oh really?
http://news.bbc.co.uk/2/hi/science/nature/3879841.stm
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.
Global changes
Plankton are microscopic free-floating marine organisms. Globally they are
of vital importance. Phyto-plankton (tiny plants) are behind 50% of the
Earth's photosynthesis. And, along with zoo-plankton (tiny animals), they
form the base of the whole ocean food web. But, over the last 20 years,
these little organisms have been undergoing a radical shake-up in the North
Sea. 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."
The decline of a particular species of phyto-plankton, which blooms in early
spring, is key to changes further up the food chain. Many small animals feed
on this spring bloom - and even time their own emergence to match it. Now it
is going, they are dying.
Dr Edwards said: "The spring bloom is declining, and the cold water
zoo-plankton that feed on the spring bloom are declining as well - and so
are the fish larvae that feed on the zoo-plankton." And so - presumably -
are other fish that feed on those larvae and the birds that feed on the
fish.
Over the edge
Martin Edwards and bird expert Sarah Wanless, from Nerc Centre for Ecology
and Hydrology, have got together to try to pinpoint how this is happening.
"We have already shown that kittiwakes are declining and declining quite
rapidly - but at the moment we don't know the mechanisms," said Dr Wanless.
"And that is why we are joining up the bird work with the plankton work, so
we can see how these links actually operate.
"What Martin Edwards and his colleagues are showing is that there is a
profound difference in the plankton in the North Sea, and we are seeing a
decline in the sand eels that many birds feed on." She continued: "We
speculate these are climate driven changes, which are working their way
right through the food chain. And we are seeing signals emerging from the
birds. "In some cases we are finding a whole lot of adult birds dead and in
other cases that the birds are abandoning their chicks."
And there might be worse to come. Because sea birds are generally long
lived, changes happen rather slowly. So what we are seeing now could be,
some fear, the tip of the iceberg. "Some species might decline to the extent
where they are no longer present," said Dr Wanless. "And kittiwakes might
well be one of the first to disappear."
Emerging picture
Amazingly the role of plankton, and how they are affected by climate, has
not been extensively studied in the past. "Work on plankton is hugely
important," said Dr Chris Reid, the Director of SAHFOS. "The world's oceans
make up more than 70% of the world's surface and 50% of the primary
production in the world comes from phyto-plankton, but as yet we have very
little idea about how this changes regionally or with time."
Now, the story behind some of the North Sea mysteries is beginning to
unfold. Dr Wanless said: "Everybody working in the North Sea is seeing big
changes, but what we need to do now is get everybody together, to try to
piece the whole jigsaw together."
