Tintinnids of the western Arabian Sea

The results of an investigation of tintinnids from the western Arabian Sea are described. A total of 134 closing-net samples was obtained from 22 stations of the German "Meteor" expedition 1964/1965. Distribution charts of the dominant species of tintinnids from the study area are presented as well as a list of the world-wide distribution of these species as derived from the literature. Tintinnids were most abundant in the surface waters. The layer from 0 - 25 m yielded a maximum 94.3% and a minimum of 61.3% of the tintinnids present from 0 - 175 m; the mean was 80%. There was no significant difference in the vertical distribution between day and night stations nor was there any indication of the influence of the thermocline upon vertical distribution of tintinnids. TS-diagrams show different water types in the western Arabian Sea. Temperatur-salinity-tintinnid -diagrams indicate regional patterns in the distribution of various species of tintinnids. Some tintinnids can be used as indicator species: Climacocylis scalaria, Parundella lohmanni and Amphorella amphora were typical for the Somali Current whereas Rhabdonella apophysata and Branditella palliata indicated the presence of East African Coastal Current water. The concentration of tintinnids in the upper 25 m raged between 4,800 and 39,300 individuals/m**3 (mean 19,000/m**3). Plasma volume of tintinnids was calculated to permit comparison of different links in the food chain. There was a mean of 51 mm**3/m**2 in the upper layer, equivalent to a concentration of 2 mm**3/m**3. Carbon values were computed from the plasma volume of tintinnids, phytoplankton and larger zooplankton. The ratio of phytoplankton plus microzooplankton carbon to large zooplankton carbon was 1 : 0.8 in the Somali Current, 1 : 0.4 in the East African Coastal Current and 1 : 1.2 in the mixing zone of these current systems. Tintinnids are one of the first links in the food chain. It is very likely that a part of the organic detritus and of the nanoplankton is transfered to large herbivores or omnivores via tintinnids and other protozoans. This mechanism might be especially effective during seasons when large phytoplankters are not available in the ocean.