The algal toxicity of silver engineered nanoparticles and detoxification by exopolymeric substances

In this study, we report that silver ions (Ag⁺) from the oxidative dissolution of silver engineered nanoparticles (Ag-ENs) determined the EN toxicity to the marine diatom Thalassiosira weissflogii. Most of the Ag-ENs formed non-toxic aggregates (>0.22 μm) in seawater. When the free Ag⁺ concentration ([Ag⁺]_F) was greatly reduced by diafiltration or thiol complexation, no toxicity was observed, even though the Ag-ENs were better dispersed in the presence of thiols with up to 1.08 × 10⁻⁵ M Ag-ENs found in the <0.22 μm fraction, which are orders of magnitude higher than predicted for the natural aquatic environment. The secretion of polysaccharide-rich algal exopolymeric substances (EPS) significantly increased at increasing [Ag⁺]_F. Both dissolved and particulate polysaccharide concentrations were higher for nutrient-limited cells, coinciding with their higher Ag⁺ tolerance, suggesting that EPS may be involved in Ag⁺ detoxification.     

Analyzing maps of dispersal around a single focus

The spatial pattern of organisms may be used to characterize their dispersal, quantify spread or estimate the point of introduction of an alien species. Their distribution may be represented by maps of individuals, or by counts or by presence/absence at known positions within a sampled area. The problems and relative merits of these different forms of data for spatial inference are discussed. Three datasets concerning dispersal from a single focus are analyzed: counts of aphids, Rhopalosiphum padi and Sitobion avenae, on barley plants, Hordeum vulgare, grown in experi- mental trays; mapped locations of couch grass, Elymus repens, tillers within plots of a field experiment; locations of sightings of the lupin aphid, Macrosiphum albifrons, as it invaded Great Britain between 1981 and 1984. A method for generating maps from counts is proposed to overcome problems caused by recording imprecision. Several statistics are used to quantify dispersal and spatial pattern in the experimental data and together provide a clear picture of the spatial pattern observed; they enabled several effects of the experimental treatments to be identified. The value of the statistics are compared. Estimates of the source of the lupin aphid invasion are obtained using the backtracking methods of Perry (1995b) and do not contradict previous suggestions.     

Ecological energetics of the sea-weed zone in a marine bay on the Atlantic coast of Canada. II. Productivity of the seaweeds

The growth of the seaweeds Laminaria longicruris, L. digitata and Agarum cribrosum were followed by SCUBA divers for two years, by punching holes 10 cm from the junction of stipe and blade, and recording at intervals the distance the holes had moved. As the holes approached the tip of the blade, new holes were punched at the base. It was found that the blades behaved like moving belts of tissue, eroding at the tips while growing at the bases, so that a total year's growth amounted to 1 to 5 times the initial length. Larger, older plants had wider and thicker blades, and the biomassincrease was roughly proportional to the square of the lengthincrease. Growth was most rapid in January to April, slow in July to October. As a conservative estimate, the summer biomass of the various species of seaweeds had a turnover of 4 to 10 times in the course of 1 year. Applying these figures to an earlier survey of biomass, it is estimated that annual production of seaweeds in St. Margaret's Bay, Nova Scotia, Canada, amounts to 603 gC/m² averaged over the whole bay, 1750 gC/m² averaged over the sea-weed zone, or 648.000 gC/m of shore line. Approximate calorific equivalents are 6030 kcal/m² over the whole bay, or 6480×10³ kcal/m of shore line.Contribution to the International Biological Program CCIBP No. 130, and Bedford Institute Contribution.     

