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Microbially mediated biogeochemical processes are crucial for climate regulation and may be disrupted by anthropogenic contaminants. To better manage contaminants, we need tools that make real-time causal links between stressors and altered microbial functions, and the potential consequences for ecosystem services such as climate regulation. In a manipulative field experiment, we used metatranscriptomics to investigate the impact of excess organic enrichment and metal contamination on the gene expression of nitrogen and sulfur metabolisms in coastal sediments. Our gene expression data suggest that excess organic enrichment results in (i) higher transcript levels of genes involved in the production of toxic ammonia and hydrogen sulfide and (ii) lower transcript levels associated with the degradation of a greenhouse gas (nitrous oxide). However, metal contamination did not have any significant impact on gene expression. We reveal the genetic mechanisms that may lead to altered productivity and greenhouse gas production in coastal sediments due to anthropogenic contaminants. Our data highlight the applicability of metatranscriptomics as a management tool that provides an immense breadth of information and can identify potentially impacted process measurements that need further investigation.

Relocation of sea turtle nests and the retention of post-hatchlings for head-starting programs are both commonly used to improve conservation outcomes and facilitate eco-tourism ventures. Currently, there is little literature surrounding the husbandry protocols required during these programs to optimize post-release outcomes. To assess the impact of varied feeding regimes on exercise performance, (which will hereafter be referred to as 'fitness'), 40 10-month-old captive post-hatchling green turtles (Chelonia mydas) were divided into four groups of 10 and fasted for either 3, 9, 10 or 15 h. The animals were then subjected to a fitness test via repetitive use of the 'righting reflex' on land. Health assessments were conducted prior to the fitness test, including; heart rate, haematocrit (Hct), heterophil to lymphocyte ratio and the measurement of 11 biochemical analytes, including pH, partial pressures of carbon dioxide (PvCO2) and oxygen (PvO2), lactate, bicarbonate (HCO3 -), sodium (Na+), potassium (K+), chloride (Cl-), ionized calcium (iCa2+), glucose and urea. Results were corrected for multiple comparisons and significant differences among groups were demonstrated for temperature, pH, HCO3 -, iCa2+, urea and lactate. To investigate physiological relationships between analytes, correlation coefficients were calculated between fitness and glucose, fitness and lactate, glucose and lactate, pH and iCa2+, pH and K+, pH and PvCO2, pH and HCO3 - and Hct and K+. Following correction for multiple comparisons, significant relationships were seen between pH and iCa2+ and pH and HCO3 -. Post-hatchling turtles appear to enter a catabolic state when exposed to short-term fasting. While this did not have a direct impact on fitness, the production of an intense energetic output from a catabolic state may induce a physiological debt. This study suggests that handling that induces a physical response should be minimized and animals should be fed within 10 h of release.

© 2019 CSIRO. Temperate intertidal shores globally are often dominated by habitat-forming seaweeds, but our knowledge of these systems is heavily biased towards northern hemisphere species. Rocky intertidal shores throughout Australia and New Zealand are dominated by a single monotypic species, Hormosira banksii. This species plays a key role in facilitating biodiversity on both rocky shores and estuarine habitats, yet we know little about the processes that structure populations. Herein we characterise the genetic diversity and structure of Hormosira and demonstrate strong restrictions to gene flow over small spatial scales, as well as between estuarine and open coast populations. Estuarine ecotypes were often genetically unique from nearby open coast populations, possibly due to extant reduced gene flow between habitats, founder effects and coastal geomorphology. Deviations from random mating in many locations suggest complex demographic processes are at play within shores, including clonality in estuarine populations. Strong isolation by distance in Hormosira suggests that spatial management of intertidal habitats will necessitate a network of broad-scale protection. Understanding patterns of genetic diversity and gene flow in this important ecosystem engineer will enhance the ability to manage, conserve and restore this key species into the future.

