"Strange things are happening in the North Sea. Cod stocks are slumping faster than over-fishing can account for, and Mediterranean species like red mullet are migrating north. Several sea birds are also in trouble. Kittiwake numbers are falling fast and guillemots are struggling to breed. And, earlier this summer, hundreds of fulmar (a relative of the albatross) corpses washed up on the Norfolk coast, having apparently starved to death.
Scientists suspect these events are linked and they are trying to work out how. Nothing is certain yet, but some believe a dramatic change in North Sea plankton is responsible. And, what is more, they blame global warming.
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Broadly speaking, as global temperatures rise, cold water species are moving out and warm water species are moving in. "The North Sea was a cold temperate ecosystem in the 1980s, but since the 1990s it has changed into a warm temperate ecosystem," explained Martin Edwards, of the Sir Alistair Hardy Foundation for Ocean Science (SAHFOS), Plymouth, UK.
"So all the cold water species of plankton have moved much further north, and they are being replaced by more sub-tropical species."
EDIT
http://news.bbc.co.uk/1/hi/sci/tech/3879841.stm