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Response of Singapore reefs to land reclamation

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... Corals in Singapore persist in a harsh environment created by chronic anthropogenic disturbances. Decades of coastal development, land reclamation and shipping activities have resulted in the release of large volumes of sediments into the surrounding marine environment [45,46]. Sedimentation rates and values for total suspended solids in Singapore exceed thresholds considered 'optimal' for most tropical reefs [46,47]. ...
... However, there are shallow fringing coral reefs around most of the southern islands, characterized by a shore-adjacent reef flat leading seaward to the reef crest and upper reef slope down to~8 m depth. This depth restriction is primarily due to relatively low light levels as a result of high sedimentation and siltation [45,46]. Consequently, suitable habitat for coral settlement is also restricted to these limited reef areas [54]. ...
... Settlement and early post settlement processes are also greatly influenced by anthropogenic impacts such as high sedimentation, which can reduce substrate availability and smother recently settled spat, and high turbidity, which reduces light and subsequent growth (see review by [31]). Considering both high sedimentation and high levels of suspended sediment reported for Singapore [45,46], it is likely that these processes are influencing rates of settlement and potentially disrupting post settlement processes on Singapore's reefs, and therefore require further examination. ...
Article
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Processes occurring early in the life stages of corals can greatly influence the demography of coral populations, and successful settlement of coral larvae that leads to recruitment is a critical life history stage for coral reef ecosystems. Although corals in Singapore persist in one the world's most anthropogenically impacted reef systems, our understanding of the role of coral settlement in the persistence of coral communities in Singapore remains limited. Spatial and temporal patterns of coral settlement were examined at 7 sites in the southern islands of Singapore, using settlement tiles deployed and collected every 3 months from 2011 to 2013. Settlement occurred year round, but varied significantly across time and space. Annual coral settlement was low (~54.72 spat m-2 yr-1) relative to other equatorial re
... Extensive land reclamation has transformed the coastline over the last century (Corlett, 1992;Lai et al., 2015), expanding Singapore's total land area by > 50% (Tan et al., 2016) but also increasing turbidity and sedimentation in surrounding marine habitats (Hilton and Manning, 1995). Sediment inputs from land reclamation and coastal construction far outweigh those from fluvial sources (van Maren et al., 2014) and are estimated to have reduced average visibility from 10 m to 2 m distance since 1960 (Chou, 1996). Additionally, Singapore's port is among the busiest in the world (Chou, 2006), as the port of call for over 500 large commercial vessels every month (Lim et al., 2017) and with a throughput of nearly 30 million shipping containers every year (Yap and Lam, 2013). ...
... Even for sediment-tolerant taxa, high sediment loads and light limitation in Singapore waters can alter calice morphology, reduce growth rates, and limit other aspects of coral condition (Ow and Todd, 2010;Browne et al., 2015). Total reef area in Singapore has declined considerably during the 20th century (Chou, 1996). Using historical maps, Hilton and Manning (1995) estimated that the total area of intertidal reefs in Singapore decreased from 32.2 km 2 in 1922 to 30.5 km 2 in 1953. ...
... A subsequent analysis by Lai et al. (2015) indicated further decreases to 17 km 2 in 1993 and 9.5 km 2 in 2011. There have also been widespread losses in the subtidal reef zone as large areas of subtidal reef have been covered by sediments and artificial structures as a result of dredging and land reclamation (Low and Chou, 1994;Chou, 1996). This has coincided with considerable decreases in coral cover at reef sites that remain, particularly for deeper habitats. ...
Article
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Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas.
... The marine environment is an important resource that supports one of the world's busiest ports and one of the largest oil refi neries (Chou, 2006). Close to 60% of the total coral reef areas of Singapore has been lost through foreshore land reclamation, while the remaining reefs are exposed to stress from the high sediment load (Chou, 1996;Dikou & van Woesik, 2006) and concerns have been raised regarding the conservation of these reefs (Todd & Chou, 2005;Chou & Tun, 2007). A mass bleaching event occurred in 1998 on a scale previously unknown (http://coralreef.nus.edu.sg/; ...
... Thus, we suggest that the environmental conditions prevailing in Singapore have led to the paucity of Xeniidae, which require high-clarity water (Fabricius and McCorry, 2006). Notably, the collection data for the zooxanthellate octocorals found in the current study indicated that none of them were collected below 4- 6 m, probably similarly due to the water turbidity and the heavy sedimentation load in Singapore (Chou, 1996;Dikou & van Woesik, 2006;Goh et al., 2009). Hence, it is also not surprising that most of the species recorded in the current survey are typical shallow reef dwellers (i.e. ...
... Because the octocorals of Singapore have experienced degradation and loss due to both natural and anthropogenic pressures (Chou, 1996;Dikou & van Woesik, 2006;Goh et al., 2009), it is imperative to include them in a long-term monitoring programme in the region, and to expand such a programme to nearby sites. Undoubtedly, octocoral diversity is indicative of the state of the reef and changes in their species composition may illuminate the changing state of the health of the reef. ...
Article
Octocorallia (Cnidaria: Anthozoa) from Singapore were collected and identifi ed in a survey conducted in 1999. Colonies collected previously, between 1993 and 1997, were also studied. The entire collection of ~170 specimens yielded 25 species of the families Helioporidae, Alcyoniidae, Paraclcyoniidae, Xeniidae and Briareidae. Their distribution is limited to six m depth, due to high sediment levels and limited light penetration. The collection also yielded Cladiella hartogi, a new species (family Alcyonacea), which is described. All the other species are new zoogeographical records for Singapore. A comparison of species composition of octocorals collected in Singapore between 1993 and 1977 and those collected in 1999 revealed that out of the total number of species, 12 were found in both periods, whereas seven species, which had been collected during the earlier years, were no longer recorded in 1999. Notably, however, six species that are rare on Singapore reefs were recorded only in the 1999 survey and not in the earlier ones. It is not yet clear whether these differences in species composition indeed imply changes over time in the octocoral fauna, or may refl ect a sampling bias. The inclusion of octocorals in Singapore reef-monitoring programs will undoubtedly shed light on possible temporal changes in their species composition. The fi ndings do indicate, however, that the fl eshy octocoral fauna of Singapore is rather impoverished compared to other reefs in the region.
... From 1962 to 1992 Singapore reclaimed 59.5 km 2 of land from the sea and continues to do so at a similar rate (Hilton & Manning 1995). These massive projects, combined with terrestrial run-off and the regular dredging of shipping lanes, have reduced the average visibility from 10 m in the 1960s to less than 2 m in 1996 (Chou 1996) and produced a sediment gradient with levels that decline with increasing distance from the mainland (Low & Chou 1994). ...
... Completely submerged at high tide, Cyrene is a large patch reef situated at the division of 2 shipping fairways. The sediment produced by continual dredging of the shipping lanes severely impacts the reefs and live coral cover is low (Chou 1988(Chou , 1996. Shorebased building projects, and the outflow from 2 rivers only 4 km away, also contribute sediment loads (Goh & Chou 1992). ...
