Abstract
In the last three decades, rapid assessment surveys have become an important approach for measuring aquatic ecosystem biodiversity. These methods can be used to detect anthropogenic impacts and recognize local or global species extinctions. We present a floristic survey of the aquatic macrophytes along the Brazilian margin of the Itaipu Reservoir conducted in 2008 and compare this with a floristic survey conducted ten years earlier. We used ordination analysis to determine whether assemblage composition differed among reservoir arms. Macrophyte species were sampled in each of the 235 sampling stations using a boat, which was positioned inside three places of each macrophyte stand to record species and search for small plants. We also collected submerged plants using a rake with the boat moving at constant velocity for ten minutes. We assigned individual macrophyte species to life form and identified representative species for each life form. A total of 87 macrophyte taxa were identified. The "emergent" life forms contained the highest number of species, followed by "rooted submerged" life forms. The extensive survey of macrophytes undertaken in September 2008 recorded more species than a survey conducted between 1995 and 1998. This could be due to changes in water physico-chemistry, disturbances due to water drawdown and the long period between surveys, which may have allowed natural colonization by other species. Additionally, differences in the classification systems and taxonomic resolution used in the surveys may account for differences in the number of species recorded. Assemblage composition varied among the arms and was affected by underwater radiation (as measured using a Secchi disk) and fetch. Five non-native species were found. Two of these non-native species (Urochloa subquadripara and Hydrilla verticillata) are of special concern because they have a high frequency of occurrence and occupy large marginal areas of the reservoir. Future surveys should be conducted to determine the habitat most frequently colonized by these species. This would allow management strategies to be developed to protect native aquatic biota and prevent interference with the recreational and commercial uses of the Itaipu Reservoir.
Highlights
Macrophytes are important components of freshwater ecosystems because they enhance the physical structure of habitats and biological complexity, which increases biodiversity within littoral zones (Esteves 1998, Wetzel 2001, Agostinho et al 2007, Pelicice et al 2008)
We present a floristic survey of the aquatic macrophytes along the Eastern margin (Brazilian border) of the Itaipu Reservoir; we compared the species composition of aquatic macrophytes in this survey with a floristic register collected between 1995 and 1998
Eight arms formed by lateral tributaries were investigated: Arroio Guaçu River (AG), São Francisco Verdadeiro River (SFV), São Francisco Falso River (SFF), São Vicente River (SV), São João River (SJ), Ocoí River (OC), Pinto River (PR) and Passo Cuê River (PC) (Fig. 1)
Summary
Macrophytes are important components of freshwater ecosystems because they enhance the physical structure of habitats and biological complexity, which increases biodiversity within littoral zones (Esteves 1998, Wetzel 2001, Agostinho et al 2007, Pelicice et al 2008). Fish diversity is positively related to macrophyte diversity in the Upper Paraná River Basin at both the large (between different ecosystems) and fine (within specific ecosystems) spatial scales (Agostinho et al 2003, 2007, Pelicice et al 2008). Depending on the limnological characteristics of the river, the reservoir may undergo rapid eutrophication, which is typically worst in the first reservoir of a series (Barbosa et al 1999) These changes can lead to the invasion and rapid development of different species and life forms of aquatic macrophytes (Pieterse & Murphy 1990). Macrophytes may become detached and obstruct turbines ( it never happened in Itaipu) and the monitoring of aquatic plants is important to energy production
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