Global warming wreaks havoc on oceans
Rising global temperatures are affecting ocean ecosystems to a far greater extent than previously acknowledged according to a new report by the World Wildlife Fund (WWF) and Marine Conservation Biology Institute (MCBI).
From the tropics to the poles, wide-spread changes in marine life are occurring in step with rising water temperatures. The newly- assembled evidence shows dramatic impacts arriving sooner than predicted.
Among the most disturbing news is research suggesting Pacific salmon may no longer find suitable habitat in the Pacific Ocean. Other effects of warming climate are appearing across the marine food chain, from plankton, penguins and polar bears to fisheries on which humans depend. Most dramatic of all is the sheer scope of the data.
“Warmer temperatures are raising the biological cost of living for marine species,” says Dr. Elliot Norse, President of MCBI. “This is true in polar seas, where climate changes have been most pronounced, as well as on tropical coral reefs, which are suffering unprecedented devastation due to heat stress.”
Release of the report marks World Oceans Day, June 8. It also coincides with a negotiating session on the international global warming treaty in Bonn, Germany.
WWF and MCBI say the findings underscore the urgent need to reduce emissions of carbon dioxide and other greenhouse gases particularly in the US and industrial countries responsible for the lion’s share of the problem.
Impact on seabirds, fish and marine mammals
The report, Turning Up the Heat: How Global Warming Threatens Life in the Sea, is based on a comprehensive review of the latest scientific literature, including work that has been accepted, but not yet published.
“These disturbing results demonstrate that global warming is coming home to roost, affecting livelihoods and wildlife Americans cherish. Our fear is that this is just the tip of the iceberg,” says Adam Markham, Director of WWF’s Climate Program. “The story will only get worse unless governments and business take the steps to stop it.”
Key findings in the new WWF/MCBI report include:
- warming could eliminate much, if not all, marine habitat for Pacific sockeye salmon, and probably other salmon species as well. Sockeyes are extremely temperature-sensitive: their metabolism increases in warmer water, requiring larger amounts of food. To avoid incurring large energy losses, the salmon must either move into deeper water or migrate northward into the Bering Sea farther from the freshwater rivers where they spawn. It is not certain they could make these adaptations.
- Drastic declines in western Alaska’s Pacific salmon populations in 1997 and 1998 appear related to changes in the marine environment caused by exceptionally high sea temperatures. These unusual conditions included a rare bloom of phytoplankton typical of waters closer to the equator (which may also have contributed to a massive die-off of seabirds). Sharply reduced size of returning salmon combined with dramatically decreased numbers suggests large-scale starvation. Similar effects were seen in Fraser River sockeye salmon in British Columbia.
- Reef fish and inter-tidal invertebrates including sea anemones, crabs and snails in California provide compelling evidence that fish and other species are shifting toward the poles in response to warming. Studies of rocky reef fishes off the California coast show the proportion of northern species declining, and southern species increasing.
- Scientists have documented decreased reproduction and increased mortality in seabirds coinciding with warmer water. Sooty shearwaters off the California coast declined 90 percent in the late 1980s and early 1990s. Cassin’s auklets have declined 50 percent. In both cases, the cause seems to be decreases in plankton which form the base of the birds’ food chain. In Alaska, the severe decline in shearwaters from 1997 to 1998 was clearly due to starvation, as the abundance of their crustacean prey was dramatically reduced in the unusually warm waters. Common murres also died by tens of thousands.
- Coral reefs, the most biologically diverse and beautiful marine ecosystems, are also at extreme risk. The upper heat tolerance for many reef corals is just a few degrees above normal temperatures. Beyond that, they expel the colourful food-producing zooxanthellae algae in a process called bleaching. If it is too warm for too long, bleached corals die. High water temperatures in 1997 and 1998 sparked unprecedented bleaching in all major tropical regions including the Pacific and Indian Oceans, the Red Sea, the Persian Gulf, the Mediterranean, and the Caribbean. Large numbers of corals are turning completely white and dying, with over 90 percent mortality in parts of the Indian Ocean.
Problems at the poles
Meanwhile, polar regions will experience more extreme temperature change, and will likely suffer even more extreme biological impacts than lower latitudes. Sea ice is diminishing in both the Arctic and Antarctic, depriving birds and marine mammals of their hunting and breeding grounds. Edges and undersides of sea ice are home to the algae that are the base of the polar food web. As ice shrinks, so does the food available at higher levels on the web, from zooplankton to seabirds. The result is serious trouble for some bird and mammal species.
In the Antarctic, annual air temperatures have been increasing since the 1950s. Average frequency of cold years has decreased by more than half from four out every five years to just one or two in five causing significant stress for species that depend on sea ice. Two closely-related species demonstrate the result: chinstrap penguins in the western Antarctic Peninsula have increased in numbers since the 1950s, while Adelie penguinshave declined. Both eat the same prey, but Adelies winter on increasingly scarce sea ice, while chinstraps prefer open water. Something similar is happening to crabeater seals, which also require pack ice. Their populations are falling, while southern fur seals, southern elephant seals and others that prefer open water are increasing, and extending their geographic ranges further south.
Canadian researchers in western Hudson Bay have documented decreased weight in adult polar bears and a decline in the birthrate since the early 1980s. They suspect the cause is earlier spring breakup of sea ice resulting from long-term global warming. The bears rely on the ice floes to provide a platform to catch their prey, seals. During the summer months, bears are shore-bound and rely heavily on fat reserves to survive. The entire population must fast for at least four months after the ice has broken up, while pregnant females in Hudson Bay must fast for eight months.
Alaska’s Bering Sea has exhibited many ecological changes over the past decade. In addition to major, long-term declines in Steller sea lion and northern fur seal populations, other mammal and bird communities appear increasingly stressed. Small forage fish, such as herring, capelin and larval fishes, have been declining for the past 5 years. Species that were previously known from more southern climes have appeared in Alaska including Pacific white-sided dolphins, albacore and yellow-fin tuna, and ocean sunfish, and herring spawned earlier than ever before.
Seals and sea lions suffered considerable declines during El Nino years. For example, studies during 1983-84 El Nino showed females had to dive deeper to find food and were away from their pups longer, causing a drop in milk production and pregnancy rates. Young seals and sea lions had reduced growth rates and higher mortality as a result.
Action sooner, not later
Ocean temperatures have been rising steadily in many areas of the globe for as long as 60 years, increasing as much as 2 to 3 degrees F in some places. With such widespread changes in marine life already occurring, the implications for even more dramatic changes in the near future are grave. While scientists cannot precisely predict the wide range of possible biological changes, the chilling observations are powerful harbingers.
“We have ample evidence that current global temperatures are significantly higher than any time in a thousand years,” said WWF’s Adam Markham. “Carbon pollution from the burning of coal and oil is projected to boost temperatures at an accelerating rate in the coming decades. The longer we wait to turn down the heat the fewer our options will be.”
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