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Abstract: In order to trace the history of dinoflagellate cyst assemblages and provide new insights in to Harmful Algal Bloom (HAB) dynamics in monsoon‐influenced tropical environments, sediment cores were collected from four different coastal locations along the west coast of India. The naturally occurring radionuclide 210Pb activity in the sediment samples were measured; and subsequently the sedimentation rates (SRs) and ages were modeled. The SRs ranged from 0.15±0.01 to 2.80±0.38cm/yr and provided coverage of time period spanning between 21 and 145yr. Cysts of potential harmful dinoflagellates (Gonyaulax spinifera, Lingulodinium polyedrum, Protoceratium reticulatum and Scrippsiella trochoidea) were observed to be present earlier than the 20th century. Among the four sediment cores, significant temporal variations in cyst abundance were observed in the sediment core, off Mangalore. Two of the cores from off Mangalore and Cannanore were dominated by autotrophic cyst assemblages (Gonyaulax membranacea and Gonyaulax spinifera) in the deeper sediment sections. However, the upper sediment sections were dominated by heterotrophic forms. Temporal shifts in cyst assemblages from autotrophic to heterotrophic dinoflagellates in the Mangalore core coincided with high deposition of shells; carbon analyses (δ13Corg and Corg:N ratio) revealed shifts in organic matter type from terrestrial to marine source. The terrigenous input in this region, influenced by the monsoonal variations, can thus affect dinoflagellate assemblage structure and lead to changes in ecosystem functioning. [Copyright &y& Elsevier]

The river ecosystems from the headwaters to the foothills in the upper mountain reach of the Ganga (Bhagirathi River) were characterized by increasing temperature, pH, total alkalinity, nutrient and BOD and decreasing current velocity, turbidity and DO. The biotic communities included benthos (phytobenthos, zoobenthos) and nekton (fish). The headwaters at Gangotri were heterotrophic and lacked fish (both grazers and predators). Functionally, the detritus and grazing chains operate in headwaters of the upper Ganga. The food chain was short and the web simple. In the middle and lower stretches, the macroinvertebrate assemblages functioned as filtering collectors and scrapers, representing detritus and grazing food chains. The abundance of scrapers indicated transition from heterotrophic to autotrophic state. The food chains and the food web became complex from the middle to lower stretches. [ABSTRACT FROM AUTHOR]