Efficiency of Transfer of Essential Substances from Phytoplankton to Planktonic Crustaceans in Mesotrophic Conditions

We assessed the efficiency of the transfer of essential substances (carbon, phosphorus, nitrogen, and fatty acids (FA), including polyunsaturated fatty acids (PUFAs)) from phytoplankton to planktonic crustaceans in experimental mesocosms in the presence and absence of fish. The experiments were conducted under mesotrophic conditions in 300 L mesocosms. We have found that transfer efficiencies from producers to consumers are different for different substances. In particular, FA, including PUFAs, are transferred less efficiently than carbon. In contrast, the efficiency of nutrient transfer, especially phosphorus, is higher than that of carbon. This evidences that zooplankton can accumulate nutrients, increasing their quality as a resource for higher trophic levels. Fish significantly reduced the efficiency of carbon transfer from phytoplankton to zooplankton per unit of water volume, but did not affect the transfer of substances per unit of biomass. Thus, the quality of zooplankton as a food resource for higher trophic levels did not decrease in the presence of fish, despite the decline in the efficiency of the transfer of the essential substances per unit of water volume under their influence. Since the efficiency of essential substances transfered from phytoplankton to zooplankton determines the functioning of the entire trophic web, we should seek ways to increase it.