Ecological determinants of depth zonation in reef-building corals

Roberts, Thomas Edward (2018) Ecological determinants of depth zonation in reef-building corals. PhD thesis, James Cook University.

PDF (Thesis)
Download (5MB) | Preview
View at Publisher Website:


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 pattern, where species rich assemblages vary across a small spatial scale that includes rapid and predictable changes in key environmental variables, such as light. These attributes allow a strong test of general hypotheses predicting biodiversity patterns, free from many of the confounding factors found in terrestrial habitats. Here, I first develop a novel method of data collection, referred to as the modified Point-Count Transect method, which is derived from avian survey methods. This approach avoids many of the pitfalls of previous sampling approaches, such as inconsistent sampling effort, poor detection of rare species, and limited sampling coverage of the gradient. I then utilise this methodology to assemble a dataset of 9,576 coral colonies representing over 300 corals species, on six reefs in three positions within Kimbe Bay, PNG to 1) test the validity of the Species Energy theory and the Mid-Domain Effect; two preeminent predictive theories of species richness gradients 2) identify the reef-scale community assembly processes which maintain the depth-diversity pattern and 3) quantify how individual species abundances vary over depth. I found that species richness is not consistent with the predictions of either theory, and instead shows a left-skewed hump consistent with results from terrestrial habitats. Examination of species turnover suggested that the hump-shaped pattern is maintained by large-scale processes acting on the regional species pool, rather than differential levels of reef-scale processes, such as competition and environmental filtering. These results demonstrate that the hump-shaped pattern is not an artefact of scale or sampling design. Finally, species-specific abundance distributions across depth revealed species' depth use to be far more specialized than previously thought, demonstrating how commonly used metrics such as depth range, are very poor descriptions of how species use this domain. In conclusion, many of the preconceptions on the patterns and processes behind the depth zonation of corals on reefs are demonstrably flawed, and should be re-examined using suitable data and analysis. Although there remains no generally applicable explanation for how the hump-shaped pattern is created and maintained, this thesis provides new ways to overcome obstacles to continued research and move the field forwards.

Item ID: 63815
Item Type: Thesis (PhD)
Keywords: abundance response curves, beta diversity, biodiversity, community assembly, community ecology, competition, coral reef, corals, deep reef refugia hypothesis, depth range, eHOF, environmental filtering, hierarchical logistic regression, life history traits, niche, priority effects, species abundance response curves, species richness, species-energy hypothesis
Related URLs:
Copyright Information: Copyright © 2018 Thomas Edward Roberts.
Additional Information:

Three publications arising from this thesis are stored in ResearchOnline@JCU, at the time of processing. Please see the Related URLs field. The publications are:

Chapter 2: Roberts, T. Edward, Bridge, Thomas C., Caley, M. Julian, and Baird, Andrew H. (2016) The point count transect method for estimates of biodiversity on coral reefs: improving the sampling of rare species. PLoS One, 11 (3). e0152335.

Chapter 3: Roberts, T. Edward, Keith, Sally A., Rahbek, Carsten, Bridge, Tom C.L., Caley, M. Julian, and Baird, Andrew H. (2019) Testing biodiversity theory using species richness of reef-building corals across a depth gradient. Biology Letters, 15 (10).

Chapter 5: Roberts, T. Edward, Bridge, Tom C.L., Caley, M. Julian, Madin, Joshua S., and Baird, Andrew H. (2019) Resolving the depth zonation paradox in reef-building corals. Ecology, 100 (8). e02761.

Date Deposited: 20 Jul 2020 02:21
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 35%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 30%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050102 Ecosystem Function @ 35%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
Downloads: Total: 173
Last 12 Months: 20
More Statistics

Actions (Repository Staff Only)

Item Control Page Item Control Page