Effects of mercury exposure on ionic regulation in the crayfish Orconectes propinquus

Hemolymph sodium, potassium and calcium concentrations were determined in crayfish (Orconectes propinquus) exposed to (203)HgCl(2) mixed with food to a concentration of 1 microg Hg g(-1). Dummy-fed animals were exposed to Hg-dosed food wrapped in dialysis tubing to control for mercury reaching the animals via leaching from food to water. Hemolymph analyses were made following 14-day Hg exposures and again after a further 21-day 'depuration' period during which all animals were fed Hg-free food. After 14 days, the mercury reached a concentration of 0.175 microg g(-1) in the hepatopancreas and approximately half this level in the gills of Hg-fed animals. No depuration occurred from the hepatopancreas although the gills lost approximately two-thirds of their labelled mercury during the depuration period. Hemolymph sodium concentrations in Hg-exposed crayfish, both fed and dummy-fed, after 14 days were significantly lower than in Hg-free controls and remained low following the 21-day depuration period. Hemolymph calcium concentrations were lower in Hg-fed animals than in dummy-fed and control animals after 14 days although calcium levels rose in all treatments after 35 days. This may have been due to the incidence of pre-molt animals in all experimental groups, although the relationship between this and mercury exposure was not established unequivocally. Hemolymph potassium levels showed no differences between treatments.     

Changes in the digestive gland of Euphausia superba during short-term starvation: lipid class,fatty acid and sterol content and composition

During a period of short-term (19 d) starvation, total lipid in the digestive gland of Euphausia superba Dana decreased from 21 to 9% dry weight. Total lipid per digestive gland decreased significantly during starvation compared to Day 0 individuals, falling from 1960 (±172) to 385 (±81) g. Polar lipid was the major lipid class utilised during starvation, falling from 1510 (±225) to 177 (±46) g per digestive gland (76 to 45%). Absolute levels of triacylglycerol fell from 300 (±41) to 76 (±5) g; however, relative levels remained unchanged. The relative level of free fatty acid increased significantly with starvation (4 to 39%) with absolute levels ranging from 79 (±1) to 156 (±20) g per digestive gland. Absolute levels of all fatty acids per digestive gland declined continually until the end of the starvation period. The long-chain polyunsaturated acids eicosapentaenoic (20:53) and docosahexaenoic (22:63), decreased with starvation from 37 to 26% and 15 to 10%, respectively whereas the saturated fatty acid, palmitic acid (16:0), increased from 15 to 20%. Cholesterol, the major sterol in this organ, increased from 17 (±20) to 44 (±13) g per digestive gland by Day 3, and by Day 19 had returned to levels found in the digestive gland of Day 0 individuals. Desmosterol followed a similar pattern to cholesterol, increasing from 3 (±1) g per digestive gland on Day 0 to 11 (±4) g on Day 3, and falling to 2 (±1) g on Day 19. Other sterols in the digestive gland, predominantly of algal origin, fell from the levels found in Day 0 individuals to near zero amounts by Day 6. The digestive gland of E. superba plays a dynamic role during shortterm starvation in terms of lipid content and composition. The relative levels of polar lipids, free fatty acids and cholesterol in the digestive gland may provide reliable indices of the nutritional condition of E. superba in the field. Sterols in the digestive gland are indicative of recent dietary composition of krill, and may also be used to quantify dietary input from individual phytoplanktonic species.     

In situ characterization of phytoplankton from vertical profiles of fluorescence emission spectra

Vertical profiling of the upper ocean with a laser/fiber optic fluorometer enabled the determination of fluorescence emission spectra of photosynthetic pigments over small vertical scales. Simultaneous acquisition of phycoerythrin (PE) and chlorophyll (chl) emission spectra allowed in situ differentiation between PE-containing cells (cryptomonads and cyanobacteria) and other chl-containing autotrophs. Further, fluorescence spectral peak shifts associated with different species of PE-containing cells resulted in even finer scale in situ taxonomic differentiation. We found that the phycoerythrin fluorescence emission maxima shifted from 578 nm near the surface, to 585 m at the base of the shallow thermocline (30% light level), and to 590 nm below the thermocline at the base of the euphotic zone (1% light level). These shifts in peak emission coincided with a taxonomic change in the PE-containing cells (as determined from analysis of discrete bottle samples) from a greater proportion of Synechococcus spp. in the upper water column to a greater proportion of cryptomonads at the base of the euphotic zone. These results indicate that the composition of the phytoplankton assemblage may be assessed in situ without sample collection.     

