Narragansett Bay Project

The Narragansett Laboratory of NMFS maintains an ecological monitoring program for Narragansett Bay A circular transect of the major axes of Narragansett Bay (figure 1) including the waters of the East and West Passages, Mt. Hope Bay, the Providence River and Rhode Island sound, is sampled once a month. Data is collected with the Mariner Shuttle (figure 2), an undulating, in-situ oceanographic sampler designed specifically for this application. It is based on a Chelsea Instruments NuShuttle, and carries a large suite of instruments for measuring the physical, chemical, and biological characteristics of the water. The instruments include:

1. A CTD-Fluorometer, for measuring conductivity (salinity), temperature, depth, and chlorophyll fluorescence (a measure of the amount of phytoplankton present)

2. A dissolved oxygen sensor

3. A continuous plankton recorder, which collects a continuous sample of the plankton in the water for later microscopic examination

4. An Optical Plankton Counter, which records the fine scale distribution of plankton sized particles

5. A Fast Repetition Rate Fluorometer, which electronically measures the instantaneous primary production rate

6. A PAR (photosynthetically active radiation) sensor

On a monthly basis, the Mariner Shuttle is deployed from the Rhode Island Department of Environmental Management's research vessel RV Chafee. It is towed at 8 knots, and undulates from surface to near bottom. Most of the instruments record one observation each second, and store the data on deck board computers, along with time stamps and GPS positions. On return to the laboratory, the calibration of the instruments is checked, and the data is processed, graphed, and published on the NarrBay.org web site.

The Mariner Shuttle project has been collecting data on Narragansett Bay since 1998. It's time series is long enough to start defining normal base-line conditions for various areas of the Bay. Long term monthly means have been calculated, and significant departures from those means are being used as an index of Bay conditions and stresses that might be associated with changes in the success of fish populations and the productivity of the Bay. Major findings of this project to date include observation of a major change in the productivity cycle, and the initial observations of serious hypoxic conditions in the Bay proper (as opposed to the Providence River). Since this sampling program started, the winter/spring bloom that traditionally dominated the Bay's productivity cycle has been either totally absent, or greatly reduced in concentration and duration. Instead of one major bloom, the Bay now undergoes a number of localized, short terms blooms, typically in the Providence River in the summer, This change in productivity has occurred concurrently with a change in the fish community, from one dominated by dermersal species, such as winter flounder, to one dominated by pelagics, such as menhaden. The Marine Shuttle surveys have also shown that hypoxic episodes in the Bay are much more common, more severe, and cover a much greater area of the Bay than was previously suspected. These findings have led to an intensified ongoing effort by researchers from RIDEM, URI, and Brown University to understand and monitor hypoxic events and their effect on Bay ecology and fisheries.

In cooperation with the State of Rhode Island's effort to reduce nutrient input into the Bay, a miniaturized nutrient sampler is being added to the instrumentation of the Mariner Shuttle. When it is deployed in early 2006, the upgraded Shuttle will add measurements of nitrate/nitrite, ammonia, phosphate, and silicate. The Mariner Shuttle will then be able to assess the effectiveness of nutrient reduction efforts, and test whether those reductions have the desired effects on the Bay ecosystem and reduce the incidence of hypoxia.

The Mariner Shuttle transects are part of the cooperative Narragansett Bay Window program, which assesses the fish and fisheries of Narragansett Bay, monitors its water quality, and studies it ecology , all in support of management of the Bay and its resources. Partners in the Bay Window program include the Rhode Island Department of Environmental Management, NMFS, the University of Rhode Island, Brown University, Roger Williams University, Narragansett Bay National Estuarine Research Reserve.