The functional ecology of mangrove fishes across the Isthmus of Panama

Aim Biogeographic history and variation in modern environmental conditions can greatly influence local and regional community structure and, more generally, ecosystem functioning. This is clearly exemplified at the Isthmus of Panama where marine communities and environments from the Caribbean Sea and the Tropical Eastern Pacific Ocean differ despite ancient connections during the Miocene and Pleistocene. Here, we compare the functional (implied from traits) and isotopic structure of mangrove fish communities from those two biogeographic regions, which have been separated by the Isthmus of Panama for ~3 my. Location Caribbean and Pacific coasts of Panama (Eastern Pacific and Caribbean Sea). Methods We gathered data on five functional traits (salinity preference, body mass, diet, position in the water column and lifespan) of mangrove fishes from the sampled regions. We also analysed δ13C and δ15C isotopic values and calculated functional isotopic metrics of the most abundant fish species inhabiting mangroves of these two regions. Results The taxonomic composition and functional and trophic diversity differed between the mangrove fish communities of the Caribbean and the Eastern Pacific. Although the species richness of both assemblages was similar, there was very little taxonomic overlap between them: Snooks (Centropomidae) numerically dominated in the Eastern Pacific, whereas grunts (Haemulidae) and snappers (Lutjanidae) dominated in the Caribbean Sea. Functional divergence (FDiv) and isotopic richness (IRic) were higher in the Caribbean than in the Eastern Pacific, indicating differences in the way fishes use mangroves in these areas. Main conclusions Taxonomic and functional characteristics of mangrove fish assemblages across biogeographic realms can be strongly influenced by local environmental factors (e.g. tidal regimes, the presence of adjacent coastal ecosystems and productivity), and these can override similarities that recent historical connections of faunas might be expected to produce. All such aspects need to be considered when seeking generalizations about ecosystem functioning.