Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 224-238. 



Review of the oceanography of Long Island Sound 



By Gordon A. Riley 



Bingham Oceanographic Laboratory 



and 



Woods Hole Oceanographic Institution* 



Summary — Long Island Sound is a shallow, semi-enclosed body of slightly brackish (23-31 /^o) 

 water with an area of about 900 nautical square miles. Moderate tidal currents permit a small seasonal 

 thermocline and slight vertical gradients in salinity, oxygen and nutrient salts. The major feature of 

 non-tidal circulation is a two-layered transport system in which a freshened surface layer moves east- 

 ward out of the Sound and is replaced by a more saline inflow along the bottom. The latter contains 

 more nutrients than the outflowing surface water, so that the transport system tends to accumulate 

 and conserve nutrients. Freshwater drainage also makes a significant contribution of nitrate. 



Phytoplankton concentrations are large, but the species composition is relatively limited. A large 

 diatom flowering occurs in late winter, following an early winter minimum, with only minor fluctua- 

 tions the rest of the year. There is sufficient mixing to prevent a large accumulation of nutrients in 

 the bottom water, so that there is neither pronounced poverty in summer nor a big autumn flowering 

 following destruction of the thermocline. Major limiting factors are the amount of efl'ective light in 

 autumn and winter and the nitrogen supply in spring and summer. Variations in light and temperature 

 from one year to the next aff"ect the winter species composition and the time of the flowering. Diatoms 

 are largely replaced in summer by naked flagellates and other nannoplankton. During one summer 

 when nitrate concentrations were higher than usual, diatoms were abundant and there was also an 

 unusually large zooplankton crop. A causal connection is indicated but not well established. 



The zooplankton consists of large numbers of small animals. Relatively few species are present. 

 The dominants are two species of the copepod Acartia which alternate seasonally. Descriptive and 

 experimental studies suggest that seasonal replacement is primarily a temperature-controlled 

 competition rather than a direct, lethal temperature effect. Experiments show that the Acartias have 

 high respiratory rates and low grazing rates compared with most other copepods that have been 

 examined and possibly are able to achieve dominance only in waters sufficiently brackish to exclude 

 more efficient oceanic species. 



Preliminary studies of bottom fauna indicate a relatively large biomass, again consisting of large 

 numbers of small animals. Fish eggs and larvae are abundant, and the Sound may be an important 

 spawning and nursery ground. However, commercial fishery statistics show no indications of a large 

 population of mature fish. 



Total phytoplankton production is about the same as in the open coastal and bank waters off" 

 New England. Most of this production is utilized in the support of small animals which do not 

 provide an adequate food supply for the efficient production of large carnivores. 



INTRODUCTION 

 Long Island Sound, like other New England waters, has been a source of interest 

 and livelihood since colonial times, and its general features are well described in early 

 expedition narratives. Scientific studies of its waters began a little more than a hundred 

 years ago with a survey of the morphometry, character of the bottom, tides, and 

 currents, jointly sponsored by the Navy and the predecessor of the present Coast and 

 Geodetic Survey. The pertinent information was printed on a series of three excellent 

 hydrographic charts in 1855. More thorough surveys of tides and currents were made 



* Contribution No. 762 from the Woods Hole Oceanographic Institution. Studies described 

 herein have been aided by the Office of Naval Research, Department of the Navy, through contracts 

 with Yale University (NR 163-118) and the Woods Hole Oceanographic Institution (N6onr— 277). 



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