The challenge of choosing environmental indicators of anthropogenic impacts in estuaries

What does impacted look like? High diversity and abundance of epibiota in modified estuaries

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.

Next generation sequence analysis of the transcriptome of Sydney rock oysters (Saccostrea glomerata) exposed to a range of environmental stressors

Sydney rock oysters (Saccostrea glomerata) were exposed to environmental stressors at contaminated field sites or in a controlled laboratory setting. RNA seq transcriptome data were generated for the gill and digestive gland using Roche's 454 pyrosequencing technology. 28,685 contigs were de novo assembled which encoded 11,671 different protein products. The data will act as a reference for future studies in ecology, immunology and environmental toxicology.

A biomarker of contaminant exposure is effective in large scale assessment of ten estuaries

Cost-effective and sensitive measures of anthropogenic stress are necessary tools in any environmental monitoring program. When implementing new monitoring tools in a region, rigorous laboratory and field studies are essential for characterizing the sensitivity and efficacy of the approach. We exposed the oyster Saccostrea glomerata to various individual contaminants through multiple exposure pathways (water- and food-borne) in the laboratory and measured two biomarker responses, lysosomal membrane stability (LMS) and lipid peroxidation (LPO). LMS was sensitive to both contaminant exposure pathways. We subsequently measured this biomarker in oysters which had been experimentally deployed at multiple sites in each of ten estuaries with varying levels of contamination associated with re-suspended sediments. There was a strong association between LMS and metal exposure, despite substantial natural variation in water quality parameters. Our results illustrate the potential use of LMS as a pragmatic indicator of biotic injury in environmental monitoring programs for re-suspended contaminated sediments.

The discrepancy in concentration of metals (Cu, Pb and Zn) in oyster tissue (Saccostrea glomerata) and ambient bottom sediment (Sydney estuary, Australia)

The current study aimed to examine the relationship between metals in sediments and metal bioaccumulation in oyster tissue in a highly-modified estuary (Sydney estuary, Australia). While extensive metal contamination was observed in surficial sediments, suspended particulate matter and oyster tissue, a significant relationship between these media could not be established. No relationship was determined between sediment quality guidelines and oyster size or weight, nor with human consumption levels for metals in oyster tissue. Moreover, oyster tissue metal concentrations varied greatly at a single locality over temporal scales of years. Oyster tissue at all 19 study sites exceeded consumptions levels for Cu. Bioaccumulation of metals in oyster tissue is a useful dynamic indicator of anthropogenic influence within estuaries, however oysters cannot be used in Sydney estuary as a valid biomonitor due to overriding internal regulation (homoestasis) by the animal, or by external natural (sediment resuspension) and anthropogenic (sewer/stormwater discharges) pressures, or both.

Assessing mechanisms of toxicant response in the amphipod Melita plumulosa through transcriptomic profiling

This study describes the function of transcripts with altered abundance in the epibenthic amphipod, Melita plumulosa, following whole-sediment exposure to a series of common environmental contaminants. M. plumulosa were exposed for 48 h to sediments spiked and equilibrated with the following contaminants at concentrations predicted to cause sublethal effects to reproduction: porewater ammonia 30 mg L(-1); bifenthrin at 100 μg kg(-1); fipronil at 50 μg kg(-1); 0.6% diesel; 0.3% crude oil; 250 mg Cu kg(-1); 400 mg Ni kg(-1); and 400 mg Zn kg(-1). RNA was extracted and hybridized against a custom Agilent microarray developed for this species. Although the microarray represented a partial transcriptome and not all features on the array could be annotated, unique transcriptomic profiles were generated for each of the contaminant exposures. Hierarchical clustering grouped the expression profiles together by contaminant class, with copper and zinc, the petroleum products and nickel, and the pesticides each forming a distinct cluster. Many of the transcriptional changes observed were consistent with patterns previously described in other crustaceans. The changes in the transcriptome demonstrated that contaminant exposure caused changes in digestive function, growth and moulting, and the cytoskeleton following metal exposure, whereas exposure to petroleum products caused changes in carbohydrate metabolism, xenobiotic metabolism and hormone cycling. Functional analysis of these gene expression profiles can provide a better understanding of modes of toxic action and permits the prediction of mixture effects within contaminated ecosystems.

Polychaete richness and abundance enhanced in anthropogenically modified estuaries despite high concentrations of toxic contaminants

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.

