Data and code for "Distance- and direction-dependent effects of macroalgae on early epilithic bacterial assemblages and coral recruitment processes"

Macroalgae could undermine coral recruitment processes by affecting reef biofilms underpinning coral larval settlement and by reducing recruit survival. However, the context-dependency of these effects and the role of epilithic bacteria in coral settlement remain unresolved. Using tiles preconditioned at three distances of two algal species in both up and down-current directions in a field experiment, we show that macroalgae shape epilithic bacterial assemblages, with strong effects 1 cm downstream of macroalgae. By exposing similarly preconditioned tiles to larvae of two coral species in ex situ experiments, we found that coral larvae preferentially settled on cryptic rather than exposed tile surfaces, with a strong decline in settlement Acropora pulchra on cryptic surfaces conditioned 1 cm up and downstream of the alga Dictyota bartayresiana and a reverse pattern Pocillopora acuta. Specific bacterial taxa within the Alteromonadaceae, Flavobacteriaceae Pirellulaceae and Rhodobacteraceae were associated with coral settlement with differences across coral-algal combinations. When tiles with coral settlers were returned to their initial positions, recruit survival was consistently reduced closer to, and particularly 1 cm downstream of, D. bartayresiana. These results highlight distance- and flow-dependent effects of macroalgae on coral recruitment processes mediated by changes in epilithic bacterial assemblages and water-mediated mechanisms.