The cool, temperate ocean waters of North America’s west coast are typically home to species that thrive in waters averaging around 10°C (50°F). But when a record-setting marine heatwave struck five years ago, warm-water species of fish, sea turtles, dolphins, and jellyfish typically only seen in places like Baja California, Mexico began showing up near the San Francisco Bay.
Now, a study published in the journal Scientific Reports documents that between 2014 and 2016, “unprecedented” numbers of southern marine species moved north into California – and as far as Oregon – in response to warmer waters. Of the reported 67 warm-water species seen during that time frame, 37 had never been documented so far from their home waters.
"Against the backdrop of climate change, we hope southern species will track northward because that's necessary for their persistence and survival," said lead author Eric Sanford in a statement. "It's perhaps a glimpse of what Northern California's coast might look like in the future as ocean temperatures continue to warm."
It started in the winter of 2013-14 when waters in the Gulf of Alaska gradually warmed. By the following fall, that warm water had moved south along the Pacific coast and into California. When saddled up with a strong El Niño event the same year, the resulting longest marine heatwave on record created a corridor between the different marine ecosystems, allowing southern species the opportunity to move northward. For example, pelagic red crabs endemic to central and southern Baja were found as far north as Newport, Oregon when temperatures increased. Similarly, spiny lobsters, another important fishery species in Baja, turned up in Bodega Bay just north of San Francisco. Most of these migrations were short lived. Nudibranchs disappeared as soon as waters cooled. On the other hand, others such as the sunburst anemone, chocolate porcelain crab, brittle star, and some barnacle species have settled into areas where they were once absent or rare.
Marine heatwaves are defined as periods of extreme sea surface temperature persisting for days to months. Over the last century, marine heatwaves have increased in frequency and duration and researchers believe more will be present in the future.
"Before our very eyes, we're seeing the species composition shift to more warm-water southern animals in just the 14 years I have been at the Bodega Marine Laboratory," said Sanford. "That's a barometer of change for these ecosystems."