Tai Chong Toh

Coral community response to bleaching on a highly disturbed reef

While many studies of coral bleaching report on broad, regional scale responses, fewer examine variation in susceptibility among coral taxa and changes in community structure, before, during and after bleaching on individual reefs. Here we report in detail on the response to bleaching by a coral community on a highly disturbed reef site south of mainland Singapore before, during and after a major thermal anomaly in 2010. To estimate the capacity for resistance to thermal stress, we report on: a) overall bleaching severity during and after the event, b) differences in bleaching susceptibility among taxa during the event, and c) changes in coral community structure one year before and after bleaching. Approximately two thirds of colonies bleached, however, post-bleaching recovery was quite rapid and, importantly, coral taxa that are usually highly susceptible were relatively unaffected. Although total coral cover declined, there was no significant change in coral taxonomic community structure before and after bleaching. Several factors may have contributed to the overall high resistance of corals at this site including Symbiodinium affiliation, turbidity and heterotrophy. Our results suggest that, despite experiencing chronic anthropogenic disturbances, turbid shallow reef communities may be remarkably resilient to acute thermal stress.

Augmenting the Post-Transplantation Growth and Survivorship of Juvenile Scleractinian Corals via Nutritional Enhancement

Size-dependant mortality influences the recolonization success of juvenile corals transplanted for reef restoration and assisting juvenile corals attain a refuge size would thus improve post-transplantation survivorship. To explore colony size augmentation strategies, recruits of the scleractinian coral Pocillopora damicornis were fed with live Artemia salina nauplii twice a week for 24 weeks in an ex situ coral nursery. Fed recruits grew significantly faster than unfed ones, with corals in the 3600, 1800, 600 and 0 (control) nauplii/L groups exhibiting volumetric growth rates of 10.65±1.46, 4.69±0.9, 3.64±0.55 and 1.18±0.37 mm3/week, respectively. Corals supplied with the highest density of nauplii increased their ecological volume by more than 74 times their initial size, achieving a mean final volume of 248.38±33.44 mm3. The benefits of feeding were apparent even after transplantation to the reef. The corals in the 3600, 1800, 600 and 0 nauplii/L groups grew to final sizes of 4875±260 mm3, 2036±627 mm3, 1066±70 mm3 and 512±116 mm3, respectively. The fed corals had significantly higher survival rates than the unfed ones after transplantation (63%, 59%, 56% and 38% for the 3600, 1800, 600 and 0 nauplii/L treatments respectively). Additionally, cost-effectiveness analysis revealed that the costs per unit volumetric growth were drastically reduced with increasing feed densities. Corals fed with the highest density of nauplii were the most cost-effective (US

Early onset of zooplanktivory in equatorial reef coral recruits

0.02/mm3), and were more than 12 times cheaper than the controls. This study demonstrated that nutrition enhancement can augment coral growth and post-transplantation survival, and is a biologically and economically viable option that can be used to supplement existing coral mariculture procedures and enhance reef restoration outcomes.

Heterotrophy in recruits of the scleractinian coral Pocillopora damicornis

Scleractinian coral recruits face multiple challenges as theyattempt to meet the metabolic demands for growth anddevelopment post-settlement. Although coral recruits ofsome scleractinian species can obtain zooxanthellae fromtheir parent colonies to enable autotrophy (Richmond 1997),the development of tentacles is essential for the capture ofparticulate matter to supplement the nutrient and energysupply of the growing juvenile coral. However, studiesexamining the onset of zooplanktivory in coral recruits arelimited (Cumbo et al. 2012).In April 2011, gravid colonies of the broadcasting coralAcropora hyacinthus were harvested from the reef off KusuIsland, Singapore (1°13′25′′N, 103°51′38′′E) for ex situspawning and establishment of larval culture (following Tohet al. 2012). The larvae were settled on tiles (2.3 cm×2.3 cm)and the recruits were tagged to determine their age. Using astereomicroscope (Nikon) with a camera setup (Canon), weobservedthat2-day-oldA.hyacinthusazooxanthellaterecruits(n=7) immobilized live 1-day-old Artemia salina naupliiwithin seconds of contact with their tentacles (Fig. 1a). The

Differential Response of Coral Assemblages to Thermal Stress Underscores the Complexity in Predicting Bleaching Susceptibility

Heterotrophy is essential for meeting the metabolic requirements of scleractinian corals but the feeding mechanisms of coral juveniles are poorly understood. In this study, we observed that two-day-old Pocillopora damicornis recruits were able to immobilize and capture Artemia salina nauplii that come into direct contact with their tentacles. The recruits were able to consume up to six nauplii h−1 and the shortest time required to fully ingest one nauplius was 1 min 25 s. This is the first study to describe the feeding mechanisms employed by coral recruits, and provided both observational and quantitative evidence to show that coral juveniles are able to commence heterotrophy at an early stage.

