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Map of the Southern Islands of Singapore showing the location of sample sites. (HW1-3: Hantu West Patch reef 1-3; H1-4:Pulau Hantu 1-4 S1-4: Pulau Semakau 1-4; J1,2; Pulau Jong 1,2; RL 1,2: Raffles Lighthouse 1,2; SS1-3: The Sister's Islands 1-3; K1,2: Kusu Island 1,2; T1,2; Pulau Tekukor 1,2; SJ1: St John's Island 1)
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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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... study was conducted at selected sites at the Southern Islands of Singapore (Fig. 1). A total of 23 sites were surveyed from January 2011 to April 2011. These were fringing reefs around the island of Raffles Lighthouse, denoted as Area 1; fringing reefs at the islands of Pulau Semakau, Pulau Hantu, Pulau Jong and patch reefs at Pulau Hantu West, denoted as Area 2; and reefs surrounding Sisters' Islands, Kusu Island, ...
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... While diadematoids are largely recognized as omnivores, they mainly feed by grazing on algae scraped from hard substrates (Bronstein and Loya, 2014;Muthiga and McClanahan, 2020). Consequently, Diadema spp., like other members of this family, are potent 'environmental engineers', capable of altering the structure and composition of entire benthic communities (Hernańdez et al., 2008;Ling et al., 2009;Bronstein and Loya, 2014;Goh and Lim, 2015). As algal growth regulators, Diadema grazing restricts algae proliferation, thereby supporting the settlement and development of slower growing benthic organismssuch as corals (Lawrence, 1975;Sammarco, 1982;Bronstein and Loya, 2014;do Hung Dang et al., 2020). ...
The Eastern Mediterranean Sea is an exceptional habitat. Its relative isolation and distinct characteristics create a unique ecosystem recognized as a marine biodiversity hot spot, where one-fifth of the species are endemic. Yet, native Mediterranean biodiversity is under increasing threat, mainly due to massive alien species invasions of Indo-Pacific origin. To date, more than 800 non-indigenous species have been reported in the Eastern Mediterranean Sea, justifying its reputation as one of the most severely affected habitats in the world in terms of marine biological invasions. Here we summarized the Mediterranean invasion dynamics of the long-spined echinoid Diadema setosum (Leske, 1778), one of the most ubiquitous Indo-Pacific sea urchin species. We show an alarming exponential population growth of D. setosum throughout the Eastern Mediterranean since 2018, following more than a decade of ‘invasion lag’ since its first detection in 2006. Molecular analyses illustrate the presence of a single genetic D. setosum clade in the Mediterranean Sea – corresponding to the Arabian Peninsula clade of this species, reinforcing the notion of a Red Sea origin. Our data support the current working hypothesis that the initial introduction of D. setosum occurred in the Northern Levantine Basin from which it gradually expanded in both north-west and south-east trajectories – in contrast to a stepping-stone hypothesis of gradual advancement from the opening of the Suez Canal. Demographic data of D. setosum along the Israeli Mediterranean coastline reveals a well-established population of broad size distributions, from juveniles to adult individuals of remarkably large size. Additionally, we provide evidence of the reproductive capacity of D. setosum in its new environment. Due to the magnitude of Diadema’s ecological footprint, it poses a severe threat to the entire Eastern Mediterranean Sea, including the Levantine Basin and South Aegean Sea, calling for rapid and coordinated action at both national and regional scales.
... The D. setosum was dominant in Northern Vietnam, and D. savignyi was rare, by contrast, in southern Taiwan (Dang et al., data unpublished). A similar pattern found in the neighboring countries, D. setosum is dominant in Malaysia [23], Singapore [24,25], Thailand [26], Hongkong [27], and the central Philippines [28]. Lessios et al., [6] reported that the distribution of D. savignyi is more oceanic around the central Pacific, whereas that of D. setosum is more coastal along the Western Pacific. ...
The large sea urchins (Diadematidae) are widely distributed worldwide, from temperate to tropical waters. Diadematidae is an important herbivore in the coral reef ecosystem through herbivore-algal-coral interaction, which maintains the reef’s health. Many studies of Diadematidae have been performed around world, but in Vietnam, there is little known about the ecology of this group. Here, we first investigated the assemblage structure of Diadematidae in Northern Vietnam. We observed 43 sites of representative coral reefs in Ba Mun - Co To, Cat Ba - Ha Long, and Hon Me. Based on the surveys, we found four species of considerable size sea urchins, of which the most common species is Diadema setosum (79.8% of the total), Enchinothrix calamaris (10.1%), E. diadema (8.3%), and D. savignyi (1.8%). Among three study regions, Hon Me is the most diverse. In addition, Hon Me also has the highest density of sea urchins. However, this value is generally low compared to that in Southern Vietnam and other neighboring countries. Further study is needed to investigate the ecology and reproductive biology of Diadematidae to provide fundamental information for sustainable exploitation and conservation.
... 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 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.
