Tuesday, November 13, 2007

Global Warming and Ecological Changes in Narragansett Bay

A year and a half ago scientists who spoke at the Long Island Sound Citizen's Summit conference, in Bridgeport, outlined some of the ecological changes taking place in the Sound and linked them to global warming. The most dramatic change, perhaps, was the shift in species composition caused by rising water temperatures -- cold water animals, like lobster and winter flounder, were being replaced by warmer water species, like summer flounder.

Not surprisingly, similar changes are being observed in Narragansett Bay. One of the most interesting is that the end of winter phytoplankton bloom that provides some of the Bay's bottom-of-the-food web food no longer occurs (I described it in the Soundon page 120 of my book). Here's what the Boston Globe reports:

A late-winter phytoplankton bloom long formed the foundation of the bay's food web. As days got longer and sunlight increased, the bloom would grow to cover almost the entire 25-mile-long bay. By early spring, the bloom would die naturally, and organic debris would settle to the bay's bottom, where creatures such as worms would feed on it and in turn become meals for fish such as winter flounder.

In the 1980s, the winter bloom stopped growing as large, and by the late 1990s it was all but gone. In temperature-controlled tanks at URI, marine biologists figured out why: It is being eaten.

Tiny marine animals called zooplankton are normally sluggish eaters in the winter. But researchers found that even a 1.4-degree increase in water temperature caused them to be more active in the tanks and to eat more, curbing the size of the bloom. Today, a longstanding summer phytoplankton bloom has become a more important food source, but it mostly feeds migratory, warm-water fish species, such as scup and bay anchovies. Without a significant winter bloom, the cold-water fish may be missing their meal.

The Providence Journal, meanwhile, reports on the changes in the Bay, the rapidly changing scientific opinion about why, and the political and budget issues that are hampering cleanup attempts:

Rhode Island-based scientists are publishing a book summarizing the last 25 years of science concerning the Bay. A key finding is that parts of the Bay function so differently from other areas, an eco-functional zoning plan should be created to better manage the bays within the Bay.

“We have found that the only constant about Narragansett Bay is change — and we’re in a period of accelerating change,” says Barry A. Costa-Pierce, director of Rhode Island’s Sea Grant program and co-author with Alan Desbonnet of the new book, Science for Ecosystem-Based Management — Narragansett Bay in the 21st Century.

“This is one of the best-studied bays in the world, and some of the surprises we’re finding are globally important,” says Costa-Pierce. The book finds that the Bay suffers from such health issues as regions of low dissolved oxygen and “a preponderance of opportunistic and nuisance species — weeds if you will — in the upper regions of the Bay.”

Some of that science points to new and disturbing ecological changes on the bottom of the Bay that may be triggered by global warming. The discovery has caught the attention of scientists around the world.

The Globe story is here, the Journal story is here. Both are must-reads.

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