No abstract

Environmental variables and benthic macroinvertebrate assemblages were spatially and seasonally examined over two consecutive years (2000)(2001)(2002)

The Bañado Carilauquen (BC) is part of the "Laguna Llancanelo" Watershed, an area of international relevance for biodiversity conservation that holds interest for oil production. Records on the biological attributes of the system's waters are scarce, particularly regarding benthic macroinvertebrate assemblages. The goal was to study the diversity of malacofauna in the BC and the relationship between its distribution patterns and water physicochemical parameters. Biological samplings and records of environmental parameters were carried out between summer of 2000 and spring of 2001 for fi ve reaches of the BC. Complete individuals and empty shells of each species were recorded for every sample, and height and width were measured for all shells. Conchological relationships were estimated and sizes compared. The relationship between presence and abundance of molluscs and environmental parameters was explored using CCA. Five gastropod species were identifi ed: Heleobia parchappii, H.hatcheri, Chilina mendozana, Lymnaea viator and Biomphalaria peregrina. A growing gradient of conductivity and hardness was detected between the headwaters (relatively soft waters) and the outlet-lake (very hard and saline waters). The distribution of molluscs is related to this gradient. Our results suggest that, except for the headwaters, the BC is hardly favourable for the development of gastropod populations. This was expressed in low species diversity, low densities, reduced sizes, fl uctuating populations and high proportion of empty shells (> 80 %).

a b s t r a c tThe goal was to examine how macroinvertebrate taxonomic richness and density respond to spatialtemporal changes and to the influence of water physicochemical characteristics along the Bañ ado Carilauquen (BC). Benthic samplings were conducted seasonally and environmental parameters were recorded in five reaches of the BC. Cluster analysis was applied to compare taxonomic richness among sites. Community structure and spatial-temporal variation were explored using logarithmic regression. CCA was applied to explore the relationship between species and environmental variables. A total of 36 taxa were identified, predominantly insects. A growing gradient of conductivity and hardness was registered between headwaters (HD; relatively soft waters) and outlet (OL; very hard and saline waters). Total density of taxa showed significant differences among sampling sites and climate seasons. A decline in richness and density was observed from HD to OL. The spatial conductivity gradient is the major factor modulating macroinvertebrate distribution along this saline arid wetland. With the exception of the headwaters, hard, eutrophic, polysaprobic and contaminated waters such of those of the BC represent critical conditions for the development of macroinvertebrate assemblages.

Regionalization in biogeography allows division of the globe into areas according to different criteria, such as combination of biotic elements, physiognomy and climate. This regionalization constitutes a hierarchical system which comprises many categories of areas, from realms to biogeographic districts