Claire Schmoker

Non-proportional bioaccumulation of trace metals and metalloids in the planktonic food web of two Singapore coastal marine inlets with contrasting water residence times.

We analyzed the concentrations of trace metals/metalloids (TMs) in the water, sediment and plankton of two semi-enclosed marine coastal inlets located north of Jurong Island and separated by a causeway (SW Singapore; May 2012-April 2013). The west side of the causeway (west station) has residence times of approximately one year, and the east side of the causeway (east station) has residence times of one month. The concentrations of most of the TMs in water and sediment were higher in the west than in the east station. In the water column, most of the TMs were homogeneously distributed or had higher concentrations at the surface. Preliminary evidence suggests that the TMs are primarily derived from aerosol depositions from oil combustion and industry. Analyses of TMs in seston (>0.7μm; mostly phytoplankton) and zooplankton (>100μm) revealed that the seston from the west station had higher concentrations of most TMs; however, the concentrations of TMs in zooplankton were similar at the two stations. Despite the high levels of TMs in water, sediment and seston, the bioaccumulation detected in zooplankton was moderate, suggesting either the presence of effective detoxification mechanisms or/and the inefficient transfer of TMs from primary producers to higher trophic levels as a result of the complexity of marine planktonic food webs. In summary, the TM concentrations in water and seston are not reliable indicators of the bioaccumulation at higher trophic levels of the food web.

Effects of eutrophication on the planktonic food web dynamics of marine coastal ecosystems: The case study of two tropical inlets

We studied the plankton dynamics of two semi-enclosed marine coastal inlets of the north of Jurong Island separated by a causeway (SW Singapore; May 2012-April 2013). The west side of the causeway (west station) has residence times of ca. one year and is markedly eutrophic. The east side (east station) has residence times of one month and presents lower nutrient concentrations throughout the year. The higher nutrient concentrations at the west station did not translate into significantly higher concentrations of chlorophyll a, with the exception of some peaks at the end of the South West Monsoon. Microzooplankton were more abundant at the west station. The west station exhibited more variable abundances of copepods during the year than did the east station, which showed a more stable pattern and higher diversity. Despite the higher nutrient concentrations at the west station (never limiting phytoplankton growth), the instantaneous phytoplankton growth rates there were generally lower than at the east station. The phytoplankton communities at the west station were top-down controlled, largely by microzooplankton grazing, whereas those of the east station alternated between top-down and bottom-up control, with mesozooplankton being the major grazers. Overall, the trophic transfer efficiency from nutrients to mesozooplankton in the eutrophic west station was less efficient than in the east station, but this was mostly because a poor use of inorganic nutrients by phytoplankton rather than an inefficient trophic transfer of carbon. Some hypotheses explaining this result are discussed.

Opinions on the Sustainable Development of Aquaculture

It is widely acknowledged that aquaculture represents the fastest growing food sector with an annual growth of approximately 10% [1]. Given the high growth rate of this sector, we must look to achieve a sustainable long-term production for the sake of the coming generations. Here we provide our opinion whereby we emphasize the need to rely and build on existing knowledge and studies, both social and environmental, as well as increasing state-of-the-art technologies on aquaculture practices. This will help to mitigate the potential impacts not only on the environment, but also on society at large, and will therefore ensure long-term sustainability. The aquaculture sector is a key industry providing a valuable food source to our increasing global population. Aquaculture, however, may also be a sector of activity which has significantly negative impacts on the environment, if not carried out in a sustainable way. One issue, for example, is the mass production of formulated feed which often contains natural fish products (fish meals and fish oils). The increasing demand for aquaculture feed (and other pet-feed) generates a high demand for fish, resulting sometimes in over-fishing of important fish stocks, thus indirectly affecting the overall sustainability of other marine resources [2].The industry is also regularly attributed to affect the natural environment drastically because of poor environmental practices. The excessive use of antibiotics, chemicals, and the intentional or unintentional destruction of important aquatic habitats such as mangroves, estuaries, and fjords; all important nursery grounds for wild fish stocks may also be generated if the industry develops without controls and regulations. Nevertheless, poor aquaculture practices may also affect nature besides the aquaculture industry itself by negatively altering aquatic resources through pollution of water bodies and sediments, inherently reducing the ecosystem carrying capacity. A number of notable negative events have occurred over the last decades that are associated with the aquaculture sector, most markedly the cases of widespread disease outbreaks. This has challenged the aquaculture sector everywhere across a range of farmed and wild organisms. Examples include infectious salmon anemia virus (ISAV), Acute Hepatopancreatic Necrosis Syndrome (AHPNS, also known as Early Mortality Syndrome or EMS) and regular Harmful Algae Blooms (HABs) occurring worldwide, generating fish and shellfish mass mortality or aquaculture products unfit for consumption [3,4]. Not only are such cases difficult for the farmers from an economical perspective (bankruptcy), but they also affect local communities which rely on the production and marketing of aquaculture products. This particular societal effect is even more important in areas where aquaculture is run as a “mom and pop business” and where cash flow is a crucial parameter that is not supported by international investments such as in large aquaculture farms. The disease control within the aquaculture industry, the social and environmental effects that are generated by aquaculture productions can be mitigated and managed by changing the industry’s habits from the initial planning stages through to the commercialization of aquaculture products. The solutions differ from one location to another, and are tied to the developmental stages of the sector in the various regions. The solution lies in the use of adapted legal framework which should be in line with social structures and environmental conditions, and the application of Best Aquaculture Technologies (BAT) such as state-of-the-art water treatment systems, water management tools, and means by which to firstly identify, then secondly to minimize and eliminate or mitigate disease occurrence and spread. Stakeholders such as government authorities, environmental companies, nature protection agencies, farmers and aquaculture associations, research institutes, not-for-profit companies, technology providers, and NGOs should ideally work together to ensure that such poor practices are an exception to the norm, and do not become the standard.