墾丁地區密集迷紋珊瑚(Leptoria phrygia)和鐘形微孔珊瑚(Porites lutea)對不同溫度環境的生理差異及馴化過程

Abstract

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The frequency and severity of global bleaching events are increasing, due to the rise of anthropogenic CO2 in the atmosphere. As our oceans keep warming up, understanding the mechanisms driving thermal tolerance in reef-building corals is of outstanding importance. In Kenting National Park, southern Taiwan, there is a ‘Variable Site’ (VS) that is influenced by the constant hot-water effluent from a nuclear power plant outlet and temperatures during the summer can be 3 °C higher that at any other site within Kenting. It is also influenced by a monthly upwelling that makes seawater temperature to fluctuate up to 8 °C in one day. In this dissertation, I collected samples of Leptoria phrygia from the VS and from a ‘Stable Site’ (SS) that is not affected by high temperature or high temperature fluctuations within Kenting and compared physiological parameters to elucidate the mechanisms this species has to survive in the VS (Chapters II and III). Results suggest that L. phrygia is a species that presents multi-symbiont association and inter-colony variation in SS: most colonies associated with Cladocopium spp. (stress-sensitive), some colonies had co-dominance between Durusdinium glynnii and Cladocopium spp., and very few associated only with D. glynnii (stress-resistant). Meanwhile in the VS, L. phrygia associated all year long with D. glynnii (>90% dominance). I found out that only those colonies with a co-dominance exhibited temporal variation, and I hypothesize that those co-dominant colonies might be able to survive future scenarios of climate change by modifying the relative abundance of both symbionts. If the environment becomes stressful, it becomes Durusdinium-dominant similar to the current situation in the VS. Furthermore, I performed a reciprocal transplantation experiment with L. phrygia and Porites lutea between both sites, to understand the acclimatisation processes to thermal stress (in the summer) and to high temperature variation throughout the year (Chapter IV). Results indicate that both species have different mechanisms to resist stress and to acclimatise to their new environment. Leptoria phrygia is dependent on the different Symbiodiniaceae association and is able to acclimatise faster than P. lutea, but only if it presents co-dominance of Cladocopium spp. and Durusdinium spp. within the colony. If they are >90% Cladocopium-dominant, then they cannot survive high temperatures in the summer in VS. In contrast, P. lutea acclimatise to the new environment slower and modified both partners physiology to confront changes in the environment. The results of this dissertation increase our knowledge on coral physiology and specifically on the differences between species. Even though both species are able to acclimatise to rapid changes in climate using different mechanisms, it is imperative to change completely our societal dependence on fossil fuels, in order to address the root causes of climate change.