Letteratura scientifica selezionata sul tema "Anadara trapezia"

Invasive habitat-forming species cause large changes to the abiotic environment, which may lead to lethal and sublethal effects on native fauna. In this study, we tested whether morphological anti-predator traits of an infaunal bivalve, Anadara trapezia, differed between areas invaded by the habitat-forming seaweed Caulerpa taxifolia and uninvaded habitats in estuaries in New South Wales, Australia. Caulerpa changes the abiotic environment in ways that may affect traits of native species. In particular, there is lower water flow, lower dissolved oxygen in the water and sediments are more silty and anoxic than in unvegetated habitat. To test our hypotheses, we collected Anadara from Caulerpa and uninvaded habitats and measured shell thickness, shell strength and resistance to opening of valves. We found that all three traits were reduced in Anadara from Caulerpa habitat compared with Anadara from uninvaded habitats. These findings are consistent with the idea that trait modifications in native fauna in response to invasive habitat-forming species can potentially increase susceptibility to predation.

Caulerpa taxifolia is a fast-spreading invasive seaweed that threatens biodiversity in temperate Australian estuaries. To date, little is known about its effects on infauna. In the present study, we describe variation in demographic and life-history traits of the abundant infaunal bivalve, Anadara trapezia, in C. taxifolia and uninvaded habitats (seagrass and unvegetated sediments) at multiple sites across three estuaries in south-eastern New South Wales. Densities of A. trapezia were always lower in C. taxifolia than on unvegetated sediment, and lower in C. taxifolia than in seagrass at three out of four sites where they were compared. Dry tissue weight of A. trapezia was also lower in C. taxifolia than on unvegetated sediment at most sites, but was only lower in C. taxifolia than in seagrass at one of four sites. Populations were dominated by larger individuals (>45 mm length), but smaller individuals (35–45 mm length) were more common in C. taxifolia and seagrass. A. trapezia shell weight and morphology was variable and appeared weakly affected by invasion. Generally, our findings are consistent with the hypothesis that A. trapezia is negatively affected by C. taxifolia. However, C. taxifolia invasion appears complex and, at some places, its effects may not differ from those of native seagrass. There is a need for manipulative studies to understand the mechanisms underlying the effects of C. taxifolia on infauna.

The salinity tolerance range of the scallop Pecten fumatus Reeve was 25-40 g 1-1, of the pipi (clam) Plebidonax deltoides (Lamarck) and the flat oyster Ostrea angasi Sowerby, 20-45 g I-1, and of the blue mussel Mytilus edulis planulatus Lamarck and the Sydney cockle Anadara trapezia (Deshayes), 15-45 g I-1. All of these bivalves absorbed substantial amounts of the amino acid L-methionine directly from seawater.

The bivalve mollusc A. trapezia has two haemoglobins, a tetrameric major haemoglobin, and a dimeric minor haemoglobin, the latter having two identical chains that are different from the chains in the tetramer. Genetic variation in the dimer results in two different haemoglobins, HbIIa and HbIIb, and it is known that the relative proportions of these two polymorphic forms vary with latitude along the eastern coastline of Australia. The HbIIb variant is more common at higher latitudes where water temperature may act as selecting agent. Comparative peptide mapping and amino acid analysis of peptides have shown that in HbIIa an aspartyl residue replaces the seryl residue found in HbIIb at residue 64, position E2 in the E helix. The E and F helices have recently been shown to be highly conserved in arcid globins and to be involved in subunit contacts in the cooperative dimers.

This site report presents an account of archaeological excavations undertaken at Eurimbula Site 1, a large open midden site complex located in Eurimbula National Park on the southern Curtis Coast, Central Queensland. Excavations yielded a cultural assemblage dominated by mud ark (Anadara trapezia) and commercial oyster (Saccostrea commercialis) and incorporating small quantities of stone artefacts, fish bone and charcoal. Densities of cultural material were found to decrease markedly with distance from the creek. Analyses of excavated material demonstrate extensive low intensity use of the site from at least c.3,200 cal BP to the historical period.

