The suprapopulation dynamics ofLernaeocera branchialisandL. lusciin the Oosterschelde: seasonal abundance on three definitive host species

Quantitative samples of the demersal fish fauna of the Oosterschelde were taken between May 1988 and July 1989. The instantaneous mortality rates of the 1988 year classes of whiting (Merlangius merlangus L.), sand goby (Pomatoschistus minutus Pallas) and bib (Trisopterus luscus L.) were estimated at 0.017 d −1 , 0.014 d −1 and 0.018 d −1 , respectively. These three species were examined for the presence of mesoparasitic pennellid copepods. Combination of host population densities and parasite infection intensities allowed for estimation of parasite population densities. Whiting were infected with Lernaeocera branchialis shortly after their arrival (April-May) in the Oosterschelde. By the end of the year approximately 80% of the first year class whiting were infected. Spawning sand gobies were infected with Lernaeocera lusci in May and June. Though the prevalence of L. lusci on juvenile sand gobies in autumn was low, the parasite population density in this period was high. First year class bib were mainly infected by L. lusci after their transition from a pelagic to a demersal behaviour in August. It is suggested that L. branchialis has one generation each year, whereas L. lusci has two. A biological model of the life cycle of both parasite species is presented.