Long-Term Effects of an Invasive Shore Crab on Cape Cod, Massachusetts

Abstract

Invasive species can cause dramatic changes in the structure of intertidal communities. In some systems, however, abundance or impacts of invaders may peak 10-20 years after invasion and decline thereafter. Hemigrapsus sanguineus (Asian Shore Crab) has been established at Sandwich, MA, on the north side of Cape Cod, since the mid-1990s. This study documented population dynamics of the Asian Shore Crab and 3 species of prey or competitors (Carcinus maenas [Green Crab], Mytilus edulis [Blue Mussel], and Littorina littorea [Common Periwinkle]) over 10 years. An additional goal of the study was to determine whether population growth of the Asian Shore Crab has slowed since its initial establishment. Density of the Asian Shore Crab increased over time, with no evidence of a density-dependent decrease in per capita growth rates. Concurrently, density of the Green Crab and the Blue Mussel declined, but there was no significant temporal trend in density of the Common Periwinkle. If observations at Sandwich are representative of sites north of Cape Cod, populations of the Asian Shore Crab are growing rapidly, and dramatic changes in community structure may be widespread.

Life History and Population Dynamics of Green Crabs (<em>Carcinus maenas</em>)

“…Jensen & Jensen [273] found that younger C. maenas in the Danish Wadden Sea favor the common cockle, Cerastoderma edule, over other prey items. Scherer & Reise [249] found that older males continue to feed on molluscs but older females feed primarily on annelid worms, although Baeta et al [262] found that different age classes and sexes of C. maenas showed no difference in diet when they occurred in the same area of an estuary in Portugal. More research should be done in the topic of differential feeding by different size classes, as it could be utilized for selective removal of certain size classes when trapping.…”

“…Individuals can be counted directly along a transect or within quadrats (see for example [52,105,125,145,248]) but this method is practical only for the intertidal zone at low tide (where mostly juveniles will be found) or in very shallow water. Extremely high densities of small juvenile crabs ranging from 200-2000 m −2 have been estimated using this method [95,109,249,250]. Divers can count crabs in subtidal areas but the type of vegetated or rocky bottom that offers suitable refuge also makes crabs very difficult to see.…”

“…Green crab adults are opportunistic omnivores, whose diet varies with season, composition of the community, size of prey, availability of prey and energy expenditure versus energy gained [116,262,269]. Green crabs are known to feed on organisms from at least 158 genera in five plant and protist and fourteen animal phyla [9,28,36,270], with members of all populations showing a strong preference for molluscs, especially bivalves such as clams, mussels and cockles [9,30,44,66,99,136,228,249,[271][272][273][274][275][276][277][278]. Additional preferred prey items include gastropod molluscs such as periwinkles [8,37,275,279], other crustaceans such as the common brown shrimp Crangon crangon [262] and recently settled small juvenile lobsters Homarus americanus [280] as well as members of their own species [101,105,106,205,249], polychaetes [281] and amphipods [30].…”

PopulationDynamics of Green Crabs (Carcinus maenas) -- A Review

“…Four of the most commonly used methods are discussed here; a review of additional methods can be found in [64]. Individuals can be counted directly along a transect or within quadrats (see for example [37,87,90,109,134]) but this method is practical only for the intertidal zone at low tide where mostly juveniles will be found or in very shallow water. Extremely high densities of small juvenile crabs ranging from 200 -2000 m -2 have been estimated using this method [72,[135][136][137].…”

“…sanguineis has essentially eliminated C. maenas in the rocky intertidal zone where it formerly was extremely abundant [134,233,[235][236][237][238][239][240] and apparently the same thing happened along the Delaware coastline [241]. In the presence of H. sanguineus, C. maenas not only occupies a less-desirable habitat but also alters its diet from bivalves, its preferred prey, to consume more algae [211].…”