The swarming behavior of certain scyphozoan clades, such as Pelagia noctiluca (Forskål, 1775), highlights an evolutionary advantage. These adaptations promote survival and reproductive success, resulting in mass occurrences. P. noctiluca, notorious for its ecological disruption and harmful stings, swarms in response to nutrient availability. This study is the first to document the co-occurrence of a swarm of P. noctiluca (120–180 ind. m−3) and a bloom of Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921 (2.68 x 103-4.32 × 103 cells L−1) in the Bay of Bengal, Indian Ocean. The study suggests that N. scintillans grazes on phytoplankton in nutrient-rich waters due to reduced competition from P. noctiluca's opportunistic feeding on zooplankton. This interaction gives N. scintillans a competitive edge, allowing both species to co-exist and significantly impact the marine ecosystem. The proliferation of N. scintillans, supported by favorable conditions, is intertwined with P. noctiluca's feeding dynamics, posing significant ecological and economic challenges. Continuous monitoring is essential to understand the swarming and migration patterns of P. noctiluca in the Indian Ocean, as their outbreaks indicate a broader ecosystem shift influenced by climate change and altered prey availability.