Coral bleaching in the Maldives
UQ PhD candidate Dominic Bryant is investigating coral reefs in the Central Maldives as part of the XL Catlin Seaview Survey. Here he shares his experiences of the third global coral bleaching events since 1998 and his hopes for the future of coral reefs.
I first joined the XL Catlin Seaview Survey as a volunteer field technician in September 2013 and started my PhD with the University of Queensland's Global Change Institute as a XL Catlin Oceans Scholar in April 2014.
In early April 2016 the first signs of the third global coral bleaching event began to be documented in the Maldives. Initial reports focused on the southernmost atoll, Addu, followed by more bleaching reports to the International Union for the Conservation of Nature and the Maldives Marine Research Centre from allover the country. Trans Maldivian Airlines sea plane pilots were sending pictures of white reef flats to the Maldives Marine Research Centre by the middle of April. It was evident the Maldives was facing a mass bleaching event with a potential mortality rate similar to the 1998 event.
A greater understanding
The 1998 event was one of the first alarms that carbon emissions were changing the planet and effecting important ecosystems such as coral reefs. However, as a global community, we collectively pressed the snooze button. Unlike during the 1998 mass bleaching event, the global and Maldivian coral reef science community is now poised to measure the full effects of this event. In 1998 there was a significant effort by coral reef scientists such as Husain Zahir at the Maldives Marine Research Centre to measure recovery of coral cover from the mass mortality event. But there was no data on pre 1998 coral cover and the composition of other organisms that live within the coral reef ecosystems because no one saw it coming. Thanks to the efforts carried out by coral reef and climate scientists in the years since 1998, we now understand the thermal thresholds for corals before they start to bleach, making it possible to predict when bleaching will start happening in different areas of the world.
In April and May 2015 the University of Queensland’s Global Change Institute, the XL Catlin Seaview Survey and the International Union for the Conservation of Nature (IUCN) carried out expeditions to collect valuable baseline information on the coral reefs before this current bleaching event. The first expedition was the XL Catlin Seaview Survey team, which covered large areas of forereefs throughout the Central Maldives region. The second expedition, which followed shortly afterwards, was the IUCN expedition, focusing on differences in coral communities and fish biomass among local community, resort, and uninhabited islands in the North Ari Atoll. Team members from the two expeditions hope the data from these expeditions will go far in understanding and protecting the reefs of The Maldives. IUCN Maldives project director Dr Ameer Abdulla invited me to join his team of coral reef scientists to survey bleaching sites in North Ari Atoll. The team, made up of coral, fish, and social scientists, aimed to understand the ecological impact of mass bleaching on coral reefs, and the social perceptions and consequences on bleaching for local islanders and resorts. This data is critical to describe the socio-ecological system that underpins interactions between Maldivian people and coral reefs.
I recorded videos along three 50 metre transects at depths of 10 and five meters. A transect is a straight-line path which is used to record scientific observations such as occurrence of different species within a dedicated space. These video transects will be analysed by counting the different types of corals found along the transect and recording their morphological shape (i.e. encrusting, massive, or branching) size classification in centimeters, and bleaching response (i.e. not bleached, pale,partially bleached, fully bleached, and recently dead). This information will be useful to understand impacts of thermal stress on bleaching severity and the vulnerability of different types of coral. Although most of the sites are heavily bleached, there is more bleaching among the Acroporidae family of corals, which are known to be far less tolerant of thermal stress than families such as Poritidae or Faviidae. Maldivian Coral Reef scientist, Hussein Zahir,who is on the expedition, explained that most of the reefs were covered in a type of macro algae known as Dictyota sp after the 1998 bleaching event, and it took three to five years to see signs of coral recovery at most sites.
I have witnessed destruction of coral reefs from coral bleaching, cyclones and Crown of Thorn Starfish outbreaks, but it is most devastating when you see reefs that have not been able to recover, and from my experience that has a lot to with proximity to human populations.
Confidence for the future
There is confidence that reefs in the Maldives will recover from this coral bleaching event if there are no future ocean warming events. This is due to a ban on the export of important herbivore fish that are essential for coral reef recovery. But the full extent of mortality and potential recovery is unknown, and it is important to establish consistent and monitoring of recovery over time to understand the full implications of this event. The XL Catlin Seaview Survey, the IUCN and the MRC have collected important baseline data on the condition of the reef prior to bleaching. The teams at the IUCN, the MRC and the GCI are now eager to resurvey these sites six to 12 months after the bleaching to measure mortality. This information would improve understanding of the affect severe temperature anomalies from climate change are having on coral reef ecosystems around the world.
I hope coral reefs will be able to survive for future generations to enjoy and rely on. This can only happen with collective behavioral change to curb global carbon emissions and prevent destruction of coral reefs at a local level.