Desalination is an increasingly common method of meeting potable water demands, but the associated ecological risks are not well understood. Seawater desalination plants discharge large volumes of hypersaline brine directly into the ocean, raising concerns about potential impacts to marine life. In order to reduce impacts of brine, newer desalination outfalls are often fitted with high-pressure diffusers that discharge brine at high velocity into the water column, increasing the mixing and dilution of brine with ocean water. However, there are few published studies of marine impacts of desalination brine, and no well replicated before-after designs. Here we report a six-year study testing for impacts and subsequent recovery of sessile marine invertebrate recruitment near a desalination outfall with high-pressure diffusers. We used a Multiple Before-After-Control-Impact (MBACI) design to test for impacts and recovery at two distances (30 m and 100 m) from a 250 ML/day plant outfall, as well as a gradient design to test the strength of impacts relative to distance from the outfall. The diffusers achieved the target of less than 1 psμ salinity difference to surrounding ambient waters within 100 m of the discharge outfall, but sessile invertebrates were nonetheless impacted. Polychaetes, bryozoans and sponges reduced in cover as far as 100 m from the outfall, while barnacles showed the opposite pattern and were more abundant near the discharging outfall. Ecological impacts were disproportionate to the relatively minor change in salinity (∼1 psμ), suggesting a mechanism other than salinity. We propose that impacts were primarily driven by changes in hydrodynamics caused by the diffusers, such as higher near-bed flow away from the outfall. This is consistent with flow preferences of various taxonomic groups, which differ due to differences in settlement and feeding abilities. High-pressure diffusers designed to reduce impacts of hypersalinity may inadvertently cause impac

Coastal waterways are increasingly exposed to multiple stressors, e.g. contaminants that can be delivered via pulse or press exposures. Therefore, it is crucial that ecological impacts can be differentiated among stressors to manage ecosystem threats. We investigated microbial community development in sediments exposed to press and pulse stressors. Press exposures were created with in situ mesocosm sediments containing a range of ‘metal’ concentrations (sediment contaminated with multiple metal(loid)s) and organic enrichment (fertiliser), while the pulse exposure was simulated by a single dose of organic fertiliser. All treatments and exposure concentrations were crossed in a fully factorial field experiment. We used amplicon sequencing to compare the sensitivity of the 1) total (DNA) and active (RNA) component of 2) bacterial (16S rRNA) and eukaryotic (18S rRNA) communities to contaminant exposures. Overall microbial community change was greater when exposed to press than pulse stressors, with the bacterial community responding more strongly than the eukaryotes. The total bacterial community represents a more time-integrated measure of change and proved to be more sensitive to multiple stressors than the active community. Metals and organic enrichment treatments interacted such that the effect of metals was weaker when the sediment was organically enriched. Taxa-level analyses revealed that press enrichment resulted in potential functional changes, mainly involving nitrogen cycling. Furthermore, enrichment generally reduced the abundance of active eukaryotes in the sediment. As well as demonstrating interactive impacts of metals and organic enrichment, this study highlights the sensitivity of next-generation sequencing for ecosystem biomonitoring of interacting stressors and identifies opportunities for more targeted application.

Ecosystems modified by human activities are generally predicted to be biologically impoverished. However, much pollution impact theory stems from laboratory or small-scale field studies, and few studies replicate at the level of estuary. Furthermore, assessments are often based on sediment contamination and infauna, and impacts to epibiota (sessile invertebrates and algae) are seldom considered. We surveyed epibiota in six estuaries in south-east Australia. Half the estuaries were relatively pristine, and half were subject to internationally high levels of contamination, urbanisation, and industrialisation. Contrary to predictions, epibiota in modified estuaries had greater coverage and were similarly diverse as those in unmodified estuaries. Change in epibiota community structure was linearly correlated with sediment-bound copper, and the tubeworm Hydroides elegans showed a strong positive correlation with sediment metals. Stressors such as metal contamination can reduce biodiversity and productivity, but others such as nutrient enrichment and resource provision may obscure signals of impact.

Ecological observation of global change processes is dependent on matching the scale and quality of biological data with associated geophysical and geochemical driver information. Until recently, the scale and quality of biological observation on natural assemblages has often failed to match data generated through physical or chemical platforms due to constraints of cost and taxonomic resolution. With the advent of next-generation DNA sequencing platforms, creating 'big data' scale observations of biological assemblages across a wide range of phylogenetic groups are now a reality. Here we draw from a variety of studies to illustrate the potential benefits and drawbacks of this new data source for enhancing our observation of ecological change compared with traditional methods. We focus on a key habitat-estuaries-which are among the most threatened by anthropogenic change processes. When community composition data derived using morphological and molecular approaches were compared, the increased level of taxonomic resolution from the molecular approach allowed for greater discrimination between estuaries. Apart from higher taxonomic resolution, there was also an order of magnitude more taxonomic units recorded in the molecular approach relative to the morphological. While the morphological data set was constrained to traditional macroinvertebrate sampling, the molecular tools could be used to sample a wide range of taxa from the microphytobenthos, e.g., diatoms and dinoflagellates. Furthermore, the information provided by molecular techniques appeared to be more sensitive to a range of well-established drivers of benthic ecology. Our results indicated that molecular approaches are now sufficiently advanced to provide not just equivalent information to that collected using traditional morphological approaches, but rather an order of magnitude bigger, better, and faster data with which to address pressing ecological questions.

