Feeding, egg production, and egg hatching success of the copepods Acartia tonsa and Temora longicornis on diets of the toxic diatom Pseudo-nitzschia multiseries and the non-toxic diatom Pseudo-nitzschia pungens

In 1987, there was an episode of shellfish poisoning in Canada with human f atalities caused by the diatom Pseudo-nitzschia multiseries, which produced the toxin domoic acid. In order to examine whether domoic acid in this dia tom serves as a grazing deterrent for copepods, we compared feeding rates, egg production rates, egg hatching success and mortality of the calanoid co pepods Acartia tonsa and Temora longicornis feeding on unialgal diets of th e toxic diatom P. multiseries and the similarly-sized non-toxic diatom Pseu do-nitzschia pungens. Copepods were collected in summers of 1994, 1995 and 1996 from Shediac Bay, New Brunswick, Canada, near Prince Edward Island, th e site of the 1987 episode of domoic acid shellfish poisoning. Rates of ing estion of the toxic versus the non-toxic diatom by A. tonsa and T. longicor nis were similar, with only one significantly different pair of values obta ined in 1994, for which A. tonsa had a higher mean rate of ingestion of the toxic than the non-toxic diatom. Thus, domoic acid did not appear to retar d grazing. Analyses of copepods with high performance liquid chromatography (HPLC) revealed that copepods accumulated domoic acid when feeding on P. m ultiseries. Egg production rates of copepods when feeding on P. multiseries and P. pungens were very low, ranging from 0 to 2.79 eggs female(-)1 d(-)1 . There did not appear to be differential egg production or egg hatching su ccess on diets of the toxic and non-toxic diatoms. Mortality of females on the toxic diet was low, ranging from 0 to 20%, with a mean of 13%, and ther e was no apparent difference between mortality of copepods feeding on toxic versus non-toxic diatoms. Egg hatching success on both diets, although bas ed on few eggs, ranged between 22% and 76%, with a mean percentage hatching of 45%. Diets of the non-toxic diatom plus natural seawater assemblages su pplemented with dissolved domoic acid, revealed similar rates and percentag es when compared to previous experiments. In summary, none of the variables measured indicated adverse effects on copepods feeding on the toxic compar ed to the non-toxic diatom.