Article
Environment-dependent variation in the morphological, physiological, or behavioural expression of a genotype is termed phenotypic plasticity. To test for small-scale morphological plasticity in the Indo-Pacific massive corals Favia speciosa (Dana, 1846) and Diploastrea heliopora (Lamark, 1816), fragments (clone-mates) from 12 colonies of each species were reciprocally transplanted among 6 new habitats located within 2 environmental gradients: a depth cline and a nearshore-to-offshore gradient in sedimentation rates and total suspended solids (TSS). After 7 mo, all fragments were collected, cleared of tissue, and 10 morphometric characters extracted from randomly chosen corallites. Reaction norms, analysis of variance, and canonical discriminant analysis describe environment-induced changes in corallite architecture. These changes are more pronounced in the depth cline than along the sediment gradient. Similarity of response is suggested by exploratory factor analysis where, for both species, size attributes dominate the first factor, antisymmetry the second, and corallite exsertion the third. Highly significant genotype x environment interactions for F speciosa indicate that, for this species, genotypes vary in the level of plasticity expressed. Light and TSS emerge as the primary correlates influencing morphological change, although other parameters might act additively, synergystically or antagonistically with them. In shallow waters, increased corallite exsertion may enhance light capture or, alternatively, protect the central (oral disc) area of each polyp from harmful UV radiation. Morphological variability, combined with environment-induced changes in pigmentation, could impede accurate identification of these taxa.
... Sewage and industrial waste treatment are also under control. However, the globally important port has taken a substantial toll on coral reefs (Chou, 1996). During the past four decades, Singapore has engaged in extensive land reclamation and coastal development projects. ...
... The waters around Singapore have been heavily affected by an increased sediment load over the past 50 years; sedimentation rates ranged from 3–6 mg/cm -2 day 1 in 1979 to 20–30 mg/cm 2 /day at certain sites in 1994 (Lane, 1991). Consequently visibility has been drastically reduced from more than 10 m in the 1960s to less than 2 m presently at certain sites (Chou, 1996).Fig. 1) at various distances from the mainland. Each site was visually surveyed during a onehour dive from deep to shallow water. ...
Conference Paper
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The coral reefs of the densely populated Republic of Singapore, present an interesting scenario to compare the effects of a particular form of human disturbance, namely land reclamation and related sedimentation processes. We present ail exploratory study from a detailed survey where sponge assemblages were assessed at 21 sites associated with patch reefs at various distances from the city of Singapore. The variation in species composition across the study area was analysed with two multivariate techniques. We identified a total of 82 sponge species belonging to 43 genera and 27 families of which Cinachyrella australiensis, Neopetrosia chaliniformis, Oceanapia sagittaria and Xeslospongia testudinaria were the most common species. The number of sponge species found in each of the 21 Surveyed sites varied substantially, namely between 12 and 38 species. Sponge assemblages at the coral reefs of Singapore were not homogeneous, and were not structured according to an in- to offshore gradient as seen in other coral reefs. There does appear to be a tendency for more disturbance-adapted assemblages in sites to the east (around St John's island) and south (Raffles Lighthouse) and more diverse sponge assemblages in the west of the study area. The Singaporean sponge communities appear to be composed of sediment and low-light resistant species, however, it is expected that ongoing chronic stress of sedimentation will probably continue to alter sponge communities.
... The omnipresent anthropogenic threats call for increased urgency to apply effective management strategies, monitoring tools and criteria to manage seagrass. Adopting appropriate monitoring tools to document seagrass distribution in Singapore is especially important as the waters are characterized by high levels of sedimentation and turbidity (Chou, 1988a;1996). Other challenges include the extent and inaccessibility of the offshore seagrass areas which, together with the limited duration of spring low tides, require effective monitoring tools to detect loss and also short-term detection methods that are accurate and precise. ...
... Meanwhile, reclamation at Pulau Ubin has been deferred for as long as the island is not required for development (MND, 2002), hence the presence of Halophila ovalis complex along the northern shore which was last seen in 2003 herbarium records, remains to be verified (Table 12.3). Pulau Tekong Kechil was reclaimed in the mid-1990s and merged together with the larger Pulau Tekong Besar (Omar, 2007c), and records of seagrass last seen at Kechil by Loo et al. in 1994 and1996 are likely lost to reclamation. Meanwhile the other areas at the northeastern and western coastlines of the reclaimed Pulau Tekong, as well as other smaller surrounding islands such as Pulau Unum (partially reclaimed) and Beting Bronok are at risk of disappearing given the massive on going reclamation at Pulau Tekong (MPA, 2010). ...
Chapter
The management of marine habitats in Singapore faces conflicting interests from various stakeholders in the public, private and industry sectors. Seagrasses form an integrated component of the marine ecological system, performing valuable roles such as providing food and refuge to marine organisms, offering a form of biodiversity and coastal protection, and improving water clarity. In Singapore's context, ongoing coastal development projects make it especially pertinent to apply cost-effective approaches to manage the remaining seagrass meadows which face various anthropogenic threats, such as oil spills, port expansion and maritime activities, reclamation and dredging works. Surprisingly, seagrass areas remain at various locations of mainland Singapore and the offshore islands, with some having a healthy cover and a rich biodiversity. To gain important perspectives on managing seagrass habitats in Singapore, an efficient strategy requires working with and not against development. Effective management approaches for long-term sustainability of seagrasses should take into account their connectivity with other habitats such as corals and mangroves, thus incorporating laws to manage seagrasses as part of the marine ecosystem and not as individual species. Apart from improving national legislation, other management components, such as regional and international cooperation, streamlining seagrass research areas to address anthropogenic threats, improving mapping and monitoring methods, raising awareness and involving various stakeholders with an interest in the environment and looking at mitigation measures including seagrass restoration, are all part of the recipe for effective management.
... The influence of sediment on the marine environment is of particular relevance in land-scarce Singapore as its expanding population and economy requires large-scale land reclamation projects to be undertaken. These projects, combined with continuous dredging of shipping lanes and terrestrial runoff, have led to chronic levels of sedimentation with underwater visibility averaging 2 m in 1996 as compared with 10 m recorded in the early 1960s (Chou, 1996). Some effects of this pressure on the local coral reefs have been documented (e.g. ...
... Some effects of this pressure on the local coral reefs have been documented (e.g. Chou, 1988Chou, , 1996Goh & Chou, 1992). Grigg & Dollar (1990) considered increased sedimentation as the most serious anthropogenic impact on coral reefs (see Rogers, 1990 for review). ...
Article
A photographic technique was used to examine morphological differences in the living polyps of Favia speciosa sampled from three sites around Singapore. Eight characters were measured, seven of which differed significantly between the three study sites. Sedimentation rates and character size were much higher at the site closest to the mainland than at the two sites further from shore. Land reclamation and dredging contribute to high sediment rates in Singapore waters; these rates decrease with increasing distance from shore. Large polyps close to the main island of Singapore are possibly a plastic, or selected for, response to high levels of sediment.
... The tropical coastal ecosystems in the Southeast Asia are important habitat for fish communities (Chou 1996;Blaber 1997) and in general, the ecology of most fish in these areas have been well studied. For example, there were studies on Leiognathidae family such as biological and reproductive aspects of Leiognathus dussumieri (James & Badrudeen 1981;Seah et al 2009), L. bindus (Balan 1963;Murty 1983), L. equulus (Lee et al 2005); length-weight relationship of Leiognathidae family (Mazlan & Seah 2006), L. brevirostris (Batcha & Badrudeen 1992), L. splendens and Gazza minuta (Jayabalan & Bhat 1997), Secutor insidiator (Jayabalan 1988;Muddula et al 2015); population dynamics of L. jonesi (Karthikeyan et al 1989), L. bindus (Murty 1986;Nagarajan 2000;Abraham et al 2011); phylogeny and morphology (Ikejima et al 2004;Chakrabarty et al 2008;Kimura et al 2008;Chakrabarty et al 2010a;Chakrabarty et al 2010b;Seah et al 2012); food and feeding habits of Leiognathidae family (Seah et al 2009), L. equulus (Lankadhikara & Wijeyaratne 2014). ...
