Factors regulating phytoplankton biomass along the Indian coast: elucidation with long-term data

Long-term variations in phytoplankton biomass from nine coastal states along the Indian coast were studied and co-related with biotic and abiotic factors. Surface water temperature, dissolved inorganic nutrients (nitrogen and phosphorous), and plankton (phytoplankton and zooplankton) biomass data were collected between 1992 and 2015. Linear regression analysis showed a considerable increase in dissolved inorganic nutrients. A substantial increase in the frequency and intensity of phytoplankton blooms (> 3 mg/m³) was observed along the Indian coast. The considerable increase in dissolved inorganic nutrient concentrations could be the major reason for an increase in phytoplankton bloom occurrences. Availability of light and periodicity in zooplankton population were also regulating phytoplankton biomass. Our results revealed that multiple factors are influencing phytoplankton biomass along the Indian coast; particularly, the increase in nutrient concentrations is promoting plankton biomass. Moreover, significant increase in zooplankton biomass can have substantial impact on the biogeochemical cycling and energy transfer to higher trophic levels.