The amino acid sequence of the iJ-chain of the principal haemoglobin from A. trapezia has been determined. The sequence was deduced from the sequences of tryptic peptides, which were fractionated using highperformance liquid chromatography and peptide mapping. Additional sequence data, particularly for the large tryptic peptides, was obtained from enzyme digests of both cyanogen bromide fragments and large citraconyitryptic peptides.

Thesis (Ph.D.) -- University of Western Sydney, Hawkesbury, 1997.
Thesis submitted for the degree of doctor of philosophy. Reprint from Records of Western Australian Museum of article entitled "Status of Anadara trapezie (Deshayes) (Bivalvia: Arcoida) from Oyster Harbour, Albany (Western Australia) as compared with east Australian populations" by M. Roseline Yardine and Barry J. Richardson bound in back. Includes bibliographical references (leaves 249-328).

This study examines the occurrence, distribution and storage of selenium in seagrass communities of Lake Macquarie, which is a heavily industrialised area of NSW, where notably high trace metal concentrations have been reported previously. Initially a suite of organisms was collected from a seagrass bed (Zostera capricornia) in the southeastern section of the lake to investigate the bioaccumulation and biomagnification of selenium. All organisms contained selenium, with sediment-dwelling organisms containing the highest Se concentrations. No consistent pattern of significant Se-metal correlations with Cu, Zn and Cd was found. Biomagnification of Se was evident, as concentrations increased from sediments and water to flora (algae and seagrass) to bivalves to Crustacea. However, this trend was not continued to the higher trophic groups of invertebrate predators and teleost fish. The bivalve Anadara trapezia was further studied. Intrinsic and extrinsic factors affecting the accumulation of Se were examined. Gender and mass were assessed in a single day study, followed by a temporal investigation of the effect of gender, reproductive cycle, temperature and salinity on Se accumulation. Gender had no effect on the accumulation of Se in A. trapezia. Se was present in all tissues (adductor, blood, foot, gills, intestine and mantle) and not immobilised or stored in a specific tissue, indicating that it plays a structural role in the tissues of A. trapezia. Se burden increased relative to size (shell length and dry mass) suggesting that Se is metabolically controlled within the organism. Se concentrations were found to fluctuate temporally because of: food availability in response to water temperatures; the reproductive cycle; and associated metabolic activities responding to temperature changes and food availability. Subcellular selenium associations in A. trapezia were examined to assist in the understanding of the fate of Se in marine tissues. Most of the Se was associated with proteins, suggesting that Se has a metabolic role in this marine organism. Proteins are intrinsically associated with the lipid bilayer of the cell membranes. A number of proteins (94, 85, 43, 36.5, 30, 23.4, 17.4 and 15 kDa) were separated by SDS PAGE from ethanol fractions. Determination of the Se concentration within individual proteins was not possible because the ratio of Se to protein was too low for further analysis. These findings indicated that Se plays a metabolic role in the tissues of the marine organism A. trapezia. The biochemical regulatory mechanism responsible for maintaining Se concentrations within the tissues is currently unknown.

This project investigated the genetic composition of natural populations of Anadara trapezia in Australia at three spatial scales : i) microgeographic (within an estuary, 50 metres to ~ 6 kilometres); ii) microgeographic (within populations, less than 50 metres); and, iii) macrogeographic (hundreds of kilometres along the coast of Australia). Allozyme polymorphism surveys using cellulose acetate strips have revealed, from 43 enzymes screened, 18 putative polymorphic loci. Comparisons of levels of heterozygosity among enzyme structural groups showed no significant differences, however, monomers were significantly more variable as a group than multimers. Significant differences in the level and distribution of polymorphism among functional groups of enzymes were observed. It appears that selection may be acting at the molecular level, not only on a particular locus, but on a group of functionally similar loci. At the macrogeographic scale, significant departures from random mating were observed in most populations. Significant differences in allele distribution among populations of A. trapezia along the east coast of Australia were found. At the macrogeographic scale, heterogeneity of allele frequencies may depend upon the distance separating the populations and surface water currents. Differentiation among population groups in this study is attributed to changes in the direction of the East Australian Current combined with onshore countercurrents. The systematic status of the disjunct western Australian population of A. trapezia was also evaluated as compared with the east coast populations. No evidence of genetic, hence evolutionary divergence was found. The results have serious implications in the management of fisheries as erroneous assumptions in fisheries management models may lead to depletion and near extinction of marine species. The research stresses the necessity of sampling at multiple scales and replication strategies. It also highlighted the complexities researchers are faced with in studies of marine bivalves, such as the presence of null alleles, deficiencies of heterozygotes, apparent inbreeding and the small geographic scales governing population structure.
Doctor of Philosophy (PhD)

