LARSEN, P.F. 2012. The macroinvertebrate fauna of rockweed (Ascophyllum nodosum)–dominated low-energy rocky shores of the northern Gulf of Maine.

Sheltered, rockweed-dominated rocky shores are one of the most characteristic habitats of the northern Gulf of Maine. Rockweed, Ascophyllum nodosum, provides essential ecological services and recently has been subject to increasing commercial harvesting. This communication documents the associated macroinvertebrate fauna (>1.0 mm) of six characteristic rockweed shores along a 350 km gradient across the northern Gulf of Maine. Seventy-four putative taxa were identified. Numbers of species at each site ranged from 21 to 40. Arthropods, predominantly the barnacle Semibalanus balanoides, accounted for 70% of the individuals encountered. Densities per station ranged from 132 to 48,023 per m². Numerical analyses demonstrated that rockweed-dominated rocky shores of the northern Gulf of Maine are characterized by nine widely distributed taxa that represent 88.6% of the individuals. These nine are S. balanoides, oligochaetes, the isopod Jaera marina, the periwinkles Littorina obtusata and Littorina littorea, nematodes, the blue mussel Mytilus edulis, the amphipod Gammarus obtusatus, and nemerteans. Seven other taxa occurred widely at low densities. Cluster analysis of sites suggests a possible faunal break in midcoast Maine.