UBC Theses and Dissertations
Investigating the ability of coral reefs to protect shorelines in the Republic of Kiribati Summers, Heather
Coral reefs support a high biodiversity, providing a natural, physical barrier from waves that protects coastal communities from shoreline erosion and inundation. The three-dimensional (3D) structural complexity of living coral communities provides frictional resistance as waves and currents pass over the reef. A shift in coral community assemblages towards small, weedy, stress-tolerant corals due to climate change and local human stressors may alter wave attenuation, threatening low-lying coastal regions facing sea-level rise. In this thesis, I investigated the effect of coral community composition on shoreline protection in Kiribati’s Tarawa and Abaiang Atolls by collecting fore reef and reef flat field data and creating 3D reconstructions of the fore reefs. I found that the 3D structure and contribution of certain coral growth forms to reef complexity varied depending on the complexity metric used. Surface rugosity and standard deviation of elevation were not significantly different between atolls, while the average terrain ruggedness was significantly greater at disturbed sites in South Tarawa dominated by the weedy species Porites rus. I show that the abundance of Porites rus and branching corals were positively related for all three complexity metrics, with the strongest positive association between Porites rus and terrain ruggedness. Lastly, I determined that South Tarawa reef flats, long mined of rocks for human use, have lower benthic roughness and receive higher offshore wave energy relative to North Tarawa. My research suggests that at current mean sea level, the difference in the diversity of coral growth forms on the fore reef across Tarawa and Abaiang have less effect on wave attenuation than other factors like coral cover, steepness of the fore reef, and benthic composition of the reef flat. Additionally, the most significant variation in wave runup will be due to parameters influencing fore reef slope and reef flat composition. As such, steeper fore reef slopes and smooth reef flats of South Tarawa are expected to dissipate less wave energy relative to reefs in North Tarawa and Abaiang. To summarize, my findings offer insights into possible trade-offs between reef resilience to climate change and shoreline protection, including shoreline vulnerabilities to sea-level rise around Kiribati.
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