Introduction to Competition Between Continuous Cultures of Phaeodactylum tricornutum and Dunaliella tertiolecta

When the diatom, Phaeodactylum tricornutum, and the microalga, Dunaliella tertiolecta, are cultured together in a chemostat at dilution factors of ∼ 0.5 day^{− 1}, the diatom develops the higher population density. At dilution factors above 1.2 day^{− 1} the inability of the diatom to assimilate nutrient as fast as it flows into the chemostat results in the microalga generating the larger population. This change in population densities is accompanied by an increase in the chlorophyll content of the diatom and a decrease in the chlorophyll content of the microalga. Two species of phytoplankton can coexist when they compete for nutrient in a chemostat providing they do not otherwise interact. When the species do interact coexistence in a stable steady state is possible providing intraspecies interactions exceed the interactions between the species. Both species adjust their consumption to minimise the concentration of nutrient in the chemostat and their growth is modified to match the dilution factor of the flow.

Key Words:

• Continuous culture
• Chemostat
• Phytoplankton
• Competition
• Adaptation.

ACKNOWLEDGMENTS

We are grateful to the Marmara Research Centre of the Turkish Council for Scientific and Technological Research and to the British Council for financial support. A referee very courteously drew our attention to the concept of weed resistance.

This paper was presented at “The 2nd Asian International Conference on Ecotoxicology and Environmental Safety” (SECOTOX 2004), Songkla, Thailand, 26-29 September 2004.

Notes

* = Experiments lasted from 7 to 16 days until it was clear which species was dominant, though a steady state was not necessarily attained.