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The sea urchin Diadema setosum is often encountered in the coral reefs in the Southern Islands of Singapore. While sea urchins have been known to play a role in regulating algal communities and influencing coral recruitment in other parts of the world, their role in Singapore reefs has not been determined. This study was conducted to determine the...
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... scatter plot between coral cover and algal cover (Fig. 7) showed a significant negative liner relationship between algal cover and live coral ...
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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...
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... These islands were selected as Pteraeolidia semperi is known to be found around them. In brief, the reefs of the four islands are dominated by dead corals and sediment with a similar coral cover of 20-30% [30][31][32], except for Pulau Jong with a lower coral cover of only 5% [31]. Subtidal sampling was conducted via SCUBA, and Life 2022, 12,1988 3 of 15 specimens were identified based on known anatomical descriptions [33]. ...
... These islands were selected as Pteraeolidia semperi is known to be found around them. In brief, the reefs of the four islands are dominated by dead corals and sediment with a similar coral cover of 20-30% [30][31][32], except for Pulau Jong with a lower coral cover of only 5% [31]. Subtidal sampling was conducted via SCUBA, and specimens were identified based on known anatomical descriptions [33]. ...
Despite the increasing recognition and importance surrounding bacterial and fungal interactions, and their critical contributions to ecosystem functioning and host fitness, studies examining their co-occurrence remain in their infancy. Similarly, studies have yet to characterise the bacterial and fungal communities associated with nudibranchs or their core microbial members. Doing this can advance our understanding of how the microbiome helps a host adapt and persist in its environment. In this study, we characterised the bacterial and fungal communities associated with 46 Pteraeolidia semperi nudibranch individuals collected from four offshore islands in Singapore. We found no distinct spatial structuring of microbial community, richness, or diversity across sampling locations. The bacterial genera Mycoplasma and Endozoicomonas were found across all samples and islands. The fungal genus Leucoagaricus was found with the highest occurrence, but was not found everywhere, and this is the first record of its reported presence in marine environments. The co-occurrence network suggests that bacterial and fungal interactions are limited, but we identified the bacterial family Colwelliaceae as a potential keystone taxon with its disproportionately high number of edges. Furthermore, Colwelliaceae clusters together with other bacterial families such as Pseudoalteromonadaceae and Alteromonadaceae, all of which have possible roles in the digestion of food.
... The average proportion of coral perimeter that was in contact with macroalgae was also higher at Kusu Island and Pulau Hantu (mean proportion of 0.237 and 0.320, respectively) than at Pulau Satumu (mean proportion of 0.024). The lower abundance of macroalgae at Pulau Satumu could be attributed to higher herbivory rates by herbivorous fishes (Bauman et al., 2017) and sea urchins (Goh and Lim, 2015). Stronger wave exposure at Pulau Satumu compared to inshore reefs including Pulau Hantu and Kusu Island (Ng et al., 2019) might also limit the settlement of macroalgal propagules and survival of loosely attached macroalgal individuals (Thomsen and Wernberg, 2005;Taylor et al., 2010). ...
Interactions between corals and macroalgae are important in influencing benthic community structures on coral reefs and have become increasingly common occurrences. However, little is known about their temporal variation as most studies have only documented them from single surveys. To investigate the dynamics of coral–macroalgal interactions, we surveyed three urbanised reefs in Singapore bi-monthly for three years. We found that the frequency of coral–macroalgal interactions varied greatly across sites and seasons. The extent of coral–macroalgal contact was positively correlated with macroalgal abundance, but the correlation differed significantly among macroalgal genera. The growth rates of Goniopora, Montipora and Pavona corals, but not Platygra, were also negatively correlated with the extent of macroalgal interactions. Overall, our results highlight that coral–macroalgal interactions are spatially and temporally dynamic, with varying effects among coral species. It is critical to consider seasonal fluctuations of macroalgae if the overall long-term impacts of macroalgae are to be understood.
... In this study the linier regression analysis did not show a significant correlation between sea-urchin density and the density of either macroalgae or seagrasses, despite the greater abundance of urchins in the sparser restored seagrass area and the greater abundance of macroalgae in the denser natural seagrass beds. It is interesting to note that these findings are similar to the results of research in Singapore [57], which also found no significant correlation between urchin and macroalgal density, and Fiji, where urchins density did not correlate significantly with either seagrass or macroalgal density [58]. However, the results contrast with a study in Karimunjawa National Park, Jepara in western Indonesia [59] where seagrass and sea urchin density were strongly and negatively correlated. ...
