A test of a functional group approach to detecting shifts in macroalgal communities along a disturbance gradient

It has recently been proposed that the functional form group hypothesis developed in the 1980s can b e used as a tool to predict changes to algal community composition resulting from disturbance.This study tested whether the functional group model could detect changes in macroalgal community structure within one bioregion, by applying the model to a habitat (high relief limestone reef) exposed to different levels of physical disturbance (wave exposure).Macroalgal community structure was examined on 3 high relief limestone reef lines exposed to high, intermediate and low levels of wave-driven physical disturbance, which were used a s a gradient of physical disturbance.Community structure was measured by determining the biomass and diversity at both the species and functional group levels.Comparisons between the 2 approaches were made using ANOVA (analysis of variance] of biornass data and derived diversity ~ndices.Multivaridte analysis techniques of ordination, Principal Axis Correlation (PCC) and ANOSlM (analysis of similarities) were used to detect patterns of assemblage change.The macroalgal assemblages were found to b e highly variable, particularly within exposure levels, when examined at both the species and functional group levels.While both approaches revealed simllar trends in the response of the algal community to physical disturbance, the functional group approach was less able to detect differences between levels of exposure.Use of the functional group approach resulted in considerable loss of information.Its use is not recommended for communities displaying high spatial heterogeneity without further ngorous testlng of the model.Furthermore, algal functional groups need to be more clearly deflned to overcome problems of assigning species to groups that do not easily fit the model.