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

Abstract

Abstract. 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.

Fish community structure on coral habitats with contrasting architecture in the Tropical Eastern Pacific

“…However, detailed analysis of the fish species composition and relative abundance in each coral community revealed that preference towards massive or branching coral architectures depends on the fishes' size and trophic preferences. Other authors have arrived at similar conclusions and have also noted the role that the mobility of fishes can play in determining species-habitat associations (Dominici-Arosemena & Wolf, 2006;Benfield et al, 2008;Alvarez-Filip et al, 2011a;Kerry & Bellwood, 2012). Our finding that the MCC sustains a more diverse and even assemblage of conspicuous fish than the BCC, can be explained by the fact that this community was richer in coral species, and hence morphologies, than the BCC.…”

“…Fishes attracted to the BCC had a strong preference for the shelter and food that pocilloporid colonies offer. For instance, the branching colonies promote the presence of small territorial fish (e.g., C. oxycephalus, O. steindachneri) and juveniles of certain species (e.g., P. colonus) as the branches and interstices of ramose corals provide a complex fine-scale microhabitat that effectively shelters them from predators (Beukers & Jones, 1997;Almany, 2004;McCormick & Hoey, 2006;Alvarez-Filip et al, 2011a;Kerry & Bellwood, 2012). Although we did not consider fish sizes in our study, we hypothesize that the fish richness recorded at the BCC (comparable to the one at the MCC) might result from the presence of small juveniles from a wide variety of species that use this type of habitat as refuge during their early life stages.…”

“…Although a strong positive relationship between habitat complexity and species diversity was first observed in terrestrial ecosystems (reviewed by Tews et al, 2004), many studies have also demonstrated strong linkages between properties of fish assemblages and the complexity of marine habitats (e.g., Risk, 1972;Luckhurst & Luckhurst, 1978;Friedlander & Parrish, 1998;Gratwicke & Speight, 2005;Alvarez-Filip, Gill & Dulvy, 2011a).…”

“…Among these habitat features, architectural complexity (defined here as the structure of the physical environment) usually plays the most important role in shaping the richness, diversity, abundance and biomass of reef fish assemblages (Luckhurst & Luckhurst, 1978;McCormick, 1994;Almany, 2004;Alvarez-Filip et al, 2011a). it is believed that a high structural complexity boosts fish diversity because it reduces interspecific competition by providing a greater spectrum of niches and resources.…”

“…The importance of dominant coral morphologies (e.g., tabular, massive, branching) has been highlighted in recent years, because it is an important coral reef attribute that shapes the reefscape architectural complexity and determines habitat usage by reef fishes (Alvarez-Filip et al, 2011a;Messmer et al, 2011;Kerry & Bellwood, 2012). For example, branching coral communities with many interstices are often used by small reef fishes for shelter (Beukers & Jones, 1997), while tabular corals congregate larger reef fishes that seek concealment for ambush predation or shade from sunlight (Kerry & Bellwood, 2012).…”