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.     

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.     

Seasonal changes in an intertidal community affected by sewage pollution

Seasonal changes in structure of a rocky intertidal community affected by sewage pollution at Quequén (Argentina) were studied over a period of 2 years. Most species showed a decrease in cover values in the polluted area. On the other hand, a small proportion of organisms favoured by organic enrichment predominated around the outfall during the period of study. Community structure was not significantly altered by frosts or windstorms. Desiccation is identified as the main physical stress. A combination of late spring high temperatures with extreme midday low-tides caused by northerly winds was responsible for heavy losses in dominant algae. Major seasonal changes in community structure were primarily due to variations in area covered by the chlorophyte Ulva lactuca, and crusts of blue-green algae and diatoms in the vicinity of the outfall. Highest diversity values were attained during either late winter or spring, due to increased abundances of several seasonal algae. Abundance of the dominant organism, the bivalve Brachidontes rodriguezi, remained stable, showing only slight, non-seasonal, changes. Since the absence of B. rodriguezi is an indication of heavy pollution, temporal stability of this species suggests that the intensity of sewage discharges did not vary over the period of study.     

Dry deposition of nitrogen and sulfur to Ponderosa and Jeffrey pine in the San Bernardino national forest in Southern California

Little is known about the concentrations, deposition rates, and effects of nitrogenous and sulfurous compounds in photochemical smog in the San Bernardino National Forest (SBNF) in southern California. Dry deposition of NO(3)(-) and NH(4)(+) to foliage of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) was correlated (R = 0.83-0.88) with historical average hourly O(3) concentations at 10 sites across an O(3) gradient in the SBNF. Mean deposition fluxes of NO(3)(-) to ponderosa and Jeffrey pine branches were 0.82 nmol M(-2)s(-1) at Camp Paivika (CP), a high-pollution site, and 0.19 nmol m(-2) s(-1) at Camp Osceola (CAO), a low-pollution site. Deposition fluxes of NH(4)(+) were 0.32 nmol m(-2) s(-1) at CP and 0.17 nmol m(-2) s(-1) at CAO, while mean values for SO(4)(2-) were 0.03 at CP and 0.02 nmol m(-2) s(-1) at CAO. Deposition fluxes to paper and nylon filters were higher in most cases than fluxes to pine branches at the same site. The results of this study suggest that an atmospheric concentration and deposition gradient of N and S compounds occurs along with the west-east O(3) gradient in the SBNF. Annual stand-level dry deposition rates for S and N at CP and CAO were estimated. Further studies are needed to determine if high N deposition loads in the SBNF significantly affect plant/soil nutrient relations, tree health, and the response of ponderosa pine to ozone.     

Susceptibility of different yeast species to environmental toxic metals

The purpose of the study reported here was to investigate the relative resistance of yeast species to various metallic and metalloid ions, with a view to gaining more knowledge on this subject, as resistant species may become dominant in habitats contaminated with the relevant metals. Saccharomyces cerevisiae, Candida albicans and Candida tropicalis were grown in media containing different concentrations of mercury (as HgCl(2)), cadmium (as CdCl(2)), lead (as Pb(CH(3)COO)(2)), arsenic (as Na(2)HAsO(4)) and selenium (as Na(2)SeO(3)) for various intervals. Invariably, the two Candida species turned out to be more resistant to all the metals studied than S. cerevisiae. The metal showing the highest toxicity for these species was mercury, with cadmium being the second, lead, the third and arsenic and selenium being the least toxic elements. Strains showing resistance to mercury were isolated, even in the case of S. cerevisiae.     

Does the cost of polygyny in house wrens include reduced male assistance in defending offspring?

Summary This study investigated whether reduced male aid in defending offspring potentially reduces the fitness of females choosing already-mated males in the house wren (Troglodytes aedon), a small, territorial songbird. Frozen snakes were placed at 23 nests of monogamously mated males and 12 secondary nests of bigamously mated males. All presentations were made during incubation stages of females attending focal nests. Snakes were placed at nests of secondary females when nests of their primary counterparts contained young 5–9 days old. Males are most attentive to primary nests during this period and should therefore be relatively inattentive to secondary mates and nests. Nevertheless, an equal proportion of monogamous and bigamous males discovered snakes within 15 min, and mean time to discovery, when discovery occurred, did not differ with nest status. Monogamous and bigamous males were also equally likely to attack snakes physically once discovered. Monogamous males appeared no more likely to discover snakes than bigamous males for two main reasons. First, although monogamous males were near focal nests (i.e., < 10 m) more often than bigamous males, monogamous males tended to stay out of view of nests for long periods. In contrast, bigamous males always went immediately to focal nests upon arriving in their vicinity. Second, about one-third of monogamous males in this study spent much of their time during trials at the far edges of their territories advertising for secondary mates. Our experiment suggests that reduced male aid in defending nests against small, diurnal predators probably does not contribute to the cost of polygyny in house wrens. Correspondence to: L.S. Johnson     

