Blue crabs were collected weekly from a lower Chesapeake Bay seagrass meadow and adjacent tidal marsh creek over 2 months (July-August 1987) and molt staged. Molting activity, determined from a total of I ,220 crabs, was greater in the grassbed than in the marsh creek, and greater for small crabs and females. The difference between the two habitats in molting activity decreased from the first to the second month of sampling, possibly in response to seasonal decline in seagrass biomass. The proportion of small (\u3c70 mm) females in both habitats was greatest on full moons. There was a lunar rhythm of molting activity by large crabs (2:70 mm), with peak molting activity on fuIl moons. SmaIl crabs demonstrated a similar, but nonsignificant rhythm of molting. We suggest that blue crabs approaching ecdysis aggregate in seagrass meadows, taking advantage of the refuge from predation that this structurally complex habitat affords. Lunar rhythmicity of molting activity may further reduce predation mortality through a dilution effect
