Richness and distribution of aquatic macrophytes in Brazilian semi-arid aquatic ecosystems

Abstract

AIM: The aim of this study was to evaluate the richness and distribution of the aquatic macrophytes in the basin of the Apodi/Mossoro River, in the semi-arid region (caatinga) of Rio Grande do Norte, Brazil; METHODS: A survey of the floristic composition of the aquatic macrophytes was made at 20 sampling stations in the basin at four seasons (August/2007, November/2007, February/2008, May/2008). Specimens of each species were collected and deposited in the Dardano de Andrade Lima Herbarium of the Universidade Federal Rural do Semi-Arido; RESULTS: We found 40 species of aquatic macrophytes, in 33 genera and 22 families. The families with the most species were Poaceae and Cyperaceae, and the most species-rich genera were Cyperus and Eleocharis. The most common plant form was amphibian (42.5%), followed by emergent (27.5%), free-floating (12.5%), rooted-submersed (10.0%), and floating-leaved (7.5%). The lowest richness was observed at the estuarine region (3 species), and the highest richness in the upper basin (17 species). The rooted-submersed Hydrothrix gardneri Hooker f. and Ceratophyllum demersum L. were observed in great abundance and frequency in the Santa Cruz Reservoir of Apodi, especially in areas close to cage farms of Nile tilapia (Oreochromis niloticus) (Linnaeus, 1758). The most common free-floating species were Eichhornia crassipes (Mart.) Solms., Pistia stratiotes L., and Salvinia auriculata Aubl., predominantly in stretches that run through urban centers; CONCLUSION: The species richness of aquatic macrophytes in aquatic environments of the caatinga is similar to that observed in other basins of Brazil. Because of the many dams and reservoirs in the semi-arid Northeast, inventory and monitoring of aquatic macrophytes have become essential, especially in basins that will receive water from the diversion of the Sao Francisco River.