Reproductive biology and distribution of stone crabs (Xanthidae, Menippe) in the hybrid zone on the northeastern Gulf of Mexico

Reproductive biology and residency patterns of over 800 stone crabs (Menippe mercenaria, M. adina, and their hybrids) were examined during an 8 mo tagging study in 1986 at artificial, concrete block reefs constructed near intertidal oyster reefs and subtidal seagrass beds in Franklin and Wakulla Counties, Florida, USA.Characteristics of adult crabs occurring intertidally in the summer included a male-biased sex ratio (5M: IF), a prevalence of M. adina and hybrids, a high frequency (71 % ) of molting males, and low sperm content (9 X 106) in males.Subtidally in the summer, the adult sex ratio was female-biased (1M : 9F), the Menippe-complex forms occurred at equivalent frequencies, and male sperm content was higher (18 X 1 0 ~) .In the fall, sex ratios became more uniform in both habitats, the intertidal male molting frequency declined (7 O h ) , and intertidal male sperm levels increased (19 X lob).Spawning frequencies and egg viability &d not differ between the species or hybrids and male sperm content did not differ between Menippe-complex forms within habitats.Although the Menippe-complex forms did not exhibit assortative mating in either habitat, the nonuniform distribution of stone crabs between habitats may result in non-random mating in the hybrid zone as a whole.