Biodiversity and productivity relationships in coral reef ecosystems

Ecosystem functions are exchanges of energetic production, consumption, and release between and among organisms and their environment. The biodiversity-ecosystem functioning concept (BEF) hypothesises that biodiversity of an ecosystem has direct, causal effects on ecosystem ofunctions. Although there has been extensive experimental and observational evidence in support of the BEF hypothesis, research has focused on temperate plant assemblages. Highly complex and diverse tropical ecosystems have not been well represented in the current body of BEF evidence. In this thesis, I aim to investigate the spatial and temporal patterns of biodiversity-productivity links in coral reef ecosystems: in reef fish productivity and coral reef accretion in reef-building corals. To understand how best to quantify productivity functions in reef fishes, I validated how multiple reef fish survey methods influence resulting ecological insights and metrics (chapter 2). I then describe a standardised database on global reef fish assemblage surveys for macroecological syntheses (chapter 3). I apply the findings from these chapters to a synthesis on reef fish assemblages (chapter 4), showing a global positive gradient of assemblage productivity with species richness. I also show positive diversity-productivity links in temporal trends. To investigate diversity-productivity links in corals, I use a novel photogrammetry comparative method I develop to quantify realised net reef accretion over a three-year period (chapter 5). I show that diversity-productivity links are not present in coral assemblages and are instead driven by abundance. This thesis addresses knowledge gaps on the role of biodiversity in coral reef ecosystem functioning two highly diverse coral reef taxa. Nuances to these dynamics show that biodiversity is integral to the growth and productivity of assemblages, but these trends are not always monotonic and linear across all taxa or ecosystem functions. The findings here present methodological tools and new avenues to better understand coral reef ecosystem functions and BEF research.