Invasive species have the potential to drastically shift the community composition of habitats through increased competitive interactions. In economically important ecosystems, this can cause populations to decline and economies to collapse. The European Green Crab (Carcinus maenas) is an omnivorous and prolific crab which has invaded much of both North American coasts, causing damage to some major bivalve fisheries. My study sought to identify the population trends of the green crab along a river estuary system in the Gulf of Maine. In addition, my study investigated the potential for interspecific competition between rock crabs (Cancer irroratus) and green crabs. Subtidal traps were placed biweekly along the shoreline of the Damariscotta River for the 2013, 2014, 2015, and 2018 summer seasons. Carapace width, total weight, sex, ovigerous status, and number of intact legs per individual were quantified for each individual of both species (N=1,208). A caged in-lab experiment was used to observe potential competition for food between rock crabs and green crabs of the same size. My study was unable to find a significant difference between 2015 and 2018 green crab catch rates, suggesting there was no population growth present. In addition, rock crabs were identified as the dominant species in my lab trials. This study suggests that competitive dominance in the native crab species could have the potential to shift the habitat of the invasive green crab to a higher position in the water column, which could limit any further population growth. As green crabs significantly contributed to the collapse of many bivalve fisheries (e.g. the soft-shelled clam), this result could help to inform more effective fisheries and aquaculture management.