25-6; Document 234

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