Explore the vast range of titles available.

Assessing fish assemblages in subtidal and intertidal habitats is challenging due to the structural complexity of many of these systems. Trapping and collecting are regarded as optimal ways to sample these assemblages, but this method is costly and destructive, so researchers also use video techniques. Underwater visual census and baited remote underwater video stations are commonly used to characterise fish communities in these systems. More passive techniques such as remote underwater video (RUV) may be more appropriate for behavioural studies, or for comparing proximal habitats where the broad attraction caused by bait plumes could be an issue. However, data processing for RUVs can be time consuming and create processing bottlenecks. Here, we identified the optimal subsampling method to assess fish assemblages on intertidal oyster reefs using RUV footage and bootstrapping techniques. We quantified how video subsampling effort and method (systematic random) affect the accuracy and precision of three different fish assemblage metrics; species richness and two proxies for the total abundance of fish, MaxN and MeanCount , which have not been evaluated previously for complex intertidal habitats. Results suggest that MaxN and species richness should be recorded in real time, whereas optimal sampling for MeanCount is every 60 s. Systematic sampling proved to be more accurate and precise than random sampling. This study provides valuable methodology recommendations which are relevant for the use of RUV to assess fish assemblages in a variety of shallow intertidal habitats.

Habitat interactions play key roles in regulating biodiversity and ecosystem functions. This is particularly important in aquatic ecosystems, where the flow of water facilitates exchanges of energy and matter. Oyster reefs, a highly degraded habitat globally and a key focus for restoration efforts, can reduce water movement and facilitate the deposition of particles around them, affecting nutrient cycling in surrounding sediments. The effects of these reefs on sediment infauna taxonomic and functional biodiversity, however, remain unknown. We sampled sediments at increasing distances from reefs at three estuaries to evaluate the relationships between proximity to oyster reefs and composition and functionality of infaunal communities and explored the potential mechanisms behind those relationships. Sediments close to oyster reefs had consistently greater amounts of labile organic matter, which in turn was positively related to the number of taxa and total abundance of infauna. Also, the functional traits of infauna, such as bioturbation and feeding modes, were related to proximity to reefs, but they were variable between estuaries indicating the importance of background estuarine environmental conditions. These results suggest that habitat linkages between oyster reefs and sediments are important in regulating taxonomic biodiversity, while functional biodiversity seems to be driven by processes operating at larger scales. Given burgeoning restoration initiatives worldwide, particularly those of oyster reefs, incorporating seascape interactions can help inform recovery of biodiversity and functions beyond the target habitat at the seascape level, which is often overlooked.

1. Along urbanised coastlines, urban infrastructure is increasingly becoming the dominant habitat. These structures are often poor surrogates for natural habitats, and a diversity of eco-engineering approaches have been trialled to enhance their biodiversity, with varying success. 2. We undertook a quantitative meta-analysis and qualitative review of 109 studies to compare the efficacy of common eco-engineering approaches (e.g. increasing texture, crevices, pits, holes, elevations and habitat-forming taxa) in enhancing the biodiversity of key functional groups of organisms, across a variety of habitat settings and spatial scales. 3. All interventions, with one exception, increased the abundance or number of species of one or more of the functional groups considered. Nevertheless, the magnitude of effect varied markedly among groups and habitat settings. In the intertidal, interventions that provided moisture and shade had the greatest effect on the richness of sessile and mobile organisms, while water-retaining features had the greatest effect on the richness of fish. In contrast, in the subtidal, small-scale depressions which provide refuge to new recruits from predators and other environmental Stressors such as waves, had higher abundances of sessile organisms while elevated structures had higher numbers and abundances of fish. The taxa that responded most positively to eco-engineering in the intertidal were those whose body size most closely matched the dimensions of the resulting intervention. 4. Synthesis and applications. The efficacy of eco-engineering interventions varies among habitat settings and functional groups. This indicates the importance of developing site-specific approaches that match the target taxa and dominant stressors. Furthermore, because different types of intervention are effective at enhancing different groups of organisms, ideally a range of approaches should be applied simultaneously to maximise niche diversity.

Biological introductions can alter the ecology of local assemblages and are an important driver of global environmental change. The first step towards understanding the impact of a non-indigenous species is to study its distribution and associations in the invaded area. In Sydney Harbour, the non-indigenous isopod Cirolana harfordi has been reported in densities up to 0.5 individuals per cm(2) in mussel-beds. Abundances of this species have, however, been largely overlooked in other key habitats. The first aim of this study was to evaluate the abundances and distribution of C. harfordi across different habitats representative of Sydney Harbour. Results showed that C. harfordi occurred in oyster and mussel-beds, being particularly abundant in oyster-beds. We also aimed to determine the role of C. harfordi as a predator, scavenger and detritus feeder by investigating the relationships between densities of C. harfordi and (i) the structure of the resident assemblages, and (ii) deposited organic matter in oyster-beds. Densities of C. harfordi were not related to the structure of the assemblages, nor amounts of deposited organic matter. These findings suggested little or no ecological impacts of C. harfordi in oyster-beds. These relationships may, however, affect other variables such as growth of individuals, or be disguised by high variability of assemblages among different locations. Future studies should, therefore, test the impacts of C. harfordi on the size of organisms in the assemblage and use manipulative experiments to control for spatial variation. This study is the first published work on the ecology of the invasion of C. harfordi and provides the starting-point for the study of the impacts of this species in Sydney Harbour.

