THE CANADIAN PRESS -- HALIFAX - Some marine species are migrating to oceans where they were once extinct because of warming temperatures and polar melt, according to scientists who say the shakeup poses risks to entire ecosystems.
Researchers said they have found evidence of various marine life forms relocating halfway around the world because of the disappearance of sea ice in the Arctic.
Chris Reid, a professor of oceanography at the University of Plymouth in England, said they discovered the presence of a microscopic plankton in the North Atlantic 800,000 years after it had disappeared from that area.
It would be the first evidence of a trans-Arctic migration for plankton in modern times and one of the first times in tens of thousands of years that water has flown freely between the two oceans after ice retreated from the Alaska coastline.
They have also spotted a Pacific gray whale off the coasts of Spain and Israel more than three centuries after it vanished from the Atlantic.
Reid said they are convinced the relocations are the result of melting ice in the North, which has opened a channel for roving species.
"They are a marker of a major transition because the last time we had an opening between the Pacific and the Atlantic was about two to three million years ago," Reid said from Plymouth before the release of the findings Sunday.
"This could have big impacts on living marine resources as well as fisheries and aquaculture."
Reid, whose research with the Sir Alister Hardy Foundation for Ocean Science was released Sunday, is collecting the material as part of a major study on the effects of climate change on marine life.
He said the species shuffle could shake up the marine food web and transform the biodiversity of the Arctic and North Atlantic ecosystems.
Scientists from around the globe say they're already documenting the effects of species relocation due to warming water temperatures.
Some changes in plankton life have been linked to the collapse of some fish stocks, as well as declines in fish-eating North Sea birds, the researchers report.
Changes in tiny animals called copepods are threatening the food supply for fish such as cod, herring and mackerel, the scientists said, adding that the North Sea has warmed by one degree over 50 years.
Some of the tiny creatures, which are rich in oil, are being replaced by smaller and less nutritious varieties because of warming waters in the Atlantic and North Sea.
Reid said species will extend their ranges if waters continue to warm and could flourish, increasing the risk of algal blooms that involve harmful phytoplankton or species like jellyfish overtaking other marine life.
Some regions, like the Baltic Sea, could see improved biodiversity because of the warmer temperatures.
"Most of the impacts are so clearly negative and the scope of change so potentially huge that, taken together, they constitute brightly flashing warning signals," said Carlo Heip, director general of the Royal Netherlands Institute for Sea Research.
The report says that in enclosed seas, species that require cooler conditions might have nowhere to go when the waters warm. Researchers predict that by 2060, as the Mediterranean warms, one-third of its 75 fish species will be threatened and six will be extinct.
The findings also raise alarms about chemical cycling in the Atlantic, one of most crucial oceans in the world for climate change and the absorption of carbon dioxide.
It is known as the global conveyor belt because deep water sinks to the bottom of the ocean and takes oxygen and carbon dioxide with it. It then moves down the Atlantic southward and then to the Pacific as a surface warm current back to the Atlantic.
It is key to the treatment of carbon dioxide produced by human activity.