The Life Cycle of the Green Crab Carcinus maenas at the Northern End of Its Range

Along the central coast of Maine most female Carcinus maenas extruded their eggs in spring. The smallest ovigerous female was 34 mm in carapace width. Mating occurred from July to October, and in all mating pairs the male was larger than the female. Megalopae and Stage 1 crabs did not settle until late August, growing only to a mean of 5.5 mm carapace width (Stage 5) before winter. Renewed growth began the following June, and juveniles grew to 13-25 mm carapace width by their second winter. Most mature males molted by the end of July, whereas mature females molted from July to October, while guarded by males waiting to mate with them. On the central coast of Maine, therefore, C. maenas matures when 2-3 years old, breeds 2-3 times, and generation time is a minimum of 3 years. Compared with warmer water populations in southern Britain and Holland, the Maine coast population of C. maenas has later settlement of megalopae, slower growth, delayed maturity, longer generation time, and a longer life span. Such differences may account for the inability of populations to establish themselves in waters much colder than those of the central coast of Maine.