New evidence shows that Pocillopora 'Pocilloporadamicornis-like' corals in Singapore are actually Pocillopora acuta (Scleractinia: Pocilloporidae)

Poleward migration of tropical corals inhibited by future trends of seawater temperature and calcium carbonate (CaCO3) saturation

Poleward range expansion of marine organisms is commonly attributed to anthropogenic ocean warming. However, the extent to which a single species can migrate poleward remains unclear. In this study, we used molecular data to examine the current distribution of the Pocillopora damicornis species complex in Taiwan waters and applied niche modeling to predict its potential range through the end of the 21st Century. The P. damicornis species complex is widespread across shallow, tropical and subtropical waters of the Indo-Pacific regions. Our results revealed that populations from subtropical nonreefal coral communities are P. damicornis, whose native geographical ranges are approximately between 23°N and 35°N. In contrast, those from tropical reefs are P. acuta. Our analysis of 50 environmental data layers demonstrated that the concentrations of CaCO3 polymorphs had the greatest contributions to the distributions of the two species. Future projections under intermediate shared socioeconomic pathways (SSP) 2-4.5 and very high (SSP5-8.5) scenarios of greenhouse gas emissions showed that while sea surface temperature (SST) isotherms would shift northwards, saturation isolines of two CaCO3 polymorphs, calcite (Ωcal) and aragonite (Ωarag), would shift southwards by 2100. Subsequent predictions of future suitable habitats under those conditions indicated that distinct delimitation of geographical ranges for the two species would persist, and neither would extend beyond its native geographical zones, indicating that tropical Taiwan waters are the northern limit for P. acuta. In contrast, subtropical waters are the southern limit for P. damicornis. We concluded that the decline in CaCO3 saturation would make high latitudes less inhabitable, which could be one of the boundary elements that limit poleward range expansion driven by rising SSTs and preserve the latitudinal diversity gradient (LDG) on Earth. Consequently, poleward migration of tropical reef corals to cope with warming oceans should be reevaluated.

Genome-wide analysis to uncover how Pocillopora acuta survives the challenging intertidal environment

Characterisation of genomic variation among corals can help uncover variants underlying trait differences and contribute towards genotype prioritisation in coastal restoration projects. For example, there is growing interest in identifying resilient genotypes for transplantation, and to better understand the genetic processes that allow some individuals to survive in specific conditions better than others. The coral species Pocillopora acuta is known to survive in a wide range of habitats, from reefs artificial coastal defences, suggesting its potential use as a starter species for ecological engineering efforts involving coral transplantation onto intertidal seawalls. However, the intertidal section of coastal armour is a challenging environment for corals, with conditions during periods of emersion being particularly stressful. Here, we scanned the entire genome of P. acuta corals to identify the regions harbouring single nucleotide polymorphisms (SNPs) and copy number variations (CNVs) that separate intertidal colonies (n = 18) from those found in subtidal areas (n = 21). Findings revealed 74,391 high quality SNPs distributed across 386 regions of the P. acuta genome. While the majority of the detected SNPs were in non-coding regions, 12% were identified in exons (i.e. coding regions). Functional SNPs that were significantly associated with intertidal colonies were found in overrepresented genomic regions linked to cellular homeostasis, metabolism, and signalling processes, which may represent local environmental adaptation in the intertidal. Interestingly, regions that exhibited CNVs were also associated with metabolic and signalling processes, suggesting P. acuta corals living in the intertidal have a high capacity to perform biological functions critical for survival in extreme environments.

