West Coast
Purple sea urchins were very abundant at Tongue Point / Strongylocentrotus purpuratus. IMG_20180615_091849 / Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0)

Sea urchin explosion decimates kelp forests off Pacific coast CBC.ca

Seafloor denuded, fisheries for red abalone and red sea urchin destroyed

Tens of millions of voracious purple sea urchins that have already chomped their way through towering underwater kelp forests in California are spreading north to Oregon, sending the delicate marine ecosystem off the shore into such disarray that other critical species are starving to death. It's similar to what has been reported in B.C.

A recent count found 350 million purple sea urchins on one Oregon reef alone — a more than 10,000 per cent increase since 2014. And in northern California, 90 per cent of the giant bull kelp forests have been devoured by the urchins, perhaps never to return.

Vast "urchin barrens" — stretches of denuded seafloor dotted with nothing but hundreds of the spiny orbs — have spread to coastal Oregon, where kelp forests were once so thick it was impossible to navigate some areas by boat.

Read linked article.