Predators drive community structure in coral reef fish assemblages

Abstract

Citation: Boaden, A. E., and M. J. Kingsford. 2015. Predators drive community structure in coral reef fish assemblages.Ecosphere 6(4):46. http://dx.doi.org/10.1890/ES14-00292.1Abstract. The importance of top-down effects in structuring ecological communities has been widely debated by ecologists. One way in which to examine these processes is to study the secondary effects of predator removal on communities. This study examined the role of predatory fishes in structuring communities of coral reef fishes, by using a network of marine reserves (the Great Barrier Reef Marine Park) as a natural experiment. We hypothesized that reefs with high densities of piscivores (marine reserves) would have distinct fish communities from those where piscivores have been depleted through fishing, due to variation in predation pressure. We predicted that predator depletion would result in ''prey release'', and a corresponding increase in prey densities along a gradient of fishing intensity, causing a change in the community composition of reef fishes. To address this, fish counts and habitat surveys were conducted at four locations on the Great Barrier Reef. At each location, comparisons were made amongst three marine park zones that varied in their exposure to fishing practices; no-take marine reserves, limited fishing areas, and open fishing areas.The density and biomass of predators varied consistently among zones at each location. Furthermore, we found strong evidence for prey release at all four locations, resulting in distinct fish assemblages amongst zones. Reefs open to fishing had much lower densities of piscivores, and higher densities of prey and herbivorous fishes compared to marine reserves. This broad pattern was consistent amongst locations, and persisted at the level of species, trophic groups, families and communities. Habitat characteristics did not vary significantly amongst zones in a consistent manner amongst locations. Although habitat relationships were strong for specialist species such as butterflyfishes, densities of predators were stronger predictors of prey density for most species, and the trophic composition of reef fish communities differed significantly amongst zones at all locations. Results from this study support the concept that top-down effects can be strong divers of prey populations and influence community structure in highly diverse systems. These data emphasize the vital role of predators, and reinforce the importance of preserving and restoring top-down trophic interactions in ecological systems.

Influence of predation risk on the sheltering behaviour of the coral-dwelling damselfish, Pomacentrus moluccensis

“…Our results, however, show that the influence of predation risk on behaviour does not always conform to this expectation, underlining the complexity of predicting how changes in predation risk will influence the relationship between damselfish and their host coral. High levels of predation are generally taken as indicators of a healthy ecosystem (Parsons 1992;Jackson et al 2001;Shurin et al 2002;Boaden and Kingsford 2015). Although high levels of predator activity may decrease the strength of damselfish sheltering in their host coral and potentially decrease the benefits host corals can derive from mutualistic damselfish, this unexpected link between predation risk and sheltering behaviour does not appear widespread among coral-associated damselfish.…”

“…Not only does predation act as a top-down regulator of prey population densities, but it is also one of the strongest drivers of prey behaviour and trophic structure of biological communities (Lima and Dill 1990;Ritchie and Johnson 2009;Estes et al 2010;Boaden and Kingsford 2015). Predator abundance and predation intensity can vary in space and time (Bernstein et al 1988;Bosiger et al 2012).…”

“…Sufficient levels of predation are essential for ecosystem functioning and the maintenance of ecological processes (Lima and Dill 1990;Catano et al 2014). Carnivorous coral reef fishes (e.g., piscivores) comprise species-rich assemblages of both long-term inhabitants of the reef habitat and transient visitors (Boaden and Kingsford 2015). Changes or spatial differences in predator biomass and predation rates are likely to have consequences for prey abundance and behaviour (Mumby et al 2012).…”

Trophodynamics as a Tool for Understanding Coral Reef Ecosystems

“…Most trophodynamic studies of coral reefs come from the Caribbean and Great Barrier Reef, which cover large spatial scales and latitudinal gradients. While biogeographic variability is constantly acknowledged, publications link conservation concern to broad topics such as management zones irrespective of reef variability or geographic position Rizzari et al, 2014;Boaden and Kingsford, 2015), and perform large scale analyses based on databases that do not account for fine-scale variation (Campbell and Pardede, 2006;Graham et al, 2008;Campbell et al, 2011;Barneche et al, 2014;Alonso et al, 2015;Aguilar-Medrano and Barber, 2016). While management zones are important to understanding human disturbance, many studies exploring fishing effects lack historical baselines, movement data, and diet relative to changing diversity and community structure (Greenwood et al, 2010;Edgar et al, 2011).…”

“…Documented declines in top predators and keystone species from anthropogenic disturbance (Dulvy et al, 2004;Sandin et al, 2008;Estes et al, 2011) have resulted in exploration of trophic cascades and assessment of ecological roles of predators in coral reef reefs (Heupel et al, 2014;Boaden and Kingsford, 2015;Rizzari et al, 2015;Weijerman et al, 2015;Thillainath et al, 2016). However, identifying trophic cascades is difficult in reef ecosystems.…”