The relationships between metal exposure, dose and response were investigated in two sediment dwelling marine bivalves: a deposit feeder Tellina deltoidalis and a filter feeder Anadara trapezia. The bivalves were exposed in the laboratory to individual metal spiked sediments: Cadmium 10 and 50 Ag/g; lead 100 and 300 Ag/g; selenium 5 and 20 Ag/g dry mass, T. deltoidalis for 28 days A. trapezia for 56 days. A. trapezia was also exposed in the laboratory for 56 days to sediments from three sites along a metal contamination gradient of cadmium, lead, selenium, zinc and copper from Lake Macquarie, NSW. Metal total tissue dose was measured in whole tissue of T. deltoidalis over 28 days and in gill, hepatopancreas and haemolymph tissues in A. trapezia over 56 days. Subcellular metal distribution, biologically active metal (BAM) versus biologically detoxified metal (BDM) was measured in whole tissues of T. deltoidalis at day 28 and in gill and hepatopancreas tissues of A. trapezia at day 56. Biomarkers of response measured in spiked sediment exposed, at day 28 T. deltoidalis and day 56 A. trapezia were: total antioxidant capacity (TAOC); glutathione peroxidase enzyme activity (GPx); total glutathione concentration (GSH+2GSSG); reduced to oxidised glutathione ratio (GSH:GSSG); lipid peroxidation (TBARS); lysosomal membrane stability and micronuclei frequency. Response indices measured in A. trapezia exposed to Lake Macquarie sediments were: TAOC, TBARS, lysosomal membrane stability, micronucleus frequency and condition index. Native A. trapezia and sediments were also collected from Lake Macquarie and measured for sediment and tissue metal concentrations, TAOC, TBARS, lysosomal membrane stability and condition index to allow comparison between chronically exposed and previously unexposed organisms. T. deltoidalis and A. trapezia accumulated metal over time in all sediment metal exposures with most reaching equilibrium tissue metal concentrations by the end of the exposure period. T. deltoidalis generally reached equilibrium with the exposure concentration for cadmium and lead but had significantly higher selenium tissue concentrations than the sediment metal at the 5 Ag/g exposure. A. trapezia tissue lead was below the sediment concentration for all exposures including in the native organisms. A high proportion of accumulated lead and copper in A. trapezia was in the haemolymph, probably associated with haemoglobin which has a high affinity for these metals`. A. trapezia cadmium tissue concentrations were higher than the sediment metal in the 10 Ag/g spiked sediment exposure and between half and one eighth the sediment concentrations in other treatments, including in native organisms. A. trapezia including the native organisms exposed to selenium sediment concentrations at or below 5 Ag/g in the Lake Macquarie mixed metal sediments accumulated significantly higher than ambient selenium tissue concentrations while those exposed to 5 and 20 Ag/g selenium spiked sediments had lower than ambient selenium tissue concentrations. The majority of accumulated cadmium, selenium and zinc was associated with the gill/mantle tissues. A. trapezia hepatopancreas contributed significant selenium concentrations in the later part of the exposure period indicating and increased contribution from dietary derived selenium. Native A. trapezia had significantly lower tissue concentrations of selenium, copper and zinc, higher cadmium and approximately equal lead compared to organisms exposed to similar sediment metal concentrations in the laboratory. T. deltoidalis detoxified around 50 % of accumulated cadmium and 70 % of lead while A. trapezia detoxified around 70 % of accumulated cadmium and 60 % of lead. Much of T. deltoidalis BDM cadmium was converted to metal rich granules (MRG), while A. trapezia had most in the metallothionein like proteins (MTLP) fraction. The conversion of lead to MRG was 75 % of the total BDM in T. deltoidalis while A. trapezia had an even distribution between MRG and MTLP. The majority of recovered selenium in both species was associated with the nuclei+cellular debris fraction, probably as protein bound selenium associated with plasma and selenium bound directly to cell walls. Selenium exposed organisms had increased BDM selenium burdens which were associated with both MRG and MTLP fractions, indicating selenium detoxification. The majority of BAM cadmium, lead and selenium was associated with the mitochondrial fraction in both species with increases in cadmium burden in this organelle of T. deltoidalis up to 7200 fold; lead 154 fold; and selenium 7 fold and in A. trapezia up to 84 fold cadmium, 50 fold lead and selenium 7 fold in exposed organisms compared to controls. The subcellular distribution of all three metals in T. deltoidalis and A. trapezia indicates active metal detoxification processes which at these exposure concentrations were unable to prevent significant metal burdens from accumulating in sensitive organelles. A contamination gradient of zinc, lead, copper, cadmium and selenium was established in Lake Macquarie sediments which emanated from the same source. A. trapezia accumulated all metals in each sediment exposure. Accumulation and tissue distribution patterns of cadmium, lead and selenium were similar to those of the single metal spiked sediment exposures. Cadmium and lead BAM burdens increased at all exposures while selenium, zinc and copper did not. T. deltoidalis and A. trapezia in the spiked sediment metal exposures generally had reduced GPx activity. This resulted in an increase in total glutathione concentrations which the reduced GSH:GSSG ratios indicated was due to a build up of oxidised glutathione. T. deltoidalis and A. trapezia had reduced TAOC in all laboratory sediment metal exposures which corresponded with increased TBARS concentrations, lysosomal destabilisation and micronucleus frequency. A. trapezia exposed to Lake Macquarie metal contaminated sediments also had a reduction in physiological condition, indicated by the reduced condition index, after 56 days at the higher metal exposures. Clear exposure - dose - response relationships have been demonstrated for T. deltoidalis and A. trapezia exposed to single cadmium, lead and selenium spiked sediments and for A. trapezia exposed to Lake Macquarie mixed metal contaminated sediments. Detoxification of all metals was evident in both T. deltoidalis and A. trapezia but detoxification capacity was exceeded for cadmium, lead and selenium leading to significant accumulation of these metals in sensitive organelles. The significant relationships, in the laboratory exposed T. deltoidalis and A. trapezia, between TAOC reduction with increased TBARS, lysosomal destabilisation and micronuclei frequency and between increased TBARS with lysosomal destabilisation and micronuclei frequency indicates that increased tissue metal dose and BAM burdens caused significant impairment of the antioxidant reduction capacity which resulted in a cascade of effects from lipid peroxidation to cellular perturbation and genotoxic damage. The reduction in physiological condition in the organisms with the highest tissue metal doses suggests the response goes beyond subcellular perturbations to whole organism and potentially population effects. Chronically metal exposed native Lake Macquarie A. trapezia did not show a clear metal exposure - dose - response relationship. Accumulation of the essential elements zinc, copper and selenium appeared to be regulated while cadmium and lead were not. TAOC was significantly reduced and TBARS significantly increased compared to reference organisms but lysosomal stability and condition were not significantly affected. The suite of interrelated biomarkers used offers a weight of evidence approach for demonstrating adverse effects of metal tissue accumulation in T. deltoidalis and A. trapezia

