Gotowa bibliografia na temat „Austrovenus stutchburyi”

The common phenomenon of sublethal predation in soft-bottom bivalves usually involves nipping of siphons. Here we show that foot cropping, hitherto documented only in Donax spp., is widespread in the New Zealand cockle Austrovenus stutchburyi (Veneridae). Depending on the locality, cropping frequency ranged between 14 and 34% of cockles, and the average proportion of the foot area cropped ranged between nine and 21%. Estimates of biomass lost to croppers at the time of sampling varied between 235 and 2040 mg ww m−2. It is emphasized that foot cropping in Austrovenus is likely to affect the population dynamics of the cockles.

Commercial harvesting often reduces densities of target species, potentially affecting transmission of parasites within the population. Rates of parasitic infection not only impact the hosts directly, but can result in wider ecosystem effects through influences on host behaviour. Commercial harvesting may therefore have important ecological consequences beyond the direct effects of removal of biomass. Clams (Austrovenus stutchburyi) are commonly infected by trematode parasites (Acanthoparyphium spp. and Curtuteria australis) and have been commercially harvested in Otago, New Zealand, since 1983. To assess the effects of harvesting on the abundance of trematodes in A. stutchburyi, the number of parasites per clam was compared in harvested and unharvested areas. The mean number of parasites per clam was 36% higher at commercially harvested sites, suggesting that harvesting enhances the local transmission of parasites. Harvesters may be able to reduce their influence on parasite infection levels in clam populations by harvesting less intensively and allowing more time between harvests for clam biomass to regenerate.

In a field experiment, the accumulation of trematode (Echinostomatidae) metacercariae by the New Zealand cockle Austrovenus stutchburyi was compared among treatments with different seabed hydrodynamics and sedimentation rates. There was no significant difference among the treatments in the rate at which cockles accumulated metacercariae, suggesting that infection rates are not influenced by water flow conditions within the normal range experienced in natural habitats. There was, however, substantial spatial variation in infection rates among the experimental plots. This result indicates that metacercarial accumulation varies horizontally as well as vertically within the intertidal zone.

A suite of 6 bone gelatin accelerator mass spectrometry (AMS) radiocarbon dates for Rattus exulans Peale and associated beta decay 14C dates for Austrovenus stutchburyi shell are presented for 4 middens at Pauatahanui, Wellington, New Zealand. Mean calibrated age ranges of Rattus exulans (520–435 BP and 350–330 BP at 95% confidence level) and shell (465–375 BP at 95% confidence level) from the 4 midden sites overlap. The agreement between Rattus exulans bone gelatin dates and associated shell provides an inter-sample comparison of 14C dating using both gas counting (beta decay) and AMS dating techniques. We examine the adequacy of the standard gelatinization treatment for bone samples, which has been employed consistently at the laboratory since 1995.

Urbanisation in coastal catchments has significantly increased not only the input of terrestrial sediment to the marine environment but also the input of contaminants. In Tamaki Estuary, Auckland, heavy metals have accumulated in the upper estuarine muddy sediments and metal contamination has been detected on downstream intertidal sandflats. Sub-lethal levels of heavy metal contamination may affect the growth and behaviour of benthic organisms, which in turn may influence key ecosystem processes and productivity. The aim of this study was to examine whether the burial rate of an ecologically important bivalve species (Austrovenus stutchburyi) differed between a contaminated and a lesser-contaminated site and whether burial rates were affected by density. A secondary aim was to determine whether the burial of Austrovenus affected sediment transport and consequently if this was affected by density. This study demonstrated no consistent difference in burial time between source populations (sites). This was explained by a lack of measured difference in the condition index and heavy metal tissue loading of Austrovenus used throughout this study. The present range of contamination measured in Tamaki Estuary, Auckland, did not have negative biological consequences on the key ecosystem engineer, Austrovenus stutchburyi. Contamination levels in Tamaki Estuary may not be high enough to cause major physiological or behaviour changes to infaunal organisms, such as Austrovenus. Sediment erodability was not significantly correlated with any measured environmental and biotic factors. Austrovenus density was the only predictor variable that could be used to explain any variation in sediment erodability. There was no significant density effects observed between the amounts of sediment eroded for densities gt; 150 ind. m-2. There was a significant difference between sediment void of Austrovenus (0 ind. m-2; smooth, flat undisturbed sediment surface) and sediment containing Austrovenus (gt;150ind. m-2; physical structure on/in the sediment surface, increase in bed roughness). These results indicate that there is little or no effect of Austrovenus on the critical erosion threshold, suggesting that in the absence or presence of Austrovenus the current required to erode 10 g m-2 of sediment would remain somewhere between 28.5 and 30.5 cm s-1. This study found that there was considerable variation in the burial rate of individuals and the greatest variation was recorded in the lowest density treatments (150 ind. m-2), which corresponded to the same density that had the greatest variation in sediment erodability. Further investigations are needed to gain a better understanding into the important roles (the importance of the various feedbacks and limitations and interrelationships) that Austrovenus play in the soft-sediment ecosystem, as losses of this species are likely to have large-scale impacts on the wider soft-sediment communities and ecosystem functioning.

