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By Jerome Cartillier, Agence
France-Presse
PARIS : The dramatic
proliferation of jellyfish in oceans around the world, driven by
overfishing and climate change, is a sure sign of ecosystems out of
kilter, warn experts.
“Jellyfish are an excellent
bellwether for the environment,” said Jacqueline Goy, of the
Oceanographic Institute of Paris.
“The more jellyfish, the
stronger the signal that something has changed.”
Brainless creatures composed
almost entirely of water, the primitive animals have quietly filled
a vacuum created by the voracious human appetite for fish.
And marine biologists say
dislodging them will be difficult.
“Jellyfish have come to occupy
the place of many other species,” said Ricardo Aguilar, research
director for Oceana, a international conservation organization.
Nowhere is the sting of these
poorly understood invertebrates felt more sharply than the
Mediterranean basin, where their exploding numbers have devastated
native marine species and threaten seaside tourism.
And while much about the
lampshade-like creatures remains unknown, scientists are in
agreement: Pelagia noctiluca—whose tentacles can paralyze prey and
cause burning rashes in humans—will once again besiege
Mediterranean coastal waters this summer.
That, in itself, is not unusual.
It is the frequency and persistence of these appearances that worry
scientists.
Two-centuries worth of data shows
that jellyfish populations naturally swell every 12 years, remain
stable four or six years, and then subside.
2008, however, will be the
eighth-consecutive year that medusae, as they are also known, will
be present in massive numbers.
The over-exploitation of ocean
resources by man has helped create a near-perfect environment in
which these most primitive of ocean creatures can multiply
unchecked, scientists say.
“When vertebrates such as fish
disappear, then invertebrates—especially jellyfish—appear,”
says Aguilar.
The collapse of fish populations
boosts this process in two important ways, he added. When predators
such as tuna, sharks and turtles vanish, not only do fewer jellyfish
get eaten, they have less competition for food.
Jellyfish feed on small fish and
zooplankton that get caught up in their dangling tentacles.
“Jellyfish both compete with
fish for plankton food, and predate directly on fish,” said Andrew
Brierley from the University of St Andrews in Scotland. “It is
hard, therefore, to see a way back for fish once jellyfish have
become established, even if commercial fishing is reduced.”
Which is why Brierley and other
experts were not surprised to find a huge surge in the number of
jellyfish off the coast of Namibia in the Atlantic, one of the most
intensely fished oceans in the world.
Climate change has also been a
boon to these domed gelatinous creatures in so far as warmer waters
prolong their reproductive cycles.
But just how many millions, or
billions, of jellyfish roam the seas is nearly impossible to know,
said scientists.
For one thing, the boneless,
translucent animals—even big ones grouped in large swarms—are
hard to spot in satellite images or sonar soundings, unlike schools
of fish.
They also resist study in
captivity, which means a relative paucity of academic studies.
“There are only 20 percent of
species of jellyfish for which we know the life cycle,” said Goy.
The fact that jellyfish are not
commercially exploited, with the exception of a few species eaten by
gastronomes in East Asia, has also added to this benign neglect.
But the measurable impact of
these stinging beasts on beach-based tourism along the Mediterranean
has begun to spur greater interest in these peculiar creatures,
whose growing presence points to dangerous changes not just in the
world’s oceans, but on the ground and in the air as well.
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