This project investigated the genetic composition of natural populations of Anadara trapezia in Australia at three spatial scales : i) microgeographic (within an estuary, 50 metres to ~ 6 kilometres); ii) microgeographic (within populations, less than 50 metres); and, iii) macrogeographic (hundreds of kilometres along the coast of Australia). Allozyme polymorphism surveys using cellulose acetate strips have revealed, from 43 enzymes screened, 18 putative polymorphic loci. Comparisons of levels of heterozygosity among enzyme structural groups showed no significant differences, however, monomers were significantly more variable as a group than multimers. Significant differences in the level and distribution of polymorphism among functional groups of enzymes were observed. It appears that selection may be acting at the molecular level, not only on a particular locus, but on a group of functionally similar loci. At the macrogeographic scale, significant departures from random mating were observed in most populations. Significant differences in allele distribution among populations of A. trapezia along the east coast of Australia were found. At the macrogeographic scale, heterogeneity of allele frequencies may depend upon the distance separating the populations and surface water currents. Differentiation among population groups in this study is attributed to changes in the direction of the East Australian Current combined with onshore countercurrents. The systematic status of the disjunct western Australian population of A. trapezia was also evaluated as compared with the east coast populations. No evidence of genetic, hence evolutionary divergence was found. The results have serious implications in the management of fisheries as erroneous assumptions in fisheries management models may lead to depletion and near extinction of marine species. The research stresses the necessity of sampling at multiple scales and replication strategies. It also highlighted the complexities researchers are faced with in studies of marine bivalves, such as the presence of null alleles, deficiencies of heterozygotes, apparent inbreeding and the small geographic scales governing population structure.