Mass brooding of the blue octocoral, Heliopora coerulea on a sedimented equatorial reef

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.

Spatial variability of fish communities in a highly urbanised reef system

Abstract The octocoral Heliopora coerulea is a gonochoric surface brooder. Although the species is common on shallow Indo-Pacific coral reefs, information on its reproductive biology is limited and spawning timings have only been reported from four locations. We report the first observations of surface brooding in H. coerulea on a sedimented equatorial reef. In April 2014, 46 and 26 brooding colonies were recorded, respectively, from reefs fringing the islands of Kusu and Lazarus in Singapore. The brooded coral larvae were tightly bound to inflated coral polyps, forming a dense white mat which blanketed the brown coral tissue. The inflated polyps also protruded from layers of sediment, which accumulated in colony crevices, such that the brooded larvae were elevated above the settled sediment. Our observations supplement existing knowledge on the reproductive timing of H. coerulea and highlight the adaptations that improve survival of this species on sediment-impacted reefs.

Spatial variability of epibiotic assemblages on marina pontoons in Singapore

Rapid coastal development has generated interest in the ecology of human-modified marine environments. Coastal defence structures such as breakwaters and seawalls are increasingly built to reduce erosion and to mitigate the impacts of sea level rise but knowledge on the marine biodiversity around these structures is lacking. Benthic cover and fish community were surveyed at nine offshore sites, comprising seven coral reefs and two seawalls, in the Singapore’s highly urbanised reef system. A total of 4943 fishes from 70 taxa were recorded, dominated by Pomacentridae (56.5%) and Labridae (17.7%). The results showed a clear spatial variation in the fish community structure across the reefs. The southwestern reefs supported fish communities that were significantly different from those in the south. Generic diversity was significantly higher at the southwestern reefs than the southern ones while the abundance and generic richness were similar. The differences in fish community structure were moderately correlated with the abundance of coralline algae, foliose and submassive corals. The seawall sites supported fish communities different from coral reefs that were adjacent to them. While abundance was similar, the former had higher generic richness and diversity than the latter. The difference in community was attributed to two pomacentrid genera (i.e. Neopomacentrus and Pomacentrus) which were more abundant at the reefs. The findings demonstrated that urbanised coastal ecosystems can contribute to supporting fish diversity.

In situ nurseries enhance coral transplant growth in sedimented waters

Berthing pontoons, one of the most ubiquitous structures in marinas, are known to provide recruitment substrate for a variety of marine biota but little has been reported on their capacity to support epibiotic organisms in tropical marinas, and even less is known about the factors that shape their distribution in such environments. We surveyed the epibiotic assemblages on the sides of pontoons in three Singapore marinas and examined the environmental conditions that influenced their distribution. A total of 94 taxa were recorded, with each marina hosting 43–65 taxa. Assemblages among marinas were highly distinct, and, key discriminants included components of biotic (alcyonarians, hexacorallians, bivalves, and annelids), as well as abiotic (sediment, bare area and shell fragments) origin. While the assemblage variation among marinas was influenced by local environmental conditions (e.g. water motion and sedimentation rate) and pontoon material, the variation in distribution within each marina was best explained by the distance of the pontoons from the marina’s entrance (epibiotic diversity and taxa richness were lower away from the marina entrance). Knowledge on the distribution of epibiotic assemblages on pontoons is essential to identify the factors that contribute to spatial variation and encourage the design and construction of ecologically-friendly marinas. Our findings suggest that improvements to pontoon design and layout would help to augment marina biodiversity, enhance the ecology of urbanised coasts, and mitigate development impacts.

Coral nurseries as habitats for juvenile corallivorous butterflyfish

ABSTRACT 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.