EGG-PRODUCTION OF ACARTIA-BIFILOSA IN THE SMALL TEMPERATE ESTUARY OF MUNDAKA, SPAIN, IN RELATION TO ENVIRONMENTAL VARIABLES AND POPULATION DEVELOPMENT

Egg production was determined for the copepod Acartia bifilosa, and re lated to environmental variables, female carbon budget, and population growth during the spring-summer-autumn period of 1994 and 1995 in the estuary of Mundaka, Spain. Field incubations were made with natural w ater and adult females collected in the polyhaline zone of the estuary . Chlorophyll ingestion rates of adult females were estimated using th e balance method in 1995. The female carbon budget was evaluated by as suming indirect estimations of respiration, phytoplankton carbon, and assimilation efficiency. Egg production rate was found to be higher in spring (maximal mean of 32.6 egg female(-1) d(-1)) and lower in autum n (minimal mean of 6.7 egg female(-1) d(-1)), but the 2 years examined were quite different in terms of egg production and the relationships of egg production to temperature and chlorophyll. Egg production rela ted positively with temperature in general, but maximal values occurre d at intermediate temperatures; this suggests a non-linear relationshi p. The relationship between egg production and phytoplankton biomass ( expressed as chlorophyll concentration) was not clear, probably becaus e there was no food Limitation. Estimates of daily carbon intake based on chlorophyll ingestion rates (between 28.2 and 228.8 ng chl female( -1) d(-1) on average) indicate that a herbivorous diet could satisfy c arbon requirements and support egg production by A, bifilosa females m ost of the time. Population peaked in summer, after spring maximal egg production rates occurred, but population abundance in the second yea r was higher while egg production was lower. As seasonal and between-y ear differences in reproductive rates and population growth were not a dequately explained by the measured environmental variables, the likel y effect of other factors and mechanisms is discussed.