Rising temperatures throw nature a curve
One in a series of occasional articles examining climate change, its effects, and possible solutions.
No longer. Winter surfers off
The bay's average annual water temperature has increased about 2 degrees Fahrenheit since 1960, and in winters it has warmed about 3 degrees. There is growing evidence that the temperature changes are breaking down carefully evolved relationships among species and disrupting the vast food web the bay depends upon.
Critical seasonal cues are misfiring, delivering new food sources to some species and new predators to others. A shrimp that traditionally migrated to warmer waters in winter is now staying year-round or returning earlier to eat young cold-water flounder. Luminescent jellies are also staying through the winter, meaning that their populations peak in spring rather than summer, exactly when fish larvae and eggs are plentiful. Scientists fear that the voracious jellies could be reduc ing fish populations and competing with them for food.
"The temperature change may not seem very big, but it gets amplified in the food web," said Jeremy Collie, professor of oceanography at the
The multitude of changes taking place in
The bay's winter warming roughly parallels a 4.4-degree rise in
The bay is also one of the places where researchers would expect to see the effects of warming first, because it is on the dividing line between southern and northern waters. In the summer, the bay is flooded with migratory species attracted to its warm water, some near the northern edge of their range. In winter, the waters are dominated by resident bottom-dwelling fish, some near the southern edge of their range. As a result, many of the species are vulnerable to temperature changes.
Because URI's Graduate School of Oceanography is located on its shores, the bay has some of the best long-term scientific records of temperature, fish abundance, and algal blooms in the Northeast, allowing scientists to document changes over time. Already, they have seen a sharp decline in commercially valuable northern fish species such as winter flounder and a rise in traditionally less-prized southern fish such as scup, and those changes cannot be explained by overfishing alone.
Disappearing food supply
Standing firm against 2-foot seas rocking a research boat a mile off Wickford, URI graduate student Jason Graff threw a red bucket overboard. Tugging on a heavy rope attached to the bucket, he hauled up a water sample and knelt to pour the water carefully into bottles that would later be measured for phytoplankton, or microscopic plants, and other barometers of the bay's health.
Almost 40 years of such weekly samples gave researchers one of their first hints that the bay was changing. 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.
URI oceanographers hope to identify other changes from the bucketfuls of water students scoop out of the bay every Monday morning from the deck of the 53-foot Cap'n Bert. Among the questions: Are new types of microscopic marine plants or animals moving in that could further change the timing of the bay's food supply? "The winter bloom is as important to the bay as grass and leaves are" on land, said David Borkman, a URI marine research associate. "It's the beginning of the productive part of the year, it gets the ball rolling . . . and it doesn't happen anymore."
Predator stays in winter
Times are not good for Narragansett Bay's winter flounder, once a prized catch of
A one-two climate punch is probably why. The flounder may not be getting enough food because of disapperance of the winter phytoplankton bloom. And now, the warming bay has fostered a new predator. The flounder has long had a winning strategy for survival: the cold. Young flounder grew in the cold waters on the bay's bottom when few predators were around. By the time hungry predators showed up when waters warmed, the fish were big and fast enough to escape.
Now, an aggressive sand shrimp called crangon is waiting for those juvenile flounder, no bigger than a pinkie nail. The shrimp has traditionally moved to warmer waters when the bay's temperature dipped. But in recent years the water has been warm enough for them to stay year-round or to return earlier to the bay and feed on whatever they find.
If the warming continues, scientists say, it is unlikely that winter flounder, already near the southern edge of its range, will bounce back in
Uncertainty for fishermen
At the start of this decade,
And some fishermen say the rules about catching them need to change too. "Global warming is changing habits in the bay, and fishing quotas have to be adjusted to deal with it," said Richard Fuka, president of the Rhode Island Fishermen's
State officials said quotas were adjusted upward in 2005 to account for the increasing number of scup, black sea bass, and summer flounder. They said they are being cautious about further quota increases to make sure that overfishing does not begin anew.
That is what fishermen base their livelihood on, he said. "But now, it's like having a misguided calendar."