... For example, there were studies on Leiognathidae family such as biological and reproductive aspects of Leiognathus dussumieri (James & Badrudeen 1981;Seah et al 2009), L. bindus (Balan 1963;Murty 1983), L. equulus (Lee et al 2005); length-weight relationship of Leiognathidae family (Mazlan & Seah 2006), L. brevirostris (Batcha & Badrudeen 1992), L. splendens and Gazza minuta (Jayabalan & Bhat 1997), Secutor insidiator (Jayabalan 1988;Muddula et al 2015); population dynamics of L. jonesi (Karthikeyan et al 1989), L. bindus (Murty 1986;Nagarajan 2000;Abraham et al 2011); phylogeny and morphology (Ikejima et al 2004;Chakrabarty et al 2008;Kimura et al 2008;Chakrabarty et al 2010a;Chakrabarty et al 2010b;Seah et al 2012); food and feeding habits of Leiognathidae family (Seah et al 2009), L. equulus (Lankadhikara & Wijeyaratne 2014). In contrast, there are limited information about the trophic ecology of twoblotch ponyfish (Chong et al 1990;Chou 1996;Hajisamae et al 1999;Hajisamae et al 2003;Bachok et al 2004;Asriyana et al 2009;Asriyana et al 2011;Zahid et al 2011;Suyatna et al 2016). Therefore, this research can be considered as the first one to study trophic ecology of twoblotch ponyfish Nuchequula blochii (Valenciennes, 1835). ...
Article
Full-text available
Trophic ecology can be used to determine feeding strategy and indirect energy flux within a fish community, and also explains the trophic interaction between different fish species in a food web. This research was aimed to study the trophic ecology of twobloch ponyfish Nuchequula blochii in Kendari Bay, Southeast Sulawesi. The samples were collected monthly during October 2016 to May 2017 using bottom gillnets with mesh size ¾, 1, 1¼, 1½, and 2 inches. Food composition was analysed using Preponderance Index whereas feeding strategy was determined using Costello method modified by Admunsen. There were 247 fish with the total length and weight ranged from 45.0-119.0 mm and 5.0-31.4 g, respectively. The fish were categorized into 3 groups based on the length and weight sizes. The length sizes were classified into small size (45.0-69.7 mm), medium size (69.8-94.3 mm) and large size (94.4-119.0 mm). Twenty three species of organisms were found in the digestive system of the twoblotch ponyfish dominated by the phytoplankton genus Thallasiothrix. There was a significant difference in the food composition of the fish based on the size groups. Small size fish fed on 9 food organisms dominated by the phytoplankton group. Medium size fish utilized 19 organisms, and large size fish consumed 21 organisms. The twoblotch ponyfish developed mix feeding strategies; specialist and generalist. The specialist strategy was used by the small fish feeding on Thallassiothrix, whereas generalist strategy was employed by the medium and large size fish feeding on the other 22 prey species.
... At this time there is interest in adopting this approach as part of ongoing conservation efforts on Singapore's reefs. Massive coastal development, land reclamation projects, and regular dredging of shipping lanes have left much of Singapore's natural coastal environment } that used to include extensive coral reefs, seagrass beds and mangroves } degraded or destroyed (Hilton and Manning, 1995; Chou, 1996; Todd and Chou, 2005). Land reclamation alone has been responsible for $60% of Singapore's coral reef area being lost (Chou, 2006). ...
... >10 mg cm À2 d À1 ). In the early 1960s, underwater visibility was approximately 10 m (Chou, 1996) whereas Secchi disc readings taken during this present study were typically $1.5 m (unpublished data). Light penetration is low; even at the least impacted site only 1.55% of surface irradiance reached 7 m depth in Todd et al.'s (2004) study. ...
... This has resulted in coral cover being restricted to relatively shallow depths (\ 8 m) (Huang et al. 2009;Guest et al. 2016;Chow et al. 2019) due to extreme light attenuation (Todd et al. 2010;Browne et al. 2014). Singapore's coral communities are generally found on compact, shallow fringing reefs and intertidal reef flats adjacent to the Singapore Strait (Chou 1996;Tun 2012;Wong et al. 2018). During warmer periods, water temperatures have increased by * 1°C above ambient levels-leading to coral bleaching (Guest et al. 2012;Chou et al. 2016;Taira et al. 2017;Toh et al. 2018). ...
Article
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Urban coral reefs are regarded as marginal communities that live under localized conditions considered detrimental for coral survival, such as high sediment load. They are also impacted by global environmental changes, especially increases in sea surface temperatures. These conditions can cause sub-optimal performance and may lead to dissociation of the mutualistic symbiosis between the coral host and its endosymbionts (Symbiodiniaceae), which provide the majority of the coral’s daily energy budget. While recent studies have explored gene transcriptional responses to extreme conditions using cultured cells of Symbiodiniaceae, it is generally unknown how their responses manifest in hospite. Here, we investigate differential gene expression of endosymbionts hosted by the common reef-building coral Pocillopora acuta, following separate and combined exposures to two major environmental stressors: heat and sediment. We report that Durusdinium largely dominate the Symbiodiniaceae population in P. acuta, which suggests that the observed differential gene expression patterns are mainly responses from this known stress-tolerant endosymbiont genus. Differentially expressed genes were detected in response to heat, and to combined heat and sediment. These genes are associated with various biological processes including apoptosis, cell proliferation, cell–extracellular matrix adhesion, DNA damage repair, lipid catabolism, and lipid homeostasis. Our study provides valuable insights regarding the role of gene regulation by the endosymbiotic dinoflagellates to help maintain health and function of the coral host, which ultimately contributes to the persistence of P. acuta in Singapore’s highly urbanized reefs.
... All three reefs are characterized by a reef flat leading seaward to the upper reef slope down to~8 m depth, with large stands of mixed macroalgal assemblages interspersed amongst corals (Bauman et al., 2017). The depth restriction is primarily due to extreme light attenuation with increasing depth (Chou, 1996). Echinopora lamellosa and Merulina amplimata are both widely distributed across coral reefs in Singapore (Guest et al., 2016) and the Indo-Pacific (Veron et al., 2016), and are hermaphroditic broadcast spawners where eggs and sperm develop within the same mesentery (Fan and Dai, 1995;Fan and Dai, 1998). ...
... Sixty years ago, corals of Singapore used to thrive at a depth of around 10 m. However, at present, the corals delimit themselves to a depth of only 2 m (Chou 1996). Despite so many constraints, the corals of Singapore exhibit a rich diversity of more than 250 species in the fringing structures of the southern part (Huang et al. 2009). ...
Chapter
Despite the debate that continues to go on, at present, corals do not qualify to be a part of the conventional blue carbon ecosystems. Nonetheless, these marine ecosystems are crucial as they provide a plethora of ecosystem services not only to humans but also to several blue carbon ecosystems. These ecosystems provide shelter to the adjacent seagrass and mangroves. Corals act as wave breakers in many parts of the world and thereby furnishes a calm and stable environment to blue carbon ecosystems lying adjacent to each other. The present chapter collated the knowledge acquired so far on the coral species count and areal cover in the different countries bordering the Indian Ocean. This chapter also discussed the various threats that make corals vulnerable on these coastlines. We observed a spatial disparity in the degree of attention paid to the corals bordering the Indian Ocean. The coral triangle region received much higher attention than that observed in the western Indian Ocean. Several countries are yet to configure the principal threats to the corals lying on their coastline. Thus, this chapter apart from detailing the present state-of-the-art identifies the arenas that require scientific attention in the Indian Ocean periphery.
... Giant clam numbers fell as they were either harvested for consumption or collected for their shells to be used as ornaments or building material (Harrison & Tham, 1973;Neo & Loh, 2014). Coastal reclamation and development of the Southern Islands, ongoing since the mid-1960s, has led to the loss of large expanses of marine habitat and almost 60% reef cover (Chou, 1996;Chou, 2008). Coral reefs such as Tanjong Teritip (Lee, 1966), Pulau Seringat, and Terumbu Bayan (Guest et al., 2008), where giant clams were previously found, have been reclaimed in their entirety. ...