This thesis investigated the population structure and spatial distribution of the cockle Austrovenus stutchburyi in estuaries and bays around the Canterbury coastline. Surveys investigated population attributes (average density and density of small cockles (< 10mm)) of Austrovenus stutchburyi in relation to physical environmental characteristics such as trace metals (copper, cadmium and zinc), sediment particle size, nitrogen and phosphorus levels, pore water and percentage organic matter of the sediment. Surface cover of flora and number of fauna present was also correlated with the density of cockles and small cockles < 10mm. MDS and PCA ordination showed that the biota was similar at 14 sites but differed significantly at the Pleasant Point Yacht Club (PPY) site. There was a positive correlation between fine sand (125 μm) and the average density of cockles and small cockles < 10 mm. High population densities of Austrovenus stutchburyi were also positively correlated with phosphorus levels, and percentage cover of Sea Grass (Ulva sp). However, Austrovenus stutchburyi density was negatively correlated with cadmium and zinc concentration, and percentage of mud present. The density of small cockles < 10 mm was negatively correlated with copper and cadmium concentration in the sediment and positively correlated with Topshell (Diloma subrostrata) numbers, Sea grass (Zostera muelleri) percentage cover, Sea lettuce (Ulva sp), percentage cover, and sediment particles sizes of < 63 μm (mud), 63 μm (very fine sand), and 125 μm (fine sand). Survival and behavioural changes of juvenile Austrovenus stutchburyi were investigated in relation to increased levels of copper, cadmium, and zinc in aqueous solution and sediment in the laboratory, and artificially increased levels in the field. In laboratory experiments in contaminated seawater it was found that, over time, copper and zinc had a detrimental effect on the percentage of juvenile cockles with their siphons extended as did copper concentration. Cockles 10 - 12 mm shell length exposed to different concentrations of copper had the lowest survival rate (25%) whilst cockles that were 5 - 7 mm in length had the greatest survival rate (69%). Cadmium did not affect survival or siphon extension in aqueous experiments. In the contaminated sediment experiments in the laboratory, the concentration of zinc (0, 20, 40, 80, 160 mg Zn/kg (dry weight)) and cadmium (0, 1.8, 5.6, 18, 36 mg Cd/kg (dry weight)) both decreased survival and burial of juvenile cockles in higher concentrations. Copper concentration (0, 5, 10, 25, 50 mg Cu /kg (dry weight)) decreased burial rates of juvenile cockles but did not affect survival. Transfer of juvenile Austrovenus stutchburyi within three sites in the Avon Heathcote Estuary during May 2007, found that site and exposure to copper, cadmium and zinc decreased the survival of the juvenile cockles. However, transfer of cockles between estuaries (Takamatua, Saltwater Creek and Avon – Heathcote Estuary) in May 2007 found that exposure to copper, cadmium and zinc had the main effect on survival of juvenile cockles. In July 2007 transfers of cockles between estuaries, site and exposure to copper, cadmium and zinc had an effect of survival on juvenile cockles. Cockle populations in the present research have shown a strong correlation with environmental variables, which can be used for management and conservation. The research in this thesis is a start to understanding the effects and implications of contaminants on survival, behaviour and recruitment of juvenile cockles. This research will benefit management strategies for increasing population numbers of Austrovenus stutchburyi.