Research Doctorate - Doctor of Philosophy (PhD)
Seagrasses are generally known for their significant role in marine and estuarine ecosystems. The growth in human population along the coastal regions, where the seagrass live, makes them very vulnerable to the human-induced disturbances. Large-scale seagrass decline has been reported worldwide due to this problem. There is an evident need to monitor seagrass population to predict future changes and to protect coastal ecosystems from further degradation. The decline of seagrass beds results in their fragmentation and appearance of smaller patches of seagrass isolated from each other, The first goal of this thesis is to study how fragmentation of seagrass beds influence their role in the ecosystem. This study focused on how fragment size and its distance from the main bed influence abundance of mobile epifauna associated with seagrass. Artificial seagrass units were constructed to mimic the seagrass fragmentation at a small scale. The result from this experiment suggested neither fragment size nor on-patch location (edge vs middle) adequately account for variation in the abundance of seagrass-associated epifauna. The distance from large beds of seagrass was important, however. Fragments placed far away from the natural seagrass were colonized to a grater degree than the fragments placed near seagrass beds. Large fragments were also colonized more than the small ones at the furthest distance from natural beds. Thus, fragmentation does not necessary lead to decease in epifaunal abundances. The small isolated patches may serve as refuge sites of the marine organisms. The second part of the thesis specifically deals with the effect of heavy metal contamination on seagrass and associated fauna. Despite the well-publicised issue of metal contamination of highly urbanised estuaries and its effect on seagrasses, this is the first study that assessed the contamination effect on the seagrass community using a range of bioindicators and biomarkers in order to obtain an integral picture of the contamination effect. It was found the seagrass, Zostera capricorni accumulated high concentration of heavy metals and provide a good correlation between the concentration in their tissues and in the sediment. Moreover, there was no evidence of impact on the seagrass biomass, shoot and leaf density. Thus, this seagrass can be used as a good bioindicator because of the above reasons, and also they are sedentary and abundant in the polluted site, which makes them easily available for sampling. The abundance of epifaunal organisms associated with the seagrass was used as a bioindicator at the community level. Only gastropods decreased in abundance in the contaminated site in spring (when the number of seagrass fauna generally higher), and this might potentially be a good bioindicator in this system. Shell dimension and fluctuating asymmetry were used as biomarkers for this purpose. It was found that a bivalve associated with seedgrass, the ark cockle Anadara trapezia, in the polluted location (Cockle Baby) showed distinct morphological characters compared to the ones in unpolluted locations. The cockles were bigger, heavier and had bigger shell-height/shell-length ratios, but appeared much less abundant, which is contradicted with historically high abundance of this species in this location (Cockle Bay). Moreover, the cockles exhibited higher shell asymmetry compared to the ones in unpolluted locations. Leaf dimensions and leaf asymetry of seagrasses, and Halophila ovalis, were also employed as biomarkers. The results revealed that there was no significant difference in leaf asymmetry of seagrass from polluted and unpolluted locations. The effect of heavy metal might have been surpassed by other factors such as nutrients, which were also high in the polluted area. Interestingly, the leaves of seagrass in the polluted location compared to unpolluted ones were longer and wider indicating that there was a possibility that the detrimental effect of heavy metals on seagrass was compensated by favourable effects of elevated nutrients. Laboratory studies were conducted to determine whether heavy metals themselves affected seagrasses. The results revealed that heavy metals exposure affected the growth of seagrass, and lead to increase in fluctuating asymmetry. Thus, leaf dimensions, shell dimensions and fluctuating asymmetry of seagrass and seagrass associated fauna were sensitive to metal pollution and they might be suitable to indicated contamination in seagrass system.