Role of essential fatty acids on the reproductive success of the copepod Temora longicornis in the North Sea

This field study focused on the transfer of dietary fatty acids (FAs) into the eggs of Temora longicornis and assessed their potential for limiting egg production and egg viability. In situ egg production rates (EPRs), hatching success and FA profiles of females, as well as eggs, were determined and compared to food indicators, i.e. particulate organic carbon, particulate organic nitrogen and FAs of size-fractionated seston samples. Individual egg production ranged from 14 to 28 eggs female(-1) d(-1), corresponding to weight-specific egg production rates (sEPRs) from 0.18 to 0.35. Based on trophic marker FAs, T, longicornis most likely fed non-selectively. FA contents of eggs ranged from 2.6 to 4.3 ng egg(-1) and correlated significantly with the FA content in seston (size class: 1 to 30 mu m). Strong similarities in FA profiles of eggs and seston, as well as correlations of absolute FA levels, indicated only minor maternal regulation of egg composition. The significant increase in EPRs with an increasing diatom food supply, as indicated by correlation with 16:1 (n-7) levels in seston and eggs, strongly compensated for the tendency to produce less viable eggs on a diatom-dominated diet. Egg viability was overall very high (77 to 94 %) at all our stations and did not relate to essential FA levels in the eggs, indicating that lipids were transferred in sufficient quantities. Thus, food quantity rather than quality determined the reproductive success of T, longicornis during our study. Stoichiometric comparisons between seston and egg composition suggested that nitrogen-containing compounds had a higher potential for limiting egg production during our study than essential FAs.