An artificial neural network approach for studying phytoplankton succession

Artificial neural networks are used to model phytoplankton succession and gain insight into the relative strengths of bottom-up and top-down forces shaping seasonal patterns in phytoplankton biomass and community composition. Model comparisons indicate that patterns in chlorophyll a concentrations response instantaneously to patterns in nutrient concentrations (phosphorous (P), nitrite and nitrate (NO2/NO3-N) and ammonium (NH4-H) concentrations) and zooplankton biomass (daphnid cladocera and copepoda biomass); whereas lagged responses in an index of algal community composition are evident. A randomization approach to neural networks is employed to reveal individual and interacting contributions of nutrient concentrations and zooplankton biomass to predictions of phytoplankton biomass and community composition. The results show that patterns in chlorophyll a concentrations are directly associated with P, NO2/NO3-N and daphnid cladocera biomass, as well as related to interactions between daphnid cladocera biomass, and NO2/NO3-N and P. Similarly, patterns in phytoplankton community composition are associated with NO2/NO3-N and daphnid cladocera biomass; however show contrasting patterns in nutrient- zooplankton and zooplankton-zooplankton interactions. Together, the results provide correlative evidence for the importance of nutrient limitation, zooplankton grazing and nutrient regeneration in shaping phytoplankton community dynamics. This study shows that artificial neural networks can provide a powerful tool for studying phytoplankton succession by aiding in the quantification and interpretation of the individual and interacting contributions of nutrient limitation and zooplankton herbivory on phytoplankton biomass and community composition under natural conditions.