Loke Ming Chou

Contrasting Patterns of Coral Bleaching Susceptibility in 2010 Suggest an Adaptive Response to Thermal Stress

Background Coral bleaching events vary in severity, however, to date, the hierarchy of susceptibility to bleaching among coral taxa has been consistent over a broad geographic range and among bleaching episodes. Here we examine the extent of spatial and temporal variation in thermal tolerance among scleractinian coral taxa and between locations during the 2010 thermally induced, large-scale bleaching event in South East Asia. Methodology/Principal Findings Surveys to estimate the bleaching and mortality indices of coral genera were carried out at three locations with contrasting thermal and bleaching histories. Despite the magnitude of thermal stress being similar among locations in 2010, there was a remarkable contrast in the patterns of bleaching susceptibility. Comparisons of bleaching susceptibility within coral taxa and among locations revealed no significant differences between locations with similar thermal histories, but significant differences between locations with contrasting thermal histories (Friedman = 34.97; p<0.001). Bleaching was much less severe at locations that bleached during 1998, that had greater historical temperature variability and lower rates of warming. Remarkably, Acropora and Pocillopora, taxa that are typically highly susceptible, although among the most susceptible in Pulau Weh (Sumatra, Indonesia) where respectively, 94% and 87% of colonies died, were among the least susceptible in Singapore, where only 5% and 12% of colonies died. Conclusions/Significance The pattern of susceptibility among coral genera documented here is unprecedented. A parsimonious explanation for these results is that coral populations that bleached during the last major warming event in 1998 have adapted and/or acclimatised to thermal stress. These data also lend support to the hypothesis that corals in regions subject to more variable temperature regimes are more resistant to thermal stress than those in less variable environments.

Feeding habits and trophic organization of the fish community in shallow waters of an impacted tropical habitat

The feeding ecology and trophic organization of 32 fish species found in an highly impacted waters from four sites of the eastern Johor Strait, Singapore has been studied. Among the wide variety of prey consumed, calanoid copepod (46.9% domination) was the most important dietary component of fishes in this ecosystem. In general, fishes show a narrow range in adaptive radiation of feeding habits, with only three main guilds identified. Spatially, a more complex guild was recorded for the habitat with more complex structure, although the number of guilds was consistent at three to four guilds. Seasonally, a change of guild organization was observed. Many fish species placed in one guild might be classified in another guild during a different season. This information facilitates the examination of complex associations of fishes and identifies groups of species that use similar resources within a specific community and can serve as a reference for feeding ecology of fishes in highly impacted tropical habitats.

Impacts of pollution on marine life in Southeast Asia

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.

Seasonal reproduction in equatorial reef corals

Summary 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 Singapores 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.

Reproductive seasonality in an equatorial assemblage of scleractinian corals

[Extract] Multi-specific, synchronous spawning of scleractinian corals was first documented on Australia’s Great Barrier Reef (GBR) in the early 1980s (Harrison et al. 1984). There, over a period of eight nights in late spring, at least 133 coral species released their gametes for external fertilisation and more than 30 species spawned on the same night on one reef (Willis et al. 1985; Babcock et al. 1986). However, the causal factors responsible for this remarkable phenomenon are still not clearly understood (see review in Harrison and Wallace 1990). Comparisons of reproductive patterns—from sites at a variety of latitudes, with contrasting seasonal and environmental conditions—can help to elucidate the ‘‘ultimate’’ causes of reproductive seasonality and synchrony (Oliver et al. 1988). Early examples of such comparisons showed that multi-species reproductive synchrony is not a characteristic of all coral communities (Richmond and Hunter 1990). In particular, studies in parts of the Red Sea and the Caribbean found that corals at those sites tended to spawn asynchronously (Shlesinger and Loya 1984; Szmant 1986). This lack of synchrony was attributed to a reduction in environmental seasonality and a narrowing in the ranges of certain environmental parameters, in particular annual sea surface temperatures (Richmond and Hunter 1990) and tidal amplitudes (the difference between mean low water springs and mean high water springs) (Oliver et al. 1988).

