The development and impacts of coral-built structure

Niche construction theory posits that organisms can systematically modify their environment in ways that alter the selection pressures experienced by themselves and other organisms. Stony corals are ecosystem engineers known for the complex structures they create that build up coral reef ecosystems. These structures are known to alter the local abiotic environment – for instance, by influencing light availability, flow regimes, and nutrient gradients – and the abiotic environment is also known to play a critical role in shaping coral survival, growth, and morphology. As such, corals present a promising but underexplored system for studying niche construction. This thesis sought to investigate potential patterns of niche construction in corals by examining their structural development and their effects on the fitness of the local coral community. First, I tracked the morphological development of wild coral colonies using biologically relevant metrics with links to organism performance and ecosystem function. The results revealed significant changes in shape as corals grew, suggesting that their ecological impacts shift throughout development as well. Second, I conducted an experiment to test how coral-built structures influence the survival and growth of nearby corals. I found that the presence of structure, whether living or dead increased survival, indicating that coral-built structures function as a form of ecological inheritance. Further, I identified specific morphological traits – namely, size, surface complexity, and volume compactness – as niche-constructing traits, due to their effect on both survival and growth of the local coral community, highlighting interesting demographic trade-offs. Overall, this thesis provides evidence of ecological niche construction in corals and identifies key traits that drive this process. In doing so, this research lays the foundation for future work investigating the evolutionary consequences of coral niche construction for coral reefs.