Exploring patterns of coral ecological niche construction in coral reef ecosystems

Abstract

Ecological niche construction is the process through which (i) organisms modify environmental states and (ii) their modifications favour the organisms’ fitness in return. Ecosystem engineers are an obvious class of putative niche constructors since they produce environmental change modulating resource flow within their ecosystems. Corals, a well-established group of autogenic ecosystem engineers, are a prime example of this class since

through their own skeletal structures, they create the reef habitats they inhabit. This thesis

aims at investigating coral ecological niche construction patterns in coral reef ecosystems.

To understand how corals modify the reef environment (i), I show that reef quantitative surface descriptors that measure coral reef engineering affect patterns of light availability among reef habitats (chapter 2). Furthermore, I performed a coral reciprocal transplant experiment to assess to what extent coral could provide diverse habitats through plasticity. I detected that high plasticity in niche-constructing traits results in a higher ability to provide diverse habitats, under different environmental conditions (chapter 3). To understand if coral engineering activity was favourable to their own fitness (ii), I have studied patterns of coral recruitment across differently engineered habitats. I showed an increase in settler presence on artificial tiles deployed in the field along a gradient of coralbuilt

structural complexity, measured as surface rugosity (chapter 4). I also showed an increase of juvenile abundance across reefs characterized by small-scale high fractal dimension and large-scale high surface rugosity, both being measures of coral engineering activity (chapter 5). With this thesis I aimed at clarifying the role of corals as ecological niche constructors, enabling a future description of coral niche construction as evolutionary agent.