The Past and Present of Maldivian Coral Reefs

Coral reefs are highly diverse, valuable, but fragile ecosystems that are experiencing unprecedented degradation from anthropogenic impacts and climate change. Degraded reefs provide poorer ecosystem services, including reduced shoreline protection and diminished livelihoods through declining reef fisheries and tourism. Maldives is a coral reef-generated nation, putting it at great risk of climate change-associated damage, namely coral mortality from warming ocean temperatures and reef drowning from rising sea levels. In this thesis, I explore the past and present of Maldivian reefs using a combination of historical research, database searches, and field investigations to ask questions about national trends in coral reef condition, resilience, and the viability of restoration efforts. The research spans three global mass bleaching events that affected Maldives in 1998, 2016, and 2024. In Chapter 1, I conducted a broad-scale, comprehensive literature review to identify research relating to Maldivian coral reefs, which revealed 590 studies published between 1832 and 2022. A topic analysis of two centuries of change in research interests reflected changing relations between people and planet, from early studies focused on discovery and description to exploitation and impact in the early to late-20th century, and then moving on to how people are reshaping the world in the 21st century. In Chapter 2, I compiled all available quantitative surveys of Maldivian reefs to estimate temporal and spatial changes in coral cover through the Anthropocene. I analysed 1023 reef surveys conducted between 1957 and 2025 to show that mass coral bleaching events caused a 90.2% loss of coral in 1998, 60.6% in 2016, and 27.7% in 2024. Given broadly comparable levels of thermal stress between events, there appears to be growing reef thermal resilience across Maldives. In Chapter 3, I undertook field surveys to measure the size structure of coral colonies across Laamu Atoll, a southern atoll in Maldives. To better understand reef replenishment and recovery from the 2016 mass bleaching, I assessed small colony density as an indicator of coral recruitment. Coral recruit densities were high throughout the atoll and across all reef zones. Comparison with recruit density estimates from similar studies in other parts of the world indicates vigorous coral replenishment, which suggests Laamu Atoll’s coral reefs remain resilient. Finally, in Chapter 4, I provide the first insight into the impact of the 2024 coral bleaching event on three islands in Maldives and compare the differences in response to heat stress between restored reefs and adjacent natural reef counterparts. In assessing bleaching resistance and resilience within and among species, I show that restored and natural reefs exhibited similar levels of bleaching during the event and moderate but encouraging levels of partial and full colony recovery immediately after it. Overall, this thesis demonstrates that Maldivian coral cover has declined over time due to a series of severe marine heatwaves and intensifying anthropogenic pressures. Despite this, it also reveals increased thermal resilience in coral reefs, demonstrated by less coral mortality with each successive coral bleaching event, promising levels of full and partial colony recovery, and strong evidence of natural replenishment. While mitigating the effects of climate change remains essential for coral reef persistence, identifying the location of more resilient reefs and individual coral colonies could help make restoration efforts more targeted and effective.<p></p>

Author dc:creator

• Rhiannon Davies (21042854)

• Coral reefs
• The Maldives
• Indian Ocean
• Coral Bleaching

Statement dc:rights

• All rights reserved

Identifier

10779/exe.31296991.v1

OAI identifier oai:identifier

oai:figshare.com:article/31296991