Dominance of the coral Pocillopora acuta around Phuket Island in the Andaman Sea, Thailand

Pocillopora damicornis (Linnaeus, 1758), a species complex, consists of several genetic lineages, some of which likely represent reproductively isolated species, including the species Pocillopora acuta Lamarck, 1816. Pocillopora acuta can exhibit similar morphological characteristics as P. damicornis, thus making it difficult to identify species-level taxonomic units. To determine whether the P. damicornis-like colonies on the reefs in the Andaman Sea (previously often identified as P. damicornis) consist of different species, we sampled individual colonies at five sites along a 50 km coastal stretch at Phuket Island and four island sites towards Krabi Province, Thailand. We sequenced 210 coral samples for the mitochondrial open reading frame and identified six distinct haplotypes, all belonging to P. acuta according to the literature. Recently, P. acuta was observed to efficiently recolonize heat-damaged reefs in Thailand as well as globally, making it a potentially important coral species in future reefs. Specifically in the light of global change, this study underscores the importance of high-resolution molecular species recognition, since taxonomic units are important factors for population genetic studies, and the latter are crucial for management and conservation efforts.

Bacterial Community Shifts during Polyp Bail-Out Induction in Pocillopora Corals

Polyp bail-out constitutes both a stress response and an asexual reproductive strategy that potentially facilitates dispersal of some scleractinian corals, including several dominant reef-building taxa in the family Pocilloporidae. Recent studies have proposed that microorganisms may be involved in onset and progression of polyp bail-out. However, changes in the coral microbiome during polyp bail-out have not been investigated. In this study, we induced polyp bail-out in Pocillopora corals using hypersaline and hyperthermal methods. Bacterial community dynamics during bail-out induction were examined using the V5-V6 region of the 16S-rRNA gene. From 70 16S-rRNA gene libraries constructed from coral tissues, 1,980 OTUs were identified. Gammaproteobacteria and Alphaproteobacteria consistently constituted the dominant bacterial taxa in all coral tissue samples. Onset of polyp bail-out was characterized by increased relative abundance of Alphaproteobacteria and decreased abundance of Gammaproteobacteria in both induction experiments, with the shift being more prominent in response to elevated temperature than to elevated salinity. Four OTUs, affiliated with Thalassospira, Marisediminitalea, Rhodobacteraceae, and Myxococcales, showed concurrent abundance increases at the onset of polyp bail-out in both experiments, suggesting potential microbial causes of this coral stress response. IMPORTANCE Polyp bail-out represents both a stress response and an asexual reproductive strategy with significant implications for reshaping tropical coral reefs in response to global climate change. Although earlier studies have suggested that coral-associated microbiomes likely contribute to initiation of polyp bail-out in scleractinian corals, there have been no studies of coral microbiome shifts during polyp bail-out. In this study, we present the first investigation of changes in bacterial symbionts during two experiments in which polyp bail-out was induced by different environmental stressors. These results provide a background of coral microbiome dynamics during polyp bail-out development. Increases in abundance of Thalassospira, Marisediminitalea, Rhodobacteraceae, and Myxococcales that occurred in both experiments suggest that these bacteria are potential microbial causes of polyp bail-out, shedding light on the proximal triggering mechanism of this coral stress response.

Nitric oxide production rather than oxidative stress and cell death is associated with the onset of coral bleaching in Pocillopora acuta

Elevated seawater temperatures associated with climate change lead to coral bleaching. While the ultimate causes of bleaching are well understood, the proximate physiological mechanisms underlying the bleaching response are not as well defined. Here we measured nitric oxide synthase activity, oxidative stress, and cell death in algal symbionts (Symbiodinaceae) freshly isolated from the reef-building coral Pocillopora acuta collected in the field under natural non-bleaching conditions and from corals experimentally exposed to elevated temperatures. Nitric oxide synthase activity in the algal symbionts was >3 orders of magnitude higher than that of the host and increased dramatically with increasing temperature and time of exposure (up to 72 h), consistent with the onset of bleaching for these corals. Oxidative stress and cell death among the algal symbionts were highest in coral holobionts exposed to intermediate as opposed to maximal temperatures, suggesting that these mechanisms are not proximal triggers for bleaching in this species. Our results point to nitric oxide production by the algal symbionts, rather than symbiont dysfunction, as a more important driver of coral bleaching under acute thermal stress in this coral.