Variation in the development of cadmium resistance in Daphnia magna straus; effect of temperature, nutrition, age and genotype

The extent to which responses to toxicants can be modified by the environment and genotype of Daphnia magna is important for interpreting the results from ecotoxicity tests. Variation in the development of cadmium resistance and its relevance for survivorship has been investigated in two genetically distinct clones of D. magna. Cadmium resistance was induced by pre-exposing daphnids to a sublethal concentration of a Cd/Zn mixture and thereafter cadmium tolerance was assessed in standard acute tests. The results showed that the ability to develop cadmium resistance is affected by temperature, but there is no consistent pattern for maternal nutrition. The age of the daphnids had no apparent effect on the development of cadmium resistance. Differences in the induction of cadmium resistance between clones were seen only under resource depression.     

Persistent organochlorine residues in soils from tropical and sub-tropical Asian countries

Soil samples from paddy fields, uplands, and urban areas (gardens and roadsides) collected from Vietnam, Thailand, and Taiwan were analysed to determine the residual levels of persistent organochlorine compounds such as DDTs, HCHs, and PCBs. DDT concentration in soil samples from Vietnam were found to be highest, with a mean value of 110 ng g(-1), and were followed by those in Taiwanese soils with a mean value of 20 ng g(-1). HCH concentrations were highest in soil samples from Vietnam (a mean value of 4.8 ng g(-1)) and were followed by those from Taiwan (a mean value of 1.4 ng g(-1)). Concentrations of PCBs were found to be highest in Taiwanese soil samples, with a mean of 95 ng g(-1). Interestingly, relatively high concentrations of PCBs in rural cultivated-soil samples from Vietnam were recorded with a mean value of 25 ng g(-1), probably suggesting PCB release from different kinds of weapons used during the Second Indochina war. The lowest concentrations of DDTs, HCHs, and PCBs were obtained in soil samples from Thailand, with mean values of 8.3 ng g(-1), 0.4 ng g(-1), and 2.7 ng g(-1), respectively.     

Constraints on group size in primates and carnivores: population density and day-range as assays of exploitation competition

Summary We hypothesise that foraging group size (FGS) and population group size (PGS) in primates and carnivores are related to quantifiable variables indexing the intensity of exploitative competition. Group size is predicted to increase with both food density and travel capabilities, as estimated by the constraint-free day-range (DR_s), i.e. the day-range of a solitary individual uninfluenced by competition from conspecifics. We test this exploitation competition hypothesis among primates and carnivores, using data on populations, species and genera. Food density was indexed by population density. Where DR_s could be estimated by regression it was found to be correlated with observed day-range (DR_m). DR_s was therefore indexed by DR_m in all species. Population density and DR_m were associated with each other, but in a multiple regression each variable contributed independently to explaining variation in group size. PGS was predicted better than FGS, but regressions involving either measure of group size were significant in all analyses. The multiple regression analyses were validated by the method of linear contrasts, which accounts for possible lack of independence among taxa. We conclude that species differences in group size are influenced by both food density and DR_s. This suggests that variation in the intensity of exploitation competition is partly responsible for differences in group size.Correspondence to: R.W. Wrangham     

Locomotory behaviour and swimming performance of the Norway lobster,Nephrops norvegicus,in the presence of an acoustic tag

Observations have been made on the locomotory behaviour and swimming performances of the Norway lobster, Nephrops norvegicus (L.), fitted with an acoustic transmitter ventrally under the cephalothorax. The walking behaviour of adult males (44 mm carapace length) appeared to be unaffected, but the tag caused significant reductions in certain measures of tail-flip swimming performance such as swimming speed and endurance. Flume-tank experiments in low water currents suggested that the transmitter would increase hydrodynamic drag during swimming by 9 to 32%, depending on lobster size. Given the weight and dimensions of the acoustic transmitters currently available, it is considered advisable to confine acoustic tracking studies to relatively large N. norvegicus.Correspondence to: C. J. Chapman