ABSTRACT: Recent papers have reported that certain marine diatoms are deleterious to copepod egg production and hatching. Diatom harmful effects can result from 2 different mechanisms: diet-induced maternal effects and external effects. We conducted 5 separate egg incubation experiments to test if phytoplankton exudates (an external effect) were harmful to copepod eggs. Exudates produced by 3 reportedly toxic diatoms, plus 2 non-diatom species, had no effects on egg hatching in the copepod Acartia tonsa. Thus, phytoplankton exudates are not likely to inhibit egg hatching. A seasonal relationship was observed between egg production and egg hatching of A. tonsa such that high egg production rate resulted in high egg hatching success (80 to 100%), but low egg production rate resulted in highly variable egg hatching success (0 to 90%).

KEY WORDS: Phytoplankton · Toxicity · Extract · Algal exudate · Egg hatching · Copepod · Acartia tonsa

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Published in MEPS Vol. 209 (2001) on January 5
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2001