Most organisms are rarely infected with just a single species of parasite and are usually simultaneously infected with a range of species. Thus, the parasite fauna of a host represents an entire community composed of multiple individuals from many different species. In nature, it is within the host that parasites can encounter conspecifics and individuals from other species. As in any ecosystem, while such interactions between parasites can be antagonistic due to competition or conflicting interests, association between different species can also be beneficial. In this thesis, I investigated patterns of associations between parasites in the New Zealand cockle Austrovenus stutchburyi through a combination of descriptive and experimental studies employing both standard ecological field techniques and molecular biology methods. It was found that the presence and infection intensity of various parasites species are not independent of each other. Among cockles, an association was found between two trematode taxa, i.e. between the infection intensity by foot-encysting echinostomes and the metacercariae of Gymnophallus sp. It was also found that the presence of the parasitic copepod Pseudomyicola spinosus was associated with greater infection intensity by the echinostomes but not Gymnophallus sp. While it was postulated that the positive association between the echinostomes and Gymnophallus sp. was due to the latter�s preference to infect cockles that are stranded on the sediment surface as a result of heavy echinostome metacercariae burden in their foot, a field experiment found that Gymnophallus cercariae did not preferentially infect cockles that have been forced to remain above the sediment surface as opposed to those that were forced to remain buried. Meanwhile, the two species of echinostomes known to encyst in the cockle�s foot, Acanthoparyphium sp. and Curtuteria australis, were found to represent cryptic species complexes. The presence of such cryptic species means that it is possible that some potential interspecific interactions are overlooked. A study of the population structure of Gymnophallus sp. found that each cockle contains multiple genetically distinct individuals and that clonal individuals rarely co-occur in the same cockle. This adds to the growing body of evidence suggesting that in addition to acting as a means of reaching the definitive host, the second intermediate host also acts to promote genetic diversity by accumulating cercariae shed by multiple first intermediate hosts in the environment. An experimental infection study conducted with Curtuteria australis cercariae deriving from singly-infected first intermediate hosts revealed that different clonal lineages varied with respect to their contribution to host manipulation. It was found that while certain lineages have a preference for host manipulation, others tend to adopt a "hitch-hiker"-type life history strategy. However, this genetic predisposition was also found to be a phenotypically plastic trait, as the presence of a higher number of manipulators seems to encourage newly-arrived cercariae to become manipulators, regardless of clonal lineage. This thesis provides evidence that patterns of interactions can affect various aspects of parasite life history. Apart from host condition, parasites can also be affected by other parasites. Studying the dynamics of mixed infections can provide informative insights for evolutionary and ecological research.

There is evidence that infaunal bivalves in New Zealand are not as abundant as they once were with overfishing and habitat modification contributing to the decline in density and health of cockles. The population biology and abundance of the bivalve Austrovenus stutchburyi (tuangi) in eight beds in four estuaries was assessed both seasonally (13 seasons) and annually (7 years) as little is known about the cockle beds in the Canterbury region of New Zealand. As with populations of similar species worldwide, there were site specific differences in population structure (density and size ranges) with the highest densities at Takamatua (>1500/m²), and the lowest at Port Levy (<350/m²). Gonad indices varied between male and female cockles. Male reproductive cycles were similar at all sites with male cockles being reproductively active year round, while females were more active in spring and summer. Temporal and spatial site specific differences occurred in cockle condition with high salinity sites having higher condition indices (CI) than low salinity sites. There were spatial and temporal variations in salinity (3-35ppt), sediment structure (fine sand through to predominantly silt), water temperature (6-20°C), nutrient supply (total volatile solids (TVS) 0.002- 0.15mg/L) and contaminant levels. Metal pollution indices (MPI) ranged between 3 and 11. Three cockle transplant trials were undertaken both within and between estuarine systems. Caged cockles survived well, and cage design needed to allow vertical movement of the bivalves within the substrate to reduce mortality. At the end of the 12 month trial, approximately 45% of the cockles remained in the plots. The condition of transplanted cockles was similar to naturally occurring cockles. Recommendations are made to optimise the success of cockle transplants. Large scale, un-caged placement of 25-30mm length cockles in the mid-low tide region of areas with stable, but not necessarily uncontaminated substrate, moderate salinity and temperature and with a reliable nutrient supply is recommended. The results from the thesis research can be applied to other infaunal bivalves in New Zealand allowing more successful restoration processes leading to increased species diversity and ecosystem functioning.

