  Toxic or allelopathic compounds liberated by toxin-producing phytoplankton
(TPP) acts as a strong mediator in plankton dynamics. On an analysis of a set
of phytoplankton biomass-data that have been collected by our group in the
North-West part of the Bay of Bengal, and by analysis of a three-component
mathematical model under a constant as well as a stochastic environment, we
explore the role of toxin-allelopathy in determining the dynamic behaviour of
the competing-phytoplankton species. The overall results, based on analytical
and numerical wings, demonstrate that toxin-allelopathy due to the
toxin-producing phytoplankton (TPP) promotes a stable coexistence of those
competitive phytoplankton that would otherwise exhibit competitive exclusion of
the weak species. Our study suggests that TPP might be a potential candidate
for maintaining the coexistence and diversity of competing phytoplankton
species.
