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

Elizabeth C Shaver,Brian R Silliman,Maite G Bucher,Julianna J Renzi

doi:10.1038/s41598-020-73568-1

Abstract

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.

Highlights

Climate change and human exploitation are driving dramatic declines in reef-building hard corals across the globe[1,2,3]
Total C. abbreviata density and total percent coral cover values for individual sites are given in Supplementary Table S1 online
We found strong, negative correlations with C. abbreviata abundance (P. argus: z10 = − 5.07, P < 0.0001, Fig. 5A; A. surinamensis: z10 = − 5.50, P < 0.0001, Fig. 5B), where an increase of one black margate was associated with a 1.3-fold decrease in snails per m2 and an increase in one spiny lobster was associated with a 1.1-fold decrease in snails per m 2

Summary

Introduction

Climate change and human exploitation are driving dramatic declines in reef-building hard corals across the globe[1,2,3]. Caribbean brain corals preyed upon by C. abbreviata snails were less resilient and more severely damaged following a warming event compared to colonies in which snails were manually removed prior to b leaching[9] Management agencies such as the US National Oceanic and Atmospheric Administration have included manual removals of C. abbreviata as part of their Acropora spp. recovery and management plans, reinforcing the important role these corallivores play in reef d ynamics[32]. Little research has been undertaken to assess the relative importance of both top-down (e.g., predation) and bottom-up (e.g., coral prey) factors on corallivore abundance Despite their global importance and threat to degraded coral populations, we do not fully understand the mechanisms governing local corallivore abundances. Besides the deltoid rock snail Thais deltoidea, which was recently been identified preying on C. abbreviata[34], predatory species have merely been suspected but not been experimentally a ssessed[30,35]

Methods

Results

Conclusion