Article
Giant clam populations in Singapore are endangered due to historical exploitation, habitat loss, and sediment pollution. Transplanting cultured giant clams onto reefs is a potential conservation strategy. This study examined the growth and survival of three initial size classes (50.0–60.0 mm, 60.1–70.0 mm, >70 mm) of cultured juvenile fluted giant clams, Tridacna squamosa, transplanted to three reef sites under two caging treatments (caged and uncaged). After 145 days, there was no significant difference in clam survival within the size classes and within caging treatments across reef sites, even though environmental conditions varied greatly between sites. However, there was a significant effect of initial size class on T. squamosa survival, with higher survival with increasing size class (50.0–60.0 mm: 11.1%; 60.1–70.0 mm: 34.1%; >70.0 mm: 46.9%). Clams in caged treatments had significantly lower survival (16.7%) than uncaged clams (43.1%), likely due to biofouling atop caged treatments reducing light availability. Growth rates in the caged treatment (2.2 ± SD 1.8 mm month−1) were also lower than those in the uncaged treatment (3.9 ± SD 2.2 mm month−1). By optimizing transplant procedures for Singapore's turbid reef conditions, T. squamosa restocking efforts could play an important role in boosting local population numbers to facilitate natural recovery.
... While the impacts of land reclamation are quickly apparent tangible and generally irreversible ( Duarte, 2002), impacts from dredging, urban runoff and shipping activities, are not immediately apparent and could manifest over a longer time scale. Dredging, for example, is a common practice in Singapore's shipping lanes ( Chou, 1996), and has been shown to have a detrimental impact on seagrasses by increasing light attenuation and reducing overall water quality ( Erftemeijer and Lewis, 2006). The proximity, intensity and frequency of dredging activities in Singapore waters is likely to be a major contributing factor that could compromise the continued persistence of seagrass meadows, with more frequent and intense dredging activities affecting the ability of seagrass to cope with additional stress ( Yaakub et al., 2013b). ...
... Human activities have caused increased levels of sediment deposition and water turbidity in coastal areas throughout the world by increasing soil erosion and runoff from land clearance, dredging and land reclamation (Ellis 1988, Vogt & Schramm 1991, Chou 1996. Increased sedimentation in freshwater rivers and streams is well documented as having deleterious effects on fauna (see review by Wood & Armitage 1997). ...
Article
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Increased sedimentation from changes in land use in coastal areas is a potentially important impact of human urbanisation. The potential impact of sedimentation on benthic infauna was quantitatively investigated in the Okura estuary, which is at the northern fringes of urban development in Auckland, New Zealand. A structured mensurative sampling programme, measuring benthic infauna and various environmental variables, is described. Of the variance in macrofaunal assemblages from 15 sites throughout the Okura estuary on 6 sampling occasions, 70% was explained by environmental variables. Proportions of ambient sediment grain-sizes, depositional categories from previous models, the amount and characteristics of trapped sediments, organic content, changes in bed height and distance from the mouth of the estuary were all useful in explaining variation in macrofaunal assemblages. Levels of sedimentation recorded in this study were sub-catastrophic (<3 cm of deposition d(-1)), corresponding to natural fluctuations in sedimentation. Bivalves generally had a negative relationship with sedimentation, while certain burrowing crabs and polychaetes were more abundant in high-deposition environments. The total amount and the grain-size characteristics of trapped sediments explained a significant proportion of the variation in soft-sediment assemblages, over and above the variation explained by ambient sediment variables. Thus, sedimentation appears to be an important structuring force in these intertidal estuarine macrobenthic assemblages.
... The coastal waters around Singapore reefs appear to be characterized by strong tidal currents and poor visibility due to siltation (Chou, 1988; Chua & Chou, 1991; Hilton & Chou, 1999). The turbid water is partly due to dredging and land reclamation activities in the area, which were observed during the present study and also have been mentioned in earlier reports (Wong, 1985, 2000; Goh & Chou, 1992; Lim et al., 1994; Low & Chou, 1994; Hilton & Manning, 1995; Chou, 1996; Loh et al., 2006). This turbidity has much impact on the reef community zonation, since the poor light penetration has a limiting effect on reef coral cover, especially on the lower reef slopes (Chuang, 1977; Chou, 1988; Lane, 1991; Goh et al., 1994; Tun et al., 1994). ...
Article
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Based on recent fieldwork, a checklist of four attached mushroom coral species (Fungiidae) is given with annotations on their abundance in Singapore waters. One species, Podabacia motuporensis Veron, 1990, is recorded as new to Singapore, so far the westernmost locality within its distribution range. Although specimens were observed and collected during earlier studies in Singapore, this species probably remained unnoticed due to its resemblance to P. crustacea (Pallas, 1766) and because it is not yet well-known. Another one, Podabacia kunzmanni new species, is new to science. Specimens of this species are usually very small. Therefore, they can easily be confused with other Podabacia species, but also with attached juvenile corals of the genus Sandalolitha. Podabacia kunzmanni was observed for the first time in 1995 on the heavily damaged reefs off Padang, West Sumatra, and later on (also in 1995) a reef off Jakarta. It is most remarkable that this new species is relatively small and appears to be most abundant on dead coral and on rubble, with little or no other coral cover around, especially on reefs under stress. Alive, the small corals stand out very clearly in contrast to their dead micro-habitat.
... Since the 1970s, sedimentation rates have risen from 3.2–5.9 mg cm−2 d−1 [5] to 15–30 mg cm−2 d−1 [6], [7], [8] with average visibility reduced from 10 m (1960s) to less than 2 m [9]. Sedimentation rates and turbidity decline with increasing distance from Singapore's mainland, resulting in spatial variations in coral species composition and reef health [10]. ...
Article
Full-text available
Sediment loads have long been known to be deleterious to corals, but the effects of turbidity and settling particles have not previously been partitioned. This study provides a novel approach using inert silicon carbide powder to partition and quantify the mechanical effects of sediment settling versus reduced light under a chronically high sedimentary regime on two turbid water corals commonly found in Singapore (Galaxea fascicularis and Goniopora somaliensis). Coral fragments were evenly distributed among three treatments: an open control (30% ambient PAR), a shaded control (15% ambient PAR) and sediment treatment (15% ambient PAR; 26.4 mg cm-2 day-1). The rate of photosynthesis and respiration, and the dark-adapted quantum yield were measured once a week for four weeks. By week four, the photosynthesis to respiration ratio (P/R ratio) and the photosynthetic yield (Fv/Fm) had fallen by 14% and 3-17% respectively in the shaded control, contrasting with corals exposed to sediments whose P/R ratio and yield had declined by 21% and 18-34% respectively. The differences in rates between the shaded control and the sediment treatment were attributed to the mechanical effects of sediment deposition. The physiological response to sediment stress differed between species with G. fascicularis experiencing a greater decline in the net photosynthetic yield (13%) than G. somaliensis (9.5%), but a smaller increase in the respiration rates (G. fascicularis = 9.9%, G. somaliensis = 14.2%). These different physiological responses were attributed, in part, to coral morphology and highlighted key physiological processes that drive species distribution along high to low turbidity and depositional gradients.
