hinders many attached species (such as mussels and barnacles) from 

 establishing themselves and surviving more than 1 year. 



Estuarine beaches are not subject to extensive wave action. Current velocity, 

 particularly during spring runoff and storms, is more important in determining 

 the particle size of the sedimentary material. 



The production of organic matter in situ is low for beaches because of the 

 absence of suitable substrata for macroalgal attachment. The largest source 

 of organic matter for beaches is uprooted macroalgae and other estuarine 

 vegetation (eelgrass, sea lettuce, and cordgrass) deposited by tidal and wave 

 action. Depending upon the degree of exposure of the beach macroalgal 

 colonization of pebbles and interstitial spaces below the surface may be a 

 source of organic matter production. Bacteria and fungi living in the 

 interstitial spaces consume organic matter produced by photosynthesis. 



Several invertebrate species are able to survive the rigors of living on 

 estuarine beaches in Maine (Larsen and Doggett 1978a). The only study of the 

 invertebrate fauna of the cobble and gravel beaches of Maine (Larsen and 

 Doggett 1978a) indicates the species composition is similar. Indeed, seven of 

 the eight most abundant species in each habitat are shared between them and 

 the top four species have similar abundances in both habitats (table 5-9). 

 All of the abundant invertebrate species on cobble and gravel beaches are 

 ubiquitous and none are unique to these habitats (Larsen and Doggett 1978a). 

 The oligochaetes and nematodes are by far the most abundant groups. They 

 inhabit the sand underlying the gravel and cobbles and also are found in 

 association with rotting wrack and the blue mussel. 



Most of the rock barnacles on the gravel and cobble beaches are small, 

 indicating that they had set the previous spring. The absence of adults 

 suggest that they had been dislocated, probably during the winter. 



Filter-feeding blue mussels usually congregate in the lower intertidal zone. 

 They wrap byssal threads around each other and around rocks which renders 

 them less vulnerable to displacement by wave action. 



Other important species inhabiting intertidal beaches include the common 

 periwinkle and the amphipod Orchestia platensis . The periwinkle grazes 

 microscopic algae, while the amphipod feeds in the wrack line. The periwinkle 

 undoubtedly becomes dislodged by waves but is motile and can reestablish its 

 position. The only common carnivore is a nemertean worm. Of the nine types 

 of intertidal habitats investigated by Larsen and Doggett (1978a), gravel and 

 cobble beaches ranked eighth and seventh, respectively, in the mean number of 

 invertebrate species per station. Each habitat averaged about 10 invertebrate 

 species per station, and the only habitat with a lower species diversity was 

 the sand beach. 



Gravel and cobble beaches differed most in the density of organisms (Larsen 

 and Doggett 1978a). Gravel beaches supported about 5000 individuals/m? , while 

 cobble beaches supported 8000/m2 . As many as 87,096 barnacles/m 2 and 21,836 

 oligochaetes/m were present at individual station locations on cobble 

 beaches. Differences in substratum stability may explain this difference in 

 density. In terms of density of invertebrate organisms at the nine intertidal 



5-96 



