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Aquatic Microbial Ecology

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AME 38:259-267 (2005)  -  doi:10.3354/ame038259

Relative importance of the different negative effects of the toxic haptophyte Prymnesium parvum on Rhodomonas salina and Brachionus plicatilis

Aldo Barreiro1,*, Cástor Guisande1, Isabel Maneiro1, Trinh Phuong Lien2, Catherine Legrand3, Timo Tamminen4, Sirpa Lehtinen4, Pauliina Uronen5, Edna Granéli3

1Facultad de Ciencias, Universidad de Vigo, Lagoas-Marcosende 36200 Vigo, Spain
2Friedrich-Schiller-Universität Jena, Institut für Ernährungwissenchaften, Dornburger Strasse 25, 07743 Jena, Germany
3Marine Sciences Department, University of Kalmar, 391 82 Kalmar, Sweden
4Finnish Environment Institute (SYKE), Research Department/Baltic Sea Protection Research, Plankton Ecology Team, 00251 Helsinki, Finland
5Tvärminne Zoological Station, 10900 Hanko, Finland

ABSTRACT: The aim of this study was to determine the relative importance of the different processes/mechanisms by which the toxic haptophyte Prymnesium parvum, cultured under different nutrient conditions, affects non-toxic phytoplankton competitors and microzooplankton grazers. P. parvum was cultured under steady-state growth in different nutrient conditions: nitrogen depleted (–N), phosphorus depleted (–P) and balanced nitrogen and phosphorus (+NP). Cells from each nutrient condition and culture cell-free filtrates, alone and combined with non-toxic prey (Rhodomonas salina), were used as food for the rotifer Brachionus plicatilis. An additional experiment was carried out to test the effect of P. parvum cells and culture cell-free filtrate on R. salina. The highest haemolytic activity values were achieved by –P P. parvum cultures, followed by –N. However, the negative effect of P. parvum on R. salina and rotifers did not correlate with haemolytic activity but with the number of P. parvum cells. –N-cultured P. parvum were the most toxic for both R. salina and rotifers, followed by +NP. Therefore, haemolytic activity is not a good indicator of the total potential toxicity of P. parvum. The growth rate of R. salina was negatively affected by cell-free filtrates but the effect of P. parvum predation was greater. Rotifers fed on both toxic and non-toxic algae, indicating that they did not select against the toxic alga. The P. parvum cell-free filtrate had an effect on B. plicatilis, although this was weak. B. plicatilis was also indirectly affected by P. parvum due to the negative effects of the toxic alga on their prey (R. salina). However, the greatest negative effect of P. parvum on the rotifers was due to ingestion of the toxic cells. Therefore, the phytoplankton competitor R. salina is more affected by P. parvum predation and the grazer B. plicatilis is more affected by ingestion of the toxic cells, the effects of excreted compounds being secondary.

KEY WORDS: Haptophytes · Prymnesium parvum · Nutrient limitation · Toxicity · Haemolytic activity · Allelopathy · Rotifers · Zooplankton · Phytoplankton

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