Distribution of Gammaridean Amphipoda (Crustacea) 



on Georges Bank 



JOHN J. DICKINSON' and ROLAND L. WIGLEY' 



ABSTRACT 



The distribution of 97 species of gammaridean amphipods is described for the Georges Bank region, based 

 on 379 samples from 326 stations. A wide variety of sampling gear was used, resulting in representation of both 

 infaunal and epifaunal species. Geographic and bathymetric distributions, and sediment preferences are summar- 

 ized for each species. The zoogeography of the gammaridean fauna of Georges Bank is discussed, and the most 

 common geographic distribution patterns are described and related to environmental parameters. 



INTRODUCTION 



This report describes distribution patterns for 97 species of 

 gammaridean amphipoda on Georges Banic. Georges Bank is a 

 submerged coastal plain that extends over 300 km east of Cape 

 Cod, Mass., and encompasses an area of approximately 19,000 

 km^ (Fig. 1). It is one of the most productive fishing grounds in 

 the world yielding thousands of metric tons of finfish and shell- 

 fish annually (Gusey 1977). In the future, Georges Bank might 

 also serve as an offshore source of petroleum. 



Gammaridean amphipoda are the most numerous group of 

 macroinfaunal organisms inhabiting Georges Bank, composing 

 49"Vo of the number of specimens in quantitative samples col- 

 lected there (Wigley and Theroux in prep.). Gammarideans are 

 important food for many juvenile bottom- feeding fish. They 

 often comprise 30% or more of the diet (Bowman'). 



The purpose of this report is to provide information useful to 

 both benthic ecologists and fisheries biologists interested in the 

 Georges Bank ecosystem. Since amphipods are known to be sen- 

 sitive to environmental aheration, the data presented in this 

 report may also be useful as a baseline in the event of petroleum 

 development on Georges Bank. 



GEORGES BANK— DESCRIPTION 

 OF ENVIRONMENT 



For purposes of this report, we define Georges Bank as that 

 part of the New England continental shelf between Great South 

 Channel (long. 69 °W) and Northeast Channel at water depths 

 <200 m (Fig. lA). The important physiographic features of 

 Georges Bank include: 1) a steeply sloping northern face; 2) an 

 area of shoals in the north-central part; 3) a gently sloping 

 southern face (Fig. IB). The bank has been shaped by glacial 

 erosion in the past, and recently by the strong tidal currents that 

 run through the shoals (Stewart and Jordan 1964). The sedi- 

 ments of Georges Bank are dominated by sands (Wigley 1961). 

 The central area of the bank including the shoals is chiefly medi- 



' Northeast Fisheries Center Woods Hole Laboratory, National Marine Fisher- 

 ies Service, NOAA, Woods Hole, Mass.; present address: National Museum of 

 Canada, Ottawa KIA OM8, Canada. 



'Northeast Fisheries Center Woods Hole Laboratory, National Marine Fisher- 

 ies Service, NOAA, Woods Hole, MA 02543. 



'Raymond Bowman, Fisheries Biologist, Northeast Fisheries Center Woods 

 Hole Laboratory, National Marine Fisheries Service, NOAA, Woods Hole, MA 

 02543, pers. commun. December 1979. 



um to coarse sand (Fig. 2A). Gravel covers the Northeast Peak, 

 but fine sands occur around most of the perimeter of the bank. 

 Silts, clays, and fine sands are the dominant components in the 

 Western Basin. 



Bottom water temperatures on Georges Bank vary a moderate 

 amount during the year usually reaching a maximum in Septem- 

 ber and a minimum in February (Colton and Stoddard 1973). 

 The greatest seasonal changes occur in the shallow central area 

 of the bank which experiences about a 12 °C annual fluctuation 

 ranging from 4° to 16°C(Fig. 3 A, B). The perimeter of the bank 

 has a much smaller annual temperature range fluctuating as 

 little as 2°C in some areas. The coldest year-round bottom 

 waters (6 °-8 °C) occur in the Western Basin and on the North- 

 east Peak. 



GEORGES BANK— AMPHIPODA 



The gammaridean amphipod fauna of Georges Bank has 

 been little studied previously. Smith and Harger (1874) collected 

 a few samples from the bank and reported the amphipods which 

 they found, but the taxonomy is now outdated and coverage of 

 the bank was incomplete. Some records of occurrence on 

 Georges Bank are given in papers of Shoemaker (1945b) and 

 Bousfield (1965). Whitely (1948) collected 42 species of epiben- 

 thic and pelagic gammarideans on Georges Bank, but he gave 

 distributional data for only one species, Monoculodes edwardsi. 



METHODS 



The distribution patterns described in this report are based on 

 samples collected by the Benthic Dynamics Investigation at the 

 Northeast Fisheries Center at Woods Hole, Mass. These collec- 

 tions were obtained as part of a survey, conducted between 1953 

 and 1965, to obtain an overview of the general composition and 

 distribution of the macrobenthos on the continental shelf be- 

 tween Nova Scotia and Florida. 



A total of 379 collections from 326 stations were utilized in 

 charting the distribution of gammarideans on Georges Bank 

 (Fig. 2B). The coverage of the bank was relatively complete 

 except for the Shoals area where fewer samples were taken due 

 to the hazards of navigating there. The samples were collected 

 with a variety of sampling gear, including 1) quantitative grabs 

 (Van Veen, Smith-Mac Intyre, Campbell), 2) epibenthic sled 

 nets (ring and meter), 3) Dibby dredges, 4) otter trawls, and 5) 

 from fish stomachs. The Smith-Mac Intyre grab (160 samples), 

 the ring net (85), and the meter net (50) were the most frequently 



