Beverly Pi Lee Goh

Novel perspectives on the bioaccumulation of PFCs--the concentration dependency.

The effects of exposure concentration on the bioaccumulation of four perfluorinated chemicals (PFCs): perfluorooctanesulfonate (PFOS), perfluoroocanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA), was investigated using green mussels, Perna viridis. Mussels were exposed to concentrations of 1 μgL(-1) and 10 μgL(-1) of each PFC for 56 days, and the bioaccumulation factors (BAF) were found to range from 15 to 859 L/kg and from 12 to 473 L/kg at 1 μgL(-1) and 10 μgL(-1), respectively. For all compounds, the BAF was larger at the lower dosage. Results suggest that the bioaccumulation of PFCs is concentration dependent. This concentration dependency can be explained by a nonlinear adsorption mechanism, which was further supported by the experimental results. The sensitivity of BAF to exposure concentration was found to be positively related to perfluorinated chain length and the binding affinity of the compounds. Bioaccumulation of long chain carboxylates and sulfonates are more easily affected by concentration changes. The validity of the conventional kinetic method was examined by comparing the results with the fundamental steady-state method: in addition to the above-mentioned batch test, mussels were also subject to 24-day exposure (1 μgL(-1) and 10 μgL(-1)) followed by 24-day depuration. Contradictions were found in the resulting kinetic BAF and model curving fittings. A new kinetic model based on adsorption mechanism was proposed, which potentially provide more accurate description of the bioaccumulation process of PFCs.

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).

Natural antifoulants from the marine cyanobacterium Lyngbya majuscula

Filamentous benthic marine cyanobacteria are a prolific source of structurally unique bioactive secondary metabolites. A total of 12 secondary metabolites, belonging to the mixed polyketide–polypeptide structural class, were isolated from the marine cyanobacterium, Lyngbya majuscula, and were tested to determine if they showed activity against barnacle larval settlement. The assays revealed four compounds, dolastatin 16 (1), hantupeptin C (4), majusculamide A (10), and isomalyngamide A (12), that showed moderate to potent anti-larval settlement activities, with EC50 values ranging from 0.003 to 10.6 μg ml−1. In addition, field testing conducted over a period of 28 days (using the modified Phytagel™ method) based on the cyanobacterial compound, dolastatin 16, showed significantly reduced barnacle settlement as compared to controls at all the concentrations tested. The results of this study highlight the importance of marine cyanobacteria as an underexplored source of potential environmentally friendly antifoulants.

In situ microcosms to study the impact of heavy metals resuspended by dredging on periphyton in a tropical estuary

Ponggol estuary, located on the northeastern coast of Singapore, is heavily impacted by reclamation, dredging, construction and shipping. Tin, lead, nickel, cadmium, copper and zinc in the particulate and dissolved fraction and in sediments were monitored biweekly in the estuary from July 1999 to June 2000. The concentrations of tin, lead, nickel, cadmium, copper and zinc were observed to range from ND-92 ppm, ND-303 ppm, ND-2818 ppm, ND-74 ppm, ND-1117 ppm and ND-137000 ppm, respectively, in the dissolved, particulate and sediments fractions. Intensive dredging activity occurred during the monitoring period, and this may have led to the resuspension and increased bioavailability of particulate metals. Periphytic algae were established on glass slides and exposed to previously measured environmental levels of heavy metals using in situ estuarine microcosms. The toxicity of heavy metals in various fractions to periphytic algae was assessed from the changes in their chlorophyll a content. Cadmium had the least significant effect followed by lead, zinc, nickel, tin and copper at all concentrations tested. A reduction in periphyton biomass (with respect to controls) of 95-100% was observed for treatments with metals in particulate form. In addition, exposure to contaminated sediments for 3 days significantly decreased chlorophyll a by 90-99% compared to controls. High concentrations of zinc (9893-17240 mg l(-1)), copper (5-11 mg l(-1)) and cadmium (1-1.8 mg l(-1)) recorded in the aqueous phase of treatment microcosms, and attributed to release from the contaminated sediments, could account for the toxicity to periphyton.

Sexual systems in scleractinian corals: an unusual pattern in the reef-building species Diploastrea heliopora

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.