Ecological communities are increasingly exposed to multiple chemical and physical stressors, but distinguishing anthropogenic impacts from other environmental drivers remains challenging. Rarely are multiple stressors investigated in replicated studies over large spatial scales (>1000 kms) or supported with manipulations that are necessary to interpret ecological patterns. We measured the composition of sediment infaunal communities in relation to anthropogenic and natural stressors at multiple sites within seven estuaries. We observed increases in the richness and abundance of polychaete worms in heavily modified estuaries with severe metal contamination, but no changes in the diversity or abundance of other taxa. Estuaries in which toxic contaminants were elevated also showed evidence of organic enrichment. We hypothesised that the observed response of polychaetes was not a 'positive' response to toxic contamination or a reduction in biotic competition, but due to high levels of nutrients in heavily modified estuaries driving productivity in the water column and enriching the sediment over large spatial scales. We deployed defaunated field-collected sediments from the surveyed estuaries in a small scale experiment, but observed no effects of sediment characteristics (toxic or enriching). Furthermore, invertebrate recruitment instead reflected the low diversity and abundance observed during field surveys of this relatively 'pristine' estuary. This suggests that differences observed in the survey are not a direct consequence of sediment characteristics (even severe metal contamination) but are related to parameters that covary with estuary modification such as enhanced productivity from nutrient inputs and the diversity of the local species pool. This has implications for the interpretation of diversity measures in large-scale monitoring studies in which the observed patterns may be strongly influenced by many factors that covary with anthropogenic modification. © 2

Nutrient enrichment of coastal waters is widely recognized as a major driver of seagrass decline. Under conditions where seagrasses are nutrient-limited, however, moderately elevated nutrient loads can enhance seagrass biomass and increase above- and below-ground consumers that support higher order predators. To improve understanding of bottom-up processes in seagrass ecosystems, we conducted a manipulative field experiment to simultaneously evaluate the responses of primary producers (seagrass and epiphytes) and the epiphyte- and the sedimentbased components of seagrass food webs to moderate and high levels of waterborne nutrients. Fifteen 7 m 2 sites in Zostera muelleri meadows were assigned randomly to control, moderate or high nutrient treatments and were enriched with 0, 1800 g and 3600 g respectively of slow-release fertilizer in above-ground dispensers. The experiment ran for 9 mo (August 2006 to April 2007) and the fertilizer was replaced every 2 mo to ensure continuous enrichment. The biomass of primary producers (seagrasses Z. muelleri, Halophila ovalis and associated epiphytes) and the abundance of predators in the epiphyte- and the sediment-based components of the food web were greater in nutrient-enriched treatments than in controls. Epiphyte grazers, deposit feeders/detritivores, suspension feeders and benthic grazers did not respond significantly to the nutrient enrichment. In general, responses to nutrient enrichment were similar for medium and high nutrient treatments except that the biomass and surface area of seagrass was greater in high enrichment sites. These results demonstrate that Z. muelleri-dominated seagrass meadows in oligotrophic systems may be resilient to greater nutrient loads. Effective conservation strategies for Z. muelleri meadows should continue to consider interactions among nutrient enrichment and other key anthropogenic stressors, particularly non-nutrient pollutants in runoff and sewage discharge. © Inter-Research 2013.

Global losses of seagrasses and mangroves, eutrophication-driven increases in ephemeral algae, and macrophyte invasions have impacted estuarine detrital resources. To understand the implications of these changes on benthic ecosystem processes, we tested the hypotheses that detrital source richness, mix identity, and biomass influence benthic primary production, metabolism, and nutrient fluxes. On an estuarine muddy sandflat, we manipulated the availability of eight detrital sources, including mangrove, seagrass, and invasive and native algal species that have undergone substantial changes in distribution. Mixes of these detrital sources were randomly assigned to one of 12 treatments and dried detrital material was added to seventy-two 0.25 m2 plots (n = 6 plots). The treatments included combinations of either two or four detrital sources and high (60 g) or low (40 g) levels of enrichments. After 2 months, the dark, light, and net uptake of NH4+, dissolved inorganic nitrogen, and the dark efflux of dissolved organic nitrogen were each significantly influenced by the identity of detrital mixes, rather than detrital source richness or biomass. However, gross and net primary productivity, average oxygen flux, and net NOX and dissolved inorganic phosphorous fluxes were significantly greater in treatments with low than with high detrital source richness. These results demonstrate that changes in detrital source richness and mix identity may be important drivers of estuarine ecosystem performance. Continued impacts to estuarine macrophytes may, therefore, further alter detritus-fueled productivity and processes in estuaries. Specific tests that address predicted future changes to detrital resources are required to determine the consequences of this significant environmental problem. © 2013 Blackwell Publishing Ltd.

