Dr Anjani Ganase talks about die-off of the most vulnerable creatures on the planet to global warming – corals. Bleaching is happening today; and this planetary indicator does not bode well for humanity.
Over the past week, marine scientists from the Great Barrier Reef Marine Park Authority have observed coral bleaching on the Great Barrier Reef (GBR). Certain areas are being described as severe, particularly along the central GBR near Townsville, a community largely dependent on the reef ecosystem for jobs and livelihoods. This year (possibly for the first time) the reefs are experiencing above average warming conditions, despite being in a La Niña phase. La Niña is associated with higher rainfall and cloud cover, conditions associated with cooling oceanic conditions. Nevertheless, many parts of the central and southern sections of the GBR are experiencing 0.5 - two degrees Celsius above the average temperature, while the northern sections of the GBR are experiencing between two to four degrees Celsius above average temperatures.
The extent of the bleaching is still unknown, as it takes scientists several days to survey sections of the reef by plane. The Great Barrier Reef is huge! It is 2,300 km of coral reefs covering an area of 344,000 km2. This is equivalent to the area of the UK, Switzerland and The Netherlands combined. There are 3,000 distinct coral reefs, 600 continental islands, 300 coral cays that house over 600 species of corals, 1,625 species of fish, 133 varieties of rays and sharks and 30 species of marine mammals – dolphins and whales.
The history of coral bleaching in the GBR
There have been five mass bleaching events on the Great Barrier Reef since 1997, with three of these events occurring in the last five years (2016, 2017 and 2020). While the mass bleaching of 1997 resulted from El Niño conditions, the events over the last five years were aggravated by climate change. There is an overall trend of more intense warming conditions resulting in more severe bleaching and coral mortality occurring more extensively across the GBR. In the future, sections of Great Barrier Reef are likely to experience severe bleaching events every year before 2030. Given the expanse and heterogeneity of the GBR, there are areas of hope where scientists have identified potential sites of refuge (cooler spots) that may assist in coral recovery of the surrounding coral reefs impacted by coral bleaching. However, all of this depends on the trajectory of global warming.
Coral reefs, especially the GBR that is relatively well managed for other stressors – fisheries, pollution, and outbreaks of coral eating crown of thorns starfish – can recover from bleaching. However, if bleaching events become too frequent (every two to three years), reefs will not be able to recover sufficiently, and the corals die off. On top of the threats of global warming, reefs are also at risk of natural disturbance events, such as cyclones that contribute to coral mortality. Extensive coral death means fewer corals to reproduce coral la