Establishing the thermal threshold of the tropical mussel Perna viridis in the face of global warming

With increasing recognition that maximum oxygen demand is the unifying limit in tolerance, the first line of thermal sensitivity is, as a corollary, due to capacity limitations at a high level of organisational complexity before individual, molecular or membrane functions become disturbed. In this study the tropical mussel Perna viridis were subjected to temperature change of 0.4 °C per hour from ambient to 8-36 °C. By comparing thermal mortality against biochemical indices (hsp70, gluthathione), physiological indices (glycogen, FRAP, NRRT) and behavioural indices (clearance rate), a hierarchy of thermal tolerance was therein elucidated, ranging from systemic to cellular to molecular levels. Generally, while biochemical indices indicated a stress signal much earlier than the more integrated behavioural indices, failure of the latter (indicating a tolerance limit and transition to pejus state) occurred much earlier than the other indices tending towards thermal extremities at both ends of the thermal spectrum.

Distribution and abundance of sea urchins in Singapore reefs and their potential ecological impacts on macroalgae and coral communities

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 distribution and abundance of sea urchins in Singapore reefs, to examine algal cover, algal biomass, algal species and live coral cover, and to determine any interactions between urchin density and algal communities that may impact coral cover. Several reefs in Singapore were surveyed using belt transects measuring 20 m by 2 m, laid down on the reef crest. Abundance of urchins, algal species, biomass, and live coral cover were determined by the use of quadrats within each belt transect. This study revealed an increasing abundance of the sea urchin Diadema setosum in reefs progressing southwards away from mainland Singapore with low density of urchins occurring in Sisters’ Island, St John’s Island, Pulau Tekukor, and Kusu Island, and the highest density observed at Raffles Lighthouse. A significant negative linear relationship between algal cover and live coral cover (P < 0.05) was established. The results of this study indicate that sea urchins may not be an important component of the herbivore guild in Singapore.

The effect of transplantation on reproduction in clonal ramets of Goniopora columna on Singapore's coral reefs

Summary Ramets of the coral Goniopora columna (Dana, 1846–1849) were excised from five large colonies at one site south of mainland Singapore and transplanted within the same site and depth (2.3 m); to a more disturbed site closer to the mainland at a similar depth (2.2 m); and to greater depth at both sites (8.9 m and 7.6 m, respectively). Ramets were left for one year, then harvested before the predicted spawning periods. Fecundity (average number of oocytes polyp−1), reproductive effort (average oocyte diameter), and polyp tissue diameter were compared among transplanted clonal ramets, control ramets, and parent colonies. Typically, fragmentation in corals results in reductions in reproductive output because energy is diverted into tissue repair, but in this case reproductive effort and fecundity did not change significantly when ramets were transplanted within the same site and depth. Clonal fragments transplanted to the more disturbed site had significantly fewer oocytes, smaller oocytes and smaller polyps after one year suggesting that energy was diverted away from normal functions in response to stressors in the new environment. Ramets transplanted to 7–9 m bleached at both sites after acute periods of reduced irradiance, resulting in high mortality and reproductive failure in surviving ramets.

Environmental correlates of Thalassia hemprichii status descriptors: an evaluation of tools for diagnostic monitoring

Abstract Accurate evaluation of target organisms is fundamental to quantify responses to disturbances, elucidate thresholds and strengthen effective management. Threats to seagrasses in Singapore are excessive nutrients and sedimentation, leading to an evaluation of descriptor utility to detect plant response to nutrient and light availability using Thalassia hemprichii as the model species. A combination of popularly used seagrass physio-morphological descriptors and epibiont biomass were measured to assess plant response to environmental quality. Results showed convincing support for the use of leaf pigments as indicators of light availability and salinity changes. Water column nitrification and phosphorus availability had strong effects on leaf nutrient content, leaf morphology and epibiont biomass. Relationships between leaf length and light contradicted expected patterns, where shorter leaves were associated with lowered light. This may be attributable to hydrodynamic or sedimentation regimes and hence, is not a reliable indicator of light limitation. There was strong support for inclusion of epibiont biomass as part of nutrient response evaluation since this descriptor correlated strongly with water column nutrients and appeared to limit light availability to the seagrass. This study demonstrated the importance of integrating various levels of plant descriptors to reliably assess seagrass status, employing different combination of descriptors to monitor specific stressors.