Assessment of Macroalgae Phytocenoses within the Black Sea Coastal Marine Area near Sochi, Russia

The paper presents changes in the structure of macroalgae phytocenoses, as well as variations in morphometric parameters of dominant macrophyte species, in the Black Sea coastal area, within the influence zone of Sochi River in southern Russia. The center of the city's agglomeration with the same name surrounds its valley, and the resort's maritime port is also located near the studied area. Complex anthropogenic impacts from several different sources and specific natural properties of water in the Sochi River create conditions for the transformation of macrophyte phytocenoses, when perennial indigenous species such as Ericaria crinita Duby (1830) are gradually replaced by pollution-tolerant annual or seasonal species. The species composition of brown (Fucophyceae), red (Rhodophyceae), and green (Chlorophyceae) algae, which are considered to be bioindicators of water pollution at different levels, was described during this study. The abundance and biomass of these species in the phytocenoses were studied. The morphometric characteristics, such as the average thallus length and weight of the dominant species, were measured. A strong negative correlation has been identified between the percentage share of E. crinita within the total abundance of macrophytes in the investigated phytocenoses and both the suspended solid content and BODult values. Additionally, it was found that as the values of these physico-chemical parameters increase, the abundance of E. crinita in the phytocenosis significantly decreases, as well as the length of its thallus. At the same time, the correlations between the average algal biomass and both suspended solids and BOD parameters were weaker. The abundance and average weight of the E. crinita thallus generally decrease from areas with minimal river inflow impact to those that are significantly affected, reaching minimum values at the station closest to the river mouth. The results of these studies have significant implications for environmental management and public health policies. The bioindication approach represents a significant advance in the assessment and management of marine environment quality in coastal areas. It provides comprehensive information about areas significantly impacted by technogenic activities in their catchment basins.