Oceanographic ecology of coral reefs: the role of oceanographic processes in reef-level biogeochemistry and trophic ecology

[Truncated abstract] Coral reefs worldwide are under increasing pressure from climate change, acidification, habitat destruction and over‐fishing. Given that reefs support some of the highest biodiversity and provide a large range of ecosystem goods and services, improved understanding of the factors controlling their productivity and function at an ecosystem level should be a high priority. This thesis explores how reef‐level biogeochemistry, and the trophic ecology of some reef organisms, may be influenced by oceanographic processes over broad temporal and spatial scales. The high productivity of coral reefs in an oligotrophic environment was historically attributed to ‘tight recycling’ of nutrients, with reef ecosystems appearing to be neither a net source nor sink of nutrients. However, as this thesis emphasizes, there is now evidence that reefs may be highly biogeochemically dynamic in both space and time, depending on the input of allochthonous (oceanic) nutrients and releasing autochthonous (internally‐produced) nutrients at appreciable rates. At Ningaloo Reef, Western Australia, the rate of phytoplanktonderived particulate organic nitrogen (PON) uptake we observed (2 – 5 mmol PON m‐2 d‐1) confirms that allochthonous particulate organic matter (POM) may supply a large proportion of the N ‘missing’ in previous reef nitrogen budgets. Further, the estimated release of autochthonous dissolved N, as high as 18 mmol NOx m‐2 d‐1, increased significantly when the supply of allochthonous POM was high. This suggests that recycling may indeed be a significant processes, albeit driven by the supply of allochthonous POM and its remineralisation by reef organisms. As well as dissolved N, the reef released POM at an estimated rate on the same order of magnitude as allochthonous POM uptake (e.g. ~6 – 8 mmol PON m‐2 d‐1).