Though not directly harmful to fisheries, scientists warn of potential ecological consequences
KOCHI, 26 August 2025: Continuous monsoon-driven river runoff combined with changing coastal conditions is behind the recent bioluminescent red tide event along Kerala’s coast, according to ICAR-Central Marine Fisheries Research Institute (CMFRI).
Field surveys conducted by CMFRI’s Marine Biodiversity and Environment Management Division (MBEMD) revealed that heavy monsoon inflows enriched coastal waters with nutrients, creating ideal conditions for the bloom of Noctiluca scintillans, a large bioluminescent dinoflagellate frequently responsible for such phenomena.
The latest mid-August observations aboard the F.R.V. Silver Pompano, extend beyond previously recorded nearshore blooms, with the team documenting spectacular bioluminescence (locally known as “Kavaru”) as well as red tide in inshore waters up to 40 km off Kochi, even at 40 metres depth zone, a remarkable observation.
The present bloom was caused by the red form of Noctiluca scintillans, which lacks its photosynthetic symbiont (Pedinomonas noctilucae), giving the water a striking orange-red appearance. Since early August, bioluminescent red tides have been reported from multiple Kerala beaches, including Koyilandy, Chavakkad, Edakazhiyoor, Nattika, Fort Kochi, Puthenthode, Purakkad and Pozhikkara.
Impact
While not directly harmful to fisheries, CMFRI scientists caution that fish tend to avoid bloom-affected zones due to reduced dissolved oxygen levels. Moreover, as Noctiluca scintillans feeds on diatoms, bacteria, other plankton, and organic matter, intense blooms can deplete food resources for fish larvae, juveniles and adults, potentially impacting commercially important species such as sardines and mackerel.
“These events underscore the need for continuous monitoring of our coastal waters, particularly during the monsoon season, as changing environmental conditions may increase the frequency and intensity of such blooms,” said Dr Grinson George, Director of CMFRI.
