Organisms that modify the availability of abiotic resources for other species can alter the structure and function of ecological communities through multiple pathways. In Florida Bay, red grouper (Epinephelus morio) engineer habitats by excavating sediment and detritus from karst solution holes and are also predators that consume a variety of benthic crustaceans and fish, some of which colonize engineered habitats. The effect of red grouper on these communities is complex as colonizing species interact with red grouper in different ways, including both direct (e.g., predator–prey) and indirect interactions. Here, I present the results of an experiment designed to test the direct effects of red grouper on faunal communities associated with Florida Bay solution holes by excluding red grouper from solution holes for four weeks. Red grouper presence generally had positive effects on the abundance, richness, and diversity of faunal communities associated with engineered habitats. Few strong interactions were observed between red grouper and colonizing species, mainly juvenile coral reef fishes. These results suggest that by acting as both a predator and habitat engineer, red grouper shape unique communities, distinct from those of surrounding areas, and influence the composition of communities associated with manipulated habitats.

Organisms that either directly or indirectly modify the availability of resources can have profound effects on the structure and function of ecological communities. This holds true for organisms that enhance habitat complexity either as a function of their morphology or through mechanical activities, such as digging or burrowing. The net positive effects of engineers on local species diversity follows from activities that allow more species to live in modified habitats compared to unmodified ones. Here, we present the results of a multiyear observational study evaluating the effects of habitat modifications made by juvenile red grouper, Epinephelus morio (Valenciennes, 1828), on the fishes and motile macroinvertebrates associated with karst solution holes in Florida Bay, FL, USA. Because red grouper have multiple roles in these systems, acting as both habitat engineers and predators that consume a variety of benthic crustaceans and fishes, their influence on associated communities is complex. We found that the presence of red grouper resulted in deeper solution holes, increased abundance and richness of the associated fauna, especially among juvenile coral-reef fishes and motile invertebrates, and significant differences in the structure of faunal communities over time. These results suggest that red grouper shape unique communities, distinct from those of surrounding areas, and strongly influence the composition of communities associated with manipulated habitats.