Sigmoid relationships between phosphorus, algal biomass, and algal community structure

The sigmoidal nature of the phosphorus-biomass relationship is quite robust, and not simply generated by a systematic variation in the relationship between algal chlorophyll to cell volume ratio and nutrient levels. The sigmoid relationship with total phosphorus persists whether algae biomass is measured by chlorophyll or biovolume. This nonlinearity may actually reflect an underlying systematic variation in one or more of the components of total phytoplankton biomass. The authors examine two functional size groups and show that the large inedible fraction exhibits a strong, nonlinear response to increasing nutrient levels, while small edible algae do not vary systematically with phosphorus. This discontinuous shift in the ratio of edible to inedible phytoplankton should be accompanied by concomitant shifts in the structure of the herbivore community. -from Authors