Simple ecological models that predict trophic responses to bottom-up forcing are valuable tools for ecosystem managers. Traditionally, theoretical ecologists have used resource-dependent functional responses to explain the modification of food chains exposed to bottom-up perturbations. These models predict alternating positive, negative and zero responses at each trophic level. More recently, ratio-dependent functional response models that predict proportional increases at each level have challenged this paradigm. The present study tested the predictions of the 2 hypotheses empirically by comparing the relative biomasses of 4 trophic levels of an estuarine seagrass food chain in relatively undisturbed, low-nutrient catchments and 'developed' catchments subjected to a prolonged period of nutrient enrichment. We found that nutrient-enriched sites had significantly greater biomass of both epiphytic algae and grazing invertebrates; however, the bottom- up forcing of nutrients was attenuated at higher trophic levels (occupied by juvenile and piscivorous fish), with no significant effect of catchment development. This disconnect in the upward cascade of energy may be due to a number of possible reasons including high levels of diversity and omnivory, trophic subsidy within the system or the strength or nature of perturbations. Although the predictions of both hypotheses failed to hold across all trophic groups, ratio dependence was prevalent at the lower levels of the food chain, which has implications for catchment management. © 2012 Inter-Research.

Food webs of many ecosystems are sustained by organic matter from other habitats. Human activities and climatic change are increasingly modifying the quality and supply of these resources, yet for most ecosystems it is unknown how the taxonomic composition of organic matter influences community composition. Along the coastline of Sydney, Australia, the once abundant habitat-forming macroalga, Phyllospora comosa, is now locally extinct. Shallow reefs are now primarily occupied by Sargassum sp. and, to a lesser extent, the kelp Ecklonia radiata. We experimentally manipulated the supply of P. comosa, Sargassum sp. and E. radiata to estuarine sediments to assess responses by macroinvertebrate communities to: (1) changing the identity of the dominant detrital resource; and (2) varying the ratio of input of different macrophytes. Estuarine sediments dosed with P. comosa supported greater abundances of macroinvertebrates than sediments receiving Sargassum sp. or the kelp E. radiata. Whereas plots receiving Sargassum sp. or E. radiata had fewer macroinvertebrates than controls, plots receiving a moderate (120 g dry weight per m(2)) loading of P. comosa had more. Mixtures of detritus dominated by P. comosa supported similar macroinvertebrate communities to monocultures of the alga. Communities in sediments receiving detritus comprised of less than one-third P. comosa were, however, distinctly different. Our study provides evidence that the ecological ramifications of species decline can extend to spatially removed ecosystems, subsidized by allochthonous materials. Even prior to extinction of detrital sources, small changes in their provision of organic matter may alter the structure of subsidized communities.

Invasive primary producers can dramatically reorganize food webs through detrital subsidies. This study assessed (1) contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries, and (2) effects of these contributions on sedimentdwelling invertebrates. In an invaded estuary, sampling of an intertidal shore indicated C. taxifolia fragments were consistently present in organic matter deposits and were particularly abundant following storms. Sampling of the alga across 6 invaded estuaries showed that the ratio of organic carbon to nitrogen (C:N) in fresh tissue varied between 7 and 16. To determine how C. taxifolia detritus influences benthic macrofaunal assemblages and whether this influence depends on the quantity and C:N ratio of C. taxifolia detritus, a manipulative field experiment was performed. On a sheltered intertidal mudflat, 0.25 m2 plots of sediment were experimentally enriched with either a high (90 g DW) or low (30 g) loading of high C:N (14) or low C:N (7) C. taxifolia detritus. Experimental enrichment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading. For some macrofauna, reducing the C:N ratio tended to exacerbate negative effects on abundances, whereas it moderated these effects for other species. Given that organic matter derived from invasive species can be transported beyond the distribution of live invaders, greater consideration should be given to the potential broad-scale effects of invasive primary producers on detrital pathways. © Inter-Research 2010.

