|Title||A framework to assess the health of rocky reefs linking geomorphology, community assemblage, and fish biomass|
|Publication Type||Journal Article|
|Year of Publication||2015|
|Authors||Aburto-Oropeza O, Ezcurra E., Moxley J., Sanchez-Rodriguez A., Mascarenas-Osorio I., Sanchez-Ortiz C., Erisman B, Ricketts T.|
|Type of Article||Article|
|Keywords||abundance; coral-reefs; Fisheries; food webs; gulf-of-california; impacts; Inverted biomass pyramid; Marine communities; marine protected areas; predators; principal-components-analysis; recovery; reserves; Shifting baselines; top; Trophic groups|
The recovery of historic community assemblages on reefs is a primary objective for the management of marine ecosystems. Working under the overall hypothesis that, as fishing pressure increases, the abundance in upper trophic levels decreases followed by intermediate levels, we develop an index that characterizes the comparative health of rocky reefs. Using underwater visual transects to sample rocky reefs in the Gulf of California, Mexico, we sampled 147 reefs across 1200 km to test this reef health index (IRH). Five-indicators described 88% of the variation among the reefs along this fishing-intensity gradient: the biomass of piscivores and carnivores were positively associated with reef health; while the relative abundances of zooplanktivores, sea stars, and sea urchins, were negatively correlated with degraded reefs health. The average size of commercial macro-invertebrates and the absolute fish biomass increased significantly with increasing values of the IRE. Higher total fish biomass was found on reefs with complex geomorphology compared to reefs with simple geomorphology (r(2) = 0.14, F = 44.05, P<0.0001) and the trophic biomass pyramid also changed, which supports the evidence of the inversion of biomass pyramids along the gradient of reefs' health. Our findings introduce a novel approach to classify the health of rocky reefs under different fishing regimes and therefore resultant community structures. Additionally, our IRH provides insight regarding the potential gains in total fish biomass that may result from the conservation and protection of reefs with more complex geomorphology. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
Reconstructing regional and global trends of reef assemblages have faced limitations mainly due to the different analytical approaches employed. The results of our study show that five community-level indicators can provide a reliable estimation of the status of a given reef across an overall gradient of community assemblages, ranging from unprotected/high fishing pressure to protected/low fishing pressure rocky reefs. Our analysis also identified a minimum set of community indicators needed to assess reef health, predict sizes of some macro-invertebrates, and fish biomass. In addition, if we assume that each reef can be used to represent an ecological stage (from pioneer to climax community) of the overall reefs, our index may be used to describe temporal changes in community structure as well.