Environmental and ecological changes associated with a marina

Anthropogenic modifications to waterways are common and their ecological consequences must be understood to effectively conserve local biodiversity. The facilitation of recreational boating activities often requires substantial alteration of natural areas, however the environmental and ecological consequences of such alterations are rarely described in the scientific literature. In this study, ecological and physico-chemical conditions were investigated in a recreational boating marina, located inside a marine park on the south-east coast of Australia. Recruitment panels were deployed for 8 weeks both inside and outside the marina, and differences in the composition of the developing fouling communities were observed. The recruitment of taxa, which often have short-lived larvae, was increased inside the marina (bryozoans, spirorbids and sponges) while the recruitment of taxa, which often have longer-lived larvae, was reduced or absent (barnacles, solitary ascidians and non-spirorbid polychaetes). Differences were also observed in environmental conditions inside the marina cf. directly outside. The marina environment had higher turbidity, temperature and pH along with higher concentrations of lead and copper in suspended sediments, while flow rates and trapped sediment loads were reduced inside the marina. The differences observed in the study suggest that there may be marked environmental changes associated with marina developments. The potential ecological consequences of these changes should be a primary consideration during the planning process, particularly for developments in locations of notable ecological value.

Differential tolerance to copper, but no evidence of population-level genetic differences in a widely-dispersing native barnacle

Despite many estuaries having high levels of metal pollution, species are found to persist in these stressful environments. Populations of estuarine invertebrates exposed to toxic concentrations of such metals may be under selection. However, in species with a wide-dispersal potential, any short-term results of localized selection may be counteracted by external recruitment from populations not under selection. The barnacle Amphibalanus variegatus is found in nearshore coastal environments as well as sheltered embayments and estuaries, including metal-impacted estuaries, from New South Wales, Australia to Western Australia. The fertilised eggs of A. variegatus are brooded internally and released as larvae (nauplii), which remain in the water-column for ~14 days before settling. Hence the species has a considerable dispersal capacity. The purpose of this study was to examine whether populations of A. variegatus from metal-impacted sites, displayed a greater tolerance to a toxicant (copper) than reference populations. Adult barnacles where collected from twenty sites within two metal-impacted and fourteen sites within two reference estuaries. Within 24 h, adults were induced to spawn and the offspring were exposed to copper in a laboratory assay. Larvae collected from the metal-impacted estuaries demonstrated a greater tolerance to copper compared to those from reference sites. To determine if selection/localised in the metal impacted sites was occurring, the genetic structure of populations at three sites was examined using an AFLP methodology. No evidence of unique population identity and or selection (outlier loci) was detected suggesting that: (1) the tolerance displayed in the assay was derived from acclimation during development; and/or (2) that the populations are open preventing the fixation of any unique alleles.

Biomonitoring study of an estuarine coastal ecosystem, the Sacca di Goro lagoon, using Ruditapes philippinarum (Mollusca: Bivalvia)

Coastal lagoons are constantly subjected to releases of chemical pollutants, and so organisms may be exposed to such toxicants. This study investigated through a multivariate approach the physiological status of bivalve Ruditapes philippinarum, farmed in Sacca di Goro lagoon. Biomarkers at different levels of biological organization (catalase, superoxide dismutase, genotoxicity, reburrowing behavior) were evaluated at three sites exposed to different environmental conditions. A seasonal trend was observed, and micronucleus frequency was significantly lowest at the relatively pristine reference site. Enzymatic activity toward oxyradicals be quite efficient since variations in responsiveness were not consistent. However, behavioral impairment was observed in reburrowing rates. Sediment concentrations showed low PAH levels and high natural levels of trace metals Cr and Ni. DistLM statistical analysis revealed a non-significant relationship between selected biomarkers and xenobiotics. Therefore other potentially toxic compounds in admixture at low doses may be involved in driving differing spatial distribution of physiological impairment.

Assessing and managing sediment contamination in transitional waters

Sediment contamination remains a global problem, particularly in transitional waters such as estuaries and coastal lagoons, which are the recipients of chemicals from multiple near- and far-field sources. Although transitional waters are highly productive ecosystems, approaches for assessing and managing their sediment contamination are not as well developed as in marine and fresh waters. Further, although transitional waters remain defined by their variable and unique natural water quality characteristics, particularly salinity, the biota inhabiting such ecosystems, once thought to be defined by Remane's "paradox of brackish water", are being redefined. The purpose of the present paper is to build on an earlier but now dated (>12years old) review of methods to assess sediment contamination in estuaries, extending this to all transitional waters, including information on integrative assessments and on management decision-making. The following are specifically discussed: chemical assessments; bioindicators; biomarkers; and, biological surveys. Assessment and management of sediment contamination in transitional waters need to be focused on ecosystem services and, where appropriate and possible, be proactive rather than reactive when uncertainty has been suitably reduced.

