American Horseshoe Crabs, Limulus polyphemus, in Mexico: Open Possibilities

Little is known about Mexican Limulus polyphemus, the southern-most population of the species. We present an overview of work on Mexican horseshoe crabs, their situation, and perceived threats and opportunities regarding the conservation of the species. Horseshoe crabs occur along the western, northern, and eastern coasts of the Yucatan peninsula, and are genetically distinct from populations in the United States. Spawning aggregations and nests are found continuously throughout the year, commonly in protected lagoons where mangrove (Rhizophora mangle, Laguncularia racemosa, Avicennia germinans, and Conocarpus erectus) and sea grass (Thalassia testudinum) communities proliferate. Populations are thought to be dwindling since the 1960s and Limulus is listed as "in danger of extinction" in Mexican legislation since 1994. The most important localities are within protected areas. Direct exploitation is not an important threat, but coastline modification (especially of mangrove areas and coastal lagoons) for housing and tourism is a major concern. Additional potential threats are the oil industry and shrimp fishery in the southern Gulf of Mexico, but their effects on horseshoe crab populations have not been assessed.