Dinoflagellate planktonic-motile-stage and benthic-cyst assemblages from a monsoon-influenced tropical harbour: Elucidating the role of environmental conditions

Estuarine, Coastal and Shelf Science(2019)

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摘要
Dinoflagellates are referred among potential bioinvaders and environmental proxies. Information from tropical regions on the coupling of cyst and motile stages of dinoflagellates characterized by high suspended-load, and high diversity but low abundance is limited. Here, the population dynamics of dinoflagellates (planktonic-motile-stages and benthic-cysts) from monsoon-influenced Cochin-harbour, southwest coast of India was investigated. A targeted sampling strategy is proposed over conventional methods to obtain better estimates of abundance and diversity. From the water column, the cyst-producing-dinoflagellates contribution was quantified for the first time, and it was up to 52% of total planktonic-motile-stages. Interestingly, the number of motile-stages versus the number of cysts for heterotrophs revealed an inverse trend and the explanation is not straightforward. This is because Cochin-harbour experiences discharges, i.e., freshwater (peak during monsoon), anthropogenic, and dredging activities throughout the year facilitating benthic-suspension, high sedimentation rate, and distinct seasonality in the availability of prey. In such an environment, motile-stages-diversity and cysts-species-richness formed potential environmental proxies. The presence of cysts of indicator taxa (Protoperidinium, Polykrikos, Lingulodinium) for nutrient-enrichment in relatively good proportions and low ranges of motile-stages diversity and cysts species-richness do signal eutrophic system. Autotrophic-cysts dominance illustrates that the heterotrophs need not be dominant in the eutrophic-system as reported in earlier studies. The dominance of euryhaline dinoflagellates (Gonyaulax spinifera, Protoperidinium pentagonum, P. leonis, Pyrophacus steinii) cysts provided additional information on cyst-producing-dinoflagellates as potential environmental indicators. The existence of 24 morphotypes belonging to potentially harmful-algal-bloom (HAB) species emphasizes HAB risks under favorable conditions.
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关键词
Dinoflagellates,Cysts,Motile-stages,Environmental indicators,Eutrophic-estuarine harbour,Monsoon
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