Composition and Distribution of Macrobenthic Invertebrate Fauna 



15 



Rhode Island, and other private and governmental 

 organizations. 



One of the most comprehensive reports on this sub- 

 ject is the monograph entitled "Physical Oceanography 

 of the Gulf of Maine" by Henry B. Bigelow (1927). He 

 describes the essential features of water temperature, 

 salinity, tidal and nontidal circulation, and seasonal 

 variation in these hydrographic features. Much detailed 

 information was added in succeeding years particularly 

 by John B. Colton and his associates at the Bureau of 

 Commerical Fisheries Biological Laboratory at Woods 

 Hole, Massachusetts, and bv Dean F. Bumpus and his 

 colleagues at the Woods Hole Oceanographic Institu- 

 tion (Stetson, 1937: Bumpus, 1960, 1961;Colton, 1964; 

 Bumpus and I.auzier, 1965; Bumpus et al., 1973; Butman 

 et al., 1980, 1982; Dorkins, 1980; Ramp et al., 1980. 

 Moodv et. al., 1984, Mountain and Hol/warth. 1989. 

 among others). Discussions of earl) oceanographic re- 

 search in this region and references to the literature 

 are given by Colton (1964), Schopf (1968a). and Wright 

 (1987). 



In brief, the main features pertaining to water circu- 

 lation in the study area are as follows: 1 ) cold water on 

 the Nova Scotian Shelf flows southwestwardly along 

 that feature and turns northward into the Gulf of Maine; 

 2) Gulf of Maine waters form a large nontidal counter- 

 clockwise gyre; 3) waters overlying Georges Bank form 

 a clockwise gyre; 4) nontidal currents generally flow 

 southwestwardly and westward across Nantucket Shoals 

 and on the Southern New England continental shelf; 5) 

 freshwater runoff from land empties by means of large 

 New England and Canadian rivers into the northern 

 and western sections of the study area; 6) incursions of 

 relatively warm high-salinity slope water enter the Gulf 

 of Maine by way of Northeast Channel; 7) tidal ampli- 

 tude is exceptionally large in the Bav of Funch' region, 

 and tidal currents are strong throughout the entire 

 New England continental shelf area; 8) the Gulf Stream 

 flows northeastward in deep water south of the New 

 England continental shelf (usually the Gulf Stream's 

 northern edge is more than one hundred miles south 

 of the continental shelf in the region south of Nan- 

 tucket Island); and 9) below the Gulf Stream in the 

 vicinity of the ocean bottom, the Western Boundarv 

 Current flows southwestwardly. 



Oceanic waters in the vicinity of the Gulf Stream 

 maintain a relatively constant salinity of about 35%o. 

 Most of the waters overlying the continental shelf have 

 a salinity range from 32 to 34%o. Salinity of inshore 

 waters, which are more stronglv influenced bv runoff, 

 fluctuate seasonally and drop to 28%o in late spring 

 when river discharge is maximum. 



Temperature of water in deep oceanic areas beyond 

 the continental shelf is typically homostenothermal. 

 Waters are warm (20°C) at the surface and cold at the 



bottom (2.5 to 5°C), and both surface and bottom 

 temperatures remain relatively stable throughout the 

 year. Conversely.the inshore waters along the coast are 

 characteristically heteroeurythermal. They are cold 

 (0°C) in winter and warm in summer, and because of 

 the shallowness and general turbulence of the water, 

 the temperature differential between surface and bot- 

 tom is relatively small. Also, there is considerable latitu- 

 dinal effect on inshore waters; in southern areas the 

 temperature does not drop as low in winter and rises 

 higher in summer than it does in northern areas. 

 Midshelf waters — those between the oceanic and in- 

 shore zones — are generallv intermediate in their tem- 

 perature regime. Temperature diversitv between the 

 surface and bottom is moderate. Seasonal changes in 

 temperature are greater in offshore shallow areas (such 

 as Nantucket Shoals and Georges Bank) than in basins 

 and other deep water areas, but the range is less than 

 that in coastal waters. Annual fluctuation in tempera- 

 ture of bottom water is considerably less than that of 

 surface waters. latitudinal effect on shelf water masses 

 is pronounced; Nova Scotian water is substantially colder 

 than other water masses within the study area, and the 

 temperature generally increases to the west and south 

 (Bigelow, 1933; McLellan, 1954; Edwards et al.. 1962; 

 Colton et al., 1968; Schopf and Colton, 1966; Schopf, 

 1967; Colton. 1968a, 1968b, 1969; Colton and Stoddard, 

 1972, 1973; Mountain and Holzwarth, 1989; Colton et 

 al. 10 ; Colton et al."; Colton et al. 1 -'; Colten et al. 13 ). 



Thermal extremes, rather than means, are believed 

 to have a marked influence on the presence or absence 

 of various kinds of benthic animals. In order to detect 

 the possible influence of thermal extremes as a limiting 

 factor, we have analyzed the invertebrate fauna distri- 

 bution in relation to the approximate annual mini- 

 mum and maximum water temperatures, and the range 

 in water temperature, to which the various taxa are 



111 Colton, J. B.,Jr.. R. R. Marak. andS. R. Nickerson. 1965a. Envi- 

 ronmental observations on continental shelf Nova Scotia to long 

 Island, March 196"). Albatross IV cruise 65-3, U.S. Bur. Commer. 

 Fish. Biol. Lab. Woods Hole, Mass., l.ab. Ret. 65-15, 3 p., '.I figs, 

 (mimeo). L'npubl. manuscript. 



11 Colton. J. B, Jr., R. R. Marak. and S. R. Nickerson. 1965b. Envi- 

 ronmental observations on continental shelf Nova Scotia to Long 

 Island, September 1965, Albatross IV cruise 65-12. U.S. Bur. 

 Commer. Fish. Biol. Lab. Woods Hole, Mass., Lab. Rel. 65-19, 3 p., 

 9 figs, (mimeo). L'npubl. manuscript. 



12 Colton, J. B.,Jr., R. R. Marak. and S. R. Nil kerson. 1966a. Envi- 

 ronmental observations on continental shell Nova Scotia to Long 

 Island. March 1966. Albatross IV cruise 66-2. U.S. Bur. Commer. 

 Fish Biol. Lab Woods Hole, Mass.. Lab. Ref. 66-6. 3 p., 10 figs, 

 (mimeo). Unpubl. manuscript. 



13 Colton. J. B.. Jr., R. R. Marak, S. R. Nickerson. and R R. 

 Stoddard. 1966b. Environmental observations on continental 

 shelf Nova Scotia to Long Island, May-June 1966. Albatross l\ 

 iiuise 66-7. U.S. Bur. Commer. Fish. Biol. Lab.. Woods Hole. 

 Mass., Lab. Ref. 66-7. 3 p., 19 figs, (mimeo). Unpubl. manuscript. 



