Towards understanding the paradox associated with the rise in algal blooms of Noctiluca sp. (Dinoflagellate) around the Indian continental waters

The recent intensification of harmful algal blooms of Noctiluca sp. in and around Indian waters has drawn global attention. India has a coastline of ∼11098 km and rich in ecological diversity. Our study indicates that this increase is presumably linked to changes in silicate concentrations in continental waters. These changes are now fuelling an ecosystem shift from silicate-dependent diatom populations to more opportunistic Noctiluca sp. We observed low silicate values (<2 µmol l −1 ) that covaried with these algal blooms. Further, a comparison of historical data from estuarine waters of the Bay of Bengal with recent measurements shows a marked reduction in dissolved silicate concentrations by at least one order. Our analysis is in agreement with a recently published model simulation, which predicts 17% reduction in the dissolved silicate fluxes due to the damming effect in Indian waters. Our long-term analysis of suspended sediment concentrations in major rivers also shows a statistically significant negative trend, suggesting a decrease in riverine inputs that modulate silicate fluxes. A modest positive correlation between the number of dams built and the occurrence of Noctiluca blooms was also observed. Our analysis therefore captures the complex interplay between socio-economic growth and the feedback response of marine ecosystems in Indian waters; however, their implications for the ocean carbon budget, Indian fisheries, and the tourism sector needs to be thoroughly evaluated.