DOI: 10.5281/zenodo.18555090
title: Data and code for "Distance- and direction-dependent effects of macroalgae on early epilithic bacterial assemblages and coral recruitment processes"

description: 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.
description: Pairs of tiles were conditioned in situ during 3 weeks at three distances (1, 10 and 100 cm) and two directions (upstream and downstream) relative to Dictyota bartayresiana and Turbinaria ornata. In each pair, one tile was sampled for epilithic bacterial assemblages (16S rRNA amplicon sequencing), and the other was used for ex situ settlement experiments. Following settlement, tiles were returned to their original field locations to monitor post-settlement survival. 

Three supplementary datasets cited in the manuscript are available : 



Dataset1 (asv_table_seq.csv) : raw bacterial ASVs counts across all samples along with their taxonomic information (Kingdom, Order, Class, Family, Genus)

Dataset2 (recruitment_data.xlsx): settlement and post-settlement survival data. The number of settlers counted on each tile surfaces during the settlement experiment. The number of living recruits on the cryptic surfaces were tracked at day 7, 21, 46 and 70 post-settlement.

Dataset3 (maaslin3_results.xlsx): results from the Maaslin3 models to identify the specific bacterial ASVs that correlated coral settlement. Four analysis, corresponding to each of the four coral-macroalgal combinations, were run --> Acropora x Dictyota, Acropora x Turbinaria, Pocillopora x Dictyota and Pocillpora x Turbinaria. 


To replicate the statistics and figures from the paper, please use the following scripts and data : 

Epilithic bacterial assemblages



script : microbiome_tile.Rmd

data: ps.filt.tile.rds (phyloseq object with processed and cleaned data)


Associations between ASVs and coral settlement 



script: settlement_asv.Rmd

data: settlement_data_apul.csv; settlement_data_pacu.csv; asv_dict_settle_core.csv and asv_dict_settle_core.csv. Rownames correspond to the tile pair. 


Recruitment analysis



script: recruitment_analysis.Rmd

data: Dataset2_recruitment_data.xlsx