Predation in a Turbulent Environment

David Lewis

Understanding the population dynamics of planktonic micro-organisms is important in a number of ways:

1. they comprise the lowest level in the oceanic food chain and are crucial to the maintenance of world fisheries;
2. some coastal varieties are toxic and can cause shellfish toxicity, fish mortality and neurological pathologies in humans;
3. they are crucial in the understanding of ocean-atmosphere dynamics, eg. by regulating the amounts of atmospheric carbon.

Until relatively recently most studies of plankton have examined their behavioural characteristics in passive fluid. However, the ocean is turbulent and this is bound to influence planktonic behaviour, as the smallest turbulence scales are comparable to the size of the micro-organisms.

In this talk some new modelling ideas are presented for studying a predator-prey type system (which is typical of the situation of larval fish feeding on microzooplankton) in homogeneous isotropic turbulence. Turbulent modifications to the planktonic 'contact rate' will be computed. This work will be combined with a new model of capture probability, to produce predictions for optimum predation strategies. Comparisons with numerical simulations and experimental data will be presented.

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