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 (E(r): eggs female(-1) d(-1)) of the copepods Acartia hudsonica Pinhey and Temora longicornis (Muller) was studied in Long Island Sound, USA, (41 degrees 00' N, 73 degrees 05' W) during spring 1990. The seston was analyzed for car bon, 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 E(r) of the 2 copepod species and the chemical composition of the seston. Protein, CHO and specific fatty acids correlated strongly with E(r) of A. hudsonica (CHO negatively). The same components were moderately correlated (score >0.6 on a same PC) with the E(r) of T. longicornis. The fatty acid requirements of A. hudsonica and T. longicornis were for high o3:w5 ratios and low 20:5 to 22:6 ratios. The fatty acid 22:6w3 was also correlated with E(r) of both species. The concentration of ciliates and the C:N ratio of seston did not affect E(r) of any of the species under any condition. Path analysis models were composed to evaluate the important mechanisms controlling the E(r) 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 chi 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 E(r) were not significant.