West Coast
Close-Up of crab on rock at beach, San Diego, United States (Getty)

CA - Warm water species here to stay five years after northern California's largest marine heatwave

Warmer waters allowed species to move far past their usual northern boundaries

This article was originally published on The Conversation.

Land–based heatwaves have a less obvious though equally important sibling: marine heatwaves. In 2013, the largest marine heatwave on record began when an unusually warm mass of water formed in the Gulf of Alaska. By the next summer, the warm water spread south, raising average water temperatures along the United States west coast by 3.6 to 7.2 degrees Fahrenheit (2-4 Celsius). In 2015, a strong El Niño event strengthened the marine heatwave further.

And so "the Blob," as oceanographers have dubbed this huge body of warm water, was born.

Interestingly, a number of species moved northward to places along the west coast of the U.S. where the water had previously been too cold for them.

We are a marine evolutionary biologist and a marine ecologist, and are currently studying these recent arrivals to the northern California coast. Through our work, we hope to understand what has allowed species to not only move with the Blob, but persist after the water cooled.

With warm water came new species

The Blob changed weather as well as ocean currents, led to the deaths of thousands of marine mammals and birds, and caused harmful algal blooms. Animals also movedduring the years of warm water with the Blob. Species that usually live in more southern, warmer waters expanded their ranges into northern California and Oregon.

Pelagic red crabs, usually found off the Baja California peninsula, washed up by the hundreds on beaches north of San Francisco. Keen naturalists were surprised to find that populations of bright green sunburst anenomes, giant owl limpets and pink volcano barnacles had in some places increased by the hundreds. Ecologists even discovered a new population of angular unicorn snails over 150 miles north of their original range edge.

The Blob was not destined to last forever. It eventually faded away and water temperatures returned to normal.

Cooling temps

Many species that arrived with the Blob didn't stay within the colder northern waters once the heatwave passed. For example, open water species like the common dolphin followed the warm waters north, then migrated back southward once waters cooled. But many coastal species are sessile – meaning they are stuck to rocks for all their adult lives. But these species are not attached to rocks when they are young. During the early larval stages, they ride ocean currents and can travel dozens of miles to find new coastlines to live on.

The Blob's warm waters and shifting currents allowed the larvae of many species to move far past their northern boundaries while remaining in their environmental comfort zone. However, when the marine heatwave ended, the real survival test began.

Our team has been tracking these northern coastal populations to see which species have persisted post-Blob. Each year our team returns to the cold, wave-pounded northern California shores to monitor existing populations and look for new recruits – young individuals that survived their larval stage and successfully settled on rocks.

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