Easing our way to change: Changes in functional diversity in the decade following protection of marine areas

Background/Question/Methods

Since environmental changes may impact the types of organisms found in communities in addition to changing abundance patterns, analyzing functional diversity along with taxonomic diversity may prove a valuable tool in assessing management outcomes.  Multiple analytical methods exist for describing functional diversity, and each of these may account for a different aspect of diversity.  However, work is needed to translate these metrics to management applications.  We propose existing functional diversity metrics can be used to assess responses to management outcomes by following changes in the range of observed trait values and abundance of organisms.  We analyzed changes in functional and taxonomic diversity in California rocky reef fish communities in the decade following their protection through the establishment of marine reserves.  Fish communities were surveyed at over 150 sites between 2001 and 2010.  Data on fish traits were collected from sources including existing literature, databases, and expert opinion.  In addition to conservation status, data on potential environmental drivers (e.g., temperature, presence of habitat-forming kelp) were also collected.  For each community we calculated taxonomic (richness, Shannon’s index) and functional (richness, Rao’s Q, community-weighted means) measures of richness and diversity and regressed these values against potential drivers.

Results/Conclusions  

A wide range of values existed for measured traits across the region, and clear spatial patterns existed in measures of functional and taxonomic diversity.  Evaluation of potential environmental drivers indicated the presence and abundance of kelp, temperature, and phytoplankton productivity had little impact on diversity metrics, while the protection of areas led to significant community changes over time.   Increases in the number of species found at sites were accompanied by increases in functional richness and diversity.  The most traits, including maximum age, maximum size, and growth parameters, increased in functional richness, while changes were also noted in the functional diversity of trophic level and growth parameters.  The community-weighted mean of maximum age also changed.  However, no changes were observed in taxonomic diversity.  Given the noted increases in species following protection, concurrent changes in functional diversity and lack of change in taxonomic diversity, results indicate the range of species inhabiting these communities may be the first observable change, followed by changes in abundance and eventual community-wide shifts in functional diversity.  Functional diversity may thus respond more strongly to change than taxonomic diversity and allow predictions of future community composition, suggesting functional measures may be useful metrics of management progress and impact.