Aquaculture has been the subject of two recent high profile reports. The first, entitled Blue Frontiers, begins by asserting ‘There is a pressing need to elevate the debate on the future of aquaculture and to place this in the context of other animal food production systems, including wild capture fisheries’. The second report made the front cover of Time Magazine and poses the question ‘Can farming save the last wild food?"
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Although the various benefits of seaweeds are well recognised, potential health hazards are much less well researched, as an instance the possible presence of concentrated levels of natural radionuclides. In present work the concentrations of natural radionuclides in seaweed cultivated in Malaysian seas are assessed using conventional HPGe γ-ray spectrometry. An edible species of seaweed has been collected from several seaweed farms located along coasts of the Andaman and South China Sea. Activity concentrations of 226Ra, 228Ra and 40K in samples collected from Langkawi are observed to be greater than those from Sabah, while 40K radioactivity levels (2.2E3 ± 100 – 3.8E3 ± 180 Bq kg−1) in all samples are noted to be well above the world average value of between 400 and 580 Bq kg−1. The estimated amount of total potassium is in the range 68 – 120 g (kg of seaweed)−1 and 53–106 g kg−1 obtained via ICP-OES, which are in line with data for New Zealand seaweed of between 43.7 and 123 g kg−1. The estimated total effective dose of 84 μSv·y−1 is lower compared to a global internal dose of 290 μSv·y−1 as reported by UNSCEAR. Accordingly, the mean cancer risk from such consumption was also estimated to be slightly lower (1.92 × 10−3) compared to the ICRP cancer risk factor of 2.5 × 10−3 based on the additional annual dose limit of 1 mSv for a member of the general public, which gives an annual mortality probability of 10−5 (1 in 100,000; ICRP, 1991). Although posing
a low risk health hazard, periodic monitoring of natural radioactivity in foodstuff remains important in seeking to ensure the radiological safety of the public.
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Experiments have demonstrated that ocean acidification (OA) conditions projected to occur by the end of the century will slow the calcification of numerous coral species and acceler- ate the biological erosion of reef habitats (bioerosion). Microborers, which bore holes less than 100 μm diameter, are one of the most pervasive agents of bioerosion and are present throughout all calcium carbonate substrates within the reef environment. The response of diverse reef functional groups to OA is known from real-world ecosystems, but to date our understanding of the relationship between ocean pH and carbonate dissolution by micro- borers is limited to controlled laboratory experiments. Here we examine the settlement of microborers to pure mineral calcium carbonate substrates (calcite) along a natural pH gradi- ent at a volcanically acidified reef at Maug, Commonwealth of the Northern Mariana Islands (CNMI). Colonization of pioneer microborers was higher in the lower pH waters near the vent field. Depth of microborer penetration was highly variable both among and within sites (4.2–195.5 μm) over the short duration of the study (3 mo.) and no clear relationship to increasing CO2 was observed. Calculated rates of biogenic dissolution, however, were highest at the two sites closer to the vent and were not significantly different from each other. These data represent the first evidence of OA-enhancement of microboring flora colo- nization in newly available substrates and provide further evidence that microborers, espe- cially bioeroding chlorophytes, respond positively to low pH. The accelerated breakdown and dissolution of reef framework structures with OA will likely lead to declines in structural complexity and integrity, as well as possible loss of essential habitat.
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Organic extracts of 20 species of French seaweed have been screened againstTrypanosoma brucei rhodesiensetrypomastigotes, the parasite responsible for sleepingsickness. These extracts have previously shown potent antiprotozoal activitiesin vitroagainstPlasmodium falciparumandLeishmania donovani. The selectivity of the extractswas also evaluated by testing cytotoxicity on a mammalian L6 cell line. The ethylacetateextract of the brown seaweed,Bifurcaria bifurcata,showed strong trypanocidal activitywith a mild selectivity index (IC50= 0.53 μg/mL;selectivity index (SI)= 11.6). Bio-guidedfractionation led to the isolation of eleganolone, the main diterpenoid isolated from thisspecies. Eleganolone contributes only mildly to the trypanocidal activity of the ethylacetate extract (IC50= 45.0 μM, SI = 4.0). However,a selective activity againstP. falciparumerythrocytic stagesin vitrohas been highlighted (IC50= 7.9 μM, SI = 21.6).
