Benthic mollusks of the Middle Paraná River floodplain, Argentina

ZILLI, FLORENCIA

Mollusks: Morphology, Behavior and Ecology.

Nova Publishers, Inc.

Año: 2012; p. 231 - 251

Spatial heterogeneity, resource availability, presence of mollusk non-nativespecies and metacommunity dynamics are key factors in structuring the molluskassemblages in the Paraná River floodplain. In this system, both bivalves andgastropods are abundant, especially in the benthos of floodplain lakes. In the presentstudy, the attributes of benthic mollusk assemblages were analyzed at in floodplainenvironments with different connectivity to the Paraná River main channel (lakesand secondary channels). Bivalves occurred in all the patches, while gastropodsshowed a lower frequency. Mollusks represented a large proportion of benthos interms of biomass and a lower proportion in terms of density. A gradient ofdecreasing abundance of mollusks was found from the lakes to the secondarychannels. The highest standing stock biomass was measured in the patches withsandy sediments and lower depth, where non-native Corbicula fluminea(Corbiculidae) had a higher abundance. No specimens of the introduced Limnopernafortunei were collected in the benthos of lakes but dense populations were foundattached to the root system of floating meadows of these same lakes and living onhard substrates of anthropogenic origin. Thus, the native species seems to have arefuge in the soft-bottom floodplain environments. Significant dissimilarities wereobtained 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 atdifferent scales and to the presence and absence of Corbicula, especially in the caseof cluster analysis performed with biomass data. For gastropods the highestsimilarity was obtained among the habitats and patches where Heleobia spp.(Hydrobiidae) was dominant. The variables that best correlated with the obtainedpatterns for bivalves, were the percentage of sand in the bottom sediments and depthof patches. No significant correlations were obtained between the environmentalvariables and the gastropods data. At the regional scale, dispersal mechanisms mightfavor a high mixing of taxa in the highly connected systems. However, in theMiddle Paraná River the presence of local filters (biotic and abiotic) and theparticular traits of taxa determine the development of diverse assemblages at theregional scale (significant differences of mollusks composition, biomass anddensity).