墾丁國家公園珊瑚礁韌性及在氣候變遷與人為擾動影響下維持珊瑚礁資源量的決定性因素

Abstract

noneClimate change and increasing anthropogenic pressures have profoundly transformed coral reef ecosystems. Increased Sea Surface Temperature (SST), ocean acidification, typhoon and bleaching events along with coastal development, eutrophication, overfishing, and many additional anthropogenic threats are affecting coral reefs from the physiological to the ecosystem level. Resilience capacities of this ecosystem have been imperiled and their persistence in the near future is doubtful. With the recent prevision on climate change, there is an urgent need to develop a resilient system, which can face future environmental modifications. Therefore, conciliating growing socio-economic demands with ecological conservation represents a challenge to sustain enduring coral reefs. In this study, we developed a transdisciplinary approach using ecosystem modeling to identify key parameters leveraging reef degradation, and their potential impact on the state of the coral reefs. To perform our project, we selected Kenting National Park (KNP), in Southern Taiwan, as this location is the shelter of an extraordinary reef biodiversity. Despite the implementation of MPAs within KNP, coral reefs have been severely degraded by increasing natural and anthropogenic disturbances. For the study, benthic and fish data from > 100 sampling locations through KNP over a three-year period (2012-2015) were combined for the initial assessment of reef ecosystem. In 2015-2017, additional seasonal surveys were performed at 11 reefs to assess impacts of punctual disturbances, such as typhoons and bleaching events. Conditions and responses of communities were related to environmental conditions as well as both terrestrial and marine anthropogenic activities. These results were combined to inform an ecosystem model encompassing 869.75 km2 of land and ocean. Modeling of coral ecosystem dynamics was based on a mass-balanced model constrained by land-sea interactions. Results of the environmental and ecological surveys (Chapter 2) showed that repeated storms in KNP kept thermal stress low, prevented extensive bleaching, and mitigated the impacts of the 2015-2017 El Niño event. Typhoons offered temporary relief to reef organisms from the threat of bleaching. However, storm-induced local shifts from coral to macro-algae dominated states were observed. Typhoon frequency in KNP is likely to be responsible for the low contribution of key coral functional groups, such as branching, foliose, and tabulate, into the benthic community. Synchronous storms and heatwaves could significantly influence local reef persistence, but could also decrease the structural complexity and diversity of Taiwanese reefs, imperiling the reefs’ capacities to cope with climate change. The major loss of structural complexity within KNP, observed in Chapter 2, has highlighted the urge to better understand relations between the species composition of coral reefs, their structural complexity and their resilience capacities. To fulfill this goal, we developed a new analystical approach based on classic ecological surveys and fine-scale depth dataset (Chapter 3). We could distinguish the relative contribution of structural complexity provided by the inhabiting organisms (micro-rugosity) from complexity derived from geological features (macro-rugosity). The relationships between rugosity patterns and reef functional groups were identified, highlighting conservation priorities of specific groups, along with sites that present higher recovery potential within KNP. Finally combining all the data from Chapters 2 and 3 with historical dataset, we built an ecological model based on the interactions between 21 reef-associated functional groups and the natural and anthropogenic disturbances occurring within KNP (Chapter 4). Ultimately, the ecological processes recreated by the proposed model highlighted water quality degradations as a major driver of reef resilience loss in KNP. Based on identified relations between the ecosystem dynamics and the anthropogenic and natural disturbances, a set of five scenario was tested to estimate their potential impacts for the development of sustainable management strategies in KNP. The overall results of this Ph.D., is offering a handful set of promising tools for scientists and managers to keep improving our understanding of reef resilience and to sustainably management reef associated resources.