Benthic invertebrates can uptake metals through diffusion of free ion solutes, or ingestion of sediment-bound forms. This study investigated the efficacy of the metal chelating resin SIR 300 in adsorbing porewater metals and isolating pathways of metal exposure. A field experiment (Botany Bay, Sydney, Australia) and a laboratory toxicity test each manipulated the availability of porewater metals within contaminated and uncontaminated sediments. It was predicted that within contaminated sediments, the resin would adsorb porewater metals and reduce toxicity to invertebrates, but in uncontaminated sediments, the resin would not significantly affect these variables. Whereas in the laboratory, the resin produced the predicted results, in the field the resin increased porewater metal concentrations of contaminated sediments for at least 34 days and decreased abundances of four macroinvertebrate groups, and richness in all sediments. These contrasting findings highlight the limits of extrapolating the results of laboratory experiments to the field environment.

The population density and size-frequency distribution of Acanthopleura gemmata, a pan-tropical intertidal chiton and conspicuous bioeroder of carbonate substrates were investigated over two years at One Tree Reef, southern Great Barrier Reef. The population on a beachrock platform was dominated by medium to large adults. The size-frequency distribution showed little variation over time, with no evidence of recruitment. A study of individually tagged chitons indicated that growth in A. gemmata is greatest in small chitons and declines with increasing size and age. A. gemmata exhibited temporally variable movement and behaviour. The abundance of A. gemmata on the platform surface decreased significantly during the colder months. We suggest that this is because of behavioural change due to the chitons residing in the platform infrastructure during winter. Some tagged chitons remained in their original home-scar throughout the study, while others moved to other homescars. Our study shows that the abundance and behaviour of A. gemmata fluctuates through time and therefore its ecological impact is also likely to exhibit temporal variation.

Despite a growing body of knowledge on the ecological consequences of loss and fragmentation of habitat-forming macroalgae, little is known about the genetic implications of such losses. Here, we investigate the genetic consequences of fragmentation caused by the loss of the habitat-forming macroalga Phyllospora comosa from 70 km of urbanised coastline in Sydney, Australia. Contrary to predictions, there appeared to be substantial connectivity among fragmented populations, although spatial autocorrelation analysis revealed that this may be an artifact of allele size homoplasy beyond scales of similar to 80 km. Genetic differentiation was not related to geographic separation of populations. This may be explained by the nature of prevailing currents (East Australian Current) that promote nonlinear dispersal in 'leaps', sourcing propagules from one area and depositing them via eddies that either come ashore or disperse. Populations that were tens of kilometers apart were often genetically different, which was likely due to barriers to dispersal, such as sandy beaches and mouths of estuaries, or rapid fertilization and recruitment of zygotes on small spatial scales. Our research provides a basis for designing a rehabilitation program for populations of Phyllospora comosa, with appropriate consideration of genetic diversity and structure.

Reproduction in the pantropical chiton Acanthopleura gemmata was examined at One Tree Island, Great Barrier Reef, near the southern limit of its distribution, using gonad histology and gonad index (GI). Gonad growth was associated with the onset of gametogenesis in mid-spring. Fully mature gonads were present from early summer until late autumn. During these months gametes at various stages of development were present in the gonads indicating a continuous pattern of gamete development and release over the six month spawning season. Following the maximum GI (March/April) there was a sharp drop in the index marking the end of spawning. In winter, the gonads entered a rest period and remained small in size. The reproductive pattern of A. gemmata at its southern limit is similar and 6 months out of phase to that reported for populations in the Gulf of Suez, at the northern limit of its distribution. This suggests that photoperiod may be an important factor in modulating reproduction. Reproduction of A. gemmata at One Tree Island is also similar to that for populations in the northern Great Barrier Reef. © 2009 Marine Biological Association of the United Kingdom.

Oyster mortality and subsequent degradation of shell matrices may influence associated epibiota by modifying processes of filtration and biodeposition and by changing habitat structure. In the Hawkesbury River, NSW, Australia, QX disease devastated aquaculture populations of the native Sydney rock oyster, Saccostrea glomerata, and threatened wild populations. To ascertain effects of this oyster mortality on associated epibiota, we compared epifaunal communities occupying 100% oyster shell cover among 5 sites along the estuary, ranging from 25 ppt salinity and live oyster density of 96 ± 13 m- 2, to 32 ppt salinity and live oyster density of 3187 ± 233 m- 2. Epifaunal richness was greatest closest to the estuarine mouth, where live oyster abundance was greatest. Epifaunal abundance, by contrast, generally increased with distance upstream, as oyster matrices were increasingly dominated by the shells of dead oysters. To ascertain the role of live and dead oysters as habitat providers, we carried out a manipulative experiment to test the hypothesis that the epifaunal assemblages that settle over a 4 month period will significantly differ among constructed matrices comprised of live, whole dead and/or degraded (single valve) oysters. Treatments containing a component of single valves, which increase the availability of interstitial spaces and provide greater surface area for attachment, supported the greatest numbers of epibiota. Matrices comprised solely of live oysters supported fewest species and numbers of organisms. Results demonstrate that death and degradation of oysters alter the structure of associated communities, even where 100% cover of shell matrix is maintained. These results have important ramifications for management strategies and retaining estuarine biodiversity in the event that disease such as QX causes local oyster extinctions. © 2009 Elsevier B.V. All rights reserved.

