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

Abstract

Reproductive biology and residency patterns of over 800 stone crabs (Menippe mer- cenaria, 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 10~). increased (19 X lob). Spawning frequencies and egg viability &d not differ between the species or habitats, the intertidal male molting frequency declined (7 Oh), In the fall, sex ratios became more uniform in both and intertidal male sperm levels 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 non- uniform distribution of stone crabs between habitats may result in non-random mating in the hybrid zone as a whole.