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Seaweed farming is often depicted as a sustainable form of aquaculture, but suspected habitat alterations and spread of algae outside farms have rendered speculations on the actual degree of sustainability. We conducted an experimental field study on Unguja Island (Zanzibar, Tanzania) to investigate the effects of off-bottom seaweed farming on a tropical seagrass ecosystem, using 1.5 × 2.5 m experimental farm plots. After 11 wk, above-ground seagrass biomass was 40% lower than in control plots, owing to a combination of lower shoot density, shoot length and leaf growth rate. Since the biomass was constant between Day 15 and 75 in the farm (F) treatment, but increased by 67 vs. 48% in the 2 controls (control treatment [C] and stick-and-line control treatment [CSL]), the effect exerted by the farm was a lack of potential biomass increase rather than an actual decrease. The effect was transplanted to associated organisms both in terms of lower seagrass epiphyte cover and changes in the abundance of 2 dominating epifauna taxa (>1 cm): sea urchins and sponges. Furthermore, the F treatment caused an accumulation of seagrass leaf litter, but did not affect sediment organic matter (SOM) content. The mechanisms behind these effects were not explicitly tested, but algal shading, emergence stress and mechanical abrasion were identified as likely contributors. Interestingly, the effects were largely restricted to 1 of the 2 seagrass species present, Enhalus acoroides, while the other, Thalassia hemprichii, remained more or less unaffected. This may be due to reduced interspecific competition or species-specific differences in morphology and stress tolerance, and could in the long-term have implications for (amongst others) associated fish communities. Although seaweed farming at the current level is less detrimental than, for example, intensive shrimp farming, and therefore should be seen as a strong option for future aquaculture developments, intensive farming on seagrasses should be avoided or at least minimized by, for example, implementing other farming methods. The risk of ecosystem-level changes in large-scale and uncontrolled farm enterprises warrants a holistic and integrated coastal management approach which considers all aspects of the tropical seascape including human societies and natural resource use.
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Laminaria longicruris, a North Atlantic kelp with rapid growth rates and large biomass, is of both economic and ecological importance in subtidal coastal ecosystems, and is a key component of a variety of food webs. This species is known to suffer sporophyte deterioration at a temperature of 23°C, and summer temperature is known to constrain its southern limit of distribution. Our research shows that reproductive output in kelp is partially regulated by temperature as well. The role of temperature in determining the allocation of blade surface to meiospore production was quantified for populations of Laminaria longicruris at three study sites along a temperature gradient in the Northwestern Atlantic. Using a stratified random sampling technique, adult sporophytes were collected at sites in Long Island Sound (41° 17' N), Portsmouth, New Hampshire (43° 03'N) and Halifax, Nova Scotia (44° 38'N) in the spring of 1992. Photoperiod and insolation were roughly equivalent for all three sites. The ratio of sorusarea (reproductive tissue) to blade (vegetative tissue). was determined by morphometric analysis and used asa measure of reproductive effort. Nonparametric statistical· analysis revealed significant variation between sites with least reproductive effort occurring near the southern limit of the·geographical distribution range (Figure 1).With increasing temperature and decreasing latitude, fewer resources were allocated to reproduction. A regression line fit to the data for the three latitudes shows a positive correlation between reproductive output and latitude, with an X-intercept occurring at 37.8° N, roughly equivalent to the known observed limit of the species (Figure 2). A second regression line fit to the data (Figure 3) shows that, theoretically, reproduction does not occur at spring temperatures above 12°C,corresponding roughly to a summer temperature of 23°. A global temperature warming of Ito 2°C could eliminate the species from the Long Island Sound estuary by causing its geographical range to retreat northward.
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Porphyra is one of the world’s most valued maricultured seaweeds and has been cultivated for several hundred years in Asia. The objective of this study was to produce critical information as a guide for the selection of an appropriate Porphyra species from coastal New England for the development of a land-based aquaculture system. Four Northwest Atlantic Porphyra species: P. leucosticta, P. amplissima, P. linearis and P. umbilicalis, were cultivated for 1 and 2weeks at saturated light intensities (100–150μmol photons m−2s−1) and six combinations of ammonium (25 and 250μmoles L−1) and temperature (10, 15 and 20°C). Specific growth rate (SGR) increased with decreasing temperature in P. leucosticta, P. linearis and P. umbilicalis and increased with increasing temperature in P. amplissima. The SGR of all species was greater at the higher ammonium concentration. Porphyra linearis had the highest SGR, increasing in biomass by approximately 16% day−1. Phycoerythrin (PE) content was higher at 10°C and 250μmoles L−1 in all species except P. amplissima. The PE content, measured as fresh weight (FW), of P. linearis (29mg g−1 FW−1) and P. umbilicalis (26mg g−1 FW−1) was significantly higher than the other two species. Tissue nitrogen content of all species measured in dry weight was on average 1.45% higher at 250μmoles L−1 than at 25μmoles L−1 ammonium concentration. Porphyra umbilicalis had the highest tissue nitrogen contents (6.76%) at 10°C and 250μmoles L−1 ammonium. Based on these results, P. linearis and P. umbilicalis should be considered as potential candidates for bioremediation with finfish and shellfish mariculture.
