The relative importance of egg production rate, hatching success, hatching duration and egg sinking in population recruitment of two species of marine copepods

Abstract

The disappearance of spawned copepod eggs can, at times, approach 100% day-1 and may be a bottleneck to population recruitment of marine copepods. We examined the egg production rate and egg hatching success of Centropages hamatus and Temora longicornis (Copepoda: Calanoida) on natural diets, and the role of delayed hatching combined with high sinking rates in removing their eggs from the water column. Cumulative hatching success within 15 days was consistently high from March to June 1996: ~80% for C. hamatus and 70% for T. longicornis. Minimum hatching time for C. hamatus was 5 days in winter and 1-4 days in spring. Minimum hatching time for T.longicornis was 3-3.5 days in winter and 1-2.5 days in spring. We measured the diameter and density of eggs of both species to estimate sinking rates from Stokes' law. Sinking rates ranged from 4.6 to 22.4 m day-1 for C. hamatus and from 13.4 to 25.4 m day-1 for T.longicornis. In shallow waters like Long Island Sound (≤20 m), in most cases virtually all the eggs may sink out of the water column before hatching starts. Therefore, we suggest that delayed hatching combined with a high sinking rate can be a significant cause for the high apparent egg mortality in copepods. We also discuss the consequences of egg sinking and asynchronous hatching in the estimation of in situ egg production.