Simulation of Bottom Phytocenosis in the Crimean Coastal Zone

Purpose. The work is aimed at simulating production processes in the bottom phytocenosis typical of the rocky soils in the Crimean coastal zone. The macroalgae uptake of the main nutrients (phosphates, ammonium and nitrates) and release of oxygen and dissolved compounds are planned to be estimated. Methods and Results. The study was based on the balance model of the macroalgae growth and interaction with the environment. The model empirical parameters were determined from the published data of the laboratory experiments. The bottom phytocenosis in the model was represented by seven algae species: Cystoseira barbata, Ulva lactuca, Ceramium tenuicorne, Cladophora glomerata, Polysiphonia nigrescens, Phyllophora truncata, Enteromorpha prolifera. The main simulation results were: annual estimates of the released and absorbed substances, seasonal dynamics of the macroalgae biomass and evaluation of the bottom phytocenosis response to the changing environmental conditions. The rate of the production processes in the model was influenced both by the external (water temperature, insolation and concentration of nutrients in water) and internal (intracellular quotas of nitrogen and phosphorus, and species-specific parameters determining efficiency of nutrient assimilation by the algae tissues) factors. According to the simulation results, the ratio of nitrogen to phosphorus in the algae tissues was significantly higher than that in the seawater and varied from 30 to 60 for different species depending on water temperature, light exposure and concentration of nutrients. Conclusions. During the periods of intensive macroalgae growth (from April to September), the rate of nitrogen and phosphorus uptake can increase by a factor of 1.5 in comparison with the winter period. Maximum contribution to water purification from the surplus nutrients was made by the green algae: Ulva lactuca, Cladophora glomerata and Enteromorpha prolifera. At that Cladophora glomerata has shown the best adaptive abilities (minimal decrease in the growth rate) under a sharp drop of nutrients concentration in water.