From
the dark depths of the open oceans vast blooms of jellyfish
are descending unforeseen upon coastal waters worldwide, reports
Adam Anson for TheFishSite. As the frequency of these
invasions increases, the threat to both tourism and fisheries
alike becomes evermore evident, but what has triggered this
increase and what can be done to stop it?
In
a scenario that seems almost too surreal to be believed, postcard-perfect
coastlines are replaced with an encroaching mass of gelatinous
bodies between one sunrise and the next. These 'swarms,' which
can cover areas up to hundreds of square miles, stretch across
horizons. In their tentacled trail the delicate balance of age-old
ecosystems can be upturned and toppled almost immediately. Worryingly,
global studies now suggest that these invasions are becoming
ever more frequent.
Although
any accurate assessment of the worldwide economic toll these
incidents are taking has not been calculated -- as a consequence
of broken fishing nets, killed fish, egg consumption and clogged
machinery - jellyfish are believed to have accounted for the
loss of hundreds of millions, if not billions, of US dollars
since the 1980s. But it is the individual incidents alone that
belie the true impact of these invasions.
A good
illustration of the force of these invasions dates back to the
early 1990s when a voracious, invasive jellyfish-like creature
known as the comb jelly was introduced into the Black Sea. After
just eight years they dominated it. According to a recent report
by the National Science Foundation, by 1990, the total biomass
of the Black Sea’s comb jellies totaled around 900 million
tons -- more than ten times the weight of the total annual fish
catch from all of the world’s oceans.
The
report, Jellyfish Gone Wild, claims that over one thousand of
these fist-sized comb jellies filled each cubic meter of water
in Black Sea jelly blooms. As the jellyfish spread destruction
in the Black Sea it moved out into the Azov and Caspian Seas
resulting in a massive crash in anchovy populations.
In
the Black sea alone it is estimated that US $350 million in
losses to the areas fishing and tourism industries resulted
from the invasion of the comb jelly, while losses from the ongoing
invasion of the Caspian Sea are expected to exceed those from
the Black Sea invasion.
A different
kind of jellyfish altogether caused havoc in Japan. According
to the report, 500 million Nomurai jellyfish, the largest of
which weigh up to 450 pounds and sport a bell up to seven feet
in diameter, floated into the Sea of Japan during the recent
summer, resulting losses of US $20 million to fishermen in just
one Japanese prefecture.
In
Australia $10 million dollars of damage was done to the shrimp
industry when invading jellyfish struck in the year 2000, and
on the other side of the globe another devastating invasion
washed up on British shores. In 2007 an extraordinarily large
swarm of jellyfish left 100,000 farmed salmon dead off the coast
of Northern Ireland in a completely unexpected attack. Reports
at the time claimed that stock worth £1million were suffocated
in their cages by the swarm, which is estimated to have covered
25 square kilometers of sea and been up to 10 meters thick.
Now
the Bering Sea has been encircled by a huge mass of jellyfish.
A full invasion could be catastrophic for the area’s fisheries
that currently produce 50 % of America's fish and shellfish.
Chesapeake's Bay's once productive waters have also fallen foul
of an invasion in recent years.
A
GROWING, BREEDING, MULTIPLYING PROBLEM
Jellyfish,
the cockroaches of the sea, grow and multiply at an incredible
rate. Many double their size every day when conditions are suitable
and others begin reproducing just days after their birth. The
self-fertilizing hermaphrodite comb jellyfish can release 8,000
eggs into the water per day. As far as scientist know these
huge blooms have been happening for an extremely long time.
Jellyfish are thought to have inhabited the world up to 500
million years ago.
However,
there has been a lot of evidence to suggest that the frequency
of these invasions are now increasing on a global scale. Scientists
believe that something has triggered the jellyfish to multiply
in greater numbers and many claim that global warming and manmade
pollutions are contributing to this trend.
Scientists
are persuaded that the sudden appearance of jellyfish swarms
are triggered when a certain change of climate indicates optimum
conditions: change in water salinity, oxygen content, currents
or temperature.
Pollution
that runs into the oceans can create a habitat called a 'dead
zone.' In these toxic zones very little life survives, however,
with the elimination of competitors the hardy jellyfish, which
requires almost no oxygen, can thrive. Currently more than 400
vast marine Dead Zones have been identified worldwide. Their
combined ocean coverage totals 100,000 square miles.
According
to Jellyfish Gone Wild, the number of global Dead Zones has
doubled about every 10 years since the 1960s. "During the
summer of 2008, the Gulf of Mexico’s Dead Zone covered
about 8,000 square miles, about the size of Massachusetts,"
says the report. It adds that 38,600 square miles of the North
Atlantic have been periodically covered by blooms of salps,
a jellyfish-like creature.
Unfortunately,
jellyfish invasions have proven very difficult to identify and
control, due to their mysterious nature and their ability to
survive in waters both extremely hot and cold the world over.
Furthermore, research into swarms has been limited and under
funded. New tools are currently in development to help identify
the individual impacts of overlapping environmental stresses
and DNA analyses.
However,
amidst the tales of woe some benefits have been found. Tentacles
of large jellyfish are providing hiding places for young predated
upon pollock in the Bering Sea; and in 2008 a jellyfish invasion
in China turned out to be a bonus for local shrimpers, who sold
the gelatinous mass on the Asian market where it is considered
a tasty delicacy.
This
report is reprinted with permission from The
FishSite.
