Copepod egg production in Long Island Sound, USA, as a function of the chemical composition of seston

The effect of the chemical composition of seston on the egg-production rates (Er: eggs female−1 d−1) of the copepods Acartia hudsonica Pinhey and Temora longicornis (Müller) was studied in Long Island Sound, USA, (41° 00′ N, 73° 05′ W) during spring 1990. The seston was analyzed for carbon, nitrogen, protein, carbohydrate (CHO) and fatty acid content as well as chlorophyll (chl) and ciliate concentrations. Principal component analysis (PCA) revealed significant correlations [score >0.7 on a same principal component (PC)] between in situ Er of the 2 copepod species and the chemical composition of the seston. Protein, CHO and specific fatty acids correlated strongly with Er of A. hudsonica (CHO negatively). The same components were moderately correlated (score >0.6 on a same PC) with the Er of T. longicornis. The fatty acid requirements of A. hudsonica and T. longicornis were for high ω3:ω6 ratios and low 20:5 to 22:6 ratios. The fatty acid 22:6ω3 was also correlated with Er of both species. The concentration of ciliates and the C:N ratio of seston did not affect Er of any of the species under any condition. Path analysis models were composed to evaluate the important mechanisms controlling the Er observed in this study. The analysis demonstrated the strength and importance of indirect relationships that were not apparent from conventional correlation statistics. The results from 4 path analysis models showed that chl and ciliates exert an important control on natural egg production rates, through their chemical composition, despite the fact that linear correlations between phytoplankton and ciliates and Er were not significant.