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.

Removal of corallivorous snails as a proactive conservation tool

Corallivorous snail feeding is a common source of tissue loss for the threatened coral Acropora palmata, accounting for roughly one-quarter of tissue loss in monitored study plots over seven years. However, corallivory by Coralliophila abbreviata is one of the few major sources of partial mortality (contrasting with threats such as bleaching, disease, or storm disturbances) that may be locally managed. We conducted a field experiment to explore the effectiveness and feasibility of snail removal. Long-term monitoring plots on six reefs in the upper Florida Keys were assigned to one of three removal treatments: 1) removal from A. palmata only, 2) removal from all host coral species, or 3) no-removal controls. During the initial removal in June 2011, 639 snails were removed from twelve 150 m2 plots. Snails were removed two additional times during a seven month “removal phase”, then counted at five surveys over the next 19 months to track recolonization. At the conclusion, snails were collected, measured, and sexed. Before-After-Control-Impact analysis revealed that both snail abundance and feeding scar prevalence were reduced in removal treatments compared to the control, but there was no difference between removal treatments. Recolonization by snails to baseline abundance is estimated to be 4.3 years and did not differ between removal treatments. Recolonization rate was significantly correlated with baseline snail abundance. Maximum snail size decreased from 47.0 mm to 34.6 mm in the removal treatments. The effort required to remove snails from A. palmata was 30 diver minutes per 150 m2 plot, compared with 51 minutes to remove snails from all host corals. Since there was no additional benefit observed with removing snails from all host species, removals can be more efficiently focused on only A. palmata colonies, and in areas where C. abbreviata abundance is high, to effectively conserve A. palmata in targeted areas.

Removal of corallivorous snails as a proactive conservation tool

Corallivorous snail feeding is a common source of tissue loss for the threatened coral Acropora palmata, accounting for roughly one-quarter of tissue loss in monitored study plots over seven years. However, corallivory by Coralliophila abbreviata is one of the few major sources of partial mortality (contrasting with threats such as bleaching, disease, or storm disturbances) that may be locally managed. We conducted a field experiment to explore the effectiveness and feasibility of snail removal. Long-term monitoring plots on six reefs in the upper Florida Keys were assigned to one of three removal treatments: 1) removal from A. palmata only, 2) removal from all host coral species, or 3) no-removal controls. During the initial removal in June 2011, 639 snails were removed from twelve 150 m2 plots. Snails were removed two additional times during a seven month “removal phase”, then counted at five surveys over the next 19 months to track recolonization. At the conclusion, snails were collected, measured, and sexed. Before-After-Control-Impact analysis revealed that both snail abundance and feeding scar prevalence were reduced in removal treatments compared to the control, but there was no difference between removal treatments. Recolonization by snails to baseline abundance is estimated to be 4.3 years and did not differ between removal treatments. Recolonization rate was significantly correlated with baseline snail abundance. Maximum snail size decreased from 47.0 mm to 34.6 mm in the removal treatments. The effort required to remove snails from A. palmata was 30 diver minutes per 150 m2 plot, compared with 51 minutes to remove snails from all host corals. Since there was no additional benefit observed with removing snails from all host species, removals can be more efficiently focused on only A. palmata colonies, and in areas where C. abbreviata abundance is high, to effectively conserve A. palmata in targeted areas.

Variabilidad temporal de la abundancia de Coralliophila abbreviata y Coralliophila caribaea (Mollusca, Coralliophilidae) en un arrecife coralino del Parque Nacional Morrocoy, Venezuela

C. abbreviata y C. caribaea son moluscos coralívoros del Mar Caribe. Evaluamos la variabilidad temporal de la abundancia y los cambios en la estructura de talla de C. abbreviata y C. caribaea en Cayo Sombrero, Venezuela (septiembre 2004-agosto 2005). Se colocaron transectas fijas de 50 metros de longitud a profundidades de tres y seis metros cada una, paralelas a la costa. Se evaluó mensualmente durante un año la densidad de ambos depredadores y se seleccionaron 30 individuos de C. abbreviata para medirlos cada mes. Las densidades de C. abbreviata en la transecta somera fluctuaron entre 1.78 ind/m2 en septiembre y 6.26 ind/m2 en mayo; las densidades de C. abbreviata en la transecta profunda estuvieron comprendidas entre 4.23 ind/m2 en enero y 7.66 ind/m2 en mayo. Las densidades de C. caribaea fluctuaron en la transecta somera entre 0 Ind/m 2 (todos los meses menos septiembre) y 0.03 Ind/m2 (septiembre) mientras que la transecta profunda fluctuó entre 0 Ind/m2 (octubre a marzo y julio) y 0.1 Ind/ m2 (abril). La mayoría de los individuos de C. abbreviata midieron entre 12 y 16 mm de longitud. El largo de la mayoría de los individuos de C. caribaea estuvo comprendido entre 10 y 15 mm.