Organic matter affects fiddler crab distribution? Results from field and laboratorial trials

Abstract

Fiddler crabs are a key benthic macrofauna group in estuarine environments. Species distribution is determined by relatively distinct zones, based on biotic and abiotic factors. As sediment organic matter is thought to be one of the most important zoning factors of mangrove macrofauna, we tested the effects of organic matter content on the intra-specific distribution of the fiddler crabs Leptuca thayeri and Leptuca uruguayensis. Organic matter content and crab abundance and size were assessed in both species by field observations, while the choice of adult or juvenile L. uruguayensis for high -or low- organic matter was tested in the laboratory. Both species showed no relationship between organic matter and crab abundance or size. Furthermore, L. uruguayensis juveniles or adults did not show any preference for specific organic matter content. Therefore, fiddler crabs intra-specific distribution in mangrove forests is not dependent of the water-land gradient decrease of organic matter.