Scleractinian coral (Cnidaria, Hexacorallia, Scleractinia) diversity of the Mersing Islands, Peninsular Malaysia

We present a comprehensive checklist of scleractinian (hard) corals for the Mersing Islands, Malaysia based on surveys conducted at 24 reefs across protected and unprotected marine areas. A total of 261 species of corals from 16 families and one incertae sedis (Pachyseris spp.) were recorded, along with ten records that are new for the east coast of Peninsular Malaysia. Compared against the IUCN Red List, 46.7% of coral species found in the Mersing Islands were of Least Concern (LC), 29.5% as Near Threatened (NT) and 16.4% Vulnerable (V). Only one recorded species, Pectiniamaxima (Moll & Best, 1984), was listed as Endangered (EN). Baseline species diversity data are essential for the monitoring and management of marine biodiversity, especially within marine protected areas. With both protected and unprotected coral reef areas in the vicinity of the widely scattered Mersing Islands, the diversity and distribution of coral species can be used as the basis for area-based conservation and management strategies. The diversity and abundance of scleractinian corals of each island or area should be surveyed periodically to ensure the appropriate level of protection is afforded to retain scleractinian biodiversity in this region.

A molecular census of early-life stage scleractinian corals in shallow and mesophotic zones

The decline of coral reefs has fueled interest in determining whether mesophotic reefs can shield against disturbances and help replenish deteriorated shallower reefs. In this study, we characterized spatial (horizontal and vertical) and seasonal patterns of diversity in coral recruits from Dabaisha and Guiwan reefs at Ludao, Taiwan. Concrete blocks supporting terra-cotta tiles were placed at shallow (15m) and mesophotic (40m) depths, during 2016-2018. Half of the tiles were retrieved and replaced biannually over three 6-month surveys (short-term); the remainder retrieved at the end of the 18-month (long-term) survey. 451 recruits were located using fluorescent censusing and identified by DNA barcoding. Barcoding the mitochondrial cytochrome oxidase I (COI) gene resulted in 17 molecular operational taxonomic units (MOTUs). To obtain taxonomic resolution to the generic level, Pocillopora were phylotyped using the mitochondrial open reading frame (ORF), resolving eight MOTUs. Acropora, Isopora, and Montipora recruits were identified by the nuclear PaxC intron, yielding ten MOTUs. Overall, 35 MOTUs were generated and were comprised primarily of Pocillopora and, in fewer numbers, Acropora, Isopora, Pavona, Montipora, Stylophora, among others. 40% of MOTUs recruited solely within mesophotic reefs while 20% were shared by both depth zones. MOTUs recruiting across a broad depth distribution appear consistent with the hypothesis of mesophotic reefs acting as a refuge for shallow-water coral reefs. In contrast, Acropora and Isopora MOTUs were structured across depth zones representing an exception to this hypothesis. This research provides an imperative assessment of coral recruitment in understudied mesophotic reefs and imparts insight into the refuge hypothesis.

Strong horizontal and vertical connectivity in the coral Pocillopora verrucosa from Ludao, Taiwan, a small oceanic island

Mesophotic habitats could be sheltered from natural and anthropogenic disturbances and act as reproductive refuges, providing propagules to replenish shallower populations. Molecular markers can be used as proxies evaluating the connectivity and inferring population structure and larval dispersal. This study characterizes population structure as well as horizontal and vertical genetic connectivity of the broadcasting coral Pocillopora verrucosa from Ludao, a small oceanic island off the eastern coast of Taiwan. We genotyped 75 P. verrucosa specimens from three sites (Gongguan, Dabaisha, and Guiwan) at three depth ranges (Shallow: 7-15 m, Mid-depth: 23-30 m, and Deep: 38-45 m), spanning shallow to upper mesophotic coral reefs, with eight microsatellite markers. F-statistics showed a moderate differentiation (FST = 0.106, p<0.05) between two adjacent locations (Dabaisha 23-30 and Dabaisha 38-45 m), but no differentiation elsewhere, suggesting high levels of connectivity among sites and depths. STRUCTURE analysis showed no genetic clustering among sites or depths, indicating that all Pocillopora individuals could be drawn from a single panmictic population. Simulations of recent migration assigned 30 individuals (40%) to a different location from where they were collected. Among them, 1/3 were assigned to deeper locations, 1/3 to shallower populations and 1/3 were assigned to the right depth but a different site. These results suggest high levels of vertical and horizontal connectivity, which could enhance the recovery of P. verrucosa following disturbances around Ludao, a feature that agrees with demographic studies portraying this species as an opportunistic scleractinian.

