Excitable plankton dynamics

Truscott and Brindley (1994) have shown that some plankton population models can produce excitable dynamics, and they suggested this as a possible explanation for the observed plankton blooms. The phytoplankton population plays the role of the fast component while zooplankton responds on a slower timescale to increased phytoplankton concentration. This allows for a transient plankton bloom, that can be triggered by various changes in the environment. 

An interesting example of a well defined localized perturbation of the plankton ecosystem was produced by the SOIREE iron fertilization experiment (Abraham et al., 2000) with the aim to test the hypothesis of iron limitation of growth in regions with high nutrient, but low natural phytoplankton concentration. As it was expected, 

Neufeld et al. (2002a) have shown that this behavior can be explained by the interplay between excitable plankton population dynamics and chaotic flow, similarly to the excitable behavior described in the previous section. In a chaotic flow a steady bloom filament profile can be generated, that does not decay until it invades the whole computational domain as an advectively propagating bloom. The condition for the existence of the steady bloom filament solution in the corresponding one-dimensional filament model is that the rate of convergence, quantified by the Lyapunov exponent, should be slower than the phytoplankton growth rate, but faster than the zooplankton reproduction rate. In this case the phytoplankton does not became diluted by the flow and the zooplankton is thus kept at low concentration unable to graze down the bloom filament. 

Hernandez-Garcfa and Lopez (2004) have considered the excitable plankton dynamics in a jet-like open flow and show the applicability of the results obtained in the excitable systems described in the previous paragraphs. 

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