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Abstract
Mangroves are essential components of interconnected tropical ecosystems, offering numerous benefits to nature and society. However, mangroves are facing the impacts of global changes due to shifts in climate and human activities, which are expected to intensify in the coming years. The world is changing, temperatures are rising, ocean pH is decreasing, water is being polluted. These factors, in combination with the conversion and overexploitation of mangroves lead to their rapid decline. To effectively preserve and restore mangroves, it is crucial to understand mangrove functionality and their responses to global change drivers. While their role in climate change mitigation and physical protection has been extensively studied, the biogeochemical processes driving mangroves’ responses to global drivers remain poorly understood. Therefore, this thesis aimed to study the impacts of global change on mangrove functionality, elucidating their role within ecosystem connectivity, with a primary focus on biogeochemical processes.
This thesis starts by exploring the general topic of cross-ecosystem connectivity in tropical coasts, with a focus on biogeochemical connectivity between mangroves, seagrass, and corals, a perspective that is relatively unexplored. In chapter 2, I quantified the studies concerning biogeochemical connectivity and provided a deep understanding about the complex interactions and feedbacks that build up tropical coastal ecosystems. Furthermore, I showed that humans can directly or indirectly disrupt the biogeochemical interactions linking these habitats together by causing eutrophication, chemical pollution, microbial pollution, improper waste disposal, and breaking the water carbonate equilibrium. While analysing the selected literature, I found several knowledge gaps that were used as a stepping stone to develop the following chapters of this thesis.
In the Synthesis, I conclude that mangroves are significantly impacted by global change drivers such as sargassum brown tides, rising temperatures, and local eutrophication. These impacts not only affect their functionality but also create a feedback loop of mangrove degradation. Additionally, mangroves play a role in decreasing local water pH and display various forms of reproduction as adaptive responses to their environment. The mesocosm experiments employed throughout this thesis have played a vital role in addressing key questions regarding mangrove functionality and the underlying biogeochemical processes. The knowledge generated in this thesis fills critical gaps in understanding mangrove ecology and can inform management practices for more efficient restoration and conservation of mangroves within connected tropical ecosystems.
