Phytoplankton characterisation in the Alappuzha mud banks during the pre-/post phases of a red-tide, Prorocentrum shikokuense Hada

Abstract

The short-term changes in hydrochemical and phytoplankton characteristics occurring in the Alappuzha mud bank (AMB) region, located on the southwest coast of India, were monitored in association with a red-tide event caused by an autotrophic dinoflagellate, Prorocentrum shikokuense Hada. Dark-brownish waters detected in the AMB region on 7 September 2016, exhibited substantially high levels of chlorophyll a (68.29 mg m-3) and peridinin (53.61 mg m-3). The dominance of large-sized phytoplankton (>20mu m), mostly of diatoms along with a moderate amount of fucoxanthin (>2.5 mg m-3), was detected in the study region during the pre-bloom period (10 and 28 August). The post-bloom period was characterised by the abundance of diatoms and dinoflagellates on 23 September, and cyanobacteria and diatoms on 14 October. The prevalence of cold (<25 oC), nutrient-rich waters in the mud bank region indicated coastal upwelling from August. The extensive development of P. Shikokuense bloom in the mud bank region indicated the biological manifestation of upwelling induced nutrient enrichments. Because P.shikokuense Hada is recognised as a temperate water dinoflagellate species, its substantial blooming in a tropical regime such as Indian waters, especially on the southwest coast (Alappuzha coast), is highly concerning ecologically and societally.