Relationships between a common Caribbean corallivorous snail and protected area status, coral cover, and predator abundance

As coral populations decline across the Caribbean, it is becoming increasingly important to understand the forces that inhibit coral survivorship and recovery. Predation by corallivores, such as the short coral snail Coralliophila abbreviata, are one such threat to coral health and recovery worldwide, but current understanding of the factors controlling corallivore populations, and therefore predation pressure on corals, remains limited. To examine the extent to which bottom-up forces (i.e., coral prey), top-down forces (i.e., predators), and marine protection relate to C. abbreviata distributions, we surveyed C. abbreviata abundance, percent coral cover, and the abundance of potential snail predators across six protected and six unprotected reefs in the Florida Keys. We found that C. abbreviata abundance was lower in protected areas where predator assemblages were also more diverse, and that across all sites snail abundance generally increased with coral cover. C. abbreviata abundance had strong, negative relationships with two gastropod predators—the Caribbean spiny lobster (Panulirus argus) and the grunt black margate (Anisotremus surinamensis), which may be exerting top-down pressure on C. abbreviata populations. Further, we found the size of C. abbreviata was also related to reef protection status, with larger C. abbreviata on average in protected areas, suggesting that gape-limited predators such as P. argus and A. surinamensis may alter size distributions by targeting small snails. Combined, these results provide preliminary evidence that marine protection in the Florida Keys may preserve critical trophic interactions that indirectly promote coral success via control of local populations of the common corallivorous snail C. abbreviata.