Quantification of bryofauna of a large Siberian river using airborne sensing and contact sampling

Permanently submerged aquatic moss growing in fast-flowing waters of the Yenisei River houses a dense community of gammarid amphipods, which are important food items for commercial fish species. The aim of the present study was to develop an algorithm for quantification of the contribution of bryofauna to the total budget of macroinvertebrates associated with the surface area of the river bottom. Moss vegetation cover was assessed using airborne imaging. A Gaussian mixture model was applied for classification of the orthomosaic. The ratio of biomass to surface of tufts of aquatic moss was obtained experimentally. The biomass of the most abundant macroinvertebrates associated with tufts of moss and with the mineral bottom substrate, gammarid amphipods, was quantified. The results show that in the depth range of 1-2 m, aquatic moss covers 29% of the bottom area. Aquatic moss housed a considerable proportion of gammarid amphipods (28.3-96.4%) of the total biomass of gammarids associated with the moss and the mineral bottom substrate during June-November. The study shows that bryofauna in fast-flowing waters of the Yenisei can contribute considerably to the secondary production of the river and should be taken into account in estimates of the forage for fish. The proposed algorithm can be used for temporal and spatial quantification of aquatic moss biomass and bryofauna per unit surface area of the bottom.