The rocks along the coast north and east of Cape Elizabeth are folded and 

 faulted igneous and metamorphic units that are locally invaded by granitic 

 intrusion (plutons) and ring dike-volcanic complexes ( a grouping of rocks 

 arranged in a circle) up to a mile in diameter (TRIGOM 1974). All of these 

 rocks are of Paleozoic and Mesozoic age. Paleozoic volcanic rocks occupy a 

 portion of the coast in Washington County (Doyle 1967). The distribution of 

 these rock types is a result of the tectonic history of the central New 

 England uplands; one of folding, faulting, and intrusion during the late- 

 Paleozoic coastal fracturing accompanying the opening of the North Atlantic 

 basin and renewed tensional movements along the Fundian Rift Zone (Ballard and 

 Uchupi 1972; TRIGOM 1974). The degree of folding, rock type, and fracture 

 patterns of bedrock ledge determine the available area that can be inhabited 

 by intertidal or subtidal biota. 



Rocky shores provide a stable substratum for colonization. Unlike sand, 

 gravel, and cobbles, boulders and bedrock substrata are not moved by wave 

 action. Stable substratum is necessary for the development of abundant and 

 dense populations of intertidal plants, and the intertidal rocky habitat is 

 second only to subtidal rocky areas in production. 



Intertidal macroalgae are physiologically hardy plants that can endure the 

 stresses of intertidal existence. The intertidal vegetation of the rocky 

 shores of Maine is dominated by large brown fucoid algae (rockweeds). Two 

 genera of great importance are Ascophyllum and Fucus . While several species 

 of Fucus can be found, Fucus vesiculosus is the most abundant. Similarly, 

 while other forms of Ascophyllum may be found in upper estuaries, Ascophyllum 

 nodosum dominates along much of the coast. Areas that are extremely wave- 

 exposed support little macroalgal growth. Encrusting macroalgae are widely 

 distributed on rocky shores. Their growth rates are slow and they contribute 

 little in productivity. 



Much of the organic matter produced by macroalgae can be released as soluble 

 material, when the plants are stressed by exposure to desiccation or fresh 

 water at low tide, or destroyed by violent wave action. 



Microbial activity occurs where microorganisms attach to the surfaces of the 

 macroalgae. The youngest (apical) parts of the plants are often free of 

 bacteria, while the older (basal) parts support a dense layer of 

 microheterotrophs , that is often so thick that it can serve as the staple diet 

 of protozoa and rotatoria. The attached microheterotrophs find an abundant 

 supply of amino acids, carbohydrates, and organic acids in the 

 microenvironment of the algal surface. These materials are assimilated and 

 regenerated into carbon dioxide (CO^ ) and inorganic nutrients. 



Exposed rocky shores support a dense and diverse assemblage of benthic 

 invertebrates (Larsen and Doggett, in press ) . The solid substratum provides a 

 secure foundation for the many epifaunal species that can anchor themselves to 

 the rock and the crevices; tide pools and macroalgae provide additional 

 habitat space for motile species. In addition, the rocks are constantly swept 

 by sea water, which ensures fairly stable conditions of salinity, temperature, 

 and moisture. 



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