Assessing functional groups of hard corals across Bermuda

Project context
Coral reefs are degrading across the Caribbean, and yet all species of corals do not seem to be equally affected. Examination of the functional traits that promote the persistence of some species despite the demise of others is needed if we are to understand why reefs are in decline. Corals in Bermuda were classified into functional groups, according to the manner in which they exhibit the primary functional characterisitics of growth, reproduction and defense. Assessment across reefs located over the North Lagoon determined that species within each functional group of coral responded to environmental gradients in a similar, theoretically-predictable manner.

Objectives
To determine how functional characteristics of each coral species affects the assemblage structure of corals on reefs located across environmental gradients of stress and disturbance. Specific objectives include:

• Determining critical traits to use for classifying corals into functional groups
• Assessing coral assemblage structure over gradients of varying light, sedimentation and wave energy.
• Statistically assessing significant patterns and comparing results to those predicted by theoretical models.

Recent findings
Analysis of coral abundance data from 64 sites on 18 reefs located across the North Lagoon reveals that different traits confer adaptive advantage in different environments. Key findings include:

• Coral assemblage structure and diversity varies greatly over small spatial scales due to quantifiable changes in light level and current speed
• Distributions of key coral species are determined by the way they each are adapted to different environmental conditions and also they way the minimize competition within locations
• Trade-offs between growth rate, aggression and reproductive rate allow species to coexist locally and regionally

Implications
Patterns of distribution that appear random are actually deterministic when viewed at the correct spatial scales and with the right statistical filters. Some level of redundancy in ecological function between species within functional groups allows corals to provide ecosystem services at an assemblage level despite changes in assemblage composition from patch to patch.

Reference: Murdoch TJT (2007) A functional group approach to predict the assemblage structure of hard corals in Florida and Bermuda. PhD Dissertation. University of South Alabama 300 pp.