The methodological consequences of the Resource-Ratio Theory application analyzing the interrelations between environmental factors and structural indicators of natural phytoplankton communities have been reviewed. The most significant benefit is the possibility of interpreting the limitation of phytoplankton development by nutrients not at the community level but at the population level. The factor regulating this process is the change in ratios of nutrients concentrations in the environment. This allows us to conclude that the limitation of the abundance of phytoplankton populations in marine ecosystems can occur, regardless of trends affecting the increases or decreases in community abundance, which changes total resource concentrations. In this regard, it becomes necessary to differentiate the methods to analyze the factors which determine general changes in community abundance and limit the development of certain phytoplankton species. The proposed approach has been tested using long-term data obtained in the coastal waters of the northwestern part of the Black Sea (Odessa Bay). The influence of environmental factors (temperature, salinity, and concentration of nutrients) on the interannual variability of structural indicators (abundance, biomass, surface area, and surface index) of phytoplankton communities of the studied water areas was analyzed. Interpretation of the results revealed compliance with known patterns of phytoplankton organization and defined the characteristics of the study area. In addition to the limiting role of mineral and organic forms of phosphorus, the limiting effect of ammonium nitrogen has been revealed. Mineral and organic forms of phosphorus also had the greatest impact on interannual changes in the indices of phytoplankton communities.
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