No abstract

Coral propagation and out-planting are becoming commonly adopted as part of reef stewardship strategies aimed at improving 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. However, long-term characterisation of the out-plant microbiome in relation to out-plant survival, and how these properties vary across reef sites, is unexplored. Therefore, at three reef sites on Opal Reef, Great Barrier Reef (Mojo, Sandbox and Rayban, 16°12′18″S 145°53′54″E), we examined bacterial communities associated with out-planted Acropora millepora coral and monitored coral survival over 12 months (February 2021–22). Bacterial communities of out-planted corals exhibited significant changes from donor colonies 7 days to 1.5 months after out-planting. Further, bacterial community composition differed for sites Sandbox and Rayban with low overall survival (0–43%) versus Mojo with higher overall survival (47–75%). After initial dissimilarity in bacterial communities of out-plants across sites at 1.5 months, and despite changes within sites over time, out-plants exhibited similar microbial communities across sites at 7 days and 6, 9 and 12 months. We hypothesise these trends reflect how bacterial communities are shaped by rapid changes in local environmental characteristics (e.g. from source to out-planting site), where out-plant bacterial communities ‘conform’ to out-planting site conditions. After initial changes, out-plant bacterial communities may then be under the influence of global environmental conditions—such as annual trends in temperature across seasons. Such outcomes indicate the importance of site selection in shaping initial coral bacterial communities and subsequent out-plant success. Importantly, continued differences in out-plant survival trajectory but similar bacterial communities across sites after 1.5 months indicate that other factors—apart from bacterial community changes—likely govern out-plant success in the longer term. Our 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 (i) microbial change during out-planting and (ii) out-plant survival to subsequently inform out-plant site selection to optimise future restoration efforts.

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.

High-latitude reefs are suboptimal coral habitats, but such habitats are increasingly considered to be potential refugia from climate change for range-shifting coral reef species. Notably, tropical reef fish have been observed along the south-east coast of Australia, but their establishment on temperate rocky reefs is currently limited by winter minimum temperatures and other resource needs, such as structurally complex habitats typical of tropical reefs. Recent expansion of the branching subtropical coral Pocillopora aliciae in rocky reefs near Sydney (34° S) could diversify the architectural structure of temperate marine environments, thereby providing potential shelter for tropical reef taxa in warming seas. Here, we investigated whether future environmental conditions (i.e. temperature increase) can influence the dominance of the subtropical branching coral P. aliciae over the resident encrusting coral Plesiastrea versipora in coastal Sydney by characterising physiological (e.g. metabolic stability) and behavioural (e.g. interspecific competitive hierarchy) traits that contribute to their competitive fitness. Our results suggest that a metabolic response, mediated by sterol and lipid metabolic pathways and provision of antioxidants, allows P. aliciae to reduce cellular stress and withstand exposure to short-term increased temperature. Conversely, P. versipora was more susceptible to heat exposure with no metabolic mediation observed. While P. versipora displayed greater aggressive behaviour when in direct contact with P. aliciae under all temperature conditions, the superior physiological and metabolic flexibility under increased temperatures of P. aliciae suggests that this species will likely outperform P. versipora under future increased temperatures. Such contrasting responses to environmental change would facilitate shifts in coral community and functional composition that could support further tropicalisation of coastal New South Wales.

This erratum is published as incorrect file format for the ESM was used and has now been corrected.Original article has been updated.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.