... Coral reefs in Singapore have been impacted by the high rates of sedimentation resulting from land reclamation activities that commenced in 1963 (Chou, 1988a;Chou, 1996;Chou, 2006). Sediment deposition, suspended particles and associated light attenuation adversely affect the reproduction, recruitment, growth and survival of reefbuilding zooxanthellate (or hermatypic) corals (Roy & Smith, 1971;Endean, 1976;Rogers, 1990;Titlyanov & Latypov, 1991;Gilmour, 2002;Dikou & van Woesik, 2006; but see Lane, 1991). ...
Article
Records of Scleractinia in Singapore have not been updated for 14 years. We present an inventory of zooxanthellate hard coral species by consolidating past work, coral collection records and recent publications, as well as conducting field surveys at eight coral reefs south of mainland Singapore. Species assessment surveys and recent literature revealed a total of 161 species. Using updated taxonomy, and including 33 new records, we report an increase in the number of species found in Singapore from 187 to 255. Raffles Lighthouse registered the largest number of species and represents the most undisturbed reefs of the sites studied. No clear relationship can be established between species richness and distance from the Mainland. The total number of species in Singapore is comparable to the reefs in neighboring countries if reef area is taken into account. Only 63.1% of total species recorded have been found in recent years, but this is not an exhaustive survey. As 12.9% of all species have been discovered in the last four years, and only 52.4% of species with distribution ranges encompassing Singapore have been found, more new records can be expected from further assessments.
... The complex hydrodynamics within the Singapore Strait (Chen et al. 2005) makes the Southern Islands an interesting archipelago to explore the effects of local hydrodynamics on planulae transport (and thus the potential for recruitment). The coral reefs are highly impacted, especially by sediment resuspended by dredging of shipping lanes and land reclamation activities (Chou 1996) and, occasionally, entire reefs are reclaimed or merged. In natural resource-scarce nations such as Singapore, it is imperative to identify areas that are potentially important sources of larvae to prioritize conservation objectives and efforts. ...
Article
Singapore's coral reefs have experienced significant anthropogenic impacts for at least 4 decades. Ongoing reef restoration efforts, however, may not be sustainable if there is no natural coral recruitment. Knowledge of coral reef connectivity, which can be identified using hydrodynamic-advection and individual-based models, can help inform reef management decisions. Here, a 2-dimensional, hydrodynamic, flexible mesh model (MIKE 21 FM) coupled with a Lagrangian particle-tracking module was used to simulate larval transport among Singapore's Southern Islands. In each simulation, neutrally buoyant, passive particles representing coral planulae were released into the hydrodynamic conditions present during the coral multi-species synchronous spawning event of April 2007. When the number of larvae released was proportional to live coral cover (between 2400 and 46 200 particles), 3 islands: Pulau Sudong, Pulau Pawai and Pulau Senang, which all lie within a military Live Firing Area, were identified as the most robust sources of larvae seeding the rest of the Southern Islands. However, when equal numbers of larvae (18 000 larvae per site) were released from all sites in an effort to identify nursery areas with the greatest potential to seed other reefs, 2 different and upstream islands, Sisters' Islands and Kusu Island, were found to be better sources of larvae. We suggest all 5 of these sites should be identified for conservation. Additional effort to enhance coral cover, and hence larval export, at Sisters' Islands and Kusu Island may help increase recruitment on downstream reefs.
... Previously, the site had been impacted by an oil tanker jetty built in the middle of the beach and thermal effluent from a nearby power plant (Todd & Chou, 2005). Both these installations are now disused, however, the area is still affected by heavily sedimented waters (Chou, 1996). Labrador beach is only 300m wide, but it represents the last remaining natural shoreline along the dramatically modified southern coast of mainland Singapore (Todd & Chou, 2005). ...
Article
To date, the majority of research on the rocky intertidal has focused on temperate rocky shore communities whereas study sites in the tropics have been relatively distant from the equator. We examined four key groups of marine organisms, i.e. macroalgae, anthozoans, decapods and gastropods, in relation to shore height and visitor pressure, at Labrador beach, Singapore (just 1°16.0'N). To reveal any vertical zonation the shore was divided into four 10m-wide zones, parallel to shore, approximately spanning high to low spring tide marks. To determine the effects of visitor pressure, the shore was also divided horizontally into three 60m long sectors; representing a gradient in distance from the public entrance to the beach. Sampling data from quadrats positioned randomly within these zones and sectors were converted into Shannon-Wiener and Margalef diversity index scores. The number of visitors to each horizontal sector was monitored, and the substrate composition in the sampled areas was assessed using point intercept transects. A total of 28 genera of macroalgae, 14 genera of anthozoans, 20 genera of decapods and 25 genera of gastropods were identified. Diversity scores for macroalgae, anthozoans and decapods were highly significantly different among the different shore heights, with the highest diversity found in the lower shore zones. Anthozoan diversity in the sector closest to the entrance of the beach, where the highest numbers of visitors were recorded, was significantly lower than the sectors further away. It requires further work, however, to identify the extent to which visitor pressure may affect marine organism diversity and distribution in the intertidal zone at Labrador Park.
... Furthermore, with a reported presence of eleven hard coral species (Huang et al., in preparation) anthozoan diversity appears to be increasing, perhaps due to improved conditions since the removal of the oil tanker terminal and power plant. Although impacted by heavily sedimented waters (Chou 1996) and surrounded by megaprojects, marine life at Labrador Park continues. Fig. 1a Low tide at Labrador Park with a Platygyra sp. ...
... Suggested reasons for this decline include the decreasing quality of the seabed due to large scale land reclamation during the 1960's to increase land area (Wong 1992) and marine pollution from suspended material from land reclamation and dredging of shipping lanes (Dikou and van Woesik 2006). Approximately 60% of total coral reefs in Singapore have been lost as a result of these anthropogenic activities and surviving reefs are subjected to stress due to high sediment loads (Chou 1996;Dikou and van Woesik 2006). Currently, the majority of the coral reefs around the Southern Islands exist as either patch reefs or fringing reefs (Ng et al. 2011). ...
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Studies concerning subtidal octocoral species from Singapore reefs are few. This study documents the diversity and abundance of octocoral communities from fringing reefs at Singapore's Southern Islands, namely, Pulau Semakau, P. Hantu and Kusu Island. Belt transects of 20 m ( 5) were employed to survey the octocoral communities at these reef sites. Morphology and sclerites of a number of collected octocoral samples were compared with paratypes obtained from the Raffles Museum of Biodiversity Research, National University of Singapore, for species identification. A total of 16 morphotypes, belonging to five octocoral genera, including Cladiella, Lobophytum, Nephthea, Sarcophyton and Sinularia, were identified in this study. Statistical analysis revealed octocoral abundance and diversity at Kusu Island reefs were higher than those around P. Hantu and P. Semakau. Conversely, octocoral community structures encountered along P. Semakau and Kusu Island were more similar than those of P. Hantu. The preliminary data presented in this study could serve as the baseline data for long term biomonitoring programs in assessing the state of coral reefs in Singapore.
... Suggested reasons for this decline include the decreasing quality of the seabed due to large scale land reclamation during the 1960's to increase land area (Wong 1992) and marine pollution from suspended material from land reclamation and dredging of shipping lanes (Dikou and van Woesik 2006). Approximately 60% of total coral reefs in Singapore have been lost as a result of these anthropogenic activities and surviving reefs are subjected to stress due to high sediment loads (Chou 1996;Dikou and van Woesik 2006). Currently, the majority of the coral reefs around the Southern Islands exist as either patch reefs or fringing reefs (Ng et al. 2011). ...
... Photosynthesis and calcification are tightly coupled in zooxanthellate scleractinian corals, with calcification approximately three times lower in darkness than in light (Kawaguti and Sakumoto 1948; Gattuso et al. 1999). In Singapore, chronic levels of sedimentation over the last 30-40 years have resulted in underwater visibility being reduced from 10 m recorded in the early 1960s to a contemporary average of 2 m (Chou 1996). This has significantly reduced the depth at which reefs can grow; resulting in a coral dead zone below 6-8 m at all but the 'best' sites. ...
