Understanding the drivers of coral bleaching for better reef management

Aquarium research

Using controlled experimental aquaria complements field research

Research on habitat variation on Indonesian reefs is providing key information on the tolerance of coral under stress that will lead to better management of reefs, particularly in light of predicted climate change impacts.

Coral reefs are vital marine ecosystems that drive productivity in tropical oceans, and directly provide resources and protection to 30 million of the world’s poorest families.

The archipelago of Indonesia lies in the heart of the coral triangle, the centre of global marine biodiversity. However this area is also one of considerable poverty, with 12% of the population living below the minimum subsistence income of $1 a day. However with a coastline of approximately 80,000km, Indonesia is endowed with rich coastal habitats that hold the ability to support the poorest reaches of the country.

Research in the Wakatobi Marine National Park has been conducted for over 15 years and identified a number of threats to the reef system which have the potential to cause difficulties for the large subsistence population that are supported there.

Corals categorised as branching were found to bleach, losing symbiotic algae and host tissues, at a much faster rate and to a greater extent than those corals classified as having boulder morphology

During the research period a number of global coral bleaching events have occurred, the effects of which were seen within the park. This provided prime opportunity to monitor coral species and habitats most affected and identify which corals suffered lethal bleaching compared to those with the ability to recover.

This research uncovered habitats with inherent resilience where corals of the same species appear to withstand a much greater degree of stress than those on the reef flat and crest. This opened up the questions of what drives these differences in tolerance and how we can use this knowledge to protect corals and their habitats in the future.

Field and aquarium research

Scientists from the University of Essex in the UK are combining research from within their state of the art research aquarium facility, with that from field experiments conducted inside the national park.

Results so far have indicated that differences in tolerance are related to the corals’ growth strategy. Corals categorised as branching were found to bleach, losing symbiotic algae and host tissues, at a much faster rate and to a greater extent than those corals classified as having boulder morphology. The underlying drivers of these differences are unknown at present, though current research is aiming to tease apart genetically driven variation from that which is environmentally regulated.

Coral stress

The future of this project involves the characterisation of reefal habitats within the Wakatobi Marine Park, such as how the environment regulates the underwater conditions in regards to light intensity, UV penetration, temperature and nutrient availability. Can the environment potentially buffer the effects of stress events or are genetic changes within the corals key to increasing their tolerance?

Studies from within the scientific literature have demonstrated that pigments in the water column can reduce the filtration of UV to the corals. However, in several study habitats, corals are exposed to air, introducing desiccation stress and extreme temperatures far above those which can potentially cause corals to bleach. How do these corals survive with no environmental features to protect them?

coral

Coral exposed in a rockpool. Corals are found in intertidal habitats with extreme daily variation

It is likely that tolerance is driven by a combination of both genetic and environmental factors, with genes acting as the primary force, but whether the environment drives physical change is currently unknown.

Current research is focusing on the effect of the growth environment on coral structure and how this impacts their ability to endure stressful periods. Using controlled experimental aquaria, long term coral growth experiments can be established in order to identify the effect of singular variables – something which is impossible in the field.

Once drivers are identified, we can establish which ones are the most important causative agents involved in increasing the tolerance of corals. This information can be used to identify coral habitats most at risk and allow direction and prioritisation in managements plans.

This will improve the current system of management allocation and allow us to not only protect those habitats most at risk, but also to protect those with the highest likelihood of survival if the worst climatic predictions materialise within the next century.

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  1. Understanding the Drivers of Coral Bleaching for better Reef Management | moralcoral - February 2012

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