Bacterial communities associated with corals out-planted on the Great Barrier Reef are inherently dynamic over space and time

Abstract

Abstract In light of accelerating pressures faced by coral reef ecosystems, coral propagation and out-planting are becoming vital components of reef stewardship strategies aimed to improve reef resilience through enhanced natural recovery and rehabilitation. The coral microbiome has a crucial role in the success of the coral holobiont and can be impacted shortly after out-planting, yet long-term characterisation of the out-plant microbiome, assessment of related survival and how this varies across sites is unexplored. We examined the bacterial communities associated with out-planted Acropora millepora corals and monitored coral survival over 12 months (February 2021-22) across three reef sites – Mojo, Rayban and Sandbox at Opal Reef (16°12'18"S 145°53'54"E), Great Barrier Reef (GBR) – with contrasting environmental features (e.g. exposure to oceanic currents and previous thermal stress impacts). Bacterial communities of out-planted corals exhibited significant changes from donor colonies 7–45 days after out-planting and bacterial community composition differed significantly across sites Sandbox and Rayban with low overall survival (0–43%) versus Mojo with higher (47–75%) overall survival. We interpret the different rate of change of coral associated bacterial community composition after out-planting, site-specific composition of bacterial communities, and differential survival of out-plants across sites to indicate the importance of site-selection in shaping coral bacterial communities and subsequent out-plant success. This research highlights, the need to resolve drivers of small-scale site differences alongside higher resolution spatiotemporal monitoring of environmental conditions to distinguish key drivers of microbial change during out-planting and subsequently inform out-plant site selection to optimise future management efforts.