The fucalean macroalga Hormosira banksii facilitates diverse rocky intertidal communities. Along the east coast of Australia, the alga can also persist in mangroves as a free-living form trapped amongst pneumatophores. We investigated (1) whether the alga has an effect on molluscan species richness and abundance in mangroves similar to that on rocky shores, and (2) whether, in mangroves, the source (phenotypically distinct estuarine or rocky shore populations) of H. banksii influences the outcome of its interspecific interactions. Sampling of 3 rocky shore and 3 mangrove sites along the east coast of Australia revealed that patches of H. banksii consistently supported a greater species richness of molluscs than adjacent substratum. Whereas the alga increased the abundance of molluscs in the mangrove forest, it had no effect or decreased molluscan abundance on the rocky shore. Transplant of H. banksii from rocky shores and estuarine tidal flats into the mangrove indicated that the source of the algae influenced the magnitude of effects. Although all algae enhanced molluscan abundance and species richness, estuarine H. banksii, which had larger vesicles and a longer thallus, supported more molluscs of more species than rocky shore H. banksii. These results support the growing consensus that the influence of foundation species at the community level is dependent on environmental conditions. As human activities place increasing pressure on coastal ecosystems, it will be important to understand the mechanisms and conditions that determine community-level effects of foundation species so that biodiversity may be conserved.

The native Sydney rock oyster, Saccostrea glomerata, is under increasing threat from QX disease, competition with nonnative Crassostrea gigas and coastal development. Knowledge of the distribution and population structure of S. glomerata and C. gigas is essential if oysters and their ecosystem services are to be successfully managed. We determined spatial patterns of abundance, condition, and size-structure of S. glomerata and C. gigas, across two key habitats, mangroves, and rocky shores of the Hawkesbury River, a highly modified estuary 50 km north of Sydney. Sampling of five sites per habitat, spanning a 15 km stretch of river, revealed abundant populations of S. glomerata, averaging 514 ± 185 m-2, in mangroves and on rocky shores. The native oyster accounted for 99% of all oysters sampled, with C. gigas found only at two of the five sites sampled within each habitat. Overall, rocky shores supported over eight times the oyster cover as mangroves. Among rock sites, live oyster cover and condition generally decreased with distance upstream. Although, at present, the Hawkesbury River estuary supports abundant wild oyster populations, ongoing monitoring of oyster populations is required to ensure that appropriate management strategies are established to ensure the persistence of this important component of the ecosystem. Our sampling of two key oyster habitats provides an important baseline against which future studies can assess change.

Alteration of physical habitat structure is a fundamental mechanism by which invaders produce ecosystem level effects. We assessed whether, along the east coast of Australia, the impacts of the non-native gastropod Maoticolpus roseus on soft-sediment habitats extend beyond the range of live populations as a result of shell export following death of animals. Sampling over an 18 month period revealed that M. roseus shells were temporally persistent in surface sediments of a coastal lagoon devoid of live populations of the gastropod. The well-preserved shells, of which 92% were entire, did not accumulate above a maximal density of 260 m(-2) due to periodic burial. Manipulation of M. roseus shell densities indicated that at densities (140 m(-2)) presently experienced within surface sediments of the lagoon, the structure provided by the shells was weakly facilitative of some invertebrate species. Further increasing shell densities to the possible future scenario of 280 m(-2), which may occur under continued expansion of nearby live populations did not, however, strengthen positive effects. To the contrary, plots with higher densities of M. roseus shells contained similar invertebrate assemblages to control plots, without shells. Consistent with the negligible effects of M. roseus shells on infauna, the foraging efficiency of the generalist predator, Carcinus maenas, and the naticid gastropod, Polinices sordidus, were not affected by addition of shells. Surprisingly, even an extreme scenario of 1600 m(-2) did not affect their predation. Thus, in this dynamic coastal lagoon, that experiences considerable sediment movement and environmental variability, the structure introduced by import of non-native shells is unimportant in structuring soft-sediment communities. Whether this unrecognised aspect of molluscan invasions impacts the ecology of more stable coastal environments remains unclear and warrants further consideration.

