Daisuke Taira

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

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.

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

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 fish communities in a highly urbanised reef system

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

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.

Coral nurseries as habitats for juvenile corallivorous butterflyfish

In reef restoration, in situ coral nurseries function primarily to culture coral material before transplantation is carried out (Rinkevich 2014). These structures can play secondary roles by generating microhabitats that provide shelter and food to reef-associated organisms (Shafir and Rinkevich 2010). However, studies documenting such ecological services are limited (e.g. Shafir and Rinkevich 2010). We report here that coral nurseries established in non-reefal environments can function as habitats for reef-dependent corallivorous butterflyfish, in this case, obligate corallivorous Chaetodon octofasciatus (Bloch, 1787) (Srinivasan 2003). As part of ongoing reef restoration efforts in Singapore, in situ coral nurseries were established on a sandy seabed at 3 m depth adjacent to a seawall along Lazarus Island, Singapore (1°13.49′N, 103°51.14′E) in 2013. The fixed table nurseries were raised 1m above the seabed and the nursery area covered a total of 500 m. There were more than 20 coral species reared at the nursery, including Echinopora lamellosa, Platygyra sinensis and Podabacia crustacea. On 27 November 2015, juvenile C. octofasciatus (<2 cm in total length) were observed swimming among Acropora and Pocillopora colonies (~20 cm diameter) that were reared at the coral nursery (Fig. 1). These juveniles were seen feeding on the coral tissues (see the Supplementary Material). On a subsequent survey (22 December 2015), the density of juvenile C. octofasciatus recorded at the nursery in Lazarus (4.0 individuals/100 m) was twice that in the surveyed area (240m; three 20 × 4m transects) on a nearby reef which was located 600 m away from the nursery (1.7 individuals/100 m; Kusu Island 1°13.32′N, 103°51.33′E). This was surprising since both sites harboured similar densities of Acropora colonies (6.3 colonies/100 m at Lazarus and 5.9 colonies/100 m at Kusu). It was also noteworthy that adult C. octofasciatus were only recorded at Kusu (3.3 individuals/100 m). Competitors such as territorial damselfish (e.g. Pomacentrus littoralis andDischistodus prosopotaenia) were only recorded in Kusu. Thus, the absence of these damselfish at the nursery might have facilitated the recruitment of juvenile C. octofasciatus. Obligate corallivorous butterflyfishes such asC. octofasciatus inhabit coral-rich habitats and their larvae are known to settle exclusively onto live coral colonies, especially those of Acropora (Srinivasan 2003). The propagation of corals in Communicated by B. W. Hoeksema

Egg capsules and veligers of the corallivorous muricid gastropod Drupella rugosa (Born, 1778)

Abstract Population outbreaks of the corallivorous muricid gastropod Drupella can cause significant coral mortality but our current understanding of their early life history, recruitment mechanisms and behaviour is limited. In this study, we observed the deposition of D. rugosa (Born, 1778) egg capsules on bare skeletal surfaces of the scleractinian coral Pocillopora acuta Lamarck, 1816. Each egg capsule measured 2.43 by 2.39 mm and contained an average of 67 embryos. Intracapsular development lasted 15 days post-oviposition, after which free-swimming veliger larvae emerged from the capsule. The larval shells of these veligers with 1⅓ whorls averaged 328 by 245 μm in size. Compared to its congeners, D. rugosa veliger larvae were the largest at hatching. Detailed descriptions of D. rugosa egg capsules and early veligers are provided to supplement current knowledge on reproductive biology and early life history of the species. Such data will provide more insights into understanding and modelling the population dynamics of D. rugosa.

Relocating bleached Platygyra sinensis facilitates recovery from thermal stress during a minor bleaching event

Abstract 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 viable measure to accelerate their recovery. During a mild bleaching event in 2014, eight bleached colonies of P. sinensis were relocated from an affected reef at Sultan Shoal, Singapore, to a reef at Kusu that was less impacted. Another eight colonies at Sultan Shoal were tagged as controls. After five months, 88% of relocated bleached colonies at Kusu showed full recovery whereas only 25% of the control bleached colonies at Sultan Shoal had recovered. The differential coral recovery among the two sites was most likely due to lower seawater temperatures and faster water flow at Kusu, which helped to mitigate the effects of thermal stress on the bleached corals. This relocation study demonstrated that relocating bleached P. sinensis to sites with more favourable environmental conditions is a viable approach to reduce bleaching impacts for this species.

Effects of nursery table slope orientation on coral survival and growth

ABSTRACT 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 slope orientation of nursery tables and the initial size of fragments, clearly differ among species due to their inherent attributes and restoration success will greatly benefit from empirical studies derived from a wider range of species.