Distribution and species composition of planktonic luminous bacteria in the Arabian Sea

Abstract

Distribution of the total viable heterotrophic bacteria and the luminous bacteria in the neretic and oceanic waters of the west coast of India was studied. Counts of viable heterotrophs fluctuated widely, generally with a decrease in their number with the depth. Luminous bacterial cells ranged from 0-36 ml^-1 and their percent fraction was stable between depths of 60 and 200 m. Significant correlation between total viable count and luminous bacteria colonies in the upper 100 m suggests freeliving nature of luminous bacteria. <i>Vibrio fischeri</i> and <i>V. harveyi</i> dominated the species composition of luminous bacteria. <i>Photobacterium leiognathi</i> was only a minor component. A few strains of <i>P. phosphoreum</i> were also recovered during the collections from deeper waters.