Benthic-pelagic coupling assessed using phytoplankton marker pigments: a case study from the Paradip port, East Coast of India

This study addresses the seasonal distribution of phytoplankton marker pigments (PMP) and the ratios (indicating freshness and fate) from water and surface sediments from the coastal port ecosystem (Paradip port, Odisha, east coast of India) and its utility in understanding phytoplankton pelagic-benthic linkages. Chlorophyll and PMP (for different groups and degradation) distribution revealed distinct seasonality, but the seasonal trend was different for water and sediments. High and low values were observed in the water column during inter-monsoons (fall/spring) and monsoons (southwest/northeast), respectively, whereas, in sediments, the reverse was recorded. However, the contribution of group-specific PMP was different: fucoxanthin > chlorophyll b > zeaxanthin > alloxanthin > peridinin dominated in water and chlorophyll b > zeaxanthin > fucoxanthin > alloxanthin > peridinin in sediment. Selective grazing and stability of sedimentary PMP (fucoxanthin, diatoms PMP, is least stable than other groups) could contribute to such differences. Relatively high chlorophyll:pheopigment ratios in the water and low pheophorbide: pheophytin in sediments indicated the dominance of actively growing microalgae and chlorophyll degradation via chlorophyllidae pathway in the water but not in sediments. These findings suggest that (i) much of the phytoplankton (primarily diatoms) is lost due to herbivory before reaching bottom sediments, and (ii) pigment contribution is determined by selective grazing in water and PMP decay constants in sediments. Documenting such information will give new insights into ecosystem assessment and algal bloom research.