Barriers and corridors of gene flow in an urbanized tropical reef system

Information about the distribution of alleles among marine populations is critical for determining patterns of genetic connectivity that are essential in modern conservation planning. To estimate population connectivity in Singapore's urbanized equatorial reef system, we analysed single nucleotide polymorphisms (SNPs) from two species of reef-building corals with distinct life histories. For Porites sp., a broadcast-spawning coral, we found cryptic lineages that were differentially distributed at inshore and central-offshore sites that could be attributed to contemporary surface current regimes. Near panmixia was observed for Pocillopora acuta with differentiation of colonies at the farthest site from mainland Singapore, a possible consequence of the brooding nature and relatively long pelagic larval duration of the species. Furthermore, analysis of recent gene flow showed that 60-80% of colonies in each population were nonmigrants, underscoring self-recruitment as an important demographic process in this reef system. Apart from helping to enhance the management of Singapore's coral reef ecosystems, findings here pave the way for better understanding of the evolution of marine populations in South-East Asia.

Among-genotype responses of the coral Pocillopora acuta to emersion: implications for the ecological engineering of artificial coastal defences

Stony corals are promising transplant candidates for the ecological engineering of artificial coastal defences such as seawalls as they attract and host numerous other organisms. However, seawalls are exposed to a wide range of environmental stressors associated with periods of emersion during low tide such as desiccation and changes in salinity, temperature, and solar irradiance. All of these variables have known deleterious effects on coral physiology, growth, and fitness. In this study, we performed parallel experiments (in situ and ex situ) to examine among-genotype responses of Pocillopora acuta to emersion by quantifying growth, photophysiological metrics (F_v/F_m, non-photochemical quenching [NPQ], endosymbiont density, and chlorophyll [chl] a concentration) and survival, following different emersion periods. Results showed that coral fragments emersed for longer durations (>2 h) exhibited reduced growth and survival. Endosymbiont density and NPQ, but not F_v/F_m and chl a concentration, varied significantly among genotypes across different durations of emersion. Overall, the ability of P. acuta to tolerate emersion for up to 2 h suggests its potential to serve as a 'starter species' for transplantation efforts on seawalls. Further, careful characterisation and selection of genotypes with a high capacity to withstand emersion can help maximise the efficacy of ecological engineering using coral transplants.

Nutrient and sediment loading affect multiple facets of functionality in a tropical branching coral

Coral reefs, one of the most diverse ecosystems in the world, face increasing pressures from global and local anthropogenic stressors. Therefore, a better understanding of the ecological ramifications of warming and land-based inputs (e.g. sedimentation and nutrient loading) on coral reef ecosystems is necessary. In this study, we measured how a natural nutrient and sedimentation gradient affected multiple facets of coral functionality, including endosymbiont and coral host response variables, holobiont metabolic responses and percent cover of Pocillopora acuta colonies in Mo'orea, French Polynesia. We used thermal performance curves to quantify the relationship between metabolic rates and temperature along the environmental gradient. We found that algal endosymbiont percent nitrogen content, endosymbiont densities and total chlorophyll a content increased with nutrient input, while endosymbiont nitrogen content per cell decreased, likely representing competition among the algal endosymbionts. Nutrient and sediment loading decreased coral metabolic responses to thermal stress in terms of their thermal performance and metabolic rate processes. The acute thermal optimum for dark respiration decreased, along with the maximal performance for gross photosynthetic and calcification rates. Gross photosynthetic and calcification rates normalized to a reference temperature (26.8°C) decreased along the gradient. Lastly, percent cover of P. acuta colonies decreased by nearly two orders of magnitude along the nutrient gradient. These findings illustrate that nutrient and sediment loading affect multiple levels of coral functionality. Understanding how local-scale anthropogenic stressors influence the responses of corals to temperature can inform coral reef management, particularly in relation to the mediation of land-based inputs into coastal coral reef ecosystems.

