Population dynamics and production of estuarine planktonic rotifers in the Southern Baltic: Brachionus quadridentatus (Hermann, 1783)

Population dynamics and production of a natural population of Brachionus quadridentatus were studied by regular field sampling at a routine station in the shallow Darss-Zingst estuary (3-7%o salinity), Southern Baltic, for two successive years. Investigations included observations of hatched resting eggs, abundance of amictic and mictic females, egg ratio, resting egg production, and mixis rate. Using egg development times from literature, instantaneous rates of growth, birth and death rates were estimated. Mixis rates increased with increasing productivity. The mean P/B value for the growth seasons was 0.89/d and the corresponding production was 9.0 mg wet weight/dm3a. Significant parasitism by microsporidians was observed during one year when up to 12% of the females were infected during June/July. B. quadridentatus served as a food source for the rotifer Asplanchna girodi, the mysid Neomysis integer, and fish juveniles. Copepods could also be considered as predators. However, on an annual basis predators seemed to be of reduced importance and the population dynamics were governed mainly by autoregulative processes.