Potential impacts of invasive crabs on one life history strategy of native rock crabs in the Gulf of Maine

Abstract

Organismal life history strategies are continually being strained by increasing environmental change, including exposure to invasive species. The rock crab Cancer irroratus is a commercially harvested species in the Northeastern US and Canada where previous studies have reported it uses subtidal habitats as a juvenile and then undergoes a habitat shift into deeper offshore waters to mature and reproduce. We demonstrate that in intertidal habitats of the Gulf of Maine, this species reaches reproductive maturity, and does so at a smaller size than has previously been recognized. Our goal here is to identify potential mechanisms by which the presence of invasive European green crabs (Carcinus maenas) and Asian shore crabs (Hemigrapsus sanguineus) may influence the success of this intertidal life history strategy of rock crabs based on the ecology and reproductive requirements of these young intertidal crabs. We experimentally demonstrate that the reproductive success of small rock crabs in intertidal habitats depends on a carnivorous lifestyle. Further, we demonstrate that juvenile rock crabs are more susceptible to predation by both invasive species than they are to cannibalism. Finally, using a numerical model to calculate lifetime rock crab fecundity, we demonstrate that this intertidal strategy is only beneficial when crabs experience reduced predation risk intertidally relative to in subtidal habitats. Together, our results demonstrate that invasive European green crabs and Asian shore crabs have the potential to greatly reduce the reproductive benefit of intertidal habitat use by young rock crabs.