On the detoxification of benthic bivalves contaminated by POPs: insights from experimental and modelling approaches

Rearing benthic bivalves that are contaminated by persistent organic pollutants (POPs) in areas with low pollution levels permits their natural detoxification. Here, we present the results of novel detoxification experiments conducted with the Manila clam (Tapes philippinarum) in the Venice Lagoon; these experiments were conducted both in summer and winter. Measurements of dioxins (PCDD), furans (PCDF), polychlorinated biphenyl (PCB) and hexachlorobenzene (HCB) concentrations in clam flesh over time after their resettlement in cleaner areas allowed for determining the minimum time required to reach safe toxicity levels. Moreover, dioxin fingerprint dynamics demonstrated successful detoxification from industrial contaminants. A simple bioaccumulation/detoxification model applied to the collected data provided for the first time estimation of detoxification rates and half-lives for POP congeners in clam flesh. This work provides a basis for considering natural detoxification as a viable solution for safely exploiting resources otherwise restricted from human consumption due to associated health risks.     

Phosphates for Pb immobilization in soils: a review

In its soluble ionic forms, lead (Pb) is a toxic element occurring in waters and soils mainly as the result of human activities. The bioavailability of lead ions can be decreased by complexation with various materials in order to decrease their toxicity. Pb chemical immobilization using phosphate addition is a widely accepted technique to immobilize Pb from aqueous solution and contaminated soils. The application of different P amendments cause Pb in soils to shift from forms with high availability to the most strongly bound Pb fractions. The increase of Pb in the residual or insoluble fraction results from formation of pyromorphite Pb₅(PO₄)₃X where X = F, Cl, Br, OH, the most stable environmental Pb compounds under a wide range of pH and Eh natural conditions. Accidental pyromorphite ingestion does not yield bioavailable lead, because pyromorphite is insoluble in the intestinal tract. Numerous natural and synthetic phosphates materials have been used to immobilize Pb: apatite and hydroxyapatite, biological apatite, rock phosphate, soluble phosphate fertilizers such as monoammonium phosphate, diammonium phosphate, phosphoric acid, biosolids rich in P, phosphatic clay and mixtures. The identification of pyromorphite in phosphate amended soils has been carried out by different non destructive techniques such as X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray absorption fine structure, transmission electron microscopy and electron microprobe analysis. The effectiveness of in situ Pb immobilization has also been evaluated by selective sequential extraction, by the toxicity leaching procedure and by a physiologically based extraction procedure simulating metal ingestion and gastrointestinal bioavailability to humans. Efficient Pb immobilization using P amendments requires increasing the solubility of the phosphate phase and of the Pb species phase by inducing acid conditions. Although phosphorus addition seems to be highly effective, excess P in soil and its potential effect on eutrophication of surface water, and the possibility of As enhanced leaching remains a concern. The use of mixed treatments may be a useful strategy to improve their effectiveness in reducing lead phyto- and bioavailability.     

The biogeochemistry of selenium in Sunan grassland,Gansu, Northwest China,casts doubt on the belief that Marco Polo reported selenosis for the first time in history

In order to clarify the historic academic problem of whether or not livestock poisoning in ancient Suzhou of Northwest China, recorded by Marco Polo in 1295, was selenosis, this study deals with the biogeochemistry of selenium in Sunan County in the Hexi Corridor, which is part of ancient Suzhou in China. It was found that quite a number of farm animals had suffered from intoxication and died as a result of grazing poisonous grasses, mostly Oxytropis DC, Stellera chamaejasme, and Achnatheru inebrians. Toxic symptoms of livestock grazing on Oxytropis DC are similar to those of selenium toxicity, for instance, hair loss and hoof lesions as described by Marco Polo. Therefore, we thought that toxic grass, probably Oxytropis DC, led to the intoxication of livestock recorded by Marco Polo. Average Se concentrations in two members of this species were 0.112 +/- 0.038 mg/kg for the root of Oxytropis glabra, 0.102 +/- 0.027 mg/kg for the stem and leaf of Oxytropis glabra, and 0.066 +/- 0.009 mg/kg for Oxytropis ochrocephala. The average soil selenium concentration was 0.205 +/- 0.127 mg/kg on grassland producing Oxytropis glabra and 0.152 +/- 0.024 mg/kg on grassland producing Oxytropis ochrocephala. The average Se concentration in other plants was 0.076 mg/kg in the root of Ephedra monosperma Mey, 0.029 mg/kg in the root of Rheum palmatum, 0.031 mg/kg in the root of Stellera chamaejasme, 0.037 mg/kg in Achnatherum inebrians, and 0.067 mg/kg in forage grass (Achnatherum splendens ohwi). Selenium concentrations in soils and plants in Sunan County are far less than the thresholds causing selenium toxicity in livestock. As a result, this study concludes that the livestock poisoning recorded by Marco Polo in 1295 might not have been selenosis.     

