Harmful algal bloom-forming dinoflagellate Prorocentrum donghaiense inhibits the growth and photosynthesis of seaweed Sargassum fusiformis embryos

Harmful algal bloom(HAB) is an ecological disaster to local mariculture.At present,its impact on macrophytes has not been well studied.In this study,we cultivated sexually propagated embryos of Sargassum fusiformis—an edible seaweed-in Prorocentrum donghaiense suspensions at different cell densities(0,0.50×10~5,0.75×10~5,1.00×10~5,and 1.50×10~5 cells/mL) for 10 days,during which growth and photo synthetic activities of the embryos were determined,and a monocultivation was set up for comparison.Results show that the relative growth rate and photo synthetic activities of the embryos co-cultivated with P.donghaiense were inhibited mostly and significantly in the cell densities of 0.75×10~5,1.00×10~5,and 1.50 × 10~5 cells/mL,and the inhibitory effects increased in overall with increased cell densities.The maximum relative electron transport rates(rETRmax) and apparent photo synthetic efficiency(α) of co-cultivated embryos were all significantly lower than monocultivation ones on the 10thday.Furthermore,the photo synthetic activity detected by chlorophyll-a fluorescence transient(i.e.,OJIP),the electron transport among electron transfer accepters of PSⅡ(photosystem Ⅱ) and that from PSⅡ to PSⅠ(photosystem Ⅰ) was restricted,which is probably responsible for the decreases of rETRmaxand α in the co-cultivated embryos.In addition,parts of the photosynthetic reaction centers of PSⅡ in the co-cultivated embryos were inactivated.Therefore,P.donghaiense bloom could restrain the development and photosynthetic activities of embryos,reduce the seedlings stock,and eventually hinder the development of S.fusiformis production industry.