Intra-Annual Variability of a Benthic Amphipod Assemblage (Crustacea: Amphipoda) in a Tropical Shallow Coastal Environment

The community structure of tropical soft-bottom macrofauna is generally considered temporally stable. Here, we document the intra-annual variability of an amphipod assemblage from a tropical benthic habitat. The study was carried out in a shallow coastal environment of the southern Gulf of Mexico, based on historical data obtained from monthly samplings from June 2007 to May 2008, which encompassed three seasons: rainy, cold fronts and dry. Water and sediment variables were recorded to characterize the habitat, and amphipods were collected to assess changes in composition, density, and feeding modes. Using habitat characteristics, the predefined climatic seasons were examined with a discriminant analysis to order the sampling months into the three seasons. A nested analysis of variance showed that, at monthly and seasonal scales, the assemblage is more variable than expected. The species richness and density varied significantly over time, mostly at the monthly scale. Furthermore, a correspondence analysis showed that the species composition was distributed seasonally; this ordination was validated by a permutational multivariate analysis of variance. Finally, a redundancy analysis between species and habitat characteristics revealed seasonal relationships between the environmental conditions and the amphipod fauna. We propose a conceptual model to summarize the joint variation of environmental and biological factors. The present study suggests that an ecological turnover occurs at the site, along with habitat partitioning among the species through time, which depends on the species and its trophic preferences.