A “source” for asteroid larvae?: recruitment of Pisaster ochraceus,Pycnopodia helianthoides and Dermasterias imbricata in Nootka Sound,British Columbia

A major recruitment of the forcipulate asteroid Pisaster ochraceus was observed in September 1987 in the channel leading into Boca del Infierno, a semi-enclosed bay on the southeastern shore of Nootka Island, on the west coast of Vancouver Island, British Columbia, Canada. Newly settled recruits were observed at high densities subtidally in the channel (mean maximal density=1.23x10⁴m^-2) and at nearby sites. Subsequent surveys in 1988 to 1991 and size-frequency distributions of adults indicated strong yearly recruitment of P. ochraceus. Recruits of P. ochraceus were found on all available substrata, including hard and soft bottoms and on benthic algae. The initial food of the recruits included newly settled mussels (Mytilus sp.), snails and barnacles. Recruitment of the forcipulate Pycnopodia helianthoides was observed in 1987 to 1989 and in 1991, while recruitment of the spinulosan Dermasterias imbricata occurred only in 1988. High densities of planktonic bipinnaria larvae were found in the bay of Boca del Infierno in late May. We hypothesise that the high density population of adult P. ochraceus found in the channel of Boca del Infierno spawns synchronously and most of the resulting embryos and larvae are retained within the bay. This area may act as a source of larvae that then disperse locally. Post-recruitment mortality was estimated by comparing the density of recruits of P. ochraceus in 1987 with the numbers of juveniles presumed to be 1 yr old in 1988. Post-recruitment mortality was in excess of 97% with few individuals surviving to 1 yr. Moreover, even after the first year, mortality or emigration of the juveniles resulted in the almost complete loss of the 1-yr cohort at North Saavedra between 1988 and 1989. This study provides evidence that the P. ochraceus population in this area of Nootka Island may not be open, but may be regularly supplied from a source of larvae in the bay of Boca del Infierno. Post-settlement processes may, however, have significant effects on the local population, resulting in a poor correlation between the rate of recruitment and the incorporation of yr-1 + individuals into the adult population.     

Sulphur status in some Swedish podzols as influenced by acidic deposition and extractable organic carbon

To evaluate the changes in sulphur pools in response to acidic deposition, two studies were made-one in southwest Sweden where podzolic B horizons originally sampled in 1951 were resampled in 1989. At the Norrliden site, northern Sweden, sulphur pools in control plots were compared to plots that had been subjected to H(2)SO(4) application between 1971 and 1976. The results show that in southwest Sweden neither organic S nor extractable SO(4)(2-) increased significantly over the 38-year period, despite a decreasing pH and a high S deposition. At Norrliden, about 37% of the applied S was still remaining in the upper and central parts of the Bs horizon, most of which was inorganic sulphate. These contrasting results are explained by intrinsic differences in the soil organic carbon status between the sites-in southwest Sweden, organic carbon concentrations were high which inhibited SO(4)(2-) adsorption. Low organic carbon concentrations and high extractable Fe/Al concentrations promoted SO(4)(2-) adsorption and caused a low subsequent SO(4)(2-) desorption rate at the Norrliden site. The results suggest that sulphate adsorption may be an important mechanism which delays the response in soil chemistry to H(2)SO(4) deposition, provided that soil organic carbon concentrations are low. Organic S retention was not shown to be an important S retention mechanism in any of the sites studied.     

