The timing of fish larvae abundance was investigated at Helgoland Roads in the southern North Sea for the years 1990, 1993–1996, 1998, and 1999. From the 44 species identified, 27 were sufficiently abundant in more than 3 years and had well defined seasonal changes to calculate their phenology. The passage of the 15%, 50%, and 85% annual cumulative abundance thresholds was used to define the “start of season”, “middle of season”, and “end of season”, respectively. The timing of a significant number of these events was correlated with the mean annual winter sea surface temperatures (SSTs) in weeks 1–10 with higher temperatures leading to earlier appearance. The timing of the end of season was also negatively correlated with the SSTs. Sole (Solea solea) is presented as an example of the general functional relationship.

No abstract

Frankfurt a. M.]Phenology and seasonality of the population response patterns of marine zooplankton provide a measure of the impact of climatic forcing upon the ecosystem, as most metazoans in the sea are periodically planktonic, usually in their pr0pagative phase. The global warming expectancy suggests intensified consideration of this aspect of ecosystem research. On the basis of the "Helgoland Roads zooplankton" time-series, such population specific investigations have been carried out. They suggest that temperature and wind stress modify the beginning, end, length and intensity of the seasonality of zooplankton populations. Climatic forcing and solar irradiation forcing of the production driven trophic cycles are basically independent of each other. The response patterns vary, depending on the life-cycle strategy of each population. Positive and negative correlation with water temperature occur, as well as larger of smaller deviations from multi-annual means, and distances from the times of greatest temperature impact and population responses. Examples are given for the different kinds of response. The results are discussed with respect to the influx of the NAO and to the annual recruitment of marine metazoans.