Plankton dynamics is a fascinating and interesting subject of research. There are lots of aspects influencing plankton dynamics. Approximately 7\% of the phytoplankton species are known to form large-scale blooms, dramatically affecting marine communities \cite{HK}. These blooms are formed because of the formation of different patches/ colonies by the phytoplankton population. Various studies have demonstrated that the formation of colonies/ patches by green alga offers considerable protection against grazing by zooplankton \cite{V}. The potent neurotoxin production by many microalgal species may have some direct or indirect effect in forming a patch and might be perceived by its grazer as group defense. The defense strategy and patch formation of toxin producing phytoplankton (TPP) may give a possible answer to the evergreen crucial ecological question of why do many microalgal species produce neurotoxins. In the present paper we propose a simple model of TPP-zooplankton interactions in which the former is assumed to be able to detect the presence of zooplankton and counteract it by forming colonies or patches and releasing some toxic chemicals in the surrounding water. We observe that the fraction of TPP population that aggregates to form colonies or patches, and the number of colonies or patches they form, plays an important role in the recurrent bloom phenomenon. We also observe that the formation of patch by the TPP decreases the grazing pressure of zooplankton resulting in stronger coupling between the interacting species determined by the fraction of the phytoplankton population that aggregates to form colonies or patches and also on the number of patches.
Mimicking the spatial self defense effect in a toxic phytoplankton - zooplankton system
CHATTERJEE, SAMRAT;VENTURINO, Ezio
2007-01-01
Abstract
Plankton dynamics is a fascinating and interesting subject of research. There are lots of aspects influencing plankton dynamics. Approximately 7\% of the phytoplankton species are known to form large-scale blooms, dramatically affecting marine communities \cite{HK}. These blooms are formed because of the formation of different patches/ colonies by the phytoplankton population. Various studies have demonstrated that the formation of colonies/ patches by green alga offers considerable protection against grazing by zooplankton \cite{V}. The potent neurotoxin production by many microalgal species may have some direct or indirect effect in forming a patch and might be perceived by its grazer as group defense. The defense strategy and patch formation of toxin producing phytoplankton (TPP) may give a possible answer to the evergreen crucial ecological question of why do many microalgal species produce neurotoxins. In the present paper we propose a simple model of TPP-zooplankton interactions in which the former is assumed to be able to detect the presence of zooplankton and counteract it by forming colonies or patches and releasing some toxic chemicals in the surrounding water. We observe that the fraction of TPP population that aggregates to form colonies or patches, and the number of colonies or patches they form, plays an important role in the recurrent bloom phenomenon. We also observe that the formation of patch by the TPP decreases the grazing pressure of zooplankton resulting in stronger coupling between the interacting species determined by the fraction of the phytoplankton population that aggregates to form colonies or patches and also on the number of patches.
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