Article
Pollutants, originating from both land and sea, are responsible for significant lethal and sub-lethal effects on marine life. Pollution impacts all trophic levels, from primary producers to apex predators, and thus interferes with the structure of marine communities and consequently ecosystem functioning. Here we review the effects of sediments, eutrophication, toxics and marine litter. All are presently major concerns in Southeast Asia (SE Asia) and there is little indication that the situation is improving. Approximately 70% of SE Asia’s human population lives in coastal areas and intensive farming and aquaculture, rapid urbanization and industrialisation, greater shipping traffic and fishing effort, as well as widespread deforestation and nearshore development, are contributing towards the pollution problem. As SE Asia encompasses approximately 34% of the world’s reefs and between a quarter and a third of the world’s mangroves, as well as the global biodiversity triangle formed by the Malay Peninsular, the Philippines, and New Guinea, the need to reduce the impacts of marine pollution in this region is all the more critical. KeywordsCoral reef-Eutrophication-Mangrove-Marine litter-Seagrass-Sediment-Toxics
... The tropical coastal ecosystems in Southeast Asia are suitable and native habitats for numerous fish communities (Blaber, 1997;Chou, 1996). The Bay of Bengal and its adjacent coastal water act as a perfect ecological niche for diversified fish and others aquatic organisms Hanif, 2019;Siddik et al., 2017). ...
Article
Climate changes and anthropogenic activities have paved the way for the dislocation of native species into areas located far away from their natural habitats. To this end, the Bay of Bengal and its adjacent coast have experienced the invasion of many alien species coming from different oceans, seas and bays around the world. Recently, a single specimen of the Twoblotch ponyfish (Nuchequula blochii) was captured. It had a total length of 69 mm and bodyweight 0.98 g. The specimen was caught at a depth of 18 m in the world's largest mangrove habitat, Sundarban, with a soft sandy bottom. Because the species N. blochii was previously recorded for the first time in the water area of Bangladesh, the single captured species above was considered as the ‘second record.’ There are several potential factors responsible for the introduction of this species in the Bay of the Bengal coast, one being the similar habitat conditions available to them. Because this species was previously reported from the water area of Bangladesh and is still appearing now, there is a possibility that it may become established in the water area of Bangladesh.
... In Singapore's highly urbanised reefs, sedimentation levels can reach up to 37 mg cm -2 d -1 (Browne et al., 2015), well above Rogers' (1990) threshold for "high" (i.e., > 10 mg cm -2 d -1 ). Decades of coastal development has caused ~60% loss of Singapore's coral reefs (Hilton & Manning, 1995), with remaining coral communities generally restricted to shallow depths (≤ 6 m) as a consequence of sediment-related turbidity and associated light attenuation (Chou, 1996;Guest et al., 2016;Heery et al., 2018). This combination of turbidity and downwelling sediments is thought to have altered the composition of coral assemblages in Singapore (Low & Chou, 1994;Chow et al., 2019) as well as affected coral morphology (Todd et al., 2001(Todd et al., , 2004. ...
Article
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Sediment rejection efficiency of five scleractinian corals was studied in situ at the western fringing reef of Pulau Hantu, Singapore. Colonies of five coral species were exposed to two sediment treatments: low (100 g cm −2) and high (200 g cm −2). Clearance was calculated from photographs taken after initial sediment deposition (100% cover on a 50-mm diameter circle of relatively flat colony surface) and again after 3 h. Results indicated that sediment rejection efficiency of corals varied significantly among species and between sediment treatments. Overall, Podabacia crustacea showed relatively high clearance efficiency at both low and high sediment levels, while Dipsastraea lizardensis exhibited the lowest clearance efficiency among all five species. All species cleared less effectively under the greater sediment load. These findings contribute to efforts to understand the responses of scleractinian corals to Singapore's heavily sedimented coastal waters.
... The total reef area in 2012, at 13.25 km 2 , was a stark contrast to an estimated 39.85 km 2 in 1953 (Tun, 2012). High sedimentation rates of 44.64 mg/cm 2 /day increased the smothering and mortality of corals (Low and Chou, 1994;Erftemeijer et al., 2012), and decreased underwater visibility (Chou, 1996). The drastic reduction in light penetration has restricted reef establishment to shallower depths (Chou and Tun, 2012). ...
... many browsers are averse to divers 10,41 , and as such their densities are typically under-estimated during visual diver surveys. This may be further compounded by low visibility on most of Singapore reefs (<3 m) 50 . ...
Article
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The removal of macroalgal biomass is critical to the health of coral reef ecosystems. Previous studies on relatively intact reefs with diverse and abundant fish communities have quantified rapid removal of macroalgae by herbivorous fishes, yet how these findings relate to degraded reef systems where fish diversity and abundance are markedly lower and algal biomass substantially higher, is unclear. We surveyed roving herbivorous fish communities and quantified their capacity to remove the dominant macroalga Sargassum ilicifolium on seven reefs in Singapore; a heavily degraded urbanized reef system. The diversity and abundance of herbivorous fishes was extremely low, with eight species and a mean abundance ~1.1 individuals 60 m⁻² recorded across reefs. Consumption of S. ilicifolium varied with distance from Singapore's main port with consumption being 3- to 17-fold higher on reefs furthest from the port (Pulau Satumu: 4.18 g h⁻¹; Kusu Island: 2.38 g h⁻¹) than reefs closer to the port (0.35-0.78 g h⁻¹). Video observations revealed a single species, Siganus virgatus, was almost solely responsible for removing S. ilicifolium biomass, accounting for 83% of the mass-standardized bites. Despite low herbivore diversity and intense urbanization, macroalgal removal by fishes on some Singaporean reefs was directly comparable to rates reported for other inshore Indo-Pacific reefs.
... Laminar growth forms have denser skeletons among the growth forms (Ng et al. 2019), which render them more prone to breakage and as such, colonies are more predisposed to deeper depths with relatively calm water (Hughes 1987). Turbinariids have been shown to be a major component of reef crest and shallow reef slope communities on both reclaimed and natural reefs in Singapore (Goh et al. 1994;Chou 1996;Chow et al. 2019). However, species of Turbinaria are in general considered to be hardy among the laminar forms and welladapted to the intertidal environment. ...
Article
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Living scleractinian corals form a narrow but often conspicuous band of marine life along tropical intertidal shores worldwide but they have generally been considered as outliers of mainstream coral communities and are thus poorly characterized. This study examined coral communities at three intertidal habitats, i.e., reef flats, sloping seawalls, and vertical seawalls, in Singapore, looking at species diversity, abundances, growth forms, and colony sizes. A total of 35 coral species were recorded, of which the majority (51%) were typically of massive growth form. Reef flats had the highest number of species (30), followed by sloping seawalls (21). Species on vertical seawalls (11) were a subset of the two other habitats. Colonies were dominantly massive (72%) and sparsely distributed with average colony densities between 0.05 and 0.4 colonies/m². Species Porites lobata-lutea complex was widespread and most abundant, comprising 21–30% of colonies in each habitat. Six other species common across all habitats were Dipsastraea speciosa, Favites abdita, Goniastrea retiformis, Platygyra verweyi, Platygyra pini, and Platygyra sinensis. Of these, only colony sizes of G. retiformis (mean ± SE, reef flats 30 ± 4 cm, sloping seawalls 9.5 ± 1.7 cm, vertical seawalls 11.7 ± 1.4 cm) and Porites lobata-lutea complex (41.8 ± 8.3 cm, 26.8 ± 6.3 cm, 12.3 ± 1.6 cm) showed significant differences (p < 0.05) amongst habitats. Relative abundances on the reef flats correlated moderately with those on the sloping seawalls (Pearson’s ρ = 0.6) and vertical seawalls (Pearson’s ρ = 0.7), respectively. Multivariate analyses showed that habitat origin (natural vs man-made) and surface rugosity (heterogeneous vs. homogeneous) were factors that significantly (p < 0.05) differentiated intertidal coral communities. Nevertheless, sloping seawall communities bore higher resemblance to those on natural reef flats than to man-made vertical seawalls in species and growth form richness and also coral densities. These findings highlight interesting opportunities for incorporating coral-friendly designs into existing man-made sloping coastal structures to encourage the growth of coral communities in the intertidal zone.
