In 2014, on a Californian beach just north of San Francisco, researchers from the Bodega Marine Laboratory noticed something unusual: a purple striped jellyfish, typically only seen in warmer Mexican waters, was lying on the beach. The discovery sparked a project in which researchers documented an unprecedented number of southern marine species in the waters of California and Oregon between the years of 2014 and 2016.
It became clear that the reason for the mass migration was the ‘blob’ of warm water that had settled off the Californian coast. The blob had moved down from the Gulf of Alaska and coincided with a major El Niño event which moved up from the equator. Together, the two phenomenon resulted in one of the longest marine heatwaves on record and the researchers found that marine animals responded to the warmer waters by extending their range northward.
‘It was like opening a temporary door between lower latitudes and northern California,’ says Eric Sanford, a marine biologist at Bodega. ‘What was unusual about this heatwave was the duration of it. The longer the temporary door was held open the more opportunity there was for these southern species to move up.’ The animals were also potentially influenced by a reversal of the usual current system which occurred at the same time.
In total, the team recorded 67 warmer-water species in the ocean near the laboratory, 37 of which had never been documented so far north before. Species included jellyfish, crabs, nudibranchs, fish, as well as larger animals such as dolphins and sea turtles. Among the 37 with new northern range limits were tropical creatures such as the striated sea butterfly, which had not been found north of Baja California in Mexico before.
When waters cooled again, many of these creatures disappeared. But some, including the sunburst anemone, chocolate porcelain crab and the brittle star, appear to have stayed the course. Sanford now wants to understand the ways in which these particular creatures may have changed genetically in order to adapt to cooler waters.
As marine heatwaves become more common, a willingness to move may prove vital for sea creatures. Against the backdrop of global warming, Sanford hopes that animals will continue to track north as it becomes necessary for their persistence and survival. However, the fact that many are already doing so reflects a concerning trend. ‘I’ve been working here at the Bodega Marine Laboratory for 14 years and just in that pretty short period of time we’re seeing this shift in marine communities to include more southern warm water species,’ says Sanford. ‘Seeing changes that quickly is really a barometer of how rapidly our oceans are changing.’
This was published in the May 2019 edition of Geographical magazine
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