Tidal and Diurnal Effects on Zooplankton Sample Variability in a Nearshore Marine Environment

Abstract

Two 26-h series of duplicate and replicate vertical zooplankton samples taken at two stations at two different times of the year showed that a periodic fluctuation correlated to the tide was present in the biomass of zooplankton and in the numbers of animals of several copepod species. Diurnally migrating species of zooplankton did not show a tidal correlation. The hour to hour fluctuations in zooplankton were generally more important than the difference between stations 1.6 km apart. Similar relations were found between the zooplankton and the tide in May and August even though there were significant differences in the composition of the zooplankton community during the two periods.Correlation coeficients between all species in all samples showed the presence of a diurnally migrating predator community and a nonmigrating prey community consisting of copepods.An experiment using sample data suggested that to obtain a reasonably accurate estimate of the mean numbers of a given species, one should make at least two vertical tows on a station at a 6-h interval.