Dr Anjani Ganase, coral reef ecologist, looks at the bleak picture through the lens of the degradation of coral reefs worldwide, and what we must do to reverse the trend towards an unsustainable existence.
El Niño climate conditions aggravated by man-made global heating caused mass bleaching on coral reefs in the northern hemisphere during the summer of 2023, and brought devastation and mortality to reefs throughout the Caribbean. In Tobago, above average temperatures persisted for three months (September to November 2023). Over the past month, these conditions have delivered a deadly blow to the Great Barrier Reef in Australia. Anomalously high ocean temperatures have been washing over the reefs for at least ten weeks, similar to the heat waves experienced in Caribbean.
Initial reports from the Australian Institute of Marine Science which conducted aerial surveys state that broadscale mass bleaching has occurred along the shallow reefs in the impacted regions particularly the northern and southern sections of the Great Barrier Reef (GBR). The full extent of the GBR spans 2,300 kms, covering an area that is equivalent to the size of Japan. The reefs span tropical and sub-tropical reef systems (in the south) and are critical to the surrounding ocean biodiversity, not to mention the Australian economy. While aerial surveys can easily detect the bleaching in the shallow reefs, in-water surveys are essential to determine bleaching on deeper sections of the reef.
Coral reefs of the GBR can extend beyond 30m depth for many outer reef sites. A total of 215 in-water surveys conducted during the last week in February confirm severe bleaching on southern reefs with mild to moderate bleaching in the northern and central Great Barrier Reef. At the moment, there are no disease outbreaks but there are localised incidents of crown-of-thorns starfish (COTS) outbreaks to the south and offshore areas of the central GBR. This starfish is natural predator of corals, but population explosions essentially results in mass grinding of corals skeletons to dust. Such added impacts limit recovery and contribute to severe degradations.
[caption id="attachment_1070098" align="alignnone" width="1024"] Coral bleaching on the Great Barrier Reef, 2017. - The Ocean Agency / Ocean Image Bank[/caption]
The last bleaching event on the GBR occurred two years ago in 2022, following 2020, 2017 and 2016. Before this, the previous mass bleaching events were in 2002 and 1998. In 2016, our research team from the University of Queensland surveyed large sections of the reefs that were basically killed by coral bleaching. Fields of branching corals extending for kilometres on end such as on Opal Reef and The Great Detached Reef that were home to vibrant marine life became barren dead fields of coral skeletons – no corals, no fish. During the 2016/ 2017 bleaching, the reefs of the Far Northern GBR were the most severely devastated. This was a clear sign of water simply becoming too hot, as these pristine reefs were remote from land-based pollution an
