The Coral Triangle, also known as the Indo-Australian Archipelago, is known for the greatest marine biodiversity on our planet. Despite its importance, the detailed evolutionary history of this biodiversity hotspot has remained largely a mystery. An international research team has now shed light on this history, reconstructing how biodiversity in the region has evolved over the past 40 million years.
This study, co-led by Dr Skye Yunshu TIAN from the University of Bonn, who conducted most of the research at the University of Hong Kong (HKU), together with Professor Moriaki YASUHARA from the HKU School of Biological Sciences, the Swire Institute of Marine Science (SWIMS) and the Institute for Climate and Carbon Neutrality (ICCN), as well as Dr Fabien L. CONDAMINE from Centre National de la Recherche Scientifique (CNRS), is now published in the journal Nature.
The researchers began their investigation by examining sediment samples from the Indo-Australian Archipelago in the lab and identifying the fossils they contained. “We wanted to understand how the marine biodiversity of the Indo-Australian Archipelago evolved and persisted, and what factors were responsible for the disproportionately high diversity in the tropics,” said first author Skye Tian.
Their findings showed that the archipelago had shown an increase in diversification since the early Miocene, about 20 million years ago. Around 2.6 million years ago, the number of species approached a plateau. Interestingly, there were no major extinction events during the entire study period. “The increase in diversity was mainly driven by the habitat factor, as tectonic collisions (movements of the Earth's plates) in Southeast Asia created vast areas of shallow marine habitats,” Skye noted.
About 14 million years ago, the region's thermal stress, or excessive heat, began to moderate. “This mitigation was critical to the development of the hotspot,” Skye continued. “During the Eocene (56 to 34 million years ago), extremely high tropical temperatures in warm climate zones hindered the increase in diversity. The subsequent cooling provided a more favorable environment for biodiversity to flourish.” However, this rich biodiversity could be in danger. “Our paleobiological results suggest that we could quickly lose the fantastic diversity of the tropical hotspot if ongoing anthropogenic warming intensifies.” Skye added.
Professor Moriaki Yasuhara further explained: “This reconstruction of the long-term history of the Coral Triangle diversity hotspot allows us to better understand how the diversity hotspot moved from the region of ‘Tethys (ancient Mediterranean)’ to the current location of the Coral Triangle and developed. This is what we did not know so clearly before. And our results also tell us why the diversity of the Coral Triangle is much higher than that of the Caribbean Sea, which is probably because the Coral Triangle did not experience a major extinction by chance.”
