Halocarbon emissions by selected tropical seaweeds exposed to different temperatures.

Abstract

Four tropical seaweeds, Gracilaria manilaensis Yamamoto & Trono, Ulva reticulata Forsskål, Kappaphycus alvarezii (Doty) L.M.Liao and Turbinaria conoides (J.Agardh) Kützing, collected from various habitats throughout Malaysia, were subjected to temperatures of 40, 35, 30, 25 and 20\xa0°C in the laboratory. An exposure range of 21-38\xa0°C is reported for Malaysian waters. The effect of the temperature exposures on the halocarbon emissions of the seaweeds were determined 4 and 28\xa0h after treatment. The emission rates for a suite of six halocarbons commonly emitted by seaweeds, bromoform (CHBr3), dibromomethane (CH2Br2), diiodomethane (CH2I2), iodomethane (CH3I), dibromochloromethane (CHBr2Cl) and dichlorobromomethane (CHBrCl2), were measured using a cryogenic purge-and-trap sample preparation system coupled to a gas chromatography-mass spectrometry. The emission rate of CHBr3 was the highest of the six halocarbons for all the seaweeds under all the temperatures tested, followed by CH2Br2, and CH2I2. The emission rates were affected by temperature change and exposure duration, but overall responses were unique to each seaweed species. Larger decreases in the emissions of CHBr3, CH2Br2, CH2I2 and CHBr2Cl were found for K. alvarezii and T. conoides after 4\xa0h at 40\xa0°C. In both cases there was a >90% (p\xa0<\xa00.05) reduction in the Fv/Fm value suggesting that photosynthetic actitivity was severely compromised. After a 28\xa0h exposure period, strong negative correlations (r\xa0=\xa0-0.69 to -0.95; p\xa0<\xa00.01) were observed between temperature and the emission of CHBr3, CH2Br2 and CH2I2 for U. reticulata, K. alvarezii and T. conoides. This suggests a potential decrease in the halocarbon emissions from these tropical seaweeds, especially where the temperature increase is a prolonged event. Strong correlations were also seen between seaweed chlorophyll and carotenoid pigment contents and the emission rates for CHBr3, CH2Br2 and CH2I2 (r\xa0=\xa00.48 to 0.96 and -0.49 to -0.96; p\xa0<\xa00.05). These results suggest that the regulation of halocarbon production versus reactive oxygen species production in seaweeds is an area worthy of further exploration.