Complex reef architecture supports more small-bodied fishes and longer food chains on Caribbean reefs

Coral community shifts towards reefs dominated by stress-resistant corals have contributed to rapid declines in the architectural complexity of reefs throughout the Caribbean. Complex reef architecture provides important niches and refuges for many reef fishes and thus widespread declines in reef complexity could have important consequences for the structure and function of fish assemblages. We explore the influence of reef architecture on fish assemblages by comparing the size and trophic structure of reef fishes along a 20 km-long 15-reef gradient of coral cover, coral species dominance and architectural complexity in Cozumel, Mexico. Our results show that reefs with high architectural complexity, in particular those dominated by robust Montastraea corals, supported fish assemblages with larger numbers of individuals in the smallest size classes (<20 cm) and longer food chains (higher mean trophic levels). The association between coral complexity and fish communities is highly size-structured and is greatest for smallest size classes. The greater abundance of both small fish and the key early life stages of larger fishes on more complex reefs suggests that architectural complexity may influence entire reef fish assemblages, even though larger fish are less dependent on reef complexity. Key reef-building corals such as Montastraea are thus likely to be disproportionately important for maintaining reef fish communities, and shifts in Caribbean coral communities may compromise fish recruitment and truncate food chains, reducing resilience and inhibiting reef recovery from degradation.