Takeaways from Mobile DNA Barcoding with BentoLab and MinION

Since the release of the MinION sequencer in 2014, it has been applied to great effect in the remotest and harshest of environments, and even in space. One of the most common applications of MinION is for nanopore-based DNA barcoding in situ for species identification and discovery, yet the existing sample capability is limited (n ≤ 10). Here, we assembled a portable sequencing setup comprising the BentoLab and MinION and developed a workflow capable of processing 32 samples simultaneously. We demonstrated this enhanced capability out at sea, where we collected samples and barcoded them onboard a dive vessel moored off Sisters' Islands Marine Park, Singapore. In under 9 h, we generated 105 MinION barcodes, of which 19 belonged to fresh metazoans processed immediately after collection. Our setup is thus viable and would greatly fortify existing portable DNA barcoding capabilities. We also tested the performance of the newly released R10.3 nanopore flow cell for DNA barcoding, and showed that the barcodes generated were ~99.9% accurate when compared to Illumina references. A total of 80% of the R10.3 nanopore barcodes also had zero base ambiguities, compared to 50-60% for R9.4.1, suggesting an improved homopolymer resolution and making the use of R10.3 highly recommended.

Gene Expression and Photophysiological Changes in Pocillopora acuta Coral Holobiont Following Heat Stress and Recovery

The ability of corals to withstand changes in their surroundings is a critical survival mechanism for coping with environmental stress. While many studies have examined responses of the coral holobiont to stressful conditions, its capacity to reverse responses and recover when the stressor is removed is not well-understood. In this study, we investigated among-colony responses of Pocillopora acuta from two sites with differing distance to the mainland (Kusu (closer to the mainland) and Raffles Lighthouse (further from the mainland)) to heat stress through differential expression analysis of target genes and quantification of photophysiological metrics. We then examined how these attributes were regulated after the stressor was removed to assess the recovery potential of P. acuta. The fragments that were subjected to heat stress (2 °C above ambient levels) generally exhibited significant reduction in their endosymbiont densities, but the extent of recovery following stress removal varied depending on natal site and colony. There were minimal changes in chl a concentration and maximum quantum yield (Fv/Fm, the proportion of variable fluorescence (Fv) to maximum fluorescence (Fm)) in heat-stressed corals, suggesting that the algal endosymbionts’ Photosystem II was not severely compromised. Significant changes in gene expression levels of selected genes of interest (GOI) were observed following heat exposure and stress removal among sites and colonies, including Actin, calcium/calmodulin-dependent protein kinase type IV (Camk4), kinesin-like protein (KIF9), and small heat shock protein 16.1 (Hsp16.1). The most responsive GOIs were Actin, a major component of the cytoskeleton, and the adaptive immune-related Camk4 which both showed significant reduction following heat exposure and subsequent upregulation during the recovery phase. Our findings clearly demonstrate specific responses of P. acuta in both photophysiological attributes and gene expression levels, suggesting differential capacity of P. acuta corals to tolerate heat stress depending on the colony, so that certain colonies may be more resilient than others.

Lipopolysaccharide treatment stimulates Pocillopora coral genotype-specific immune responses but does not alter coral-associated bacteria communities

Corals are comprised of a coral host and associated microbes whose interactions are mediated by the coral innate immune system. The diversity of immune factors identified in the Pocillopora damicornis genome suggests that immunity is linked to maintaining microbial symbioses while also being able to detect pathogens. However, it is unclear which immune factors respond to specific microbe-associated molecular patterns and how these immune reactions simultaneously affect coral-associated bacteria. To investigate this, fragments of P. damicornis and P. acuta colonies from Taiwan were subjected to lipopolysaccharide (LPS) treatment to stimulate immune responses and measure bacteria community shifts. RNA-seq revealed genotype-specific immune responses to LPS involving the upregulation of immune receptors, transcription factors, and pore-forming toxins. Bacteria 16S sequencing revealed significantly different bacteria communities between coral genotypes but no differences in bacteria communities were caused by LPS. Our findings confirm that Pocillopora corals activate conserved immune factors in response to LPS and identify transcription factors coordinating Pocillopora corals' immune responses. Additionally, the strong effect of coral genotype on gene expression and bacteria communities highlights the importance of coral genotype in the investigation of coral host-microbe interactions.

