Effects Of Temperature And Extracts Of Macroalgae And Seagrass On The Growth And Carbohydrate Yield Of Marine Benthic Dinoflagellates

Marine benthic dinoflagellates have been mainly found on macroalgae, seagrass, coral reefs and sediment sand from tropical and subtropical waters. Many species in this group are capable of producing toxins or involved in seafood toxicity, which cannot only destroy marine environment, but also threaten the safety of seafood and the development of fishery. In the past, scientists mainly focused on the study of planktonical blooms caused by planktons rather than benthic algae. But as primary producers in the benthic food chains, benthic algae are as important as planktons. Scientifists have paid increasingly more attention to benthic dinoflagellates because of more and more toxins have been identified in recent years. Studies of benthic dinoflagellates have become a significant field in the international research of harmful algae.In this paper, four Hainan strains of benthic dinoflagellates, Gambierdiscus pacificus, G. caribaeus, Ostreopsis ovata and O. lenticularis, have been identified to study their growth characteristics and carbohydrate yield at different temperatures. The effects of different extracts of four species of macroalgae and seagrass on the growth of G. pacificus have also been studied.The results are as followings:1. Even though in vivo fluorescence, Chl a content and Fv/ Fm could insome level reflect the growth of algae, they could not gauge reliably andconstantly the biomass, growth phase and growth condition of benthicdinoflagellates examined in this study.2. The preference temperature for G. pacificus and G. caribaeus was20-35°C. Neither strains could survive at 15°C. The specific growth rate of G.pacificus was found to be highest at 25°C(0.40 d-1) and the maximum cell densitywas recorded at 30°C(5625 cells mL-1), while G. caribaeus reached the maximumcell density and the highest growth rate at 20°C. Through measuring thecarbohydrate yield of G. pacificus and G. caribaeus at their tolerable temperatures, we found that the cell carbohydrate production were highest at the temperature range which was suboptimal for cell growth. The non-attached carbohydrate yield were always higher than those of attached carbohydrate yield in each of the temperature and growth phase in our study. The carbohydrate concentration was statistically higher during the decaying phases compared to that of the stationary phases.3. The preference temperature range for two Ostreopsis species were from 17.5 to 32.5°C. At 17.5°C, the two species could not grow. The highest cell density was recorded at 32.5°C, thus the upper thermal limit might be 32.5-35°C. O. ovata had higher growth rate at 30°C and 32.5°C. The cell density reached 14225 cells m L-1 at 32.5°C. The highest cell density for O. lenticularis was also recorded at 32.5°C(6433 cells m L-1), while its highest growth rate was at 25°C. The higher carbohydrate yield for the two species was at 17.5°C.4. The effects of the different extracts of four species of macroalgae and seagrass on the growth of G. pacificus were different:(1) G. pacificus could grow and the maximum growth rate was higher than control group.(2) The growth rate of G. pacificus was inversely proportional to the concentration of the extracts.(3) The growth of G. pacificus was much slower than those of controls.