The bioerosive potential of the intertidal chiton Acanthopleura gemmata on One Tree Reef was determined by quantification of CaCO3 in daily faecal pellet production of individuals transplanted into mesocosms after nocturnal-feeding forays. Mean bioerosive potential was estimated at 0.16 kg CaCO3 chiton-1 yr-1. Bioerosion rates were estimated for populations on two distinct chiton habitats, reef margin (0.013 kg CaCO3 m-2 yr-1) and beachrock platform (0.25 kg CaCO3 m-2 yr-1). Chiton density on the platform was orders of magnitude greater than on the reef margin. The surface-lowering rate (0.16 mm m-2 yr) due to bioerosion by the beachrock population is a substantial contribution to the total surface-lowering rate of 2 mm m-2 yr-1 previously reported for One Tree Reef across all erosive agents. At high densities, the contribution of A. gemmata to coral reef bioerosion budgets may be comparable to other important bioeroders such as echinoids and fish. © 2008 Springer-Verlag.

1. Trade-offs between competitive ability and tolerance of abiotic stress are widespread in the literature. Thus, condition-specific competition may explain spatial variability in the success of some biological invaders and why, in environments where there is small-scale environmental variability, competitively inferior and superior species can coexist. 2. We tested the hypothesis that differences in abiotic stress alter the outcome of competitive interactions between the native Sydney rock oysters Saccostrea glomerata and exotic Pacific oysters Crassostrea gigas by experimentally testing patterns of intra- and interspecific competition across a tidal elevation gradient of abiotic stress at three sites on the east coast of Australia. 3. At low and mid-intertidal heights, exotic C. gigas were able to rapidly overgrow and smother native S. glomerata, which grew at c. 60% of the exotic's rate. In high intertidal areas, where C. gigas displayed about 80% mortality but similar growth rates to S. glomerata, the native oyster was not affected by the presence of the exotic species. 4. Asymmetrical effects of the exotic species on the native could not be replicated by manipulating densities of conspecifics, confirming that effects at low and mid-intertidal heights were due to interspecific competition. 5. Our results suggest that the more rapid growth of C. gigas than S. glomerata comes at the cost of higher mortality under conditions of abiotic stress. Thus, although C. gigas may rapidly overgrow S. glomerata at low and mid tidal heights, the native oyster will not be competitively excluded by the exotic due to release from competition at high intertidal elevations. 6. The success of trade-offs in explaining spatial variation in the outcome of competitive interactions between C. gigas and S. glomerata strengthen the claim that these may be a useful tool in the quest to produce general predictive models of invasion success. © 2007 The Authors.

Accelerating rates of species extinction and invasion have sparked recent interest in how changes in plant community composition can be propagated through food webs. Research in this area has, however, been largely restricted to considerations of how det

Bioengincers modify habitats via their own physical structures and substantially increase local diversity in marine ecosystems. On rocky shores, there are large overlaps in the composition of communities associated with bioengineers that form complex mat-like composition of communities associated with bioengineers that form complex mat-like habitats. We investigate the potential for redundancy in habitat provision by these types of habitats by comparing diverse molluscan assemblages associated with Perumytilus purpuratus mussel beds and algal turfs of Corallina officinalis var. chilenis, Gelidium chilense and Gastroclonium cylindricum. At three times between Spetember 2003 and January 2004, we sampled tje molluscan assemblages associated with each bioengineer at similar tidal heights on two rocky shores ont he coast of central Chile. Of the 31 molluscan species identified, 30 were found in Corallina and 19-22 were identified from the other habitats. The pool of species found associated with each bioengineer overlapped greatly, demonstrating the potential for redundancy in habitat provision and little habitat-specificity. However, multivariate and unvariate analyses showed all bioengineers except Gastroclonium contained a unique molluscan assemblage for at least one time of sampling because of variation in frequency of occurrence, richness and total abundance. Recent studies have highlighted many anthropogenic and natural processes that directly influence the diversity and compoistion of bioengineering species on rocky shores. We demonstrate that the loss of any particular bioengineer would not substantially later the overall pool of molluscan species on the rocky shores of Chile. The loss of any bioengineer except Gastroclonium would, however, result in decreased local biodiversity becasue the molluscan assemblages in Perumytilus, Corallina and Gelidium each contained a significantly differemnt community structure for at least one time of sampling.

