International Journal of Biomathematics and Systems Biology Official Journal of Biomathematical Society of India Volume 1, No. 1, Year 2014 The role of space in marine plankton ecosystem in presence of toxin producing phytoplankton Anal Chatterjee 1 and Samares Pal 2 1 Department of Mathematics, Sheikhpara A.R.M. Polytechnic, Sheikhpara-742308, India. E-mail: chatterjeeanal172@gmail.com 2 Department of Mathematics, University of Kalyani, Kalyani- 741235, India. Email: samaresp@yahoo.co.in Received: 10 April 2014 Accepted: 2 July 2014 Abstract. In this paper, we investigate the complex dynamics of a nutrient phytoplankton zoo- plankton reaction-diffusion system with Holling type-II functional response. In this model, it is assumed that phytoplankton releases toxic chemical for self defense against their predators. The model system is studied analytically and the threshold values for the existence and stability of var- ious steady states are worked out. Moreover we have found out a condition for diffusive instability of a locally stable equilibrium. Also it is shown that the system undergoes Hopf bifurcation when the maximal zooplankton conversion rate crosses a certain critical value. Computer simulations have been carried out to illustrate various analytical results. Key words: Phytoplankton, Zooplankton, Toxic, Bloom 1 Introduction Dynamics of food-web population models largely depends on nutrients. Tiny plankton populates in the surface waters of the oceans, rivers, and lakes. An algal bloom or marine bloom or water bloom is a rapid increase in the population of algae in an aquatic system which is generally caused by high nutrient levels and favorable conditions. Plankton populations comprise a large number of different species and are in the bottom of the food chain. In addition, effects of toxin producing phytoplankton play a vital role in marine plankton ecology. After the pioneering work of [1], many papers on plankton dynamics have been appeared in the literature. 2 Corresponding author: Tel.:+91-33-25666571 ; Email: samaresp@yahoo.co.in ISSN: 2394-7772