Corallivory varies with water depth to influence the growth of Acropora hyacinthus, a reef‐forming coral

Abstract

AbstractA long‐held paradigm is that water depth has a strong influence on coral performance mainly due to the rapid attenuation of light. Yet, many factors influence coral performance across reefscapes, including corallivory. How coral demographic performance changes with water depth and the intensity of corallivory has not been tested but is intriguing because fish abundance and community composition change substantially with water depth. We tested the independent and interactive effects of water depth and corallivory on the growth rates of a reef‐building coral, Acropora hyacinthus common throughout the Indo‐Pacific. Our study was conducted on the fore reef of Mo’orea, French Polynesia, where shallower coral populations have recovered more quickly than deeper populations after a major disturbance that culminated in 2010. Contrary to predictions of the light‐attenuation paradigm, water depth (5 vs. 10 vs. 17 m) did not influence coral growth, regardless from what depth corals were collected. However, the effects of corallivory varied by depth as coral predators significantly reduced the growth rates of A. hyacinthus at 5 and 10 m depth, where the abundance of corallivores and rates of corallivory were greatest. There were no effects of predation on coral growth rates at 17 m, where the intensity of corallivory was lowest. Our results imply that corallivory is not a dominant factor establishing the distribution of A. hyacinthus corals across water depth. Instead, we found that partial predation may limit the potential for recovery of A. hyacinthus in relatively shallow water, where this coral is most abundant. As the frequency and intensity of disturbances impacting coral reef ecosystems increase with climate change and other anthropogenic factors, chronic predation on corals by corallivorous fish may play an increasingly important role in coral community recovery.