Halocarbon emissions by selected tropical seaweeds exposed to different temperatures.

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 °C in the laboratory. An exposure range of 21–38 °C is reported for Malaysian waters. The effect of the temperature exposures on the halocarbon emissions of the seaweeds were determined 4 and 28 h after treatment. The emission rates for a suite of six halocarbons commonly emitted by seaweeds, bromoform (CHBr 3), dibromomethane (CH 2 Br 2), diiodomethane (CH 2 I 2), iodomethane (CH 3 I), dibromochloromethane (CHBr 2 Cl) and dichlorobromomethane (CHBrCl 2), were measured using a cryogenic purge-and-trap sample preparation system coupled to a gas chromatography–mass spectrometry. The emission rate of CHBr 3 was the highest of the six halocarbons for all the seaweeds under all the temperatures tested, followed by CH 2 Br 2 , and CH 2 I 2. 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 CHBr 3 , CH 2 Br 2 , CH 2 I 2 and CHBr 2 Cl were found for K. alvarezii and T. conoides after 4 h at 40 °C. In both cases there was a >90% (p < 0.05) reduction in the F v /F m value suggesting that photosynthetic actitivity was severely compromised. After a 28 h exposure period, strong negative correlations (r = −0.69 to −0.95; p < 0.01) were observed between temperature and the emission of CHBr 3 , CH 2 Br 2 and CH 2 I 2 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 CHBr 3 , CH 2 Br 2 and CH 2 I 2 (r = 0.48 to 0.96 and −0.49 to −0.96; p < 0.05). These results suggest that the regulation of halocarbon production versus reactive oxygen species production in seaweeds is an area worthy of further exploration. [Display omitted] • Tropical seaweeds including the commercially farmed Kappaphycus alvarezii emit high concentrations of CHBr 3 and CH 2 I 2. • Temperature levels and the exposure duration to the temperature affect halocarbon emissions by tropical seaweeds. • Longer exposure to increasing temperature levels could reduce halocarbon emissions. • Responses to temperature and exposure duration are species-specific. [ABSTRACT FROM AUTHOR]