Prenatal assessment of anterior abdominal wall defects and their prognosis

Eighty-eight cases of abdominal wall defect with and without other lesions were ascertained by reviewing all labour room records in the West of Scotland, all surgical admissions to the Royal Hospital for Sick Children, Yorkhill, and all post mortems at Royal Hospital for Sick Children between 1978 and 1981. The affected cases comprised 39 terminations of pregnancy (17 of anterior abdominal wall defect without neural tube defect). 20 spontaneous stillbirths and 29 livebirths. All 10 cases of body stalk anomaly, 37.5 per cent of 16 gastroschisis cases and 53 per cent of 62 exomphalos cases had additional severe abnormalities. Abnormal karyotypes were present in seven out of 19 exomphalos cases but all karyotypes from 10 gastroschisis and 6 body stalk anomaly cases were normal. No correlation was found between the maternal serum AFP levels, the amniotic AFP levels and acetylcholinesterase results and the size of the lesion. It is proposed that anterior abdominal wall defects detected prenatally should have chromosome analysis and careful ultrasound to exclude associated severe anomalies before coming to a decision about termination. This policy was implemented in six pregnancies complicated by fetal gastroschisis without severe associated anomalies which were identified in the second trimester and continued to term. Immediate surgical repair was achieved in each case, although two of the infants succumbed from later complications of gastroschisis closure and one from respiratory distress syndrome. The remaining three infants made a satisfactory recovery.     

PCDDs and PCDFs in human adipose tissue from the EPA FY82 NHATS repository

Analysis for tetra- through octachloro-PCDDs and PCDFs was completed for 46 tissue samples prepared from the U.S. Environmental Protection Agency (EPA) National Human Adipose Tissue Survey (NHATS). The samples were prepared as composites from over 900 specimens to represent the nine U.S. census divisions and three age groups (0–14, 15–44, and 45 plus years). The data demonstrate that PCDDs and PCDFs are prevalent in the general U.S. population and that differences exist with age.     

Rh isoimmunization following genetic amniocentesis

A series of 8009 genetic amniocenteses were retrospectively examined to evaluate the relationship of the procedure to Rh isoimmunization. Of the 615 Rh negative women giving birth to Rh positive infants and estimated to be at risk, thirteen (2·1 per cent) were sensitized subsequent to the amniocentesis. Eleven of the sensitizations occurred early in the programs, and a combination of experience and ultrasound performed concurrently with the amniocentesis appear to have reduced the risk of isoimmunization to that of control data from the literature.     

Changes in sea urchin populations after the destruction of kelp beds

In St. Margaret's Bay, Nova Scotia, Canada, there are large areas in which sea urchins (Strongylocentrotus droebachiensis) have eliminated beds of kelp (Laminaria spp.). Sites were identified where destruction of kelp beds had taken place 1, 2, 3, 3.5 and 4 years ago. With increase of time since kelp disappearance, the sea urchins showed decreased growth rate, reduced gonad size, but an increase in numbers resulting from high recruitment rates in the first two years after kelp bed destruction. These sea urchin populations, by their browsing, effectively prevent the regeneration of kelp. There is, as yet, no evidence of the sea urchin populations being starved out to allow the kelp to return.     

The role of behavioral responses to predators in modifying urchins' (Strongylocentrotus droebachiensis) destructive grazing and seasonal foraging patterns

We documented spatial and temporal patterns of urchins (Strongylocentrotus droebachiensis) and periwinkles (Littorina littorea) in three habitats: a persistent Laminaria longicruris and L. digitata bed; an urchin dominated barrens, and the edge of the kelp bed that formed a boundary between the two. Urchins were rare in the kelp and, when present, always large and well hidden, a pattern we interpret as a response to crab and lobster predation. Urchins were abundant in the barrens, and, in the summer when predaceous fish were active during the day, foraged only at nigh. We observed the formation of a dense urchin feeding front along the kelp bed edge, and these urchins remained exposed and feeding even during the summer. Laboratory experiments demonstrated that aggregations are an effective defense against some predators, and that the presence of crabs increases the tendency of large urchins to aggregate. We hypothesize that healthy Laminaria spp. beds persist because kelp bed associated predators keep urchins at low densities and in hiding. A reduction in predation pressure permits urchin densities to increase to the point where they form aggregations, which provide better defense than hiding. These aggregations then graze destructively on Laminaria spp., forming barrens. These barrens seem to be a new, stable configuration of the system.