Plague of Jellyfish outbreaks a sign of nature out of sync
Pastor Dale Morgan
Plague of Jellyfish outbreaks a sign of nature out of sync*
PARIS, June 18 (AFP) Jun 18, 2008
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," explains
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.
Dislodging them will be difficult, marine biologists say.
"Jellyfish have come to occupy the place of many other species," notes
Ricardo Aguilar, research director for Oceana, a international
conservation organisation.
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
paralyse 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 boost 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," explains 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 things, 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 are 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.
And 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.