How climate change affects sea life

NARRATOR: Sea temperatures are rising. This is bad news for those fish that need cooler water, such as cod. Its entire reproductive system is dependant upon cool winters. Other species, which thrive in warmer waters, however, are multiplying and migrating like never before. Anchovies, red mullet and cuttlefish are just some of climate change's migrants. As yet, though, their numbers haven't increased massively. But the grey and harbor seals of the North and Baltic Seas are already profiting from the influx of new neighbors. Their diets are now much more varied, and with the stocks constantly being replenished, these seals won't go hungry. Research by the Alfred Wegener Institute for Polar and Marine Research shows that other species are also benefiting from climate change. These Pacific oysters have found a new home on the German island of Sylt. Their numbers have multiplied with remarkable speed.

KARSTEN REISE: "The way these Pacific oysters have adapted to life on the mudflats of Sylt was a massive surprise for us. They were brought here because it was thought that they would fatten up, but that they wouldn't reproduce because the water is too cold. But we soon found out that lower temperatures on their own didn't stop them from breeding. Plus, temperatures in the North Sea have increased so much in the last 10 years that conditions are now ideal for the Pacific oysters. They're reproducing at a tremendous rate."

NARRATOR: One big advantage is that the Pacific oyster has no natural enemies here. Would-be predators can't open the shells. The phenomenon of migrating animals is nothing new.

REISE: "These mudflats are experiencing a kind of biological globalization almost unparalleled anywhere else on Earth. It's likely that the Vikings brought these sand gapers with them from North America. Eight hundred years later the American common slipper limpet came to Europe in a similar fashion. The larvae of these razor clams probably caught a ride in the ballast tanks of a ship coming over from America. That must have happened only 30 years ago."

NARRATOR: In future, biologists expect to see ever more significant changes in marine ecosystems.