From meso to hyperhaline: the importance of Neotropical coastal lagoons in supporting the functional fish diversity at regional scale

Shallow coastal habitats are ruled by fluctuating environmental conditions, which lead to shifts in fish communities. Functional groups of habitat use and trophic strategy were used to address the responses of fish composition and diversity, since comparisons of rich tropical systems are often complex through species-based approaches. We hypothesized that fish groups will have specific affinities in response to the prevailing environmental conditions, especially those reflecting the prevalence of oceanic or estuarine conditions, where guilds of habitat use would perform better as indicators. Despite the importance of other environmental factors (i.e. temperature and transparency), salinity was the key structuring factor irrespective of the coastal lagoon. Although harbouring the greatest biomass of piscivores, the harsh environmental conditions at Araruama lagoon were related to low diversity. A great number of indicator species, typically of marine affinity, was found at the Saquarema lagoon, probably due to the continuous and broad connection to the sea leading to the predominance of euhaline conditions. Despite the presence of non-native species (i.e. Oreochromis niloticus), the Marica lagoon function as an important refuge for freshwater groups. Our results stressed the key role played by coastal lagoons of varied water conditions in supporting fish diversity at regional levels.

Automated summary

This study examined the responses of fish communities in shallow coastal habitats to fluctuating environmental conditions using functional groups to address habitat use and trophic strategy. It was found that different environmental conditions have specific effects on fish groups, with salinity being the key factor structuring coastal lagoons. The characteristics and environmental conditions of different lagoons can lead to variations in fish diversity.