... By the time the coral translocation programme started in 1993, sedimentation from reclamation around the Ayer Islands had already caused visibility to fall below 3 m (Nathan, 1994). Sediment pollution and associated turbidity have been a major issue for Singapore's marine life since the late 1960s (Chou, 1996;Todd et al., 2010;Guest et al., 2008;Guest et al., 2016), leading to reduced light penetration (Todd et al., 2004), coral cover (Goh & Chou, 1992), coral growth (Browne et al., 2015), and recruitment rates (Dikou & van Woesik, 2006). Hence, it is possible these deleterious effects were already occurring at the Ayer Islands prior to amalgamation. ...
Article
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Singapore is a small city-state that has grown rapidly in terms of its economy and population during the past 50 years. Almost 180 km² of coastal land required for development and infrastructure has been created through reclamation. This, however, has come at a significant cost to natural marine habitats. One example is the formation of Jurong Island, developed by the amalgamation of seven offshore islands (collectively known as the Ayer Islands) to accommodate Singapore's expanding petrochemical sector in the 1980s. Little is known of the habitats and biodiversity that these islands previously hosted hence, the aim of this study is to assess what was lost. This was achieved by reconstructing the historical extent of habitats on the Ayer Islands using GIS software applied to topographic maps of Singapore from 1969, 1983, 1993, and 2002. Map analysis showed up to 10.08 km² of coral reefs and 5.25 km² of mangrove forest in 1969, which were all lost by 2002. Anecdotal evidence suggests that, prior to reclamation, the species richness of the coral reefs around the Ayer Islands was comparable to those of other reef habitats in Singapore today.
... Coral cover in reefs beyond 6m depth have also greatly reduced due to the high sedimentation , limiting the available habitat for other reef organisms. The coral community now comprises more sediment-tolerant species (Chou 1996). Global threats such as elevated sea surface temperature have also impacted Singapore's coral reefs. ...
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he Singapore Blue Plan 2018 (hereafter ‘The Blue Plan’) is a proposal for the conservation of marine ecosystems, prepared by members of Singapore society, and submitted to the Government for consideration. It was initiated by marine biologists with academics, volunteers, stakeholders, and concerned citizens. The Blue Plan synthesizes the current state of knowledge for marine environments, reviews relevant legislature and advocates comprehensive sustainable methods to manage this important ecosystem
... Singapore has undergone extensive land reclamation and coastal development (Lai et al. 2015), resulting in high rates of sedimentation and levels of total suspended solids far exceeding those considered optimal for tropical reefs. Average underwater visibility has declined from ~10 m in the 1960s to < 5 m in the mid-1990s (with local temporally ephemeral [from several minutes up to 1−2 d] reductions of visibility associated with passing ship traffic and high wind-driven currents reducing visibility to ~2 m) (Chou 1996). In comparison, Pulau Tioman has limited coastal development, and underwater visibility is typically >10 m. ...
... Most of these islands have well-developed fringing reefs, characterized by a reef flat (0-2 m depth) extending seaward to the upper reef slope (3-5 m depth) and down the slope to ~8 m depth. This depth restriction is primarily due to extreme light attenuation with increasing depth as a result of high sedimentation and turbidity (Chou 1996). Consequently, most algal cover in Singapore is restricted to the reef flats and upper reef slopes. ...
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Temporal and spatial variations in Sargassum ilicifolium thallus density and length were investigated on equatorial coral reefs in Singapore from November 2011 to October 2012. Thalli density varied little throughout the year, however, we found strong seasonal patterns in thallus length and identified temperature as the significant driver. S. ilicifolium reached maximum length in December (110.39 ± 2.37 cm) during periods of cooler water temperatures, and minimum length in May (9.88 ± 0.48 cm) during periods of warmer water temperatures. Significant spatial variation was also observed for both thallus density and length of S. ilicifolium among reefs. Within reefs, densities of S. ilicifolium were higher on reef flats (20.40 ± 0.40 individuals · 0.25 m⁻²) compared to upper reef slopes (5.66 ± 0.23 individuals · 0.25 m⁻²). Our findings highlight that marked seasonality in the growth of canopy‐forming macroalgae can occur within equatorial reef systems where temperature ranges are restricted (<3°C). This article is protected by copyright. All rights reserved.
... Singapore's coral reefs are impacted by shipping activities and extensive land reclamation. Over the last four decades turbidity levels have reduced underwater visibility from 10 m in the early 1960s to an average of ∼2 m (Chou 1996). Contemporary turbidity levels exceeded 150 mg l −1 and sediment accumulation can reach up to 37 mg cm −2 day −1 (Browne et al. 2015). ...
Article
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.
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The sexual system in corals refers to the spatial and temporal pattern of sexual function within an individual coral polyp, colony or population. Although information on sexual systems now exists for over 400 scleractinian species, data are still lacking for some important reef-building taxa. The vast majority of scleractinians are either simultaneous hermaphrodites or gonochoric with other sexual systems rarely occurring. Diploastrea heliopora is one of the most ubiquitous and easily recognised reef-building species in the Indo-West Pacific; however, surprisingly little is known about its reproductive biology. The aim of the present study was to examine the reproductive biology of D. heliopora colonies on chronically impacted, equatorial reefs south of Singapore. Here we show that in Singapore, D. heliopora is a broadcast spawner with predominantly gonochoric polyps. Colonies, however, contained male, female and a low proportion of cosexual polyps during the 14-month sampling period. The most plausible explanation for this is that polyps switch sexes with oogenic and spermatogenic cycles occasionally overlapping. This leads to colony level alternation of sex function within and between breeding seasons. While this sexual system is atypical for scleractinians, it supports molecular evidence that D. heliopora is phylogenetically distinct from species formerly in the family Faviidae.
Article
1. Giant clams have been a sustainable resource for millennia, but unregulated harvesting has led to local extinctions within the Indo-Pacific region. Giant clam mariculture can produce large numbers of juveniles for restocking wild populations where natural recruitment is low or absent. 2. Singapore is surrounded by more than 60 small islands, many with fringing reefs. These reefs, however, experience increased turbidity and sedimentation resulting from massive coastal development projects and regular dredging of shipping lanes. 3. Seven reefs off Singapore's southern islands were surveyed (9670 m2) for giant clams. Also, an experiment was conducted to determine the growth of Tridacna squamosa reared in aquaria under three light treatments: ∼50% ambient photosynthetically active radiation (PAR); ∼25% ambient PAR; and ∼ 12% ambient PAR. Finally, 144 clams (T. squamosa) were transplanted to four reefs around Singapore to study survival and growth in a heavily impacted environment. 4. A total of 23 adult clams from three species were found during the survey, representing a mean density of 0.24 per 100m 2. Most clams were found at Raffles Lighthouse, Singapore's 'best' reef. No juvenile clams were encountered. In the aquarium experiment, clam growth was significantly different among the three light treatments, with growth greatest in the ∼50% ambient PAR treatment. Of the 144 transplanted clams, 116 (80.6%) were recovered after 7 months. All specimens had increased in size, with growth rates among reefs ranging from 3.3mmmonth-1 (SD = 1.3 mm) to 4.8mm month-1 (SD = 1.6 mm). 5. Results suggest that, despite high levels of sedimentation and turbidity on Singapore's reefs, giant clams can survive and grow well. Restocking efforts using maricultured clams may be effective in enhancing the dwindling local populations. It is not clear, however, whether a self-sustaining community can be established as high sedimentation may hinder larval settlement and survival.
