Consistent deleterious effects of vermetid gastropods on coral performance

The strength of species interactions is a key driver of ecological dynamics, yet relatively little is known about spatial, temporal, or among-individual variation in interspecific interactions. Here, we evaluate variability in the strength of interactions between a guild of sessile vermetid gastropods and a reef-building coral, Pocillopora verrucosa. Vermetid gastropods are sessile, tube-building snails that feed on drifting particulate matter via extruded mucus nets. Previous work indicates that vermetids can reduce growth and survival of neighboring coral colonies, though the generality of this result (e.g., among coral genotypes, and across environmental gradients) is unknown. Here, we manipulated the presence/absence of vermetids on 10 patch reefs within each of 6 field sites, and quantified the growth and survival of small transplanted corals (taken from three distinct colonies) over 155 days. Two-way ANOVA indicated that vermetids had deleterious effects on both coral growth and survival, and that these effects did not vary substantially across sites spanning an area of ~ 350 ha. Generalized linear mixed models were used to account for correlated responses of corals across environmental gradients, and these analyses indicated that the effects of vermetids were also consistent among coral colonies (i.e., putative genotypes that likely differed in phenotype, zooxanthellae/microbial composition, environmental history, etc.). Deleterious effects of vermetids on corals thus appear to be consistent in space and across coral colonies.

► Vermetid gastropods are poorly studied members of coral communities.
► Hierarchical field experiments confirm deleterious effects of vermetids on corals.
► Effects of vermetids were consistent across six sites and three putative genotypes.
► Results suggest coral populations may be universally prone to vermetid effects.