Larsen and coworkers (1979) present limited data on exposed rocky shore 

 communities. They report up to 55 species at one station and densities of the 

 barnacle Balanus balanoides up to l60,000/m2 Compared to the other eight 

 intertidal habitats sampled by this team, high energy rocky shores rank first 

 in terms of both density and numbers of species. 



Table 4-10 gives a qualitative assessment of the abundances of selected 

 species of various exposed sites in Maine (Doggett et al. 1978). The blue 

 mussel, Mytilus edulis , is often dominant in the low intertidal zone, commonly 

 attached to the thallus of Irish moss, Chondrus crispus , forming a Mytilus- 

 Chondrus mat. Predators (i.e., Thais lapillus , Asterias spp . , Carcinus 

 maenas , and Cancer borealis) and herbivores (i.e., Littorina littorea, Acmaea 

 testudinalis , and Strongylocentrotus droebachiensis ) are also present at most 

 sites. More potential predators, such as starfish and crabs, are present in 

 tide pools in exposed locations than in those in more protected locations. 

 The amount of actual predation that occurs when the tide is high is unknown. 



Some species are dependent on other species for protection and/or sustenance. 

 Such is the case with oligochaetes and nematodes, which are usually found in 

 association with mussels or in Irish moss mats. The mussels probably provide 

 nourishment in the form of pseudofeces for these animals. The amphipod Hyale 

 nilssoni dwells among mussels and sometimes barnacles, where it can avoid 

 desiccation. 



Algae provide substratum for a number of species. The polychaetes Spirorbis 

 borealis and Fabricia sabella are often found attached to the macroalgae 

 Ascophyllum or Fucus . Bryozoans and hydrozoans also attach to these algal 

 species. The gastropod. Lacuna vincta , is often found grazing on sea lettuce 

 ( Ulva ) or kelp ( Laminaria ) . 



Sponges, Halichondria panicea, and the holdfasts of kelp harbor a variety of 

 species. Polychaetes, Lepidonotus squamata ; brittle stars, Ophiopholis 

 squamata ; and the mussel Musculus niger are found in these protective 

 habitats . 



Suspension feeders represent the most abundant feeding type on rocky shores. 

 The dominant barnacle, Balanus balanoides , and blue mussel are dependent on 

 phytoplankton for food. The common green sponge, Halichondria panicea , is 

 also a suspension feeder. 



Other characteristic species of rocky shores are herbivores. The periwinkles, 

 Littorina littorea , L. obtusata , and L. saxatilus, the limpet, Acmaea 

 testudinalis , the gastropod Lucuna vincta , the chiton Tonicella ruber, and the 

 sea urchin, Strongylocentrotus droebanchiensus , all graze on algae on the rock 

 surface. The herbivore L. littorea grazes on ephemeral algae and in doing so 

 allows Irish moss to establish itself in the cleared space (Lubucheno and 

 Menge 1978). 



The principal predator on rocky shores is the whelk (Menge, 1976, 1978a, and 

 1978b; and Lubucheno and Menge 1978). Other invertebrate predators include 

 the crabs, Carcinus maenas and Cancer irroratus , and the starfish, Asterias 

 vulgaris . These species are found commonly on most of Maine's rocky shores. 

 Other predators may move into the intertidal zone at high tide. 



4-80 



