Florida, horseshoe crabs: Populations, genetics and the marine-life harvest

Abstract

American horseshoe crabs (Limulus polyphemus) breed in every coastal county of Florida, U.S.A., and yet the data available on the status of this species in Florida are limited. The east and west coasts of Florida have genetically distinct populations of horseshoe crabs, but it is not known if there is further genetic structuring. To fill these gaps, we compile data from a number of sources: genetic analysis of tissue samples from 13 sites, breeding activity from an on-line public database, population estimates from multi-year trawl and seine surveys, and spawning activity from a long-term study. Neighbor-joining and STRUCTURE analyses support at least five genetically distinct management units within both the Atlantic and Gulf coast populations of Florida horseshoe crabs. We find that in some parts of Florida, horseshoe crabs breed throughout the year, but in other parts there are distinct breeding seasons. Florida populations are generally smaller than those in more northern states, particularly along the east coast, but there are few indications of decline except in the Indian River area. Finally, we compile data on the harvest of horseshoe crabs in Florida and discuss the effect of the marine-life fishery, which has not been tracked in other states.