Multivariate methods and artificial neural networks in the assessment of the response of infaunal assemblages to sediment metal contamination and organic enrichment

A 4-year annual sediment survey was conducted in an organically enriched tidal channel to compare the performance of univariate community descriptors, traditional multivariate techniques (TM) and artificial neural networks (AANs), in the assessment of infaunal responses to moderate levels of sediment metal contamination. Both TM approaches and the SOM ANN revealed spatiotemporal patterns of environmental and biological variables, suggesting a causal relationship between them and further highlighting subsets of taxa and sediment variables as potential main drivers of those patterns. Namely, high values of non-natural metals and organic content prompted high abundances of opportunists, while high values of natural metals yielded typical tolerant assemblages of organically enriched areas. The two approaches yielded identical final results but ANNs showed the following advantages over TM: ability to generalise results, powerful visualization tools and the ability to account simultaneously for sediment and faunal variables in the same analysis. Therefore, the SOM ANN, combined with the K-means clustering algorithm, is suggested as a promising tool for the assessment of the ecological quality of estuarine infaunal communities, although further work is needed to ensure the accuracy of the method.

Indicators of environmental stress: cellular biomarkers and reproductive responses in the Sydney rock oyster (Saccostrea glomerata)

We measured a suite of common biomarker responses for the first time in the Sydney rock oyster Saccostrea glomerata to evaluate their utility as biological effects measures for pollution monitoring. To examine the relationship between biomarker responses and population level effects, fertilisation and embryo development assays were also conducted. Adult oysters were deployed in two contaminated estuaries and a reference estuary in Sydney, Australia. The concentrations of various contaminants (metals and polycyclic aromatic hydrocarbon, PAHs) were quantified in oyster's tissue from each site and both metals and total PAHs were significantly elevated in contaminated estuaries relative to the reference estuary. Lysosomal membrane destabilisation, lipid peroxidation levels and glutathione (GSH) concentrations were measured in the digestive gland of oysters. Of all biomarkers measured, lysosomal membrane destabilisation proved to be the most useful indicator of oysters facing anthropogenic stress and we suggest this may be an especially useful biomarker for incorporation into local environmental monitoring programs. Moreover, lysosomal membrane destabilisation showed good correlations with fertilisation, normal embryo development and estuary status. GSH and lipid peroxidation were not as valuable for distinguishing between estuaries exposed to differing levels of anthropogenic stress, but did provide additional valuable information regarding overall health status of the oysters.

Bacterial communities are sensitive indicators of contaminant stress

With many environments worldwide experiencing at least some degree of anthropogenic modification, there is great urgency to identify sensitive indicators of ecosystem stress. Estuarine organisms are particularly vulnerable to anthropogenic contaminants. This study presents bacterial communities as sensitive indicators of contaminant stress. Sediments were collected from multiple sites within inner and outer zones of three heavily modified and three relatively unmodified estuaries. Bacterial communities were censused using Automated Ribosomal Intergenic Spacer Analysis and analysed for a suite of metal and PAH contaminants. Shifts in both bacterial community composition and diversity showed strong associations with sediment contaminant concentrations, particularly with metals. Importantly, these changes are discernable from environmental variation inherent to highly complex estuarine environments. Moreover, variation in bacterial communities within sites was limited. This allowed for differences between sites, zones and estuaries to be explained by variables of interest such as contaminants that vary between, but not within individual sites.

Relationships between body burdens of trace metals (As, Cu, Fe, Hg, Mn, Se, and Zn) and the relative body size of small tooth flounder (Pseudorhombus jenynsii)

Several studies have described strong relationships between body size and the accumulation of trace metals in animal tissues. However, few of these studies have utilized aging techniques to control for age related effects. We utilized relative body size (gy(-1)) of a model flounder species, Pseudorhombus jenynsii, in order to control for age related effects on growth and size measurements. We investigated links between relative body size, concentrations of trace metals in flounder muscle tissue, physico-chemical variables (temperature, salinity, pH, and turbidity), and levels of trace metals in the sediment. Flounder were sampled using an otter trawl net in the inner areas of eight estuaries that were either heavily modified or relatively unmodified by urbanization and industrial activity. Our results indicate that this commonly eaten fish is accumulating significant levels of some trace metals in their muscle tissue, both in relatively unmodified and heavily modified estuaries. Concentrations of Cu, Zn and Fe in muscle tissue, as well as temperature, showed a negative relationship to the relative body size of flounder. In contrast, Se and Hg in muscle showed a positive relationship to relative body size. Observed growth patterns indicate that these effects are not driven by age related differences in metabolic activity. Instead, our results suggest that differences in food supply or toxicological effects may be responsible for the observed relationships between relative body size and concentrations of Cu, Zn, and Se in muscle tissues. The use of otolith aging and growth measurement techniques represents a novel method for assessing the relationships between trace metal accumulation and the relative body size of fish in a field environment.