Initial report of settlement patterns of brachyuran megalopae at Sapelo Island, Georgia, U.S.A.

Settlement of brachyuran megalopae on passive samplers was first attempted in Georgia by Fitz and Wiegert (unpubl.). They deployed cylindrical samplers at Sapelo Island from August-November 1989. Here we report on an expanded sampling effort conducted during July-October 1992 and April-June 1993. Our objective, in common with other Atlantic and Gulf of Mexico coast initiatives, was to obtain information on the timing and relative density of recruitment to the population of blue crabs, Callinectes sapidus, but we also collected large numbers of other brachyuran megalopae and we discuss these data here as well. In 1992, C. sapidus megalopae first appeared on samplers in August and was highest in October. The number of blue crab megalopae collected was relatively small and we report only trends in the data and compare our data with those from other regions. Of the total number of blue crab megalopae collected in the fall, almost 54% were found on a single day (30 October). The fall peak occurred on lunar day six, 5 days after the new moon. In the fall (1992), C. sapidus was the least abundant species collected contributing 2% to the total species composition. In the spring (1993), only 12 C. sapidus megalopae were collected out of a total of 334 brachyuran megalopae (4%). In addition to C. sapidus, seven different species/genera of crab megalopae were collected, four of which were collected frequently. Of those, Uca spp. were consistently the most abundant in both fall and spring. Other abundant species were Panopeus herbstii, Neopanope sayi and Eurypanopeus depressus. C. sapidus settlement was negatively correlated with water temperature and salinity. Most blue crab megalopae collected were associated with a water temperature of 22°C and a salinity of 21‰. All other taxa except N. sayi were positively correlated with water temperature. All species showed considerable monthly variability between surface and bottom samplers, but only N. sayi showed a significant difference over the entire sample period.