Swarming of holoplanktonic gastropod (Creseis acicula Rang, 1828) in Andaman Island during southwest monsoon, possible reasons and its global swarming records.

This article focuses on the occurrence and causative factors of swarms of the pteropod species *Creseis acicula* in Port Blair Bay, Andaman Islands, and compares these findings with global reports of similar swarms. The study observed dense swarming of *C. acicula* in the outer bay region, particularly Aberdeen Bay, with maximum abundance during low tide, where pteropods dominated the zooplankton community. Physico-chemical parameters indicated well-mixed warm waters with adequate nutrients supporting phytoplankton growth, but nearly all pteropod shells collected were empty, suggesting that the swarms may represent aggregations of empty shells transported by oceanographic processes rather than live organisms. Globally, *C. acicula* swarms are irregular and associated with warmer temperatures and high productivity, with recent swarm reports shifting toward higher latitudes, possibly reflecting environmental changes. The study also notes that swarming events can have ecological and economic impacts, such as causing dermatitis in humans and disrupting industrial operations.