Long-term stability of the seasonal succession of different zooplankton species in a brackish water lagoon (southern Baltic Sea)

Long-term zooplankton monitoring data of a shallow brackish water lagoon (southern Baltic Sea) were analysed regarding the stability of the seasonal development of single species or genera. Median values and the interquartile ranges of normalised monthly mean densities of the species and the frequency of their occurrence were used to characterise the species. Correlations of cumulated sums (CUSUM) of the yearly time series were used to point out the number of significant correlations as a measure of the stability of the yearly development patterns. A very stable yearly succession pattern of the zooplankton species over the whole investigation period was found. Thereby, the copepod Eurytemora affinis, rotifers with a development peak in summer and the larvae of the polychaete Marenzelleria neglecta which were found regularly in the late autumn were characterised by a high number of significant correlations (67.5–81.8%) between the years. This indicates relative stable yearly development patterns for this species. In contrast, the copepod Acartia tonsa and rotifers of the genus Synchaeta showed a higher inter-annual variability marked by a lower number of significant correlations between the years (45.9% and 52.4%). The result of a canonical correspondence analysis which showed associations between species and abiotic parameters fits very well with the seasonality of every single species. Nevertheless, the very stable temporal change of dominance between E. affinis and K. cochlearis f. tecta at the end of May cannot be directly explained by changes of abiotic parameters because these parameters exhibit a higher temporal variability.