Williams, D., Cameron, C., Miller, M. W.

Effectiveness of corallivorous snail removal

2011

NOAA

SEFSC PRBD-2011-11

10

Interim Report

"There has been a marked decline in the abundance of the Caribbean elkhorn coral, Acropora palmata in recent decades. Natural and anthropogenic factors such as disease, storm damage, and bleaching interact synergistically to affect the health and abundance of these corals. However, the effects of predation by invertebrates on corals in the Florida Keys and Caribbean are often overlooked as a major source of disturbance on corals. The corallivorous snail, Coralliophila abbreviata, can be found grazing on at least 14 species of scleractinian corals in the Caribbean (Miller, 1981) including coral genera Acropora, Montastraea, Diploria, and Agaricia. Acropora palmata appears to be a preferred host for C. abbreviata, supporting faster growth and higher fecundity compared to other coral hosts (Johnston and Miller, 2007). Coralliophila abbreviata can consume A. palmata tissue at a rate of up to 16 cm2 snail-1 day-1 (Brawley and Adey, 1982) and may account for ~25% of chronic tissue loss on A. palmata colonies in the Florida Keys (Williams and Miller, in press). These predators may indirectly contribute to further live tissue loss by vectoring disease conditions among host colonies (Williams and Miller, 2005, Sutherland et al., 2010) or even attracting other predators such as butterflyfish (Brawley and Adey, 1982). Because the snails are fairly sedentary predators, remaining on a single host colony for weeks or longer (as long as live tissue remains available) we proposed that snail removal could prove to be a useful management strategy for decreasing the amount of predation on corals as well as possibly reducing the spread of diseases. We initiated a pilot experiment to characterize the costs and benefits of manually removing snails at a moderate spatial scale (150m2 plots), replicated at six sites in the upper Florida Keys. This interim report describes the effort expended and effectiveness in terms of maintaining reduced snail densities and decreasing predation. The effectiveness in terms of overall A. palmata colony fate is being evaluated within our long-term A. palmata monitoring effort and will be reported in the future."

FY2011 CRCP Project ID 20727; Project Title: O171 Evaluation of ESA listed Acropora spp. Status and Actions for Management and Recovery; Principal Investigator: Margaret W. Miller