CS29 Phytoplankton & Primary Production
Date: Tuesday, June 11, 2002
Location: Poster Session - VCC
 
MorierD, Maurice Lamontagne Institute, Fisheries and Oceans Canada/Université du Québec à Rimouski, Mont-Joli, Canada, Dominique_Morier@hotmail.com
Starr, M, , Maurice Lamontagne Institute, Fisheries and Oceans Canada, Mont-Joli, Canada, Starrm@dfo-mpo.gc.ca
Levasseur, M, , Maurice Lamontagne Institute, Fisheries and Oceans Canada, Mont-Joli, Canada, Levasseurm@dfo-mpo.gc.ca
Demers, S, , Institut des Sciences de la Mer (ISMER)/Université du Québec à Rimouski, Rimouski, Canada, Serge_Demers@uqar.qc.ca
 
VIRUSES-INDUCED MORTALITY OF PHYTOPLANKTON IN THE ST. LAWRENCE ESTUARY: APPLICATION OF THE DILUTION TECHNIQUE
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Phytoplankton mortality is an important process in the dynamics of pelagic ecosystems. In the past, loss processes of phytoplankton populations were attributed mostly to external factors such as sedimentation and grazing by zooplankton. However, the physiological death and subsequent lysis of phytoplanktonic cells such as induced by viral pathogens has rarely been addressed. During the summer of 2001, we monitored weekly phytoplankton cell lysis in the St-Lawrence estuary. Esterase concentration was used as an indicator of cell lysis whereas the dilution technique was used to quantify the impact of viruses on phytoplankton populations. During the course of the summer, the collapse of two major phytoplankton blooms coincided with increases in both viral abundance and dissolved esterase concentrations. Results from the dilution experiments indicate that viruses-induced phytoplankton mortality may reach up to 17% per day for some dominant groups whereas it may be negligible for others. These results provided further support to the hypothesis that viruses can have a significant impact on the structure of pelagic ecosystems by directly influencing the succession and dynamics of phytoplankton species.