陳昭倫Chaolun Allen Chen潘爾瑪Stéphane Pierre de Palmas2020-10-19不公開2020-10-192020http://etds.lib.ntnu.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=id=%22G080350006S%22.&%22.id.&http://rportal.lib.ntnu.edu.tw:80/handle/20.500.12235/111545noneMesophotic Coral Ecosystems (MCEs) are the continuation of the shallow water coral reefs into the twilight zone, at depth between 30 and 150m. These ecosystems are supporting a rich biodiversity into which light-dependent corals (Scleractinia Bourne, 1900) are among the dominant ecosystem engineers. Recent investigations on these ecosystems have shown that they support an exceptional biodiversity and often have high levels of endemism with numerous new species adapted to the low light environment. As MCEs are often located relatively farther away from the coastlines and deep below the sea surface, it has been suggested that they could face lower intensity and frequency of disturbances, providing temporary refuge for reefal organisms. MCEs could as well act as a source of propagules for shallow water communities, replenishing their populations following disturbances and thus facilitating the overall resilience of the ecosystem. In any case, the role that MCEs could play for future coral reefs is still debatable given the current extent of our knowledge about these ecosystems. In Taiwan for instance, there is very little information about the diversity in scleractinian corals below 30m in depth. Therefore, level of similarity between shallow and mesophotic biodiversity in scleractinian corals as well as the degree of genetic specialization with depth for these species are unknown. Lastly, the ability for mesophotic populations to serve as source of propagules has never been assessed, obscuring the role that MCEs could play for future Taiwanese coral reefs. The aim of this PhD project was to fill the gaps of knowledge about MCEs from Taiwan using Ludao (also called Green Island) as a reference. Investigation of the MCEs from Ludao, at depths between 38 and 60m, allowed the examination of low-gradient slopes associated with extended covers of sand and rubbles, which are known to limit the development of the MCEs. However, the presence of numerous small to large patches of hard substrates allows the development of a diverse scleractinian fauna. A minimum of 103 scleractinian species (plus two other reef-builders) were collected at mesophotic depths, including at least 12 new records for Taiwan. One scleractinian coral with large bathymetric distribution around the island (Pocillopora verrucosa Elis& Solander, 1786) was used as a model to investigate possible genetic specialization and population differentiation with depth, and to estimate levels of migration between shallow and deep zones. First, the use of molecular taxonomic markers on P. verrucosa collected from three locations at depth ranging from 7 to 45m excluded the presence of any genetic specialization related to depth. Then, the use of microsatellites markers to analyze the same specimens show little to no differentiation withdepth, but rather a unique population pool with recent vertical (among depth) and horizontal (between sites) migration signals. These results suggest that P. verrucosa from Ludao is a panmictic population. Despite the relatively limitated MCEs development around Taiwan, these ecosystems around Ludao support a rich diversity in scleractinian corals species, and among all P. verrucosa harbors high levels of genetic diversity along its bathymetric distribution with vertical and horizontal migration. MCEs from Ludao could potentially act as a refuge and contribute to the replenishment of the shallow water populations following major disturbances, thus benefiting the ecosystem resilience. However, the role of potential refuge is demonstrated here for only one species and, despite potentially concerning species with similar life history traits at the same location, this role should now be investigated for other scleractinian species and other taxa in order to evaluate if future coral reefs of Taiwan could be functionally similar to their contemporary reefs. In conclusion, this study illustrates how the integration of molecular tools is of great importance to evaluate MCEs’ role for future coral reefs and further suggests MCEs around Taiwan should receive more attention and protection, especially in the context of rapid decline of the shallow water coral reefs.noneMesophotic Coral EcosystemsScleractinian coral diversityMolecular diversityPopulation geneticsDeep Reef Refuge Hypothesis