Variation in hatching success and egg production of Eurytemora affinis (Calanoida, Copepoda) from the Gulf of Bothnia, Baltic Sea, in relation to abundance and clonal differences of diatoms

Abstract

We monitored the hatching frequencies and clutch sizes of Eurytemora affinis, and environmental variables in the Gulf of Bothnia, between May and October 2003. We tested the hypothesis that the hatching frequency of the copepod would be negatively affected during time periods with high diatom concentrations. Results from two stations showed significant differences between the different sampling occasions, with the lowest observed hatching frequency during the spring diatom bloom. The reverse was true for clutch size, with the highest average egg number during the diatom bloom. These results were not correlated to ambient temperature, salinity or chlorophyll a (Chl a). In a separate laboratory experiment, nine different local clones of the diatom Skeletonema costatum were used as food for adult E. affinis females, in order to screen for possible differences in toxicity within the Skeletonema community. The resulting average copepod hatching frequency varied between 5 and 75% for the different clones, indicating that there can be large within-species variation in the toxic properties of diatoms. The significance of such variations in natural communities remains to be tested in future studies. © The Author 2006. Published by Oxford University Press. All rights reserved.