Information on the benthic invertebrates of Maine's sand beaches comes from 

 the work of Larsen and Doggett (in preparation ) mainly within the 

 characterization area and Croker and his students (Croker et al. 1975; and 

 Croker 1977) just to the south of the characterization area in southern Maine 

 and New Hampshire. 



The results of Larsen' s and Doggett' s study indicate that the benthic 

 macrofauna inhabiting the sand beaches of Maine cannot be considered a single 

 community. This fact can be illustrated in two ways. First, the percentage 

 composition of higher taxa changes along the coast from crustacean-dominated 

 beaches in the south to annelid-dominated beaches in the north (figure 4-28) . 

 Secondly, a complex, computer classification of the data identifies four 

 faunal communities (table 4-12), three of which are characteristic of three 

 geographically distinct segments of the coast (figure 4-29). The most 

 significant discontinuity occurs in the area of Boothbay Harbor and separates 

 the southwestern beaches (site-group A) from the more northeasterly beaches 

 (site-groups B and C) . 



The most likely explanation for the above distribution involves differences in 

 summer water temperature. Bousfield and Laubitz (1972) suggest that the coast 

 of Maine may be divided into two zoogeographic zones: zone A, northeast of 

 Penobscot Bay, where summer water temperatures are <53°F (12°C); zone B, the 

 southwestern area where temperatures reach 6l°F (16°C). Species requiring 

 warm temperatures for reproduction are excluded from the northeast, and warm- 

 sensitive species cannot compete in the southwest. 



Although the zoogeographic boundary hypothesized by Bousfield and Laubitz 

 (1972) does not coincide exactly with the major discontinuity identified by 

 the Larsen and Doggett data analysis, this may simply be a function of time of 

 sampling combined with the cyclic temperature changes that the Gulf of Maine 

 is known to undergo (Hopkins and Garfield 1979; and Taylor et al . 1957). 



The separation of the five northeastern beaches into site groups B and C is 

 more difficult to explain. Garfield (Bigelow Laboratory, West Boothbay 

 Harbor, ME; personal communication; March, 1979) believes that other, as yet 

 undefined, oceanographic features (i.e., high nutrients, tidal fluctuations, 

 temperature, salinity, and upwelling systems) may be responsible, but the 

 possibility exists that physical and/or biological factors too subtle to be 

 recognized from the existing data are responsible. 



Besides water temperature, Dahl (1953) lists ice action, air temperature, food 

 conditions, interspecific competition, and wave action as factors important to 

 intertidal organisms. Of these, the latter three are most important in Maine. 



Interspecific competition has been noted between two species of amphipods 

 (Bousfield 1973). Orchestia platensis is a colonizer of upper beaches that is 

 excluded by species of the more specialized amphipod genus Talorchestia . 

 Competition between amphipod species is presently being investigated in 

 southern Maine by Drs. Croker and Hatfield of the University of New Hampshire, 

 Durham, NH. 



4-88 



