generally are covered with algae and are dominated by barnacles, but in some 

 areas, particularly those with large tidal amplitudes, rough periwinkle and 

 mites are the only species present at the highest tidal level. Lower 

 intertidal rocky areas usually are covered by a dense growth of algae, which 

 is grazed by the common and smooth periwinkles and the limpet. Crustaceans 

 common to the algae-covered lower zones are isopods , amphipods , and green 

 crab. Pockets of mussels are found in association with oligochaetes , 

 nemerteans, and nematodes. Mites, chironomid larvae, and the predatory whelk 

 are characteristic of these zones. Irish moss and its associated animals 

 notably are absent in these protected areas. 



Suspension feeders are the most abundant feeding type on rocky shores. The 

 dominant rock barnacle and the blue mussel are dependent on phytoplankton for 

 sustenance. Other common species are the herbivorous periwinkles (common, 

 smooth, and rough) and the limpet, all of which graze on algae on rock 

 surfaces. Lubucheno and Menge (1978) state that the limpet, which has the 

 potential to control algal populations, generally is too scarce to have any 

 effect. 



The principal predator on protected rocky shores is the whelk (Menge 1975, 

 1978a, 1978b; and Lubucheno and Menge 1978), which preys upon other intertidal 

 animals (e.g., blue mussels and barnacles). The dense algal canopy at 

 protected sites reduces desiccation stress and provides more habitat for the 

 snail to graze on than that at exposed sites. The whelk and another common 

 predator, the green crab, commonly are found on most of Maine's protected 

 rocky shores. Other predators (e.g., fish) may move into the intertidal zone 

 at high tide. No information is available on the extent and composition of 

 this mobile component. 



Intertidal streambeds . The streambed environment has not been studied in 

 Maine. The biota of streambeds is unquestionably different from that of 

 surrounding intertidal areas because the sediments of streambeds are 

 different, they are exposed to water of low salinities, and they are not 

 exposed at low tide. 



Eelgrass is often abundant in streambeds, as are mud shrimps, hermit crabs, 

 soft-shelled clams, and mummichogs. Factors such as currents, sediment 

 stability, sediment type, and salinity determine which plants or animals 

 dominate. 



Intertidal beach . Beaches in Maine are composed of sand, gravel, and 

 cobble. Sand beaches are predominantly marine and therefore are discussed in 

 chapter 4, "The Marine System." Gravel and cobble beaches, which are more 

 widespread in estuaries, are reviewed below. 



Most beaches originate from the reworking of submerged glacial deposits by 

 waves. They are composed of either one particle type or mixed types. The 

 most common mixtures are gravel-cobble and gravel-sand. Boulders also may be 

 scattered on gravel or cobble beaches. In fact, beaches composed of "pure" 

 cobble or gravel are rare in Maine. The low intertidal and midintertidal 

 areas of estuarine beaches have a mud, sand-gravel, or cobble matrix under the 

 surface layer of pure gravel or cobble. Gravel and cobble beaches are 

 relatively harsh environments for organisms, although they are not as harsh as 

 sand beaches. The movement of gravel or cobbles, particularly during storms, 



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