This thesis examines sublethal stress responses in the common New Zealand estuarine bivalve, Austrovenus stutchburyi (cockle). The approach used throughout this thesis is a refinement of the biological indicator approach of Adams (1990), in which biomarker data are collected primarily at the individual and sub-organismal levels, but with additional measurements at the population and community levels. In this research several biochemical and physiological biomarkers are used to assess effects of contaminants on energetics, fecundity and growth of cockles. Adenylate energy charge (AEC) and total adenylate nucleotide pool (TANP) are biomarkers that have previously not been used with A. stutchburyi, and provide new information on energy cycling for this species. RNA concentration has also not previously been used with cockles, and this biomarker is correlated with growth. Glycogen concentration and condition indices are used to indicate reproductive potential and overall health. In order to fully investigate the utility of this comprehensive suite of biomarkers, their performance in laboratory and field situations was tested. Temporal variability in AEC, TANP and glycogen was analysed over two years for two populations of cockles in a northern harbour. The results indicated seasonal patterns for all biomarkers, with AEC reaching a maximum value in spring, TANP being lowest in winter, and glycogen concentration being high over spring and summer. Variability in biomarker response between cockles sampled at low tide and high tide was analysed in a laboratory experiment simulating exposure to air during low tide. Adenylate energy charge was found to be significantly lower in cockles after exposure to air for 4 hours, highlighting the importance of standardised collection protocols. These initial patterns, as well as spatial variability in biomarker response, were further investigated at several sites within a second harbour south of Auckland. There was little among site difference in glycogen concentration, and the data suggested that differences in site characteristics, such as sediment quality and type, were driving the mixed response patterns of AEC, TANP and condition. Because of inherent variability in field conditions, a series of laboratory experiments was then undertaken to assess responses under carefully controlled conditions. Cockles were challenged with PAHs, chlordane and tributyltin at two different doses, and biomarker response (AEC, TANP, glycogen and RNA) measured. One trial examined the effects of a one-off pulse of contaminant, in which sediment containing cockles was dosed at the outset of a 14-day experiment with a high concentration of contaminant. A daily dose of this same concentration of contaminant was supplied to the sediment for 14 days in a second trial to assess effects of a more continuous discharge. There were virtually no significant differences in biomarker response between treatments and controls for either trial, suggesting that the experimental setup may have been causing sublethal stress in some way. Finally, in order to maximise experimental control whilst maintaining environmental realism, a manipulative field experiment was undertaken in which cockles were transplanted from an uncontaminated site to a series of uncontaminated and contaminated sites in one of Auckland's major harbours. Biomarker response (AEC, TANP, glycogen and RNA) was measured in the transplanted and the autochthonous populations two weeks and eight weeks after transplantation. An ability to regulate adenylate nucleotides was detected, as cockles transplanted to contaminated sites had reduced TANP but maintained AEC levels. There were significant differences in glycogen and RNA among sites, with highest levels detected in cockles transplanted to an uncontaminated site. This suite of biomarkers showed great utility for use in environmental quality assessment. It is recommended that an approach such as that used in the Mussel Watch programme in the United States be employed for cockles, in order to monitor estuarine ecosystem health in New Zealand. The transplantation of cockles to estuaries where there are concerns about environmental quality, and the use of TANP, glycogen and RNA concentration to assess sublethal stress, has potential as a sensitive and cost-effective environmental monitoring technique for estuaries in New Zealand.