The coral species Acropora millepora is able to adapt to a warmer climate. This has been revealed by research conducted by biologist Jos Mieog. There’s a limit to its adaptability, however. If the earth continues to warm up at the rate its going, parts of the Great Barrier Reef, one of the most impressive natural areas in the world, may change into slimy algal goo. Mieog will be awarded a PhD by the University of Groningen on 4 September 2009.
Coral is created when coral polyps lodge on the sea bottom in shallow waters and make themselves a hard chalky exoskeleton. Secure in their exoskeletons, they filter part of their food from the water. However, because coral usually grows in nutrient-poor water, it relies to an important degree on single-cell algae (Symbiodinium genus) for its food; these live in the coral’s cells and produce glucose via photosynthesis. While the coral grows on the glucose, the algae profit from the protection offered by the coral. A relationship like this that benefits both parties is known as symbiotic.
If the symbiosis between coral and algae is disturbed, the coral will starve and bleach. This is what happens if the coral is no longer covered by water or becomes ill, for example. However, if the sea water becomes too warm, symbiosis can also be disturbed and coral bleaching occur. In the past two decades, climate change has resulted in a strong increase in coral bleaching, with massive damage to coral reefs as the result. This is why many scientists are extremely worried about the future of coral reefs. Jos Mieog has discovered that some types of coral can adapt to minor changes in temperature by getting food from a different type of algae, one better able to cope with warmer water.
Mieog has demonstrated that the fitness (which includes heat resistance and speed of growth) of the coral species Acropora millepora is heavily dependent on the type of algae that the coral houses. He has developed a new DNA analysis method (based on real-time PCR) which can accurately determine which type of algae are housed in a certain coral. Previously, researchers assumed that most corals housed one single type of algae. However, Mieog has discovered that many of the corals on the Great Barrier Reef not only house the dominant type but also low concentrations of a more heat resistant algae. If the water temperature rises and one type of algae is affected, the coral can exchange it for the more heat resistant type. Thus the coral is able to adapt to temperature increases of between one and one and a half degrees.
Mieog: ‘The IPCC, the UN organization investigating climate change, is estimating a world-wide temperature increase of one and a half to two degrees this century, if we succeed in significantly reducing our CO2 emissions. My research has revealed that some coral species can adapt to temperature change surprisingly quickly. But even if we were to stop emitting CO2 today, the biodiversity of the Great Barrier Reef is going to continue to decline. According to some researchers, many coral reefs may well be on a “slippery slope to slime”, i.e. they may become slimy algal goo. Although my research results are hopeful, we will still have to work hard to keep that natural wonder healthy.’
Jos Mieog (1977) studied Biology in Nijmegen. His research was conducted at the Department of Marine Benthic Ecology and Evolution of the University of Groningen and at the Australian Institute of Marine Science (AIMS). The research was financed by NWO. Mieog now lives in Australia where he is continuing his coral research. His thesis is entitled The flexibility of the coral-algal symbiosis in the face of climate change: investigating the adaptive bleaching hypothesis.
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