Distribution and Habitat Use of the Invasive Carcinus maenas L. (European Green Crab) and the Native Cancer irroratus (Say) (Rock Crab) in Intertidal Zones in the Upper Bay of Fundy, Canada

Carcinus maenas (European Green Crab) is an invasive marine portunid crab that has established populations globally outside of its native range and has been implicated in declines of benthic invertebrates in invaded ecosystems. Observations of Green Crab on intertidal mudflats in the upper Bay of Fundy have increased in recent years. We assessed the distribution and relative abundance of crab populations in Chignecto Bay, an arm of the upper Bay of Fundy, by trapping Green Crab and native Cancer irroratus (Say) (Rock Crab) at mudflats and in rocky intertidal zones in 2013 and 2014. Spatial distribution of Green Crabs indicated a preference for rocky intertidal habitats and greater abundance geographically lower in the Bay, which would correspond with an initial introduction at the mouth of the Bay and subsequent inward expansion. Abundance declined drastically from 2013 to 2014, suggesting that Green Crab may not yet be well established in Chignecto Bay. Carapace width indicated that crab age may be less variable further into the Bay, suggesting these sites may only be colonized in years with favorable environmental conditions. The population may be vulnerable under poorer conditions in other years, like 2014, when high overwintering mortality is a possible cause for the observed decline. There was not a corresponding decline in native Rock Crab. While Green Crab abundance is currently relatively low in Chignecto Bay, and their impact on mudflats likely minimal, prolonged favorable environmental conditions could lead to an increased presence.