Record numbers of warm-water sea creatures shifted northward during a recent marine heatwave, reveals new research.
During the water heating up off the West Cost of the United States from 2014 to 2016, scientists noticed creatures typically seen only in places off the coast of Mexico, showing up hundreds of miles further north in Californian waters.
These included warm-water species of jellyfish, crabs, fish, molluscs and even dolphins and sea turtles.
A study, published in the journal Scientific Reports, documents an “unprecedented” number of southern marine species moving northward into California and as far north as Oregon.
Of 67 rare, warm-water species sightings observed by the research team and citizen scientists, 37 had never been documented so far north before.
Among the 37 with new northern range limits are tropical creatures such as the striated sea butterfly, which had not been found north of Baja in Mexico. It is the first record of them in the state of California.
Another unexpected visitor was the pelagic red crab, normally restricted to the waters off central and southern Baja.
But during 2014-2016, when water temperatures were 3.5 to seven degrees Fahrenheit warmer than usual, the crabs were seen as far north as Newport, Oregon.
And the molt of a spiny lobster – an important fishery species in Baja – turned up in Bodega Bay.
Study lead author Professor Eric Sanford, of the University of California, Davis, said: “Against the backdrop of climate change, we hope southern species will track northward because that’s necessary for their persistence and survival.
“It’s perhaps a glimpse of what Northern California’s coast might look like in the future as ocean temperatures continue to warm.”
He said “The Blob” of warm water moved from the Gulf of Alaska south along the Pacific coast, a major El Nino event worked its way from the equator north to California.
Together, the events created unusually warm water conditions and one of the longest marine heatwaves on record.
Prof Sanford explained that marine heatwaves temporarily open a door between lower latitudes and the northern coast.
He said the longer that door is open, the greater the number of southern species that can step through it.
The 2014-2016 event was so long and warm, it allowed southern species to enter California and move northward.
Current reversals, where water flowed northward from Monterey Bay, also aided the species on their journeys.
The combination led to the record-breaking number of species moving northward, according to the study.
But Prof Sanford said most of the species were only short-term visitors. For instance, brightly coloured nudibranchs disappeared almost as soon as the water cooled.
But some seem to have established a foothold in Northern California. These include the sunburst anemone, chocolate porcelain crab, a brittle star and some barnacle species.
Prof Sanford said the southern species were absent or rare from Bodega Bay, off California, in the 1970s, but are now fairly common in the area.
The research team view such geographical shifts as an indication of how marine the communities may continue to respond to warming oceans, as more heatwaves are expected in the future.
Prof Sanford added: “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.
“That’s a barometer of change for these ecosystems.”