Wednesday, 5 October 2016

VOC's from the reefs

Until this year, the knowledge of volatile organic compounds (VOC’s) produced by coral reefs was limited. VOC’s such as hydrogen sulphide (H2S), carbonyl sulphide (COS) and dimethyl sulphide (DMS) can be released from their places of production in the ocean into the atmosphere, where DMS becomes known as DMSa (atmospheric dimethyl sulphide). Of these, DMSa is of particular interest due to its role in cloud formation which reflects the sunlight before it reaches the ocean, controlling both the temperature of the atmosphere and phytoplankton growth in what is known as the CLAW hypothesis (Charlson et al, 1987). Swan et al (2016) looked at this DMS being emitted from branching coral and reef seawater at the Great Barrier Reef.

By collecting headspace volume from bubble chambers that contained live branching coral (Acropora sp.) put in filtered reef seawater, then running the collected VOC’s through a gas chromatograph coupled with a mass spectrometer, this study showed that sulphur based VOC’s were only emitted into the atmosphere from corals that produced mucus, with DMS being the most dominant compound released. Emission of these VOC’s continued under anoxic conditions when the coral had a thin coating of mucus rather than a thick coating, although under aerobic conditions coral with a thick coating of mucus released the most DMS.

This study was useful in showing that the emission of sulphur VOC’s into the atmosphere by Acropora sp. are dependent on the conditions in their surrounding environment. The amount of mucus produced by the coral is thought to be a defence mechanism to the conditions they’re exposed to, such as turbulence from waves at low tide, desiccation and UV radiation. The more mucus they produce, the more DMS that’s produced to cause more cloud formation, and the lower the exposure of the coral to UV radiation. Due to this link that has been shown in this study, I believe that it is highly significant in showing how DMS produced by Acropora sp. can be a massive benefit to this species. For the future, I think it would be interesting to conduct a similar study with other species to see if this pattern is continued.


Reference paper: Swan, Hilton. B., Crough, Robert. W., Vaattovaara, Petri., Jones, Graham. B., Deschasseaux, Elisabeth. S. M., Eyre, Bradley. D., Miljevic, Branka., and Ristovski, Zoran. D. (2016). Dimethyl sulphide and other biogenic volatile organic compound emissions from branching coral and reef seawater: potential sources of secondary aerosol over the Great Barrier Reef. Journal of atmospheric chemistry. 73(3): 303-328 https://www.researchgate.net/publication/291419716_Dimethyl_sulfide_and_other_biogenic_volatile_organic_compound_emissions_from_branching_coral_and_reef_seawater_potential_sources_of_secondary_aerosol_over_the_Great_Barrier_Reef     
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5 comments:

  1. Tabby Figgins6 October 2016 at 12:45

    Hi Amy,

    Thanks for the review. The study mentions that with reduced mucus production the amount of DMS released also reduces. Although some coral possess the ability to produce DMSP (Raina et al 2013), the majority seems to be produced by the symbiotic Bacteria within the corals tissues.
    My question is - do you think the reduction in DMS is actually a result of the bacteria producing less DMSP due to the anoxic conditions, rather than the coral? Is the thinner layer of mucus just a byproduct of this?

    Raina J-B, Tapiolas D .M., Foret S., Lutz A., Abrego D., Ceh J., Seneca F.O., Clode P.L., Bourne D.G., Willis B.L., Motti C.A.(2013) DMSP biosynthesis by an animal and its role in coral thermal stress response. Nature. 502. 677-680.http://www.nature.com.plymouth.idm.oclc.org/nature/journal/v502/n7473/full/nature12677.html

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  2. Unknown7 October 2016 at 13:35

    Hi Tabby,

    This is a very interesting question! In the study by Omari et al (2015), it was found that anoxic conditions enhance phytoplanktonic DMS production and inhibit the consumption of DMS by bacteria. Due to this, I think it's fair to say that bacteria are to blame for the pattern shown in the study by Swan et al (2016), if not in whole then at least in part. With regards to the mucus, I think the Acropora coral produce it as a direct effect of the desiccation and UV radiation they're exposed to at low tide rather than as a byproduct as it is seen to be a protection mechanism; the mucus appears to be almost too handy for it to be a coincidental byproduct.

    Thanks for your question, I hope I was able to answer it.
    Amy

    Omori, Y., Tanimoto, H., Inomata, S., Wada, S., Thurne, K., Pohnert, G. (2015). Enhancement of dimethylsulfide production by anoxic stress in natural seawater. Geophys. Res. Lett. 42(10): 4047-4053

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  3. Eleni7 October 2016 at 18:11

    Hi Amy,

    Thanks for your review. I think it is really fascinating that corals have such an influence on the emission on VOC's. I agree with your suggestion to continue this study with other species.
    Do you think that cold water corals are also able to emit VOC's or is it something specific for warm water corals? I think it is worth it to conduct the study also on other reefs to see if the corals all react the same as at the Great Barrier Reef. Maybe the emission of VOC's there is only a result of the hole in the ozone layer over Australia? What do you think?

    Thanks,
    Eleni

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    Replies
    1. Unknown10 October 2016 at 21:18

      Hi Eleni,

      I think that cold water corals can still emit VOC's as they are still subject to sunlight and therefore some UV radiation. Of course, I think that the VOC's produced by cold water corals will be in lower abundance than their warm water counterparts, due to a higher amount of sunlight and increased UV exposure in the warmer climates. On the other hand it may just be that there is a higher amount of sulphur VOC's that are produced in the warm water corals which triggers cloud formation, and that actually there is a higher amount of other VOC's being produced in cold water corals. It would be interesting to study this in further depth to see if this is the pattern shown, or if these VOC's are being produced as a result of the hole in the ozone layer. Whatever the outcome, I think it'd be an interesting question to look into!

      Thanks,
      Amy

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  4. Colin Munn19 October 2016 at 22:52

    Here's a relevant news item about a study on the effects of DMS from GBR on weather patterns.

    http://www.abc.net.au/news/2016-10-14/how-the-great-barrier-reef-coral-impacts-rainfall/7928714?section=environment

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