Relation between heavy metal concentrations in salt marsh plants and soil

The aim of the research reported here was to investigate the relation between heavy metal concentrations in salt marsh plants, extractability of the metals from soil and some soil characteristics. In April 1987, Spartina anglica and Aster tripolium plants and soil were collected from four salt marshes along the Dutch coast. The redox potential of the soil between the roots of the plants and at bare sites was measured. Soil samples were oven-dried and analyzed for chloride concentration, pH, fraction of soil particles smaller than 63 microm (f < 63 microm), loss on ignition (LOI) and ammonium acetate and hydrochloric acid extractable Cd, Cu and Zn concentrations. The roots and shoots of the plants were analyzed for Cd, Cu and Zn. Because drying of the soil prior to chemical analysis might have changed the chemical speciation of the metals, and therefore the outcome of the ammonium acetate extraction, a second survey was performed in October 1990. In this survey A. tripolium plants and soil were collected from two salt marshes. Fresh and matched oven-dried soil samples were analyzed for water, ammonium acetate and diethylene triaminepentaacetic acid (DTPA) extractable Cd, Cu and Zn concentrations. The soil samples were also analyzed for f < 63 microm, LOI and total (HNO(3)/HCl digestion) metal concentrations. Soil metal concentrations were correlated with LOI. Drying prior to analysis of the soil had a significant effect on the extractability of the metals with water, ammonium acetate or DTPA. Plant metal concentrations significantly correlated only with some extractable metal concentrations determined in dried soil samples. However, these correlations were not consistently better than with total metal concentrations in the soil. It was concluded that extractions of metals from soil with water, ammonium acetate or DTPA are not better predictors for metal concentrations in salt marsh plants than total metal concentrations, and that a major part of the variation in metal concentrations in the plants cannot be explained by variation in soil composition.     

Proximate and elemental composition and energy content of mesopelagic crustaceans from the Eastern Gulf of Mexico

The proximate and elemental chemical compositions of 25 species of pelagic decapod and mysid crustaceans collected from the eastern Gulf of Mexico (27°N; 86°W, 1984 to 1989) was examined. Water level ranged from 63 to 95% and increased slightly with species' increased depth of occurrence. Protein levels were generally high (1.5 to 18.3% wet wt, WW; 27.6 to 62.4% ash-free dry wt, AFDW) and comprised the primary organic component in the majority of species. Protein, both as % WW and % AFDW, decreased with increased depth of occurrence. In contrast to protein, lipid levels were low (0.5 to 8.9% WW; 5.7 to 60.9% AFDW), and increased with increased depth of occurrence. Carbon and nitrogen best mirrored measured lipid and protein levels when considered as non-protein carbon and non-chitin nitrogen, respectively. C:N ratios increased with increased depth, consistent with changes in protein and lipid with depth. Because of their compositional attributes, resident Gulf of Mexico species have a low total wet weight energy content relative to species from more productive regions. Energy content showed no significant trend with depth. Vertical migration patterns were distinctly different between shallow-and deep-living gulf species and these differences were largely responsible for the relationships observed between composition and depth. In migrating species, the protein and nitrogen content were higher, the lipid and carbon contents and C:N ratio lower, than in non-migrating species. Three deep-living species of the genus Acanthephyra were found to be compositionally atypical, resembling shallow, migrating types rather than other deep-living, non-migratory species.     

Community response to hazard information

The impact of flood hazard information on public acceptance of a selected flood mitigation strategy was assessed by an analysis of the content of newspaper reports of community reaction and letters to the editor. The impact of personal delivery of a flood hazard map on individual perception of risk and attitude to such information was assessed using personal interviews. The results indicated that media coverage of the flood hazard information reduced public criticism of the works. This result must be partially attributable to the dramatic style of media coverage and the fact that the media only emphasized the positive value of the works. The interview demonstrated that personal delivery of the information raised perception of risk, improved comprehension of flood risk, had no impact on acceptability of risk but discouraged some respondents from seeking such information in the future. Factors to explain the last negative change were identified to be the format of the map sheet and low salience of flood hazard. On the basis of all results, methods to improve community response to hazard information are provided.     

Population dynamics of Mytilicola intestinalis in Mytilus edulis in south west England

The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent.