Phytoplankton inhibition of copepod egg hatching: test of an exudate hypothesis

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 tan 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 (80 to 90 %).