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Last Updated: Jul 14, 2008 - 9:47:56 AM |
The biggest threat
is called mnemiopsis, an animal that measures about 10 centimetres
(four inches) and is not technically a jellyfish but has a gelatinous
and translucent appearance. It is not harmful to humans.
The species has never before been seen this far north in Europe and
could change the region's entire ecosystem.
"Officially it was first seen a year ago... We know they survived the
winter. Suddenly at the end of July there were a lot of them," said
Lene Friis Moeller, a researcher at Gothenburg University's marine
ecology department.
The mnemiopsis belongs to the ctenophore family and is now firmly
established in the waters off Sweden's east and west coasts.
Originally from the United States, it has already shown just how much
damage it can do in the Black Sea where it spread at the end of the
1980s, likely dumped there by ships emptying the water in their holds
while in port.
"We have seen from the Black Sea that they can
have a big impact on the ecosystem. The main thing is that they eat the
plankton that the fish eat .. and can thereby change the whole food
chain," Friis Moeller said.
Numerous fish species have
already disappeared from Swedish waters, though pollution and
overfishing have done their bit too. The mnemiopsis probably spread
north on board ships that travelled to Sweden from the Netherlands.
Fishermen are worried that the alien species will make the situation
even worse.
"We are very concerned about that. We initiated a program with
Gothenburg University to get a better understanding of the existence of
jellyfish," said Axel Wenblad, the director of the Swedish Board of
Fisheries, a government agency.
The species has the capacity to reproduce quickly - it is
hermaphroditic and can self-fertilise - and is also very resistant.
"If we find out that there is a significant risk, what can we do about
it? Frankly speaking, we can't do very much," Wenblad admitted.
Sweden has more than 2 000 professional fishermen, who each year catch
around 330,000 tonnes of fish and crustaceans, an industry worth around
one billion kronor (about R1-billion).
In August, alarm bells also rang over the discovery of giant Japanese
wild oysters in Swedish waters.
"We can't be sure where they are coming from," said Anna-Lisa Wrange, a
marine biologist at the Tjaernoe laboratory in western Sweden.
One explanation could be that the oyster larvae may have been
transported to Sweden by the sea current and established themselves
during optimal conditions, given the relatively warm temperatures this
summer.
In the 1980s, Swedish oyster growers tried to breed
the species, known as Cassostrea Gigas and which is common in European
oyster parks, but failed because the water was too cold for them to
reproduce.
"We have no idea if they will survive the Swedish winter," Wrange said.
If they do, the giant oysters could disturb the balance in the
ecosystem since they tend to settle in blue mussel beds and could lead
to a decline in that population if the two species are found to be
rivals.
This could "change the entire fauna. For example, sea
birds eat blue mussels as food. They can't really eat those oysters,
they're very spiky and large to digest, plus they are very hard to
remove," she said.
There is no scientific information on why
these two invading species are now found so far north but climate
change appears to have played a role.
"There seems to be a
link to climate changes that have occurred in the past few years," said
Wrange, stressing however that more scientific studies were needed.
Climate change could also be responsible for a mysterious virus that
killed about 250 seals in Danish and Swedish waters this summer, said
Tero Haeroenen, a scientist at the Swedish Museum of Natural History.
The outbreak started on the small island of Anholt, in the Kattegatt
waters between Denmark and Sweden.
The as-yet unidentified virus, which attacks the seals' respiratory
systems, has also been detected in the Baltic Sea.
There is no help yet available for the stricken seals.
"We have to identify the virus first, which is very difficult,"
Haeroenen said.
The infected seals die a horrible death.
"It is a very painful death because in the end they suffocate. Their
lungs are clogged by mucus," he said, adding that the virus does not
spread to humans.
Source:Ocnus.net 2008
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