Quantitative and seasonal abundance of Siphonophores along the southwest coast of India and the Laccadive Sea

Abstract

The quantitative specieswise numerical abundance and seasonal distribution of Diphyid and Abylid siphonophores were studied in detail for the first time, based on 128 zooplankton samples out of 243 samples collected and analysed at bimonthly intervals. The samples were collected between Mangalore and Cochin from neritic waters and from Laccadive Sea on the oceanic region during August 1966 and December 1967. This study has been carried out very systematically for numerical specieswise estimation of polygastric and eudoxid stages of 24 different Diphyid and Abylid species of siphonophores, as there was no such investigation on this group. The results revealed that Diphyes chamissonis is the dominant species in the area studied constituting 35.5 % of the total. Most of the species are equally distributed in the neritic and oceanic provinces and that too during the southwest monsoon and northeast monsoon months coinciding with high plankton production, mainly influenced by surface current and upwelling of the area studied. Their inter-relationship is also critically discussed in this account.