Pleustonic colonies of cnidarians (Physalia physalis, Porpita porpita and Velella velella) found along the coastal belt of Sri Lanka

Abstract

Three species of the free-floating, colonial hydrozoans namely Physalia physalis L., Porpita porpita L. and Velella velella L., found along the coastal belt of Sri Lanka are reported here with their morphological descriptions and respective abundance. The study was conducted from March 2017 to April 2018, implementing monthly coastal surveys at 26 sampling stations along the coastal belt of Sri Lanka. The abundance of stranded colonies of those species was assessed using line transects and the specimens were identified taxonomically. Of the porpitids found in this study, V. velella was reported for the first time in Sri Lankan waters while P. porpita was re-reported trustworthy as its initial record was just a sighting. The siphonophore P. physalis was also re-reported and it always represented the lowest abundance among the stranded colonies of the three species. The highest abundance of all the species was from May to August on the southwest coast of Sri Lanka, and from November to February on the northeast coast. There was a significant size difference in colonies of each species between the two coasts.