Cascading effects of fishing on Galapagos rocky reef communities

Abstract

A replicated comparison of heavily and lightly fished areas in the Galapagos suggested that fishing predators led to an increase in herbivores and a dramatic shift in the algal community toward crustose barrens. We sampled 10 highly fished and 10 lightly fished shallow rocky reefs in the southeastern area of the Galapagos Marine Reserve, Ecuador. Negative associations between con- sumers and resources suggested top-down control. At cold sites, there was a negative association between slate-pencil urchins Eucidaris galapagensis and non-coralline algae. In addition, at cold sites, pencil urchins were less abundant where there were many predators. An indirect positive asso- ciation between predators and non-coralline algae occurred at warm and cold sites. Fishing appeared to affect this trophic cascade. The spiny lobster Panulirus penicillatus, the slipper lobster Scyllarides astori, and the Mexican hogfish Bodianus diplotaenia were significantly less abundant at highly fished sites. Urchin density was higher at highly fished sites. Non-coralline algae were nearly absent from highly fished sites where a continuous carpet of the anemone Aiptasia sp. was recorded and the algal assemblage was mainly structured by encrusting coralline and articulated calcareous algae.