Survey of Intertidal Organisms on Mount Desert Rock

Schnell, Marine

From the abstract: "Mount Desert Rock (Lat: 43.97 Lon: -68.13) is a 1.2-hectare island 40 km off the Maine coast. The intertidal ecology of Mount Desert Rock (MDR) is unique due to its distance from the mainland and its breeding colony of Herring Gulls (Larus argentatus) and Great Black-backed Gulls (Larus marinus). Compared to Mount Desert Island (MDI), rough periwinkles (Littorina saxatilis) and smooth periwinkles (L. obtusata) are notably more abundant, and common periwinkles (L. littorea) are much less abundant, which aligns with the relative abundance of periwinkles that Johannesson (1988) found on the remote island of Rockall. Littorina littorea, an introduced species, may be less abundant due to its long planktonic larval stage. Young L. littorea produced on MDR may disperse widely and rarely recruit to the island, whereas Littorina obtusata and L. saxatilis have direct development and are able to maintain a more consistent population. This phenomenon may also explain lower abundances of two introduced species of crabs: green crabs (Carcinus maenas) and shore crabs (Hemigrapsus sanguineus). In terms of gull impact on the intertidal zone of MDR, prey species of Larus argentatus and L. marinus were less abundant than on MDI and were found lower in the intertidal. These species include sea stars (Asterias spp.), sea urchins (Strongylocentrotus droebachiensis), and crabs (Cancer irroratus, C. borealis, and Carcinus maenas). These observations are supported by the findings of Ellis et al. (2007), who found that the predation pressure from gulls is an essential part of the ecology of the intertidal zone."