Coral density and predation affect growth of a reef-building coral
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Coral density and predation affect growth of a reef-building coral A. A. Shantz • A. C. Stier • J. A. Idjadi
Received: 8 April 2010 / Accepted: 5 November 2010 / Published online: 21 November 2010 Ó Springer-Verlag 2010
Abstract The influence of predation on the growth of stony corals has gained increased attention, although the degree to which coral conspecific density can modify the effects of corallivores remains poorly studied. Here, a field experiment was used to quantify the independent and combined effects of coral colony density and coral predators on the skeletal growth of massive Porites. Predator exclusion increased coral growth by 20%. Increasing coral density increased growth by 30%. However, the effect of predators was independent of coral density. Possible alternative mechanisms for increased skeletal growth at higher colony density include changes in near-field flow, resulting in increases in photosynthetic activity, nutrient uptake, or the increased accessibility of coral mutualists. Keywords Predation
Corallivore Density dependence Porites
Communicated by Environment Editor Prof. Rob van Woesik
Electronic supplementary material The online version of this article (doi:10.1007/s00338-010-0694-2) contains supplementary material, which is available to authorized users. A. A. Shantz (&) Northeastern University, Marine Science Institute, Nahant, Massachusetts 01908, USA e-mail: [email protected] A. C. Stier Department of Biology, University of Florida, Gainesville, Florida 32611-8525, USA J. A. Idjadi Department of Biology, Eastern Connecticut State University, Willimantic, CT 06226, USA
Introduction Stony coral colonies often occur in high densities, which can affect their growth, competitive ability, and survival by modifying abiotic (Thomas and Atkinson 1997; Sebens et al. 2003; Reidenbach et al. 2007) or biotic (Idjadi and Karlson 2007) conditions. For example, Vermeij and Sandin (2008) showed a positive effect of conspecific density on the mortality of recently settled Siderastrea radians, and evidence suggests that heterospecific aggregation in adult fungiid corals can depress growth rates (Elahi 2008). Similarly, studies of population regulation theory highlight the importance of prey density as a modifier of predator–prey interactions via processes such as predator dilution/aggregation and predator swamping (Murdoch 1994). Yet, despite the fact that corallivores are well known to affect the demography of corals (Meesters et al. 1994; Aeby and Santavy 2006; Cole et al. 2008; Pratchett et al. 2009), few studies have explored how the size of coral aggregates affects predation on stony corals. A rare exception was a recent study in which Jayewardene et al. (2009) quantified predation rates via grazing scars on Porites compressa transplants placed in differing densities of existing live coral. This study found lower bite frequencies at higher coral densities, which was evidence of predator dilution. However, some coral predators (e.g., butterfly fishes) are cryptic in their foraging (e.
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