Wednesday, July 30, 2008

Narragansett Bay Isn’t What It Used To Be

By Chip Young

What it is like five years after the 2003 Greenwich Bay fish kill

August 20th will mark the fifth anniversary of the calamitous Greenwich Bay fish kill.  This catastrophic ecological event left the shores of beaches and coves surrounding Greenwich Bay covered in dead fish and shellfish, all primarily suffocated by the lack of oxygen in the local waters.

The fish kill was the result of a “perfect storm” of factors, which scientists were not oblivious to, but were in no position to do anything to halt.  In fact, researchers from the Bay Window Monitoring Program, of which I am a member, predicted its occurrence right down to the very day.  Their prescience was based on the data they were collecting, which showed the growing lack of dissolved oxygen, warmer temperatures and the coming neap tide, which is when there is the least tidal fluctuation, which minimizes the mixing of the saltwater of Narragansett Bay with freshwater from rain, and the natural river and stream flows.

The public outcry over the visual and visceral shock of seeing that much marine life washing up dead led to an immediate response from state government.  A Governor’s Narragansett Bay and Watershed Planning Commission was formed to look into the matter and take action, with hundreds of local experts involved from government, private and public sectors.  Attacks were launched on the nutrient loadings into Narragansett Bay from wastewater treatment plants and stormwater runoff.  These nutrients, from human sources and the use of nitrogen-rich fertilizers, were seen by many as an oxygen-depleting powder keg, the fuse of which was lit by the accumulated factors of weather, temperatures and other small but important variables.

There has been progress in trying to assure that we don’t experience another fish kill of that magnitude.  (Some fish kills occur naturally every summer, and should’t be a cause of panic.)  But Bay Window researchers and scientists are now keeping a close eye on the entire Bay as the warm weather and rains of August approach, especially during the neap tides scheduled for August 8 and 23.  You’ll be able to read more about what is happening underneath the waves as regards the possibility of another fish kill in this space we near those dates.  For now, below is a take on how Narragansett Bay has been gradually changing through the years, and what that evolution means to Rhode Islanders, written by my highly respected Bay Window colleagues Mark Gibson and Candace Oviatt.  These two scientists have been studying the Bay for years, know it inside out, and what they see and say is well worth your while.

NARRAGANSETT BAY: CH-CH-CHANGES
By Mark Gibson and Candace Oviatt

In late June, Department of Environmental Management scientists from the Bay Window monitoring partnership observed through aerial flyovers and purse seine sampling an estimated 24 million menhaden with an average weight of one pound apiece, in Narragansett Bay. The fish were predominantly located in the Upper Bay and Providence River.

That is a lot of fish, an amount not seen since the 1970s.

The massive influx of this keystone species that lures fishermen and predatory fish such as striped bass and bluefish is nearly double that of the noteworthy 2007 bumper crop of menhaden that attracted media and public attention.  But there are other major changes going on in Narragansett Bay that are not as visible as churning schools of fish on the surface.

Narragansett Bay itself has noticeably warmed in the recent past.  Yes, that is global climate change manifesting itself right here in our backyard. The Bay is gradually taking on the characteristics of a mid-Atlantic estuary such as what you would experience in Maryland and the Carolinas.  Over the past 30 years, the average mean temperature of the Bay has gone up two degrees Fahrenheit; the average mean winter temperature has increased four degrees.  For temperature-sensitive marine creatures, that is a huge change.

Due in part to the warming of the Bay, traditional natural cycles of Bay organisms are either taking place earlier, or not at all.  The system has changed.  The winter/spring “bloom” of plankton, which used to be the starting point for a cascade of ecological processes up the food chain, has become a fragment of itself.

It all begins with the plankton. Phytoplankton, the microscopic plant life in the Bay, once thrived in enormous amounts in February and March, during that winter/spring bloom. Once, the small plants would bloom extensively and virtually free from zooplankton predators (think small, shrimp-like creatures), and sink naturally to the bottom. This occurred because the zooplankton were inactive in the cold winter water and not able to feed on the abundant phytoplankton. The phytoplankton sinking to the floor of the Bay would become welcome meals for bottom mud dwellers such worms and shellfish.  Now, with warmer winter water in the Bay, the zooplankton do not go dormant. They remain active in their newly warmer surroundings, and graze the phytoplankton well in advance, limiting their blooming in the traditional way of the Bay.

In addition, the tiny, clear, barrel-shaped jellyfish you see throughout the Bay, known as “ctenophores” (TEEN-oh-phores), have also benefited from the balmier temperatures.  They are arriving in the Bay early than usual, in June rather than September, where they feed on the small marine life (for example, small fish larvae).  Some scientists believe that the changes that we are seeing in the kinds of fish occurring in these waters are related to this jellyfish predation on fish larvae. Yet more changes for Narragansett Bay.

The rise in water temperature is causing major changes in the organisms that live in the Bay and how the whole ecosystem works.  It is also switching the balance of power in fisheries from species that live on the bottom like flounders and hakes, to those that live in the water column such as butterfish and scup.  That already has measurable economic impacts locally; as winter flounder are worth up $2.00 per pound to commercial fishermen, while menhaden and scup only yield $0.10 to $0.75 per pound.

This shift in types of fishes over the past 30 years of warming waters is interesting because the total biomass of fish has remained about the same. That biomass just consists of different species. Little known year-round resident bottom fish such as hogchokers and oyster toadfish are declining, as they are replaced on a much more seasonal basis by visitors such as stripers and summer flounder.  Warm water may be the primary cause, think Bay Window researchers, but they are also concerned that a lack of oxygen along the bottom of the Bay—a condition called “hypoxia,” which was the main factor in the notorious 2003 Greenwich Bay fish kill—may also play a significant role.

Other factors are contributing to changes in the Bay as well. The water quality is getting better as we reduce pollutants from wastewater treatment facilities and we eliminate old cesspools.  Shell disease—an emerging new disease—is affecting the iconic animal of Narragansett Bay, the lobster.  Newly arrived invasive species of crabs and other organisms are out-competing our native Bay creatures for existence.  At the same time, the overall productivity of Narragansett Bay seems steady. 

Global climate change may be here to stay and Narragansett Bay is changing. How? That is what Bay Window scientists are focusing on; examining the information they accumulate day in and day out.  We need to find those answers because the health of this incredible, dynamic system is critical to the future economic and environmental well being of each and every one of us.

-  Mark Gibson, deputy chief of Fish and Wildlife for the R.I. Department of Environmental Management, and Candace Oviatt, professor of oceanography at the University of Rhode Island Graduate School of Oceanography, are both members of the Bay Window Monitoring Program Steering Committee.