Insights from complete-incomplete brood sex-ratio disparity

An assertion deeply rooted in the ornithological literature holds that sex-specific mortality causes a sex ratio disparity (SRD) between complete and incomplete broods. Complete broods are thought to reflect the primary sex ratio before any bias introduced by developmental mortality. Contrary to this view, however, complete and incomplete broods should exhibit identical sex ratio distributions even when the sexes experience differential mortality, as shown in the classic paper of Fiala (Am Nat 115: 442–444, 1980). Therefore, in partially unsexed samples, primary sex ratio biases cannot be distinguished from biases caused by differential mortality. In addition, complete broods do not represent primary sex ratio more accurately than incomplete ones and might even be misleading. Despite Fiala’s prediction, SRD does occur in some empirical studies. We show that this pattern could arise if (1) primary sex ratio affects chick mortality rates independently of sex (direct effect), (2) primary sex ratio covaries with a variable that also affects mortality rate, or (3) sex differential mortality covaries with overall mortality rate (indirect effects). Direct effects may cause stronger SRD than indirect ones with a smaller and opposite bias in the overall sex ratio and could also lead to highly inconsistent covariate effects on brood sex ratios. These features may help differentiate direct from indirect effects. Most interestingly, differences in covariate effects between complete and incomplete broods imply that influential variables are missing from the analysis.     

Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal

With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s⁻¹ and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect, in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced shelf/slope waters. Bacterioplankton abundances (<2 × 10⁹cells l⁻¹) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the thymidine uptake rates along CB (average of 1.46 pM h⁻¹) and WB (average of 1.40 pM h⁻¹) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the oligotrophic northwestern Sargasso Sea (<7 × 10⁸ cells l⁻¹; av 1.0 pM h⁻¹). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m⁻² d⁻¹) than in the CB (306 mg C m⁻² day⁻¹). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous organic matter, in particular in the western Bay, is important for meeting their carbon demand.     

Analysis and decomposition of condensed tannins in tree leaves

The decomposition of leaf litter is controlled by several factors. One factor that may play an important role is the content of condensed tannins (proanthocyanidins). Here we designed a combined method to isolate proanthocyanidins from leaf extracts, to convert them to anthocyanidins, and to quantify individual anthocyanidins exactly with a new, simple, but sensitive high-performance liquid chromatography method. We used this method to show composition of proanthocyanidins and to monitor degradation of proanthocyanidins and individual constituents in leaf litter in an aquatic environment over time. Despite the rapid decrease in the initial concentrations, a fraction of the proanthocyanidins remained detectable for several weeks.     

Trophic variation with length in two ommastrephid squids, <Emphasis Type="Italic">Ommastrephes bartramii</Emphasis> and <Emphasis Type="Italic">Sthenoteuthis oualaniensis</Emphasis>

From 1998 to 2001 a total of 200 Ommastrephes bartramii (27 paralarvae) and 170 Sthenoteuthis oualaniensis (14 paralarvae) were sampled from the Central North Pacific. One group of non-paralarval O. bartramii (n = 30) was sampled from farther northwest in 1996. The δ¹⁵N of mantle muscle of non-paralarval O. bartramii ( = 12.4‰) was significantly greater than that of non-parlarval S. oualaniensis ( = 8.1‰) (P < 0.001). The δ¹⁵N of whole paralarvae of O. bartramii ( = 6.4‰) was not significantly different than parlarvalae of S. oualaniensis ( = 6.1‰) (P = 0.528). There was no significant difference between the mantle muscle δ¹⁵N values of male (n = 95, = 13.3‰) and female (n = 18, = 12.9 ‰) O. bartramii greater than 300 mm mantle length (ML) (P = 0.15). There was also no significant difference between the mantle muscle δ¹⁵N values of male (n = 15, = 7.2‰) and female (n = 26, = 7.3 ‰) S. oualaniensis in the same size range (P = 0.41). Overall there was a distinct logistic increase in δ¹⁵N with mantle length for O. bartramii, whereas S. oualaniensis showed an exponential increase in δ¹⁵N with mantle length that was stronger within individual years than with all samples combined. In general, adult O. bartramii are more than a trophic level above S. oualaniensis (4.3‰, 1.3 TLs). Because of the nature of the sampling protocol, this study could not separate spatial and temporal effects on the δ¹⁵N signals from each squid species. This study demonstrates the ability of stable isotope analyses to differentiate trophic levels between squid species as well as track trophic changes across size ranges from paralarvae to adults. Additional research is needed to validate these trophic changes across size within individuals.     

Animals on marine flowers: does the presence of flowering shoots affect mobile epifaunal assemblage in an eelgrass meadow?

