Tidal, diel and seasonal effects on intertidal mangrove fish in a high-rainfall area of the Tropical Eastern Pacific

Mangroves are recognized as nursery areas for a large number of marine organisms. Yet many properties of this nursery function and its equivalence between geographical areas remain poorly understood, especially in macrotidal estuarine systems. In this study, we investigated the influence of tides, diel and seasonal variation on intertidal mangrove fish assemblages in a high-rainfall area of the Tropical Eastern Pacific region. Over one year, block net sampling was undertaken during spring and neap tides during both night and day. Four sites along the length of a subtidal channel were sampled to account for salinity gradients. Clupeidae dominated catch abundances of a 50 species-rich assemblage. Catch weights, however, were dominated by Lutjanidae, Tetraodontidae and Ariidae. Fish biomass was low, likely as a result of a poor benthic in-and epi-faunal biomass in a mangrove system of low nutrient status and extremely rainy conditions. Higher salinity creeks yielded significantly greater catches and higher number of species than low salinity creeks. A depauperate freshwater fish fauna in this beogeographical region, unable to compensate for the lack of marine-estuarine species in a low salinity environment, may explain this pattern. A notable increase in rainfall at the end of the year correlated to a decrease in mangrove fish biomass. Partially in agreement with studies from other macrotidal areas, specific combinations of tidal magnitude and diel cycle explained recurring changes in fish assemblage structures, clearly observed at the species level, but not in the number of species or biomass. These results indicate not only how important tidal and diel cycles can be for fish habitat use in macrotidal mangroves, but also highlight how regional (biogeography) and local (geo morphology, precipitation) factors should be incorporated into further investigations of mangrove ecosystem equivalence over large geo graphical scales.