Benthic mollusks of the Middle Paraná River floodplain, Argentina

ZILLI, FLORENCIA

Mollusks: Morphology, Behavior and Ecology.

Nova Publishers, Inc.

Año: 2011;

Spatial heterogeneity, resource availability, presence of mollusk non-native species and metacommunity dynamics are key factors in structuring the mollusk assemblages in the Paraná River floodplain. In this system, both bivalves and gastropods are abundant, especially in the benthos of floodplain lakes. In the present study, the attributes of benthic mollusk assemblages were analyzed at in floodplain environments with different connectivity to the Paraná River main channel (lakes and secondary channels). Bivalves occurred in all the patches, while gastropods showed a lower frequency. Mollusks represented a large proportion of benthos in terms of biomass and a lower proportion in terms of density. A gradient of decreasing abundance of mollusks was found from the lakes to the secondary channels. The highest standing stock biomass was measured in the patches with sandy sediments and lower depth, where non-native Corbicula fluminea (Corbiculidae) had a higher abundance. No specimens of the introduced Limnoperna fortunei were collected in the benthos of lakes but dense populations were found attached to the root system of floating meadows of these same lakes and living on hard substrates of anthropogenic origin. Thus, the native species seems to have a refuge in the soft-bottom floodplain environments. Significant dissimilarities were obtained for the biomass and density for both taxa (Bivalvia and Gastropoda) among habitats. Different linkage groups were obtained for bivalves and gastropods. In the case of bivalves the formed groups were related to the connectivity at different scales and to the presence and absence of Corbicula, especially in the case of cluster analysis performed with biomass data. For gastropods the highest similarity was obtained among the habitats and patches where Heleobia spp. (Hydrobiidae) was dominant. The variables that best correlated with the obtained patterns for bivalves, were the percentage of sand in the bottom sediments and depth of patches. No significant correlations were obtained between the environmental variables and the gastropods data. At the regional scale, dispersal mechanisms might favor a high mixing of taxa in the highly connected systems. However, in the Middle Paraná River the presence of local filters (biotic and abiotic) and the particular traits of taxa determine the development of diverse assemblages at the regional scale (significant differences of mollusks composition, biomass and density).