Seagrass decline and loss have been reported worldwide. Restoration is an increasingly popular approach to improving ecosystem services and may become a mitigation measure for seagrass habitat loss. However, in Indonesia seagrass restoration is still at a trial stage and small scale. This study aimed to compare the seaweeds and sea urchin communities in restored seagrass beds and in control areas (natural seagrass beds) around Barrang Lompo Island, Indonesia. Sea urchin and seaweed community structure was compared using non-metric multidimensional scaling and Bray-Curtis cluster analysis, while (as an indicator of ecosystem service provision) species contribution to the difference in sea urchin and seaweed community structure was analysed using SIMPER (similarity of percentages); both analyses were implemented in PRIMER v7. Regression analysis in SPSS v25 was applied to evaluate the correlations between sea urchin and seaweed density, sea urchin and seagrass density, seaweed and seagrass density. The results indicate that, although the ability to harbour associated organisms differed, restored seagrass beds can provide habitat for associated organisms and improve ecosystem services.
... Tatsuya, Miyuki & Akira (2016), also 73 reported that grazing and high densities of D. setosum control algal coverage and density on the 74 seaweed bed ecosystems along the central coast of Japan. However, in Singapore reefs, D. 75 setosum is not an important component of the herbivore guild (Goh & Lim, 2015). Seasonal 76 changes have also been reported in the size of the gut of some sea urchins related to changes in 77 food availability (Lawrence, Lawrence & Watts, 2013), there were no changes in D. setosum in ...
Sea urchins are keystone herbivores that greatly influence primary productivity, algal abundance and scleractinian coral recruitment. The long-spined black sea urchin Diadema setosum is widespread and abundant in reef flats throughout the Philippines. Prior studies regarding the feeding preference of D. setosum have been conducted overseas, but little is known about the impact of the echinoid herbivory on reef flat communities in the Philippines . Feeding preferences of D. setosum on four common marine plant species, Halimeda macroloba , Ceratodictyon spongiosum, Padina sp., and Enhalus acoroides were investigated at the University of the Philippines Visayas Marine Biological Laboratory, located in Taklong Island National Marine Reserve (TINMR), Guimaras. Two food choice experiments were conducted; choice feeding and no-choice feeding. The outcome of choice feeding experiments, expressed as consumption (in g) and percent consumption (%), were used to determine its feeding preferences. The two most preferred feeds determined were then used in no-choice feeding experiment to measure its consumption rate (g⸱echinoid ⁻¹ ⸱hr ⁻¹ ). Results of the choice feeding experiment show that D. setosum significantly prefers C. spongiosum (4.83 ± 2.56 g consumption or 32.2%) and H. macroloba (3.73 ± 2.27 g or 24.8%), and avoids E. acoroides (only 0.17 ± 0.22 g or 1.13%) (F= 5.423, p < 0.05). The no-choice feeding experiment between preferred feeds show H. macroloba was consumed more (0.22 ± 0.16 g⸱echinoid ⁻¹ ⸱hr ⁻¹ ) than C. spongiosum (0.15 ± 0.05 g⸱echinoid ⁻¹ ⸱hr ⁻¹ ) although there was no significant difference (p > 0.05) in consumption rate. Results of the no-choice feeding experiment may have been affected by poor water quality and are considered inconclusive. Nevertheless, the study supports the ecological role of D. setosum as an important herbivore that regulates certain macroalgal species in TINMR through its grazing activities.
... Larvae were pooled together, cleaned with 0.2 µm filtered seawater (FSW), and kept in aerated tanks prior to experiments. Six locally abundant macroalgal species (Lee et al., 2009;Goh and Lim, 2015) were collected from Kusu and maintained in aquaria 2-3 days prior to experiments. The algal species collected were Bryopsis pennata var. ...
... Individuals of Sargassum sp. and Bryopsis sp. were used for this experiment as these algae are locally abundant and have been shown to reduce post-settlement survivorship in previous studies (Lee et al., 2012;Goh and Lim, 2015). The study was conducted on the fringing reef crest and flat of Sister's Island where Sargassum sp. and Bryopsis sp. were relatively abundant on the reef crest and flat, respectively (≥10 individuals per site). ...
