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Endangered Gulls Are Warming To Climate Change

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Climate change has created winners as well as losers, according to a study of changing ecosystems in the North Sea. Among the winners are black-backed gulls, which are thriving on a diet of swimming crabs that have migrated from warmer waters off Portugal.

The shallow North Sea has warmed four times faster than the global average, rising just over one degree celsius since the 1980s. The warmer waters have provided a new home for Henslow’s swimming crabs, which spend more time on the surface than any other crab, making them easy prey.

The changing ecosystems could have a knock-on effect that extends even further as the land-nesting gulls deposit nutrient-rich guano, which can encourage other species.

A team led by Dr Richard Kirby of Plymouth University found that an increase in crab larvae in plankton in the North Sea was followed three to four years later by an increase in breeding pairs of the gulls that feed on the crabs. Their research is published today in the Royal Society journal Biology Letters. Dr Kirby said: “What is really interesting is that we may have found a cascade of effects in the North Sea food web, all induced by a change in the temperature of the sea.â€

“We already knew that there are more swimming crab larvae in the North Sea plankton in warm years than in cold years. Now we have shown that an increase in the larvae of swimming crabs in the plankton is followed by an increase in adult crabs the following year, and this in turn is followed three to four years later by an increase in the number of lesser black-backed gulls.â€

Dr Kirby’s research had already shown an increase in the number of Henslow’s swimming crab as the North Sea has warmed. The scientists speculate that the linkages in the marine food web from crabs to gulls could indicate a pathway for the transfer of nutrients from the sea to the land.

Another researcher Christophe Luczak, said: “We already know that guano — bird droppings — around seabird colonies can influence the local ecology by acting as a fertiliser.â€

Dr Gregory Beaugrand, who performed the statistical analyses in the study, said: “Our work demonstrates the importance of temperature in structuring how energy flows through a marine ecosystem like the North Sea.â€

The lesser black-backed gull, Larus fuscus, is slightly smaller than a herring gull. Britain is home to 40 per cent of its total population and it is on the amber list of endangered birds.



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