Diversity of Benthic Invertebrates Fauna and Secondary Production in Southern Caspian Sea Basin, Case Study on Tajan River Estuary

摘要

Macro benthic invertebrate assemblages were investigated monthly, from March 2006 to March 2007, at six stations in Tajan river estuary, a south eastern Caspian Sea coastal estuary, in order to estimate secondary production consumable for extensive finger fish releasing and to investigate the factors affecting this production. Benthic assemblages comprised 9 taxa, of which Ballanus sp., Chironomus plumosus and Cerastoderma lamarki were the main contributors to both overall biomass and secondary production. Annual secondary production varied from 4.55 g AFDW m super(-2) year super(-1) (Ash Free Dry Weight), in the upper Tajan estuary, to 78.06 g AFDW m super(-2) year super(-1) (Ash Free Dry Weight) in the center of the estuary area. Multivariate correlations between environmental variables and the Macro benthic assemblage biomass highlighted the role of the water level, temperature, sediment organic carbon content and dissolved oxygen in the differentiation of the communities in the estuary. Composition, biomass and secondary annual production of Macro benthic communities were dramatically affected by changes in water residence time and summer drought crises. The isolation of this habitat limits the recovery of other invertebrate benthic assemblages during drought periods. Only populations of two species, Balanus sp. and C. plumosus, seemed to be able to recover quickly after the drought crises, which, in turn, could compromise the overall secondary production, with negative effects on the released fish survival. During summer water renewal, when agricultural activity is intense and nutrient inputs should be regulated in this estuary to reduce the risk of benthic mass mortality and to ensure a sustainability of this environment.