Aquatic Sciences Meeting, Albuquerque 2001

SS22 Strategies To Reduce Mortality in Marine and Freshwater Phytoplankton

Date: Wednesday, February 14, 2001, Time: 12:15:00 PM

Location: Acoma/Zuni/Tesuque

Granéli, E, , Marine Sciences Dept., Kalmar University, Kalmar, Sweden, edna.graneli@hik.se

Holswilder, J, , Agriculture Dept., Karlskrona County Administration, Karlskrona, Sweden, joho@k.lst.se

Nilsson, J, , Marine Sciences Dept., Kalmar University, Kalmar, Sweden, Jonas.Nilsson@hik.se

Legrand, C, , Marine Sciences Dept., Kalmar University, Kalmar, Sweden, Catherine.Legrand@hik.se

INCREASED GRAZER DETERRANCE AND ALLELOPATHY BY ALEXANDRIUM TAMARENSE CELLS GROWN UNDER P-DEFICIENT CONDITIONS

Alexandrium tamarense was cultivated in semi-continuous cultures under 2 ratios of N and P-deficient and under nutrient sufficient conditions. During steady state, cells from all treatments were 14C labelled and fed to the copepod Acartia tonsa together with Skeletonema costatum, or only Skeletonema-cells as controls. Toxicity in Alexandrium tamarense was highest in the extremely P-deficient and lowest in the extremely N-deficient treatment. Acartia tonsa ingested higher quantities of A. tamarense cells in the extremely N-deficient treatment. The copepods fed on A. tamarense cells in all treatments, as a result they died or were paralysed at the end of the experiment. However, when fed on Skeletonema costatum monocultures the copepods thrived. When growing together, S. costatum cell numbers were much lower than when growing by itself. Also, 14C uptake was much lower for the mixed cultures. This shows that A. tamarense has an allelopathic effect on S. costatum. Thus, A. tamarense seems to be an ecological well fitted species. Due to its capacity to increase toxicity and allelopathy under nutrient deficient conditions this species out-compete others and deter grazers minimising losses.

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Aquatic Sciences Meeting, Albuquerque 2001

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