Leading groups of benthos and parameters of bottom waters and bottom sediments in the Obskaya Guba and adjacent regions of the Kara Sea

Composition and distribution of macrobenthic communities in the Ob estuary (Obskaya Guba) and the adjacent Kara Sea shelf were studied during Cruise 54 of R/V Akademik Mstislav Keldysh. From the Ob River esruary to open parts of the sea gradual changes of bottom biocenoses included changes in leading taxa. Along with increase in salinity freshwater and brackish water taxa were replaced by related forms adapted to dwelling in seawater. Comparison of original data with results of previous investigations revealed considerable spatial and temporal variations of bottom communities in the studied area. The main environmental factors determining fauna distribution in the estuarine zone are discussed. An extensive biocenosis dominated by Portlandia aestuariorum in the Ob estuary was found for the first time.