Live coral cover may provide resilience to damage from the vermetid gastropod Dendropoma maximum by preventing larval settlement

Dendropoma maximum is a vermetid gastropod (a sessile tube-forming snail) commonly associated with living corals throughout shallow-water reefs of the Indo-Pacific. Recent work suggests that, once established, this species can adversely affect growth and survival of corals. Here, we test the hypotheses that disturbances to live coral substrates (e.g., creation of bare patches) facilitate successful larval settlement and subsequent population growth of D. maximum, and conversely, that live coral inhibits D. maximum settlement. In the shallow lagoon of Moorea, French Polynesia, we selected patch reefs where D. maximum was either present or absent (to evaluate potential effects of resident adult conspecifics on recruitment) and established focal quadrats on each reef. In each quadrat, we either experimentally removed 50 % of live coral cover or left the quadrat with 100 % live coral cover. In addition, we deployed units of bare substrate (coral rubble) to each reef. We conducted a census of deployed substrates and quadrats after 6 months and found that D. maximum settled irrespective of resident vermetid populations, and only onto nonliving surfaces (i.e., cleared patches in quadrats, coral rubble, and marine epoxy). In laboratory experiments, we exposed larvae of D. maximum to live coral and found species-specific effects on survival of D. maximum larvae. Porites lobata and Pocillopora sp. killed larvae of D. maximum, Porites rus caused weaker mortality, and Millepora sp. had no effect on larval survival. Collectively, these results suggest that D. maximum requires disturbances that create bare patches to successfully settle onto reefs, and that a high cover of living corals contributes resilience to reefs by limiting settlement opportunities of a species known to reduce coral growth and survival.