Copepod Egg Hatching Success is Reduced by Maternal Diets of a Non-Toxic Strain of the Dinoflagellate Alexandrium tamarensis

A unialgal diet of a non-neurotoxic strain of the dinoflagellate Alexandrium tamarense strongly modified egg production and hatching success in the copepod Temora stylifera, even though grazing rates were relatively constant over time. Both exponential and stationary cultures of A. tamarense reduced egg production and hatching success, but the effect of stationary cultures on hatching success was dramatic, with egg viability dropping to 0% after 24 h of feeding. HPLC analyses revealed that the A. tamarense clone was non-neurotoxic, with a mean toxin content of about 0.005 fmol per cell, indicating that adverse effects were not due to saxitoxins or neosaxitoxins. 1H NMR analyses also revealed that diatom-derived PUSCAs (polyunsaturated short-chain aldehydes) were not responsible for reduced hatching rates, since these compounds were absent in A. tamarense as compared to the diatom Skeletonema costatum. Extracts of A. tamarense and the diatom-derived PUSCA 2-trans-4-trans-decadienal were also assessed in terms of biological effects on sea urchin embryo cell divisions. A. tamarense did not show anti-mitotic properties, as extracts did not block first-cell cleavage compared to decadienal. However, A. tamarense extracts did block fertilization success when sea urchin oocytes were first incubated for 30 min in extracts and then fertilized, as opposed to S. costatum extracts, which did not affect normal elevation of the fertilization membrane. This is the first report that dinoflagellates produce antiproliferative compounds, other than PUSCAs, that can potentially reduce copepod egg production and hatching success