Under climate change, enhanced storminess may increase the magnitude and rate of detrital loading to the benthos, potentially altering sediment chemistry and/or physical disturbance of sediments. To assess whether the impact of detrital loading on invertebrates in intertidal sediment sparsely vegetated by seagrass is negatively affected by increasing the frequency and/or intensity of the disturbance, high (90 g dry weight) or low (30 g dry weight) quantities of shredded Zostera capricorm were added to experimental plots at high (intervals of 8 wk, on a total of 3 occasions) or low (added once) frequency. Macroinvertebrate assemblages were sampled 8, 16 and 24 wk after the first detrital enrichment. Plots subjected to frequent detrital addition contained up to 50% fewer macroinvertebrates, representing 50% fewer taxa than plots disturbed only once. This pattern was independent of disturbance intensity and emerged after only 2 detrital additions. Only at the low frequency of addition did the increased quantity of detritus influence macroinvertebrate assemblage composition, halving the number of animals by Week 24. Physical disturbance, not sediment chemistry, drove the frequency effect. Generally negative impacts of frequent detrital enrichment on infaunal populations occurred despite small positive effects of high detrital enrichment on the biomass of microphytobenthos, the food source of many sediment-dwelling invertebrates. These results suggest that, even though climate warming may increase the amount of detritus that is washed up onto intertidal sediments, its greater effect on soft-sediment communities is likely to come through increasing the frequency of storms.

Studies on rocky intertidal gastropods indicate habitat complexity and body size to be major determinants of dispersal patterns. Considerations of effects of habitat complexity and body size on soft sediment gastropods are, however, less common. In neither habitat has the interaction between habitat complexity and body size been considered despite the increasing recognition in the general ecological literature that complexity effects are body-size-dependent. We tested independent and interacting effects of habitat complexity and body size on movement of the mud-whelk, Pyrazus ebeninus, by marking large (61-85 mm) and small (31-55 mm) snails in sites with low and high densities of pneumatophores and determining the distance and direction of their dispersal over periods of 1 week, 2 weeks and 1 month. Contrary to our expectation, we found no effect of pneumatophore density on the distance of snail migration over each of the temporal scales; net distance travelled by snails was determined only by body size and idiosynchratic, site-specific factors. The direction of snail movement was, by contrast, influenced on some temporal scales by both pneumatophore density and snail size. Over 1 week, site effects dominated patterns of movement and neither size of snail nor density of pneumatophore produced statistically significant effects. As the temporal scale increased, effects of size and pneumatophore density became increasingly apparent. Over the 1-month period, large snails at all sites and small snails at sites with high pneumatophore density migrated down the shore, while small snails at sites with low pneumatophore displayed non-directional movement. Thus, overall this study provides only weak support for effects of pneumatophore density on snail movement. In combination with other studies, our results suggest that, in comparison to on rocky shores where habitat complexity has strong effects on the distribution, abundance and behaviour of gastropods in soft-sediment sys

Patterns of spatial variation of molluscan communities associated with coralline algal turfs were evaluated over 1,000 kin of the coast of Argentinean Patagonia. A hierarchically-nested experimental design was used to determine the relative importance of

It is well known that adult dispersal is common in soft bottom intertidal and shallow subtidal communities. We here report on the first study that attempts to quantify the effects of both immigration and emigration on patches of soft sediment communities

Classical resource- and the less studied ratio-dependent models of predator-prey relationships provide divergent predictions as to the sustained ecological effects of bottom-up forcing. While resource-dependent models, which consider only instantaneous prey density in modelling predator responses, predict community responses that are dependent on the number of trophic levels in a system, ratio-dependent models, which consider the number of prey per consumer, predict proportional increase in each level irrespective of chain length. The two models are only subtly different for systems with two or three trophic levels but in the case of four trophic levels, predict opposite effects of enrichment on primary producers. Despite the poor discriminatory power of tests of the models in systems with two or three trophic levels, field tests in estuarine and marine systems with four trophic levels have been notably absent. Sampling of phytoplankton, macroinvertebrates, invertebrate-feeding fishes, piscivorous fishes in Kooloonbung Creek, Hastings River estuary, eastern Australia, subject to over 20 years of sewage discharge, revealed increased abundances in all four trophic levels at the disturbed location relative to control sites. Increased abundance of phytoplankton at the disturbed site was counter to the predictions of resource-dependent models, which posit a reduction in the first trophic level in response to enrichment. By contrast, the increase in abundance of this first trophic level and the proportionality of increases in abundances of each of the four trophic groups to nitrogen loading provided strong support for ratio dependency. This first evidence of ratio dependence in an estuarine system with four trophic levels not only demonstrates the applicability of ecological theory which seeks to simplify the complexity of systems, but has implications for management. Although large nutrient inputs frequently induce mortality of invertebrates and fish, we have shown that