Effects of temperature on the growth and carbohydrate production of three benthic dinoflagellate species from Hainan Island, South China Sea

Dinoflagellates in the genera Ostreopsis and Gambierdiscus are typical members of the marine benthic community particularly in tropical areas. Their geographic distribution has shown an increasing expansion towards temperate waters recently due to the global warming and climate changes; however, the knowledge is little of how the increasing temperatures might influence the physiological characteristics of Ostreopsis spp. and Gambierdiscus spp. Here, we carried out experiments to understand the effect of different temperatures on the growth, chlorophyll a content, and carbohydrate yield of Chinese strains of Ostreopsis cf. ovata, O. lenticularis, and Gambierdiscus caribaeus. Specifically, seven temperatures (15, 17.5, 20, 25, 30, 32.5, and 35 degrees C) were set for the two Ostreopsis species and five temperatures (15, 20, 25, 30, and 35 degrees C) were set for G. caribaeus. Our results suggested that both Ostreopsis (both species were 17.5-32.5 degrees C) and Gambierdiscus (20-35 degrees C) could survive a wide range of temperatures, consistent with the record worldwide. Cell density and chlorophyll a content were observed to be higher at high temperatures (30 and 32.5 degrees C) for both Ostreopsis species whereas G. caribaeus reached the maximum cell density and highest growth rate at 20 degrees C. Higher carbohydrate yield was detected in the suboptimal temperatures for all three dinoflagellates especially during the decaying phase. Our study reveals the optimal temperatures for the growth of three benthic harmful dinoflagellate species and provides insight into how the increasing temperature will affect their abundance as well as distribution.