Severe marine heatwaves are now more common around the globe due to rapid climate change caused
by human actions. This increase in marine heatwaves is resulting in an unprecedented uptick in the
frequency and severity of mortality within marine ecosystems, including on coral reefs. The degradation
of coral reefs will result in the collapse of ecosystem services that sustain over half a billion people
globally.
A new study published in the journal Current Biology shows that marine heatwaves on coral reefs are
biologically distinct from, but can cause and/or be more detrimental than coral bleaching events. This study
was led by researchers from the University of New South Wales Sydney, University of Newcastle, University of
Technology Sydney, James Cook University, and the NOAA Coral Reef Watch program. A major finding of this
investigation is that Marine heatwaves are causing rapid heat-induced mortality of coral colonies as well as
coral skeleton dissolution. This leads to the loss of the complex three-dimensional coral reef framework,
which serves as habitat for many reef organisms. During heatwave-induced mortality events, exposed coral
skeletons are, within days, encased by a complex biofilm of algae and bacteria. Their metabolic activity
accelerates calcium carbonate dissolution to levels that significantly exceed documented accretion rates of
healthy corals in normal seawater conditions. This bioerosion reduces the coral's skeletal density and hardness, and
increases porosity.
This study demonstrates that severe heatwave-induced mortality events should be considered
biologically distinct events that cause even more extreme damage than bleaching or mass bleaching on
coral reefs. Heatwave mortality events, and rapid reef decay, will increase in frequency as marine
heatwaves intensify. The results further show that immediate actions are necessary, on a global scale
to reduce marine heatwave events and the destruction they cause.
Citation: Leggat, W, Camp EF, Suggett DJ, Heron SF, Fordyce AJ, Gardner S, Deakin L, Turner M, Beaching LJ, Kuzhiumparambil U, Eakin CM, Ainsworth TD. Rapid coral decay is associated with marine heatwave mortality events on reefs, Current Biology (2019), https://doi.org/10.1016/j.cub.2019.06.077
