What is the compensation depth for phytoplankton? How does it differ from the critical depth? Solution Planktons are two types phytoplanktons and these are weakly swimming and free floating microalgae and photosynthetic whereas zooplanktons are fast swimming and feed on phytoplanktons. The compensation depth for phytoplankton is mainly useful to denote the growth of phytoplankton blooms and it is defined as the depth at which the net growth rate of phytoplankton is zero. The compensation depth of phytoplankton bloom is 0.1 to 1% (above this depth population grows) where solar radiation is going to reach adequately for their survival. The critical depth is defined as the critical depths is differ from it in which the phytoplankton biomass cannot grow adequately after a certain depth interval.