Macrozoobenthos in tributaries of the lower reaches of the ponoy river (Kola peninsula, Russia) in the habitats of young atlantic salmon (Salmo Salar L.) and brown trout (Salmo Trutta L.)

Abstract

The study of the composition, abundance and biomass of zoobenthos was carried out in the mouth of the tributaries of the lower reaches of the Ponoy River to determine the state of the ecosystems of the river and assess the feeding resources for salmonid fry. Quantitative samples were collected in August 2017 in brooks (5 samples), in the pools (13 samples) and riffles (13 samples) of large tributaries. The basis of zoobenthos is formed by oxyphilic invertebrates. We found 52 taxa, mostly belonging to the insects the orders of Diptera (14 species), Ephemeroptera (10), Trichoptera (10), and Plecoptera (5). The abundance of zoobenthos averaged 655±82 ind./m2 and 3,4±0,67 g/m2, the riffles differ from the pools of a slightly larger biomass of organisms. The basis of biomass is formed by: in the brooks – Ephemeroptera (Metretopus borealis) and Trichoptera (Potamophylax latipennis); the pools of the tributaries – Gastropoda (Radix intermedia) and Ephemeroptera (Heptagenia dalecarlica, Ecdyonurus joernensis); riffles – Gastropoda (Radix intermedia), Trichoptera (Arctopsyche ladogensis) and Ephemeroptera (Heptagenia dalecarlica, Ecdyonurus joernensis). An analysis of the abundance of zoobenthos indicates poor feeding conditions for juvenile salmonids. There were no significant differences in the biological diversity of communities of biotopes (brooks, pools, riffles), Shannon's index (by biomass) is 1,19–1,59, the Simpson's index – 0,28–0,44. An analysis of the trophic structure of benthic invertebrate communities has shown that the basis of biomass is formed by gathering collectors (brooks) and scrapers (pools and riffles in large tributaries). The number of species detected, the abundance of zoobenthos, and the level of feeding conditions for juveniles of salmonids are small in comparison with the southern regions, due to the harsh climate and the short period of fauna formation. Also, compared to the southern regions, there are no significant differences between the zoobenthos of the pools and the riffles. Probably, cold oxygenated water allows rheophilic oxyphilic species to dwell not only in the riffles, but also in the pools, and the low trophicity of the watercourses limits sedimentation.

Keywords

• invertebrate organisms
• trophic structure
• feeding conditions
• tributaries