Article: Global warming threatens marine life
By Jim Lobe
As if overfishing and
coastal pollution were not destructive enough, global warming posed a
potentially lethal threat to many marine species.
From tropical coral
reefs to polar-ice edge communities, and from tiny zooplankton to polar bears,
scientists have documented worrying declines in marine life which they believed
could be at attributed, at least partly, to the impact of global warming.
The new report,
"Turning Up the Heat: How Global Warming Threatens Life in the Sea" -
compiled by the World Wildlife Fund (WWF) and the Marine Conservation Biology
Institute (MCBI) - warned that whole species could be wiped out by warmer
waters.
The report was based on
an extensive review of studies and a meeting earlier this year of some of the
world's leading marine researchers. It said that warmer surface air
temperatures, which most scientists blamed on the emission of greenhouse gases,
also were gradually warming the world's oceans.
Surface water
temperature had risen by about one degree Celsius over the past century and
were expected to increase by up to another three degrees in the next 100 years
if emissions - caused mainly by the burning of fossil fuels like oil and gas -
continued at current rates.
Marine life already was
threatened by a number of human activities, the report pointed out. Overfishing
had resulted in the collapse of major fisheries, and destructive fishing
practices like bottom trawling had devastated the habitat of the sea floor.
Coastal development and
other activities that resulted in the pollution of coastal waters had converted
whole areas of the oceans into so-called "dead zones," while the
invasion of alien species, often carried in ships' ballast water to distant
habitats, has wiped out many native marine species around the world.
"Global climate
change is an additional stress on already stressed species and ecosystems, and
may be the 'straw that breaks the camel's back' for many types of marine
life," according to the 47-page report.
The increasingly
frequent appearance of the El Nino weather phenomenon during the past 20 years
provided a glimpse into the impact that can be expected from long-term global
warming, the report said.
El Nino results from
changes in atmospheric pressure in the Pacific Ocean and is associated with
higher sea surface temperatures and sea levels, lower nutrients, and increased
intensity of storms and storm surges.
Recent El Ninos have
proved lethal to marine life, with the death of up to 98% of coral reefs in
some regions. El Nino also has wreaked havoc in stocks of sardines and
anchovies in Perua, marine iguanas and kelp forests off California and some
species of seals, sea lions and seabirds.
Some scientists believe
that global warming itself may be increasing the frequency of El Nino.
It occurred in five of
the first seven years of the 1990's, a sharp increase from its pattern of the
previous 7,000 years of every two to 8.5 years. The 1997-98 El Nino was the
strongest on record.
Rising marine
temperatures, according to the report, influence all kinds of ocean conditions,
including sea levels, critical to the survival of microscopic phytoplankton,
the base of the food web; and the circulation of the deep ocean between the
poles and the tropics.
Because polar regions
will experience the greatest overall temperature change from global warming,
the biological impacts - many of which have already been observed - will be
greatest there.
Sea ice, which provides
a platform for many marine mammals and penguins, as well as a surface for algae
that produce phytoplankton, is diminishing in both the Arctic and the
Antarctic, according to the report.
"As this area
diminishes, so does the food available to each higher level on the web, from
zooplankton to seabirds," the report says. Penguins in Antarctica and
Crabeater seals are already declining in some areas as the ice recedes.
Reef fish and intertidal
invertebrates, such as anemones, crabs and snails in California provide
evidence that fish and other species are shifting toward the poles in response
to ocean warming, the report said.
In Europe, researchers
also have observed a trend of species of butterflies and birds to gradually
move north to live out their live cycle. A University of Leeds study found that
many bird species in Britain had moved an average of 12 miles to the north over
the past 20 years.
Coral reefs have proved
to be particularly sensitive to warming.
As surface temperatures
have risen in recent years, many reefs have bleached - meaning they expel the
colourful algae that produce the foods on which they rely - and, if
temperatures remain too high for too long and bleaching persists, the corals
die.
That is happening around
the world, according to the report. "In 1998, the hottest year in at least
six centuries, coral suffered the most extensive and severe bleaching and
subsequent mortality in the modern record."
New studies have found
that Pacific salmon, especially sockeye, are particularly vulnerable to
temperature changes which affect their metabolism. The warmer the water, the
more food they need to stay alive.
In 1997-1998, higher sea
temperatures during the winter may have led to the collapse of western Alaskan
salmon populations, according to the report which concluded that the Pacific
sockeye and other salmon species may soon be at risk of extinction.
Similarly, reductions in
phytoplankton caused by warmer sea temperatures have devastating effects on
predators, such as seabirds and marine mammals, at the top of the food web.
Scientists already have
established a connection between warmer water and declining reproduction and
increased mortality among different species of seabirds and seals and sea lions
along the US Pacific coast affected by the El Nino phenomenon. (IPS)
