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The jellyfish
are coming!
Scientific opinion is divided: some claim that jellyfish numbers
are exploding; others say that's complete nonsense. What we do
know for certain is that jellyfish are an increasing global problem
for coastal activities. And we also know that coastal authorities are
hardly aware of this at all and that they are doing little to combat
the jellyfish. So it's time for a wake-up call.
It is thought that, worldwide, jellyfish account for
40 billion dollars of damage in the sectors of tourism,
aquaculture, nuclear power stations and fishing. This
estimate doesn't include all the costs, because there
are gaps in the available information.
The potential revenue from tourism in coastal areas
has been cut by a third in recent decades because
of increasing numbers of jellyfish in coastal seas.
Climate change is pushing some species of jellyfish to
other locations. For example, the life-threatening box
jellyfish can now be found in much more northerly seas
than previously and the poisonous mauve stinger from the
Mediterranean is now often found in the seas off Scotland.
The harmful American sea walnut is increasingly
found in Dutch coastal seas and estuaries, and
the highest densities and largest animals can be
found here now.
Nomur's jellyfish can be as large as a Volkswagen
Beetle and weigh 250 kg. It is a major threat to fishing.
Claims for damages can lead to international tensions
because the polyps can be in one country, while the
adult jellyfish cause damage in another.
Offshore construction activities such as wind farms,
piers and breakwaters create habitats where jellyfish
flourish. Jellyfish polyps like to nestle on these
artificial structures. This is not a factor that is taken
into account during coastal development activities.
Jellyfish benefit from the destruction of
ecosystems by human activities such as
over-fishing, sea waste and fertilisers.
For more information
about the
research being conducted by Deltares and
the Netherlands Institute for Marine Research
looking at jellyfish in the North Sea, and
the development of forecasting models:
Jellyfish have been with us for at least 510 million years
(since the middle Cambrian) and so they are much
older than fish. Even so, we know almost nothing about
their behaviour and habitats, and that prevents us
from developing effective counter-measures.
Millions are spent to keep jellyfish away from the
beaches of the Mediterranean. But to little effect,
because the cause of the problem is not being tackled.
With jellyfish shredders, which destroy live jellyfish
at sea, the cure is worse than the disease. The jellyfish
graveyards disrupt the local ecosystem as the pieces
of jellyfish rot. And some species actually reproduce
faster if they are cut up.
Apps that advise fishermen about jellyfish
levels when planning fishing trips are useful
but the underlying data is still inadequate
and so the apps are not precise enough.
DELTARES , SEPTEMBER 2014
