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Planktonic protozan feeding - effects of hydrodynamic regimes on swimming and food detection


The objective of this project is to gain a mechanistic understanding of the effects of turbulent water motion on protozoan swimming behavior in a pelagic environment.
We know that turbulent water motion can affect the feeding rates of planktonic metazoa by increasing encounter rates with prey particles. Analogously, theoretical calculations and experiments with planktonic protozoa, which are one to two orders of magnitude smaller, show mixed results. Overall, planktonic protozoa seem too small to be directly affected by an increase in encounter probabilities with prey particles under turbulent motion, at least at the energy levels normally found in the ocean. However, protozoa and even bacteria do present physiological, and possibly behavioral changes attributable to differences in the intensity of the hydrodynamic regime. These changes can indirectly alter prey detection and feeding rates.
Protozoan swimming behavior, both in terms of speed and the frequency o changes in direction, greatly affects encounter rates in the mostly dilute prey environments in which pelagic protozoa live.
In this project, swimming behavior of protozoa will be analyzed using video imaging and digitizing techniques, and the effects of hydrodynamic motion assessed. These possible effects are going to be analyzed in interaction with prey quantity and quality variables.
The importance of the project lies in further understanding the complex interactions of environmental variables and the microbial components of pelagic food webs. Since protozoa are postulated to be main controllers of bacterial populations, insight will be gained on the factors governing bacterial grazing rates. The mechanistic approach ensures the generality of the results that will be obtained.


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