Characterization of light absorption coefficient of red Noctiluca scintillans bloom in the South Eastern Arabian Sea

Abstract

Summary The red Noctiluca scintillans bloom was observed off Cochin in the South Eastern Arabian Sea (SEAS), affecting a very large area during July–August 2016. The surface water samples from the bloom region were collected to study the physical, biological and light absorption characteristics. The bloom affects the food chain by their voracious predation on the species of both first and second trophic levels. The N. scintillans cell density during the bloom was estimated at 4.73 × 105 cells l−1. In the phytoplankton absorption coefficient spectra, the accessory pigments displayed peaks in the 488–558 nm regions, which represent the characteristic carotenoid pigment (red colored pigment) for the bloom of red Noctiluca. Signature of the coastal upwelling was found from the salinity and temperature distribution, which was measured prior to the bloom occurrence. From the sea surface temperature (SST), it is also confirmed the presence of fresh water from the Cochin estuary. Increased productivity near coastal region, along with episodic events of strengthening of the upwelling, favors the proliferation of smaller diatoms. The plankton succession from smaller diatoms to larger diatoms and dinoflagellates, favors the proliferation of the red Noctiluca. The occurrence of blooms of red N. scintillans, which feed on phytoplankton, mainly diatoms, and other dinoflagellates, could be a threat to larvae of oil sardine during the upwelling period, and may negatively impact on the commercially important fishery of oil sardine, in this region.