The notorious Henslow swimming crab. Image credit: University of Plymouth
Named after John Stevens Henslow, the Cambridge professor who gave up his place on the Beagle to Charles Darwin, Polybius henslowii—or the Henslow swimming crab—finds it most comfortable in the warm waters off the coast of Portugal.
Warming ocean currents, however, have allowed the active, swimming, predator to migrate north—and the impact of its presence is beginning to ripple through North Sea ecosystems.
Even these sand crabs are nervous at the thought of a Henslow swimming crab invasion. Image credit: Balaji.B/Flickr
Richard Kirby, who led a study investigating an increase of the planktonic larvae of North Sea decapods, explained:
The North Sea is now one degree C warmer than it was 30 years ago, and as it has warmed the number of crab and shrimp larvae in the plankton and adults on the sea bed has increased.
One reason for this increase is the influx of Henslow swimming crabs which, unlike other shrimps and crabs, are able to travel long distances in groups by swimming through the open ocean.
As the number of microscopic decapod—or shrimp and crab—larvae have increased, the number of native bivalves and young flatfish have decreased. It is an excellent example, researchers remarked, of how climate change is propagated through food webs.
Predictions of global climate change suggest that the seas around our coasts will continue to warm. This may mean that we see the appearance of yet more warm water species that could change the ecology of the North Sea further.
The fact that Henslow swimming crabs can occupy part of a coastal ecosystem most crabs cannot means they have the potential to significantly impact the North Sea as an invasive species.