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The recovery of bleached corals is crucial in ensuring the persistence of the coral reef ecosystem function. This study investigated whether relocating bleached Platygyra sinensis colonies was a vi...

Transplanting nursery-reared corals is among one of the most common approaches to assist the recovery of degraded reefs. The nursery phase is considered essential for providing a favourable environment for coral fragments to grow into suitable sizes before transplantation to natural reef substrates. Several types of coral nursery designs have been used, but the effect of nursery table slope orientation on survival and growth of coral fragments has not been fully evaluated. Survival and growth of coral fragments from four species (Pectinia paeonia, Podabacia crustacea, Pocillopora acuta, Merulina ampliata) on three inclinations of nursery table top (horizontal (0°), diagonal (45°) and vertical (90°)) were monitored over six months. The effects of slope orientation on survival and growth of fragments were not significant among species except P. acuta, for which survivorship and growth decreased significantly only on vertical nursery tables. The conditions required for coral propagation, such as slop...

Seawalls, which have replaced many natural shorelines in coastal cities, are increasingly built to alleviate the impacts of rising sea levels. To mitigate the consequential loss of biodiversity, novel approaches such as ecological engineering have been adopted to enhance the biodiversity on these artificial structures. However, the majority of research to date has focused on physical modifications of intertidal seawalls, and such habitat enhancement efforts are labour- and cost-intensive. We examined the feasibility of transplanting nursery-reared scleractinian corals on subtidal seawalls in Singapore with the help of volunteers. Fragments of six hard coral species (Pocillopora damicornis, Hydnophora rigida, Merulina ampliata, Podabacia crustacea, Echinopora lamellosa, Platygyra sinensis) were tested. Fragments of all species fared well in the nurseries with a mean survival rate of 98.5% and 1.1 to 4-fold increase in live tissue area. Six months after transplantation to a seawall, only 50% of P. damicornis transplants survived, while those of M. ampliata decreased in size. Transplants of the other four species exhibited sustained growth and high survival rates (>90%), suggesting that they were more suitable than the former two species as candidates for transplantation onto subtidal seawalls. Scleractinian cover at the transplant site increased from 3% to 20% and generic richness increased from two to eight. The estimated project costs were almost US$ 23,000 if only researchers were involved in the effort, but the inclusion of volunteers in fieldwork and data analyses could help to bring the expenditure down by up to 23%. The study demonstrated the feasibility of transplanting corals onto subtidal seawalls to mitigate the impacts of coastal development, and highlighted its potential for application on other artificial structures. The findings also show that synergy between the community and scientists helps to reduce overall costs and is beneficial for biodiversity enhancement initiatives.

In situ nurseries have been a crucial part of coral reef restoration initiatives for the past two decades. However, the advantages over direct transplantation in sedimented waters has yet to be examined. In the present study, we showed that Pachyseris speciosa and Pocillopora damicornis fragments reared in in situ nurseries (NR) in Singapore’s sedimented waters grew significantly faster (by three to five times) than those which were directly transplanted (DT) onto the substrates. The increased growth rate during the nursery phase augmented the size of NR transplants, and had a flow-on effect on their performance during the post-transplantation phase. Overall, the maximum diameter of the NR transplants was 1.8–2.7 times larger than DT transplants after 11 months. The growth enhancement of the nursery-reared transplants improved the cost-effectiveness of our restoration effort: the estimated cost per centimetre growth of NR transplants was one-fifth of the DT corals despite the additional costs incurred to construct the nurseries. These results highlight that coral nurseries are beneficial to reef restoration in chronically sedimented waters.

Coral bleaching events have been predicted to occur more frequently in the coming decades with global warming. The susceptibility of corals to bleaching during thermal stress episodes is dependent on many factors and an understanding of these underlying drivers is crucial for conservation management. In 2013, a mild bleaching episode ensued in response to elevated sea temperature on the sediment-burdened reefs in Singapore. Surveys of seven sites highlighted variable bleaching susceptibility among coral genera-Pachyseris and Podabacia were the most impacted (31% of colonies of both genera bleached). The most susceptible genera such as Acropora and Pocillopora, which were expected to bleach, did not. Susceptibility varied between less than 6% and more than 11% of the corals bleached, at four and three sites respectively. Analysis of four of the most bleached genera revealed that a statistical model that included a combination of the factors (genus, colony size and site) provided a better explanation of the observed bleaching patterns than any single factor alone. This underscored the complexity in predicting the coral susceptibility to future thermal stress events and the importance of monitoring coral bleaching episodes to facilitate more effective management of coral reefs under climate change.