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

While the expansion of macroalgae on coral reefs is a global concern, the spatial scales and mechanisms through which macroalgae inhibit coral recruitment processes and the role of epilithic bacteria in coral settlement remain inadequately understood. Using tiles preconditioned at three distances of two algal species in both up and down-current directions, we show that macroalgae shape early epilithic bacterial assemblages, with strong effects 1 cm downstream of both algae. When exposing the tiles to larvae of two coral species in ex situ settlement experiments, the coral Acropora pulchra showed reduced larval settlement on cryptic surfaces conditioned 1 cm up and downstream of the alga Dictyota bartayresiana, whereas the coral Pocillopora acuta showed the reverse pattern. Specific bacterial taxa within the families 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 on the reef, recruit survival was consistently reduced closer to, and particularly 1 cm downstream of, D. bartayresiana. These results demonstrate that macroalgae structure coral recruitment processes at centimeter scales through distance- and flow-dependent effects and indicate that these effects may be, at least partially, mediated by epilithic bacterial assemblages.