THE ecosystem of the North Sea is changing with devastating implications for fisheries and wildlife, according to new research.Scientists say record sea temperatures are killing off the sea's normal species of plankton - the microscopic organisms on which all life in the sea depends - and that, as a result, fish stocks and sea bird populations are declining.

THE ecosystem of the North Sea is changing with devastating implications for fisheries and wildlife, according to new research.

Scientists say record sea temperatures are killing off the sea's normal species of plankton - the microscopic organisms on which all life in the sea depends - and that, as a result, fish stocks and sea bird populations are declining.

The new research has been carried out by the Sir Alistair Hardy Foundation for Ocean Science in Plymouth which has been monitoring plankton in the North Sea for more than 70 years.

They say an unprecedented heating of the sea, caused by global warming, has driven the cold-water species of plankton hundreds of miles to the north.

They have been replaced by smaller, warm-water species that, according to the scientists, are less nutritious.

"The whole ecology of the North Sea has changed quite dramatically," said Dr Chris Reid, the foundation's director.

He said the foundation had detected a collapse of the known system and this was aggravating the decline in fish stocks which were failing to recover as a result of cuts in fishing quotas.

Cod, already at the southern limit of its range, was likely to become extinct in the North Sea within the next few decades.

Dr Reid said an even greater warming of the sea was likely and, consequently, further changes in the eco-system.

Sea temperatures could eventually resemble those of the Atlantic coast of Spain or further south.

The new research suggests that stocks of young cod in the North Sea are at their lowest for 20 years while the number of wild salmon has almost halved over the past two decades.

Meanwhile, warm-water fish like red mullet, horse mackerel and pilchards were becoming more common.

Research by the RSPB has found that seabird colonies off the Yorkshire coast suffered their worst breeding season since records began, with many nests abandoned. Breeding has been poor for several years.

The society is blaming the slump in sand eels which normally breed in their millions and provide a staple diet for many seabirds and the larger species of fish.

The eels feed off the plankton which is now disappearing from the North Sea.

Hugh Sims, chief executive of the Lowestoft Fish Producers Organisation, said the latest research confirmed what fisherman had been saying for years – that they were not to blame for the decline in fish stocks.

"For many years fisherman have been forced to reduce the size of their catches because they were accused of depleting stocks by over-fishing. But the decline has continued and there are obviously many other reasons for it," he said.

Mr Sims said there was less cod in the North Sea and more fish from southern climes.