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Populations of broadcasting reef corals often exhibit marked reproductive seasonality and spawning synchrony. Within speciose coral assemblages there is often considerable overlap of spawning periods among species, resulting in multi-species spawning events (or “mass coral spawning”). Earlier geographical comparisons of reproductive synchrony suggested a reduction in the extent of mass spawning with proximity to the equator. In contrast, recent studies have revealed that reproductive seasonality and spawning synchrony within and among species are features of coral assemblages on equatorial reefs. Here we review the proposed causes of synchronous spawning among reef corals and discuss how recent findings about reproduction of corals from Singapore's equatorial reefs shed light on these various theories. Sexual reproduction in broadcasting corals requires external fertilization, so reproductive seasonality (leading to spawning synchrony) within populations is probably highly adaptive because synchrony increases the chances of gametes meeting, enhances the possibility of outbreeding and may swamp opportunistic predators. No coastal location is truly aseasonal, with even equatorial reefs experiencing marked (albeit less pronounced) rhythmic changes in sea surface temperature. Consequently, if species respond similarly but independently to timing cues to synchronize reproduction within populations, mass spawning is just as likely to occur in equatorial coral assemblages as it is at higher latitudes.
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Anthropogenic nutrient pollution has been identified as one of the key stressors of coastal ecosystems. However, the paucity of long-term nutrient records limits our understanding of both the extent of nutrient pollution as well as of the ecological impacts. Here, using coral skeletal phosphorus (P/Ca), we reconstructed a half-a-century record of seawater phosphate at Port Dickson, Malaysia. The P/Ca in the coral revealed an up to 8-fold increase in coral P/Ca from the late 1970s to 2000s, likely linked to increases in fertilizer use (R² = 0.47) and variabilities in rainfall (R² = 0.17). The rise in coral P/Ca in coincided with a contemporaneous 18 % decrease in coral skeletal density, suggesting phosphate enrichment may impact the growth and structural integrity of reef-building corals. Given the importance of both agriculture and heavy reliance on coral reefs by populations in Southeast Asia, our study highlights continue the need to develop environmental management upstream of coastal zones.
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The effect of increased levels of suspended sediment on fertilization success in the scleractinian coral Pectinia lactuca was investigated in a laboratory experiment following a mass coral spawning event on reefs off Singapore. Egg–sperm bundles were collected from tank-spawned coral colonies collected from the field several days prior to the anticipated mass spawning. Eggs and sperm from each colony were separated and distributed systematically across replicated treatments (N = 9) with three concentrations of fine suspended sediment. Spawning and embryo development in Pectinia lactuca followed a pattern similar to other scleractinian coral species. There was a significant effect of increased suspended sediment concentration on fertilization success (P < 0.05). Both high- (169 mg l−1) and medium- (43 mg l−1) suspended sediment treatments decreased fertilization success compared to controls. These results imply that increased turbidity levels (whether chronic, such as in the waters around Singapore, or short-term, caused by a dredging operation)—when coinciding with the coral spawning season—may affect the reproductive success of corals and compromise coral recruitment and recovery of degraded reefs.
Article
Zoanthids of the order Zoantharia (Anthozoa: Hexacorallia) exhibit high intraspecific morphological variability, but whether this is due to polymorphism, phenotypic plasticity or a combination of both remains unknown. To address this knowledge gap, in November 2010, eight colonies each of Zoanthus sansibaricus and Palythoa tuberculosa were sampled from three reefs off the south of mainland Singapore and transplanted to a shallow experimental site. The colonies were then distributed under two types of treatment frames: control and shaded. After 87 days, morphometric characters were extracted from macro-images. Reaction norms, principal components analysis, analysis of variance and canonical discriminant analysis all demonstrated light-induced changes in morphology. Patterns of plastic changes were similar for both species: shaded colonies had larger polyps as compared to control colonies. The presence of plastic responses in zoanthids may facilitate their colonization of a broad range of habitats as well as help them to withstand temporal changes in their environment.
Conference Paper
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Since the mid-1960s, Singapore's coral reefs have been impacted by a variety of anthropogenic disturbances such as coastal development, land reclamation and seabed dredging. Up to 60% of reefs have since been lost, and the remaining ones are more compact and shallow due to chronic sedimentation and unstable bottom rubble that is easily moved about by currents. Since the late 1980s, various attempts at restoring and rehabilitating Singapore's reefs were initiated and an appraisal of these efforts is timely. We reviewed these reef restoration experiences and synthesized the lessons that are useful for future restoration strategies. The restoration approaches to date broadly include: mitigation measures, substrate modification, optimising methods for rearing scleractinian larvae, use of fragments and corals of opportunity (i.e. naturally fragmented corals and coral juveniles that have recruited on loose rubble) in in situ and ex situ coral nurseries, as well as transplantation of nursery-reared coral juveniles and fragments to degraded reefs and seawalls. The El Niño event in 2010 elevated sea surface temperatures and caused widespread bleaching of hard corals, which affected reef restoration efforts. However, the episode offered insights into the bleaching susceptibility of certain species as well as their suitability for rearing in nurseries and transplantation to other environments. The results from the various projects underscored the need to incorporate adaptive and flexible management strategies in reef restoration and the experience can be applied to future reef restoration to improve success.
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Sediment settling on corals interferes with their feeding and photosynthesis. Near-shore construction and dredging activities can result in increased sedimentation and significantly impact coral reefs. It is well known that coral species differ in their ability to cope with sediment stress, yet within-species variation for sediment rejection is much less understood. In this study, fragments of Diploastrea heliopora retrieved from four different colonies (genotypes) were subjected to three levels of acute sediment (silicon carbide powder) exposure in a controlled aquarium tank environment. After five hours, significant differences in surface area cleared were found for both treatment and genotypes. Significant differences among genotypes were also found for mass of sediment removed. Previous researchers have discussed how reefs under stress may become populated by hardy genotypes and our results suggest that the necessary intraspecific variation exists for such a process in Singapore.
Article
Giant clams have been cultured for decades, yet few formal studies have examined their reproduction and early life history. Here we present two experiments that provide baseline information on the effects of micro-algal feeding, temperature and salinity on fertilization success and development of the fluted giant clam, Tridacna squamosa. The effect of different micro-algae feeds, i.e. Tetraselmis suecica (CS-187), Chaetoceros mulleri (CS-176), and yeast, on veliger survival was tested. Mixed-algal diet of 1:1 v/v T. suecica + C. mulleri + yeast resulted in approximately double larval survival by 24 h but no significant differences were identified between the uni-algal and mixed-algal diets at 48 h. Temperature and salinity were examined using a 2 × 2 design; with temperatures of ~22.5°C and ~29.5°C, and salinities of 27 ‰ and 30 ‰. At ~29.5°C fertilization success was significantly greater than at ~22.5°C, but higher temperatures were detrimental to the development of trochophores. There were no significant differences in either embryo or trochophore numbers for the salinities tested. The results indicate that both micro-algal diet and temperature can affect T. squamosa larval initiation and development; knowledge that can be used to improve their mariculture.
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