Marine Habitats in One of the World’s Busiest Harbours

Singapore’s limited marine territory of approximately 600 km 2 supports one of the world’s busiest harbours. Over 133,000 vessels (above 75 gross tonnes) called at the port in 2004. Thirty-five percent comprised regional ferries linking Singapore with various ports of Indonesia’s Riau province. Other vessels were mainly containers and tankers which facilitate movement of 1 billion gross tonnes of cargo through the port. To accommodate such intense shipping activity and provide safe navigation to the heavy vessel traffic, the port waters cover 82% of Singapore territorial waters. Most of the port provisions are located in the seas south of the main island, particularly the south-western sector (Figure 1). Wharf and berthing facilities dominate the southwestern coastline, which have been transformed by coastal reclamation. Fairways, anchorages and vessel manoeuvring areas intermesh between the fifty-odd smaller offshore islands scattered mostly in the southern waters. A spectrum of marine habitats typical of tropical regimes is found in this heavily utilized marine environment. Fringing and patch reefs are present among the southern islands together with seagrass meadows and mangrove stands, all varying in areal extent. A range of seashore types including rocky, sandy and muddy exists. The seafloor is now mostly dominated by mud bottoms as most of the sand deposits have been exhausted for reclamation while the continuous rain of suspended sediment adds more silt. Threats from shipping include vessel movement, grounding and accidental spillage of hazardous materials. Other activities such as land reclamation, seabed dredging and the dumping of dredged spoils contribute to increased suspended sediment, modification of hydrodynamic patterns and changed tidal speeds at different locations. High energy wash from increasing numbers and operating frequency of fast-going vessels such as high-speed passenger ferries scour exposed shores and reef flats. Large tracts of razed corals on reef flats provide evidence of grounding by flat-bottom barges, often connected with a nearby development activity. The spillage of 28,500 tonnes of heavy marine fuel oil into the sea

More evidence for pervasive paraphyly in scleractinian corals: systematic study of Southeast Asian Faviidae (Cnidaria; Scleractinia) based on molecular and morphological data.

Coral taxonomy and systematics continue to be plagued by a host of problems. Due to high phenotypic variability within species, morphological approaches have often failed to recognize natural taxa, and molecular techniques have yet to be applied to many groups. Here, we summarize the levels of paraphyly found for scleractinian corals and test, based on new data, whether paraphyly is also a significant problem in Faviidae, the second-most speciose hermatypic scleractinian family. Using both DNA sequence and morphological data we find that, regardless of analysis technique (maximum parsimony, maximum likelihood and Bayesian likelihood), many conventional taxonomic groups are not monophyletic. Based on two mitochondrial markers (COI and a noncoding region) that we amplified for 81 samples representing 41 faviid species and 13 genera, five genera that are represented by more than one species are paraphyletic, as is the family Faviidae. The morphological characters currently used to identify these corals similarly fail to recover many genera. Furthermore, trees based on both data types are incongruent, and total evidence analysis does little to salvage conventional taxonomic groupings. Morphological convergence, phenotypic variability in response to the environment, and recent speciation are likely causes for these conflicts, which suggest that the present classification of corals is in need of a major overhaul. We propose more detailed studies of problematic faviid taxa using standardized morphological, mitochondrial, and nuclear genetic markers to facilitate combining of data.

The status and impact of introduced freshwater animals in Singapore

Abstract Singapores location at the centre of major air and shipping routes has resulted in the introduction of numerous species of freshwater animals from various parts of the world. To date, some 37 introduced freshwater fishes, turtles, molluscs and prawns have become established here. Studies show that the introduced species have not significantly affected the fauna in pristine forested streams. This is probably because much of the native freshwater fauna includes acid-water species, whereas introduced ones prefer more neutral and harder waters. Of the 54 native Singapore freshwater fishes, the greater majority (over 80%) are forest species adapted to living in acid waters. These species have suffered mainly because of forest clearance and more than 50% of this fauna is now extinct. A similar situation occurs for freshwater prawns. The conservation of the native freshwater fauna in Singapore should thus centre on the preservation of their natural forest habitat. There is a potential danger posed by imported fishes which originate from soft, acid waters in Africa, South America or other parts of Southeast Asia. Thus far, only one or two species have managed to establish themselves in Singapore. Legislation and appropriate quarantine measures will be needed to ensure that alien tropical acid water species do not become established here.

Impacts of sedimentation on soft-bottom benthic communities in the southern islands of Singapore

Benthic community data from eight stations around Pulau Semakau, an island south of Singapore, were collected during three surveys and analysed to determine changes in community structure under different sediment regimes resulting from construction activity at the eastern part of Pulau Semakau. Multidimensional Scaling (MDS) Configurations indicated distinct changes in the abundance, family number and diversity of benthic invertebrate fauna, which corresponded to sedimentation rate. SIMPER analysis suggested that polychaetes tolerate increased sedimentation better than crustaceans and molluscs. Sedimentation rate and other physico-chemical parameters were also investigated to determine the relationship between environmental factors and benthic community structure. Results from Principal Component Analysis (PCA) showed that sedimentation rate, sediment composition and ammonia concentration were the most important factors impacting the benthic community.

Heavy metal levels in marine sediments of Singapore

Marine environmental levels of the metals copper (Cu), zinc (Zn), lead (Pb) and cadmium (Cd) were measured from sediments collected around 20 coastal locations around Singapore, over a 2-year period. Sediment-size analysis was conducted on sediment samples, and Atomic Absorption Spectrophotometry was used in the analyses of sediment heavy metal concentrations. The levels of heavy metals in marine sediment was largely dependant on sediment particle size, as illustrated by the correlation of sediment size with Multidimensional Scaling (MDS) configurations of sediment metal concentrations. In addition, the proximity to shipping activity, and the release of anti-fouling paint from boats also influence heavy metal concentrations in marine sediments of Singapore.