Eelgrass, Zostera marina, produces two types of shoots: morphologically simple vegetative shoots and highly branched flowering (reproductive) shoots, the latter found only in summer months. We examined whether the abundance and diversity of mobile epifaunal assemblage are affected by the presence of flowering shoots in an eelgrass meadow of Otsuchi Bay, northeastern Japan. Comparisons of epifauna in natural vegetation revealed that density and species richness did not differ significantly between sites consisting of both flowering and vegetative shoots, and those only of vegetative shoots. A transplant experiment, conducted to examine the colonization rates of epifauna to defaunated eelgrass planted with different combination of vegetative and flowering shoots, showed no obvious variation in abundance and species richness. At species level, the density of some species such as a tanaid Zeuxo sp. and a polychaete Platynereis sp. was higher at sites and/or treatments with flowering shoots, whereas that of some gastropods, such as Lirularia iridescens and Siphonacmea oblongata was higher at sites without flowering shoots. The species-specific response led to dissimilarity of epifaunal assemblage between sites and among treatments with different densities of vegetative and flowering shoots. Similar patterns observed for natural vegetation and the transplant experiment suggest that the variation in assemblage structure is caused by habitat selection of each species, for example, the utilization of flowering shoots as feeding ground and nursery by Zeuxo sp.     

Nutrient transfer in a marine mutualism: patterns of ammonia excretion by anemonefish and uptake by giant sea anemones

Many symbioses involve multiple partners in complex, multi-level associations, yet little is known concerning patterns of nutrient transfer in multi-level marine mutualisms. We used the anemonefish symbiosis as a model system to create a balance sheet for nitrogen production and transfer within a three-way symbiotic system. We quantified diel patterns in excretion of ammonia by anemonefish and subsequent absorption by host sea anemones and zooxanthellae under laboratory conditions. Rates of ammonia excretion by the anemonefish Amphiprion bicinctus varied from a high of 1.84 μmole g⁻¹ h⁻¹ at 2 h after feeding, to a basal rate of 0.50 μmole g⁻¹ h⁻¹ at 24–36 h since the last meal. Conversely, host sea anemones Entacmaea quadricolor absorbed ammonia at a rate of 0.10 μmole g⁻¹ h⁻¹ during the daytime in ammonia-enriched seawater, but during the night reduced their absorption rate to near zero, indicating that ammonia uptake was driven by zooxanthella photosynthesis. When incubated together, net ammonia excretion was virturally zero, indicating that host anemones absorbed most of the ammonia produced by resident fish. Adult anemonefish weighed about 11 g under laboratory conditions, but on the coral reef may reach up to 64 g, resulting in a maximal potential ammonia load of >200 μmole h⁻¹ produced by two adult fish during daylight hours. In contrast, host sea anemones weighed about 47 g in the laboratory, but under field conditions, large individuals may reach 680 g, so their maximal ammonia clearance rates may reach about 70 μmole h⁻¹ during the daytime. As such, the ammonia load produced by adult anemonefish far exceeds the clearance rate of host anemones and zooxanthellae. Ammonia transfer likely occurs mainly during the daytime, when anemonefish consume zooplankton and excrete rapidly, and in turn the zooxanthellae are photosynthetically active and drive rapid ammonia uptake. We conclude that zooplanktivorous fishes that form mutualisms with coral reef cnidarians may serve as an important link between open water and benthic ecosystems, through the transfer of large quantities of nutrients to zooxanthellate hosts, thus enhancing coral reef productivity.     

Distribution of a marginal population of <Emphasis Type="Italic">Mytilus edulis</Emphasis>: responses to biotic and abiotic processes at different spatial scales

Physical and biological processes interact to produce pattern in nature. Pattern is scale dependent as processes generating pattern are heterogeneous in time and space. We tested some causes of variation in abundance and distribution of three marginal populations of sublittoral blue mussels, Mytilus edulis, in the non-tidal northeastern Baltic Sea. We studied the role of substrate inclination, perennial algae and siltation along local wave exposure gradients on mussel distribution over a regional salinity gradient. We found marked differences on regional scales (p < 0.001) with lower densities and biomasses of mussels with declining salinity. Along local gradients, mussel densities increased with increasing exposure (p < 0.001) and declining slope and sedimentation (p < 0.01). Site specifically, densities of blue mussels and the perennial red algae, Furcellaria lumbricalis, were positively related, results supported by a colonisation experiment. Also, young post-recruits showed significant relations to adult biomass, wave exposure, algal biomass, bottom slope and sediment cover. Findings showed that the relative importance of the determinants affecting blue mussels at the edge of their range vary with scale and are affected by the density and size structure of mussel populations. The study provides an indication of the types of factors that may be invoked as causes of spatial variation in marginal blue mussel populations and reinforces the need to consider multiple aspects when distributional patterns are assessed.