Inter-decadal changes in fish communities of a tropical bay in southeastern Brazil

Abstract

Long-term evaluations of coastal fish communities worldwide have in many cases showed a decrease in the species richness and abundance as a result of anthropogenic impacts. Fish communities in two zones (inner and outer) of a tropical bay in southeastern Brazil were sampled monthly during six years over two decades (1983–1985, 1993–1995, 1999–2001) using identical sampling methods. Over time, an increase in temperature and a decrease in water transparency were detected, while salinity remained stable. Fish assemblage was dominated by benthivorous species both migrant and resident species. The fish assemblage structure differed significantly between the two bay zones. Significant decreases in the fish richness, abundance and biomass were detected over time. The highest decreases in the species richness was recorded between 1983–1985 and 1993–1995 for the marine migrants in both bay zones and for the resident and marine straggler species in the outer zone. Dominant species such as the clupeoids Anchoajanuaria, Anchoa tricolor,Harengula clupeola, the gerreid Eucinostomos argenteus,the sciaenid Micropogonias furnieri, the atherinopsid Atherinella brasiliensis and the ariid Genidens barbus decreased over time, whereas the mugilid Mugil liza increased. Persistent differences in the fish assemblage structure between the two bay zones over the three periods can be attributed at least in part to differences in environmental variables between the zones and seem to be a key ecological element to maintenance of biodiversity. This is the first study to examine long-term changes in the fish community of a tropical bay in Brazil.