Reef Predators Thin Fish Ranks But Don't Pick Favorites—Except the Invasive Ones

Our meta-analysis of ten predation experiments on coral reefs reveals how mesopredators affect the diversity of young reef fish communities. We analyzed every published field experiment where researchers had manipulated predator presence on artificial reefs and tracked what happened to recruiting fish communities.

We found that across all studies, reefs with mesopredators had 60% lower fish abundance and 35% lower gamma diversity. Alpha diversity—the number of species within individual patches—dropped by 36%. At first glance, this looked like ecological disaster. But when we used rarefaction to account for the fact that fewer total fish automatically means fewer species detected, the story changed completely. Rarefied alpha diversity showed virtually no change. Beta diversity increased by 15% in the presence of predators, but this effect also disappeared after rarefaction.

What struck us most was how consistent this pattern was across different predator species and reef systems. The mesopredators were acting as generalists, eating fish in proportion to their abundance rather than selectively targeting particular species. However, invasive predators may represent a different concern. The peacock grouper, intentionally introduced to Hawaii, has become a numerically dominant mesopredator in invaded communities. The lionfish invasion in the Atlantic represents another case where non-native predators might have fundamentally different impacts.

Our findings have important implications for coral reef conservation. We found that most native mesopredators don't seem to cause disproportionate biodiversity loss—they're more like lawnmowers than selective weeders. However, invasive predators may pose greater threats to reef biodiversity.

As climate change and human impacts continue reshaping reef communities, we need to understand not just whether predators reduce diversity, but how different types of predators might interact with other stressors.

Citation

Stier, Adrian C.; Stallings, Christopher D.; Samhouri, Jameal F.; Albins, Mark A.; Almany, Glenn R. (2017). Biodiversity effects of the predation gauntlet. Coral Reefs.

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