Die saisonalen Veränderungen der Copepodengemeinschaft in einem oligotrophen Meeresgebiet - dem nördlichen Golf von Aqaba (Rotes Meer)

Abstract

The Gulf of Aqaba displays features of a typical subtropical ocean such as its oligotrophic condition during most of the year and a dominance of picoplanktonic primary producers and, contrary to other subtropical areas, a distinct hydrographical and biological seasonality. The aims of this thesis is to determine the influences of the seasonality observed in temperature and chlorophyll a on the copepod community and especially on the clausocalanid population of the northern Gulf of Aqaba.Mesozooplankton samples were taken with a Nansen net equipped with 200 µm mesh size. Copepods were by far the most abundant taxon of the total mesozooplankton (76%). Appendicularians ranked second in abundance (2.5%), closely followed by chaetognaths (2.4%). Within the copepods, the calanoids dominated, representing between 42 and 83%, followed by cyclopoids (8 - 46%) and poecilostomatoids (6 27%). The dominant calanoid copepods belonged to the families of Clausocalanidae (27%), Paracalanidae (20%), Acartiidae (5%) and Mecynoceridae (4%). Positive correlation coefficients were established for taxa preferring higher temperatures and negative ones for copepods which occurred in higher abundance during the colder part of the year. The dominant clausocalanids were represented by four species: Ctenocalanus vanus, Clausocalanus farrani, C. furcatus and C. minor (first record in Red Sea). The seasonal changes in abundance, the reproductive activity (in terms of gonad maturation) and the feeding behaviour of the clausocalanid females were investigated. Only for Ctenocalanus vanus a distinct negative correlation between the temperature, and the abundance and reproductive activity was established. Feeding experiments with the clausocalanid species revealed that the ingestion rates were food density dependent rather than size dependent. No distinct difference in the feeding pattern could be observed between Ctenocalanus and Clausocalanus were established.