TEMPORAL VARIABILITY IN COPEPOD FECUNDITY DURING 2 DIFFERENT SPRING BLOOM PERIODS IN COASTAL WATERS OFF PLYMOUTH (SW ENGLAND)

The temporal variation in egg production of the planktonic copepods Calanus helgolandicus, Temora longicornis and Pseudocalanus elongatus was studied during two different spring bloom periods in 1989 and 1990 by weekly sampling at two permanent stations in coastal waters off Plymouth (SW England). Copepod egg production was estimated in situ by incubating individual adult females in filtered seawater for 24 h (72 h until hatching for P. elongatus) at the field surface temperature. The relationship between copepod egg production rates and: (i) chlorophyll a concentration (total and >10 mu m size fraction), (ii) temperature and (iii) initial copepod gut pigment content was investigated. The spring bloom periods were very different in both years, with the occurrence of a Phaeocystis sp. bloom in 1990, which negatively affected the feeding and fecundity of copepods. Egg production rates in spring 1989 were significantly correlated with chlorophyll a concentration (particularly with the >10 mu m fraction), field temperature and copepod gut pigment contents. In spring 1990, egg production rates were also correlated with copepod gut pigment contents, but no significant correlations were obtained with temperature or with chlorophyll a concentration, as a consequence of the lower egg production rates obtained during the Phaeocystis sp. dominance period. These results show that food availability is the factor which mainly affects the fecundity of neritic copepods in short time periods.