Washington, Jun 8 -- As if overfishing and coastal pollution were not destructive enough, global warming posed a potentially lethal threat to many marine species, two major environmental organisations reported Tuesday.
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 ares 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)
The above article by the Inter Press Service appeared in the South-North Development Monitor (SUNS).