Responses of urban reef corals during the 2016 mass bleaching event

Predicting the bleaching responses of corals is crucial in light of frequent heat stress events to manage further losses of biodiversity and ecosystem functioning, especially for reefs impacted by urbanisation. We examined if the coral cover and community at various Singapore sites changed during the 2016 global coral bleaching event. Bleaching prevalence varied widely among sites in June 2016, and was best explained by site and coral species. While some sites were minimally impacted, others registered significant decreases in coral cover and community changes persisting till March 2017, when normal colouration was mostly regained by corals. Bleaching susceptibility was associated with larger corallites in hermaphrodites and smaller corallites in gonochores (probably due to the cost of maintaining dual sexual functions in hermaphrodites), and with increasing proximity between polyps (likely because thermal damage would be less contained among polyps with greater physiological integration). However, bleaching resilience-the capacity to regain baseline pigmentation-was poorly explained by the traits studied. Our findings suggest that the interplay between local conditions and species composition strongly affects bleaching outcomes on urbanised reefs, and underscore the utility of coral traits for predicting bleaching responses to help in formulating appropriate management strategies.

From marine park to future genomic observatory? Enhancing marine biodiversity assessments using a biocode approach

Few tropical marine sites have been thoroughly characterised for their animal species, even though they constitute the largest proportion of multicellular diversity. A number of focused biodiversity sampling programmes have amassed immense collections to address this shortfall, but obstacles remain due to the lack of identification tools and large proportion of undescribed species globally. These problems can be partially addressed with DNA barcodes ("biocodes"), which have the potential to facilitate the estimation of species diversity and identify animals to named species via barcode databases. Here, we present the first results of what is intended to be a sustained, systematic study of the marine fauna of Singapore's first marine park, reporting more than 365 animal species, determined based on DNA barcodes and/or morphology represented by 931 specimens (367 zooplankton, 564 macrofauna including 36 fish). Due to the lack of morphological and molecular identification tools, only a small proportion could be identified to species solely based on either morphology (24.5%) or barcodes (24.6%). Estimation of species numbers for some taxa was difficult because of the lack of sufficiently clear barcoding gaps. The specimens were imaged and added to "Biodiversity of Singapore" (http://singapore.biodiversity.online), which now contains images for > 13,000 species occurring in the country.

Allelopathic effects of macroalgae on Pocillopora acuta coral larvae

Allelopathy has been proposed as a key mechanism mediating coral-algal interactions; however, few studies have tested macroalgal allelochemicals on coral larvae. In this study, we examined the effects of crude extracts from four macroalgal species on Pocillopora acuta larvae under different exposure conditions. Larval mortality increased considerably with increasing concentrations of Bryopsis sp., Endosiphonia horrida, and Lobophora sp. extracts. Increasing E. horrida and Lobophora sp. extract concentrations also substantially decreased larval settlement. No detectable effects on larvae were observed in Hypnea pannosa extracts. Further, while larval mortality increased with exposure duration to Lobophora sp. extracts, larval settlement was enhanced at 12 h exposure, but reduced at shorter and longer durations. Our results emphasize that macroalgal chemical effects are highly dependent on macroalgal species and exposure conditions. On reefs dominated by allelopathic macroalgae, the survivorship and settlement of coral larvae are potentially constrained, thereby limiting the recovery of degraded reefs.

