Natural gradients in altitude, depth or latitude capture systematic variation in environmental variables that can be exploited to test hypotheses on the role of various processes in generating and maintaining patterns of biodiversity. The depth zonation of reef-building corals is one such natural gradient, where species rich assemblages vary across a small spatial scale that includes rapid and predictable changes in key environmental variables, such as light. Here, I first develop a novel method of data collection to avoid many of the pitfalls of previous sampling approaches, such as inconsistent sampling effort, poor detection of rare species, and limited sampling range. I next quantified the depth distribution of 9,576 coral colonies representing over 300 corals species within Kimbe Bay, PNG to 1) test the validity of two preeminent predictive theories of species richness gradients 2) identify the community assembly processes which maintain the depth-diversity pattern and 3) quantify how individual species distribute over depth. I found that species richness is not consistent with the predictions of either predictive theory tested, and instead shows a left-skewed hump pattern consistent with results from terrestrial habitats. Examination of species turnover revealed the hump-shaped pattern to be maintained by large-scale processes acting on the regional species pool. While intermediate scale processes, such as environmental filtering, were influential, small scale processes, such as competition, were largely undetectable. Finally, species-specific abundance distributions across depth revealed enormous variation, demonstrating that metrics such as depth range, are very poor descriptions of how species use this domain. In conclusion, I challenge many preconceptions on the patterns and processes behind the depth zonation of corals on reefs, and provide new ways to overcome obstacles to continued research.
Ed was raised in Sydney, and moved north to Townsville in 2005 to attend JCU. During stints working as a SCUBA instructor and maintaining coral reef aquaria at ReefHQ, he escaped on research expeditions to the Coral Sea, and Far Northern GBR, becoming increasingly involved in the deeper regions of coral reefs. After leaving ReefHQ in 2011, he decided it was about time to finish uni, and returned to JCU. In 2013 an opportunity to research largely unknown submerged reef habitats on the GBR arose, and this became the subject of his honours thesis. He graduated with first class honours in environmental science in 2013, after researching largely unknown submerged reef habitats on the GBR, and was successful in acquiring an AIMS@JCU PhD scholarship in 2014 under the supervision of Professor Andrew Baird, Dr Tom Bridge, Professor Geoff Jones, and Dr Julian Caley.