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Optimal stocking density of the marine red algaAgarophyton vermiculophyllumwas determined to maximize the produc-tivity and nitrogen removal in biofloc effluent.Agarophyton vermiculophyllumwas cultured at 0.2, 2, 4 and 8 g L−1(FW)stocking densities, 160 ± 10μmol photons m−2s−1and 12:12 L:D photoperiod for 20 days.Agarophytonvermiculophyllumwas cultured in effluent from a juvenileParalichthysbiofloc tank culture system and von Stosch–enriched (VSE) medium at 20 °C. The total nitrogen and phosphorus concentration of VSE medium was adjusted to thebiofloc level, 1000μmol L−1and 33μmol L−1, respectively. Specific growth rate was significantly higher at 0.2, 2, 4 and 8g L−1in both media. However, the productivity was significantly higher at 8 than 0.2 g L−1in both media. Tissue carboncontents were not significantly influenced by the medium at 8 g L−1(34.9% in VSE and 34.0% in biofloc). However, tissuenitrogen content was significantly higher at VSE medium than at biofloc medium at 8 g L−1(3.7% in VSE and 3.4% inbiofloc). The carbon removal rate was highestat the highest stocking density, 1.98 mgC g−1DW day−1(VSE) and1.89 mgC g−1DW day−1(biofloc), respectively. Also, the nitrogen removal rate was highest at the highest stockingdensity, 0.21 mgN g−1DW day−1(VSE) and 0.19 mgN g−1DW day−1(biofloc), respectively. The nutrient removal wasnot significantly influenced by medium at 4 and 8 g L−1. These results show thatA. vermiculophyllumcan grow and havethe potential to remove nutrients in the biofloc medium at high nitrogen concentrations.
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Higher sterols are universally present in large amounts (20–30%) in the plasma membranes of all eukaryotes whereas they are universally absent in prokaryotes. It is remarkable that each kingdom of the eukaryotes has chosen, during the course of evolution, its preferred sterol: cholesterol in animals, ergosterol in fungi and yeast, phytosterols in higher plants, and e.g., fucosterol and desmosterol in algae. The question arises as to which specific properties do sterols impart to membranes and to which extent do these properties differ among the different sterols. Using a range of biophysical techniques, including calorimetry, fluorescence microscopy, vesicle-fluctuation analysis, and atomic force microscopy, we have found that fucosterol and desmosterol, found in red and brown macroalgae (seaweeds), similar to cholesterol support liquid-ordered membrane phases and induce coexistence between liquid-ordered and liquid-disordered domains in lipid bilayers. Fucosterol and desmosterol induce acyl-chain order in liquid membranes, but less effectively than cholesterol and ergosterol in the order: cholesterol> ergosterol > desmosterol > fucosterol, possibly reflecting the different molecular structure of the sterols at the hydrocarbon tail.
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Kappaphycus alvarezii was cultured in vitro under salinities ranging from 15 to 55 psu for 35 days to determine the differential effect on growth rate, carrageenan yield, and cellular structure. Plants kept in 15 psu died after 3 days, while plants cultured in 55 psu presented low growth rates during the entire experimental period (0.28% day−1 ). Plants cultured in 25, 35, and 45 psu showed growth rates normally associated with this species (between 3% and 4% day−1 ) and similar cellular morphology. Carrageenan yield was significantly higher in plants cultured in 25 psu in relation to the other treatments. As observed by light microscopy, plants cultured in 15 psu showed cellular turgidity and increased cell wall thickness, both consequences of hyposalinity. Chloroplasts and other membranous organelles underwent rupture and considerable disorganization in ultrastructure. Although branches from the 55 psu samples showed plasmolysis, cells were able to maintain chloroplast integrity, despite their rudimentary features. In high salinities, great concentrations of floridean starch grains were observed in subcortical cells, indicating their probable participation in osmoregulation. Based on these results, we defined the range of 25 to 45 psu as the limits of saline tolerance for K. alvarezii. While new field studies are required to confirm these results, it can be concluded that new sites, such as inactive or abandoned shrimp tanks with salinities up to 25 psu, could be considered for commercial farming.
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