Disease assessment in 'coral gardening' nurseries in the Maldives and implications for coral restoration success.

Coral diseases are an increasing threat to continuously degrading reefs as disease abundance and virulence are expected to increase in the future. Active conservation measures, specifically coral restoration projects, are increasingly being implemented worldwide. Yet little is known about the implications of disease occurrence in a restoration context. This study describes white syndrome pathogenesis in 2 coral genera, farmed in 2 mid-water rope nurseries located in a reef and a lagoon habitat in the Maldives. Over a 112 d monitoring period, disease metrics were obtained from 336 Pocillopora and 96 Acropora fragments to assess the impacts of unmitigated disease progression in coral nurseries. Disease had low prevalence (2.2%) and incidence (0.007) in reef-farmed Pocillopora, but survival (91%) was significantly reduced in comparison with the unaffected lagoon-farmed Pocillopora (99%). In contrast, lagoon-farmed Acropora showed high disease prevalence (78.5%) and incidence (0.064), and a lower survival (79%) than disease-unaffected reef-farmed Acropora (98%). These findings had distinct implications for coral gardening success. While Pocillopora was considered suitable for outplanting, especially since subsequent mitigation interventions were successful, the diseased, lagoon-reared Acropora posed a potential risk to the restoration site and was unsuitable for outplanting following 1 yr of farming effort. Our findings demonstrate that unmitigated diseases can cause major setbacks to restoration success. Coral gardening projects are likely to be particularly susceptible; therefore, disease monitoring and risk management are imperative. Since there is currently a lack of available diagnostic and mitigative tools, this study aims to provide case study data for restoration practitioners.