... Larvae were pooled together, cleaned with 0.2 µm filtered seawater (FSW), and kept in aerated tanks prior to experiments. Six locally abundant macroalgal species (Lee et al., 2009;Goh and Lim, 2015) were collected from Kusu and maintained in aquaria 2-3 days prior to experiments. The algal species collected were Bryopsis pennata var. ...
... Individuals of Sargassum sp. and Bryopsis sp. were used for this experiment as these algae are locally abundant and have been shown to reduce post-settlement survivorship in previous studies (Lee et al., 2012;Goh and Lim, 2015). The study was conducted on the fringing reef crest and flat of Sister's Island where Sargassum sp. and Bryopsis sp. were relatively abundant on the reef crest and flat, respectively (≥10 individuals per site). ...
Scleractinian corals are vulnerable to a range of environmental disturbances, but generally suffer the highest rates of mortality during early life-history stages, i.e., from larval settlement until a few months post-settlement. Variations in survival rates of corals during this period play a key role in structuring adult coral populations. Many coral reefs have experienced reductions in herbivory rates due to overfishing and consequent increases in macroalgae, however, the effect of increased coral-algal interactions may vary between coral life-history stages and among locations. Therefore understanding the relative importance of different drivers of mortality across early life-history stages, under a range of environmental conditions, is essential to effectively manage and restore coral reefs. To date, however, relatively few studies have (a) examined coral-algal interactions across several early life-history stages (i.e., from planulae to juvenile colonies) and (b) done so in highly disturbed reefs close to large urban centers. We investigated the effect of algal-coral-herbivore interactions on early life history stages in the coral Pocillopora acuta on coral reefs off mainland Singapore, a heavily disturbed "urbanized reef environment". Larval settlement rates were estimated in the presence of six macroalgal species ex situ. The effect of direct interaction with two macroalgal species on newly settled spat was examined in situ and the effect of reduced herbivory was tested with exclusion cages on naturally settled 9-month-old juveniles in situ. We found significant reductions in P. acuta settlement in the presence of four macroalgal species. Newly settled spat of P. acuta had significantly lower survivorship when in contact with Sargassum sp. on the reef crest but not with Bryopsis sp. on the reef flat. Herbivore exclusion reduced survivorship of juvenile corals, which was associated with increased sediment accumulation, but not with algal biomass. Our results suggest coral recruitment on heavily disturbed reefs can be impacted by species-specific macroalgal Frontiers in Marine Science | www.frontiersin.org 1 October 2018 | Volume 5 | Article 385 Leong et al. Coral-Algal Interaction in a Disturbed Reef System effects via reduced settlement on ephemeral substrata and reduced survivorship when in direct contact with Sargassum sp. Furthermore, recruitment may be negatively impacted by reductions in herbivory, possibly via increased abundance of epilithic algal matrix leading to sediment trapping.
... Much of our understanding, however, of the ecosystem function of urchins comes from disturbed systems which have been heavily overfished, including East Africa (Carreiro-Silva and McClanahan, 2001;McClanahan et al., 1994), French Polynesia (Bak, 1990;Done et al., 1991;Peyrot-Clausade et al., 2000), and parts of Asia (Dumont et al., 2013;Goh and Lim, 2015). It has been hypothesised that overfishing released urchins from predation, in turn increasing their relative contribution to ecosystem processes such as grazing and bioerosion (McClanahan and Shafir, 1990;Steneck, 2013). ...
Urchins are ubiquitous components of coral reefs ecosystems, with significant roles in bioerosion and herbivory. By controlling urchin densities, triggerfishes have been identified as keystone predators. However, the functional linkages between urchins and triggerfishes, in terms of distributional patterns and concomitant effects on ecosystem processes, are not well understood, especially in relatively unexploited systems. To address this we censused urchins and triggerfishes on two cross-shelf surveys on the Great Barrier Reef (GBR) at the same times and locations. We also evaluated the role of urchins in bioerosion. Although urchin abundance and triggerfish biomass varied by 80% and nearly 900% across sites, respectively, this variability was driven primarily by shelf position with no evidence of top-down control on urchins by triggerfishes. Low urchin abundances meant urchins only played a minor role in bioerosion. We highlight the potential variability in functional links, and contributions to ecosystem processes, among regions.
