A trait-based approach to coral community ecology : linking colony morphology to demography and ecosystem function

Abstract

Finding general links between traits shared across species and organism performance should allow for generalised predictions of both community dynamics and ecosystem processes. In reef-building coral communities finding these trait-process links has been difficult, but past studies highlight that morphology plays a key role. This thesis investigated how continuous morphological traits link to coral community-level processes such as demographic variation, responses to disturbances, and ecosystem function.

Continuous, morphological traits were shown to resolve growth form categories in continuous space and highlighted how shape within a growth form changes with size. Morphological traits were linked to variation in demographic parameters, including net growth, growth variability and survival. Variation in volume compactness was linked to colony mortality risk, and variation in both net growth and growth variability, capturing a biomechanical trade-off axis where colonies can either have low mortality, slow growth, and low year to year variation in size, or U-shaped size- mortality curves, faster growth, and high year-to-year variation in size.

Community weighted averages of morphological traits highlighted how morphology results in asymmetric responses to both cyclones and mass bleaching events. Volume compactness greatly increased following both cyclones and bleaching. This loss of more structurally complex colonies in the community will likely have major implications for associated species and habitat function, suggesting that these traits can be used as community scale indicators of both susceptibility to disturbances and ecosystem function. The trait framework developed in this thesis provides a set of quantitative tools for exploring a variety of processes important for corals and the communities they support by establishing generalised and causal links between organism variation and ecological phenomena.