Spatial and temporal distribution of mesozooplankton in the Gulf of Aqaba and the northern Red Sea in February/March 1999

Abstract

The distribution pattern, taxonomic composition and community structure of mesozooplankton was studied along a transect with 10 positions between the Gulf of Aqaba and the northern Red Sea. Five positions were resampled two or three times during a cruise of RV 'Meteor' in February/March 1999. In spite of char differences in the density stratification between the Gulf of Aqaba and the northern Red Sea, the mesozooplankton composition was very similar: Copepods were by far the most abundant taxon, contributing 76-95% to the total community. The remainder was composed largely of ostracods, chaetognaths, appendicularians and molluscs. The mesozooplankton of the deeply mixed stations was homogeneously distributed, at all other stations the hulk of the mesozooplankton (>70%) was concentrated in the mixed surface layer with peaks of calanoids, cyclopoids and appendicularians in the vicinity of the chlorophyll a (Chl a) maximum layer. Ostracods and poecilostomatoids dominated the layers below. Standing stocks within the total water column (550-1200 m) varied between 93 and 431 x 10 3 individuals m 2 for copepods and 5-76 × 10 3 individuals m -2 for other mesozooplankton with highest numbers in the northern Gulf of Aqaba, where vertical mixing was deep (400-500 m) and Chl a and mesozooplankton distributions homogeneous throughout the water column. Towards the south, the mixed depth decreased from 300 m in the central Gulf of Aqaba to 50 m in the Red Sea. Cluster analysis separated three distinct groups of stations, compounding the observed differences between the northern Gulf of Aqaba (Position I) and the other positions. The analysis also revealed temporal differences between the February and March sections of the cruise, indicating the winter-spring transition. The stations sampled in March are characterised by a higher total abundance and by a higher percentage of appendicularians and ostracods than the stations sampled in February.