... For instance, Huang et al. (2009) observed 161 species in 2006-2007, a level of diversity on par with surveys at more remote locations within the surrounding region (Harborne et al., 2000;Affendi et al., 2005;Huang et al., 2015). Macroalgal competitors of coral include the genera Bryopsis and Sargassum (Lee et al., 2012) but cover on the reef crest is generally low at ≤20% (Guest et al., 2016), though this varies considerably between sites, as well as in relation to abundances of the urchin, Diadema setosum (Goh and Lim, 2015). Guest et al. (2016) found no evidence of phase shifts between coral and macroalgal dominated states over time. ...
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.
... Pulau Satumu) where sediment-generating activities are less intense (Low & Chou, 1994;Tun, 2012), Shannon indices were consequently the lowest at Lazarus and highest at Raffles. This variation in biological community development was also evident from the wide range in percentage coral cover across plots which, with the exception of REUs at Raffles, were generally lower than contemporary live coral cover estimates at their respective reefs (~40% at Raffles and Kusu,~20% at the Sisters', and~5% at St John's and Lazarus) (Goh & Lim, 2015;Tun, 2012). While this may suggest a limit on the effectiveness of the REUs to support hard coral establishment, it is also plausible that the disparity was a result of the prevailing hydrodynamic conditions which influenced the degree of successful coral recruitment across Singapore's reefs. ...
Artificial reefs provide substrates that facilitate the rapid recruitment of marine biota such as corals and fish, and are commonly employed as coral restoration tools to assist recovery in degraded areas. While this strategy is successful in the immediate years post-deployment, its contribution to restoration over longer time scales is less well understood. The biological communities on Reef Enhancement Units (REUs), which had been deployed for more than a decade on Singapore's sediment-affected coral reefs, were surveyed. The diversity of sessile lifeforms on the REUs was significantly higher in 2014 (H′ = 1.03) than 2004 (H′ = 0.60). Hard corals and coralline algae contributed most to the temporal dissimilarity and turf algae remained the dominant lifeform category in both years. In 2014, hard corals and abiotic components contributed most to the spatial dissimilarity among the six REU plots that were surveyed. Shannon diversity values of these plots ranged from 0.74–1.3. Scleractinian cover ranged from 0.4–31.5% and differed significantly among the plots. The REUs also augmented ecosystem functioning at their respective plots. Colonies from 10 of the 30 scleractinian genera recorded were sexually mature, and a total of 119 sessile and mobile reef taxa utilized the REUs for food and habitat. The results demonstrate that artificial reefs can contribute to the development of biological communities and ecosystem functioning in degraded coral habitats over the long run, and underscore the need for long-term monitoring to validate the effectiveness of reef restoration efforts.
... This is the basis of a structurally complex community with high biodiversity, high productivity and intricate food webs. Diverse communities of macroalgae (Chou and Lim, 1984;Lee et al., 2015a,b), sponges (Lim et al., , 2012a; other cnidarians (gorgonians, Goh et al., 1997;soft coral, Benayahu and Chou, 2010), flatworms, crustaceans, molluscs, echinoderms (Lane and Vandenspiegel, 2003;Goh and Lim, 2015), ascidians and fish are associated with Singapore's coral reefs. Strong El Niño effects were observed in 1998 and 2010 when widespread bleaching of organisms harbouring symbiotic dinoflagellates was observed (Guest et al., 2012). ...
Rapid and sustained coastal development, land reclamation, and intense use of surrounding waters by shipping, have changed the original land- and seascape of Singapore in the last two centuries. Reclaimed land now account for more than 30% of the current land area, with a concomitant loss of intertidal and subtidal habitats across most of the southern shoreline of Singapore mainland as well as other offshore islands. The extent of coral reefs, mangroves, mudflats, seagrass beds, estuarine reefs, sandy and rocky shores has diminished considerably, so much so that man-made habitats such as seawalls, tidal canals, swimming lagoons and other artificial structures now form significant marine habitats in their own right. These remarkable changes in the marine environment have affected marine organisms to a greater or lesser extent, based on the very limited information available on marine habitats in Singapore prior to large-scale reclamation. However, the present extent and diversity of marine life that can be observed in Singapore today is still impressive. Much remains to be discovered and deciphered in terms of their biology and ecology. New records and species new to science continue to be described, even as new coastlines are built, and organisms continually adapt to a changing environment characterized by chronic disturbance. This review serves as a snapshot of the current state of knowledge of marine habitats and biodiversity in Singapore based on existing literature. Key threats and knowledge gaps are also highlighted.
