Thomas Edward Roberts - AIMS@JCU

Thomas Edward Roberts

thomas.roberts@my.jcu.edu.au

PhD
College of Science and Engineering

Thomas Edward Roberts

thomas.roberts@my.jcu.edu.au

PhD
College of Science and Engineering
Coral Depth Zonation: Its nature and significance

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.

Coral Depth Zonation: Its nature and significance

2014 to 2018

Project Description

The aims of this PhD project are to reveal the ecological mechanisms maintaining the depth zonation of reef-building corals. The greatest limitation to continued research is a lack of adequate data, and developing a new methodology to overcome this is the first aim. This methodology will then be applied in the field to assemble a dataset capable of meeting the requirements of modern statistical methods. The project will then use the assembled data to a) test general ecological theories of species richness gradients, using corals over depth; b) assess the relative influence of local assembly processes on the species richness gradient, and c) use a modeling approach adapted from terrestrial ecology to capture the way individual species utilise their depth range, and move towards a greater understanding of coral species ecological niches over depth.

Project Importance

Understanding how species diversity is created and maintained is a fundamental aspect of ecology. For reef-building corals, the depth zonation of species reflects how each species interacts with its environment, to establish its ecological niche. By revealing some of the processes at work, a greater understanding can be achieved of how species are likely to respond to changes in their environment.

Project Methods

The project is centered around a core dataset, which consists of ~10,000 individual coral colonies, recorded over a significant depth gradient, and identified to species level. This data was collected in Kimbe Bay, Papua New Guinea, over several field seasons. To overcome the logistical limitations of working at depth, a new survey method was developed, which formed a publication, and the first chapter of the thesis. Two oft invoked predictive hypotheses of species richness gradients (the mid domain effect, and the species energy theory) were then tested, using species accumulation models and range-resampling models. To assess the influence of local scale community assembly processes (such as competitive interactions and environmental filtering), a multi-scale null model approach was developed, and used on the empirical data collected. Finally, the abundance response curves of each species over its depth range were assessed using Huisman-Olff-Fresco hierarchical logistic regression models to capture species response curves over depth.

Project Results

So far, the project has shown that existing depth records of coral species are significantly erroneous, particularly when considering deeper regions. The research also suggests that environmental filtering is a strong influence in community assembly over depth, but there is little influence of competitive processes. Neither set of local processes control the depth diversity pattern however, and both the species energy theory and mid-domain effect fail to adequately capture the empirical pattern. The results of the three main data chapters are awaiting publication, and will be released imminently. Overall, the most interesting outcome of this project is unveiling how much more there is to learn about the coral diversity over depth.

Keywords