Annotated checklist for stony corals of American Sāmoa with reference to mesophotic depth records

An annotated checklist of the stony corals (Scleractinia, Milleporidae, Stylasteridae, and Helioporidae) of American Sāmoa is presented. A total of 377 valid species has been reported from American Sāmoa with 342 species considered either present (251) or possibly present (91). Of these 342 species, 66 have a recorded geographical range extension and 90 have been reported from mesophotic depths (30–150 m). Additionally, four new species records (Acanthastreasubechinata Veron, 2000, Favitesparaflexuosus Veron, 2000, Echinophylliaechinoporoides Veron & Pichon, 1980, Turbinariairregularis Bernard, 1896) are presented. Coral species of concern include species listed under the US Endangered Species Act (ESA) and the International Union for Conservation of Nature’s (IUCN) Red List of threatened species. Approximately 17.5% of the species present or possibly present are categorized as threatened by IUCN compared to 27% of the species globally. American Sāmoa has seven ESA-listed or ESA candidate species, including Acroporaglobiceps (Dana, 1846), Acroporajacquelineae Wallace, 1994, Acroporaretusa (Dana, 1846), Acroporaspeciosa (Quelch, 1886), Fimbriaphylliaparadivisa (Veron, 1990), Isoporacrateriformis (Gardiner, 1898), and Pocilloporameandrina Dana, 1846. There are two additional species possibly present, i.e., Pavonadiffluens (Lamarck, 1816) and Poritesnapopora Veron, 2000.

Molecular assessment of Pocillopora verrucosa (Scleractinia; Pocilloporidae) distribution along a depth gradient in Ludao, Taiwan

It can be challenging to identify scleractinian corals from the genus Pocillopora Lamarck 1816 in the field because of their large range of inter- and intra-specific morphological variation that co-occur with changes in the physical environment. This task is made more arduous in the context of a depth gradient, where light and water current could greatly affect the morphology of the corallum. Pocillopora verrucosa (Ellis & Solander 1786) in Taiwan was previously reported exclusively from shallow waters (<10 m in depth), but a recent observation of this species in the mesophotic zone (>40 m in depth) questions this bathymetric distribution. We used the mitochondrial open reading frame and the histone 3 molecular markers to investigate the vertical and horizontal spatial distribution of P. verrucosa around Ludao (Green Island), Taiwan. We genotyped 101 P. verrucosa-like colonies collected from four depth zones, ranging from 7 to 45 m, at three sites around the island. Of the 101 colonies sampled, 85 were genotyped as P. verrucosa, 15 as P. meandrina, and one specimen as an undescribed Pocillopora species. P. verrucosa was found at all depths, while P. meandrina and the undescribed Pocillopora specimen were limited to 15 m depth. P. verrucosa has a large bathymetric distribution around Ludao and could benefit from the refuge that the mesophotic zone offers. This study illustrates the difficulty of identifying Pocillopora corals in the field and emphasizes the relevance of molecular taxonomy as an important and complementary tool to traditional taxonomy for clarifying vertical and horizontal species distribution. Our results also illustrate the need in conservation biology to target species genetic diversity rather than just species diversity.

A PRELIMINARY CHARACTERISATION OFSYMBIODINIUMDIVERSITY IN SOME COMMON CORALS FROM SINGAPORE

The symbiosis between corals and Symbiodinium dinoflagellates is considered a major driver of the distribution and health of reefs worldwide. This study investigated the genetic identities and diversity of Symbiodinium in seven coral species (Porites lutea, Porites lobata, Acropora millepora, Merulina ampliata, Diploastrea heliopora, Pachyseris speciosa, Pocillopora acuta) from three shallow reefs around Singapore (Kusu Island, Pulau Tekukor, Pulau Satumu). Analyses of 31 colonies using denaturing gradient gel electrophoresis of the nuclear internal transcribed spacer region indicated the dominance of C and D Symbiodinium clades. The latter clade was the predominant symbiont in Pachyseris speciosa collected from Pulau Tekukor but those sampled from Pulau Satumu hosted C27, providing evidence for variable symbiosis in this species. The prevalence of the D clade – noted for their stress tolerance (e.g. to elevated temperatures and sedimentation) – in three of seven coral species examined could underlie the importance of this particular symbiotic relationship for the persistence of Singapore’s impacted reefs. Further characterisation of Symbiodinium communities may provide insights into corals’ response to stress and their bleaching patterns in the future.