Threshold responses of floating meadow fish communities to floodplain forest cover in the lower Amazon River

Forest cover is positively associated with fish biomass and fisheries yield in the Amazon River floodplain, and many species enter flooded forests to feed, spawn, or seek refuge from predation. Floating macrophyte beds, known as floating meadows, in Amazon floodplains support high fish diversity and serve as nursery habitat for many fishes of high commercial importance. We surveyed fish from floating meadows in floodplain lakes along the lower Amazon River to evaluate variation in fish abundance in relation to forest cover and local environmental variables. Species associations with forest cover were estimated with threshold indicator taxa analysis (TITAN2). The analysis identified taxa that gradually increased in abundance and occurrence as forest cover increased. Many species gradually increased at approximately 40% forest cover in the local landscape. Taxa that decreased as forest cover increased exhibited thresholds, whereby their abundance and occurrence declined rapidly when forest cover exceeded approximately 9% and when it was about 20%. Small-bodied, sedentary species with equilibrium and opportunistic life-history strategies (i.e. functional groups) and Cichlidae and Characidae (taxonomic groups) were indicators of high forest cover, whereas large-bodied, migratory species with periodic and intermediate life-history strategies and Serrasalmidae were indicators of low forest cover. Our findings could be used to predict how the taxonomic and functional structure of fish communities inhabiting floating meadows would respond to deforestation.