Quantitative distribution of copelates salps and doliolids (pelagic tunicates) in Indian ocean

Abstract

North-western part of the Indian Ocean sustains the maximum density for these pelagic tunicates. Other areas of high densities are located off the coast of India and northern part of the Bay of Bengal. Low values may be confined towards the south of the subtropical gyre and are always found there but may extend into the south-eastern part of the Bay of Bengal and southern Arabian Sea. Areas of high abundance are more widespread during the south-west monsoon period than in the north-east monsoon period. In regions north of the equator the surface circulation is in direct accordance with the seasonal monsoon and this in turn affects the distribution of these pelagic tunicates. Effect of temperature, salinity and oxygen on the abundance of copelate population has been studied by multiple regression analysis. Estimated relative importance of these factors indicates that dissolved oxygen has maximum influence followed by interaction of temperature and oxygen, and salinity.