AQUATIC VEGETATION OF NEARSHORE AND FLOATING MEADOW OF A LARGE OXBOW LAKE IN THE BRAZILIAN PANTANAL

Abstract

The objective of this study was to characterize the floristic and phytosociological composition of aquatic macrophytes occurring on the nearshore and on floating meadows of a large oxbow lake in the Pantanal wetland, in order to identify the degree of similarity between these biological compartments. Therefore, we sampled 100 plots of 0.5 x 0.5 m on floating meadows and 100 nearshore. We recorded 42 species, being 30 nearshore and 38 on floating meadows. The richness observed on floating meadows was little superior to the recorded nearshore, and the similarity between the compartments was relatively high (Jaccard = 61.90). Four species occurred exclusively nearshore, while 12 species were restricted to floating meadows. The outstanding species for their frequency and a high percentage of cover nearshore were Ludwigia helminthorrhiza (Mart.) H.Hara and Eichhornia azurea (Sw.) Kunth. On floating meadows, Cyperus blepharoleptos Steud. presented the highest importance value (61.3). The emergent and amphibious life forms were the most common in both compartments. The similarity between both formations is an expected outcome, once the floating meadows can develop from nearshore plants and contact them during displacements within the lake. We highlight the high number of exclusive species recorded on floating meadows, which can be explained by environmental (related to the interaction between species and environmental characteristics) or spatial factors (dispersal capacity) that favor the colonization of the floating meadows by species absent nearshore.