Coral reef bleaching

Off the coast of Australia, the corals on the Great Barrier Reef are bleaching and dying.

One key reason is the heat. A quick glance at the history of sea surface temperatures in the region shows why the bleaching has become more common and widespread in recent decades.

6 thoughts on “Coral reef bleaching

  1. The heat most likely accounts for almost all the damage.

    >Our study shows that we cannot climate-proof coral reefs by improving water quality or reducing fishing pressure. Reefs in clear water were damaged as much as muddy ones, and the hot water didn’t stop at the boundaries of no-fishing zones. There is nowhere to hide from global warming.

    https://theconversation.com/year-on-year-bleaching-threatens-great-barrier-reefs-world-heritage-status-74606

    1. Of course bleaching varies from year to year, dependent on local temperatures. But a rise in temperatures increases the risks dramatically, which is why bleaching is now far more common than, say, before the 1980s. The coral scientists say that other factors play a role but are much less important than temperature. I suspect any temperature threshold will be location dependent, based on local factors.
      Ed.

  2. Certainly bears watching.

    A few observations:

    * I’m struck by how the rate of increase appears to have decelerated after 1970 or so compared to 1900 to 1970 though radiative forcing was much more significant after 1970. Buoy measurements didn’t really start til 1980 or so, so there is some uncertainty with that trend.

    * high temperatures are indeed correlated with coral die off. But then too are low temperatures. How many fewer coral deaths have occurred from presumably fewer low temperatures?

    * high temperatures are also correlated with another coral death factor: high levels of sunshine – cause and effect?

    * “which is why bleaching is now far more common than, say, before the 1980s. “ Do you have evidence that this is so? How common were coral surveys and measurements in 1980 compared to now?

    * Guard against confirmation bias – many factors of coral bleaching ( Wiki ):
    – increased temperatures
    – decreased temperatures
    – oxygen starvation
    – increased solar irradiance
    – increased sedimentation
    – bacterial infections
    – changes in salinity
    – herbicides
    – low tide and exposure
    – cyanide fishing
    – elevated sea levels
    – mineral dust
    – four common sunscreen ingredients!

    * Regarding sunscreens, I have a doctor friend who frequents tropical locations where he snorkels. He was concerned about coral death in the places he visited. I told him only half jokingly that he was the one killing the corals by bringing his own toxic effects directly to them like the sunscreen cause identified above.

    * Most coral are symbiotic organisms with algae or protozoa which provide the coral with their metabolic energy of photosynthesis along with phytoplankton. How much do coral benefit from increased carbon dioxide for photosynthesis?

    * coral have been around, though not identically, for about a half a billion years! Were they so delicate, it doesn’t seem likely that they would have survived orbitally induced warm periods ( HCO, Eemian ) which lasted for many millenia or the much higher temperatures before that which lasted tens of millions of years.

    * spatially, coral appear to have been quite adaptable. They populate various regions, except for the coldest and darkest waters. These regions experience a still very large range of temperatures, including some normally very warm waters indeed.

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