Mixed bloom of diatoms (Skeletonema costatum (Greville) Cleve, 1873 and Lauderia annulata Cleve, 1873) in coastal waters at Kalpakkam, southeast India, during the northeast monsoon

Abstract

The present study reports a dual-species bloom of marine diatoms Skeletonema costatum (Greville) Cleve, 1873 and Lauderia annulata Cleve, 1873, observed during the northeast monsoon of 2019 in the Kalpakkam coastal waters, southeast coast of India. Phytoplankton density during the bloom event ranged from 1.01 – 1.90×10⁶ cells L⁻¹, with an average of 1.39×10⁶ cells L⁻¹. Skeletonema costatum and L. annulata contributed approximately 53.7 % (7.4×10⁵ cells L⁻¹) and 16.65 % (2.8×10⁵ cells L⁻¹) of the average population density. High fluctuations in chlorophyll-a (chl-a) concentrations (0.49 – 6.44 mg m⁻³) and physico-chemical parameters, viz., turbidity (0.25 – 2.5 NTU), Suspended Particulate Matter (SPM) (7.32 to 39.84 mg L⁻¹), and ammonium (10.29 – 31.59 μM) were observed during the bloom. Statistical analysis revealed that temperature, salinity, and turbidity were crucial in the bloom formation. The results indicated phosphate might be a limiting factor rather than nitrate and silicate. The available reports indicate that the co-bloom of S. costatum and L. annulata is the first of its kind and a rare occurrence in the Bay of Bengal coastal waters.