Intermittently open and closed lakes and lagoons (ICOLLs) are globally important estuarine systems that are separated from the ocean by a sand beach barrier or berm. The barrier may open or close naturally because of sand and sediment movement or be manually opened by estuarine managers in times of flooding. As intermittently closed systems, it is important to understand the potential for eutrophication and what are the best indicators. This study investigated water quality, sediment quality and benthic processes in four shallow ICOLLs in Sydney, Australia, that experience a range of nutrient loadings. Manly and Curl Curl Lagoons experience higher turbidity and concentrations of pelagic Chl-a compared to Dee Why and Narrabeen Lagoons. They also differ with respect to general morphology with Manly and Narrabeen deeper and more linear while Curl Curl and Dee Why are shallower and more circular. Relationships between nutrient loading and traditional water quality indicators of eutrophication such as chlorophyll-a, turbidity and dissolved oxygen appeared to be moderated by lagoon morphology and hydrology, which control the ratio of pelagic to benthic production and net accumulation of sediment organic matter. We found that all the lagoons investigated were net heterotrophic, with Narrabeen and Manly the least and the most heterotrophic respectively. Ratios of total organic carbon (TOC):benthic community respiration (CR) varied among lagoons and were likely related to the dominance of refractory organic matter in Narrabeen (~ 99%), and more labile organic matter in Manly and Curl Curl Lagoons (~ 90%). Benthic community respiration increased with nutrient loading rates across the lagoons, suggesting that benthic processes are a critical indicator of eutrophication in these shallow systems. In contrast to the generalised conceptual model of eutrophication in coastal systems whereby nutrient pollution causes a reduction in benthic primary productivity at the expense of increased pelagic primary productivity, our results suggest that benthic microalgal productivity in shallow ICOLLs plays an important role in buffering against eutrophication of the water column but may also contribute to organic enrichment of sediments.

Urbanization and its resulting environmental stressors are often managed within terrestrial, freshwater, or marine realms separately. This is problematic for the many cities situated at the intersection between these realms, because stressors and associated management actions can affect multiple realms simultaneously and impacts may be compounded at boundaries. Here, we describe management approaches operating within and across realms, and identify impediments to cross-realm urban management. We find that management that fails to consider connectivity either within or between realms at best delivers only small-scale benefits and at worst can produce large-scale unintended negative outcomes. In contrast, management that explicitly considers inter-realm connectivity can generate large benefits relative to the cost of interventions. Successful cross-realm management requires consideration of connectivity, scale (temporal and spatial), and ecological processes across more than two realms, and is underpinned by an integrated and collaborative approach that provides multiple benefits.

While the consequences of bioinvasions are becoming clearer, our understanding of the environmental and ecological factors driving them is limited due to the complexity of the invasion process. Invasion success can be considered to be influenced by characteristics of the receiving assemblage (habitat, food, community interactions) and disturbances. Studies on the effects of the receiving assemblage have typically focused on a single or small subset of species, rather than on complex, multitrophic assemblages. We used an experimental assemblage consisting of more than 30 taxa from multiple trophic levels to evaluate the importance of the presence of this community and disturbance on colonisation by a generalist invader. To achieve this, we compared colonisation between a disturbed and undisturbed community. In addition, we evaluated the effects of the presence of organic matter of a different source (simulating a disturbance event affecting different habitats) on colonisation. A model generalist invader, the isopod Cirolana harfordi , was introduced to patches of oyster beds with (1) undisturbed (live) assemblages, (2) disturbed assemblages, (3) organic matter (using organic matter of a different source), or (4) no assemblage or organic matter. Our results indicated that the presence of an assemblage (disturbed or not) fostered colonisation; however, colonisation was less successful when the assemblage was undisturbed. Results also indicate that for a disturbance event to affect the colonisation of C. harfordi , it has to directly affect the invaded assemblage. These results add to the understanding of the factors driving invasions, which is important to design management strategies.

The invasive isopod Cirolana harfordi occurs in great densities in oyster-beds in Sydney Harbour and is the second most abundant taxon in terms of biomass. A previous observational study did not find any relationships between densities of C. harfordi and variability in local assemblage structure; this result could, however, be confounded by the enormous variation in the composition of the assemblage between locations. Using manipulative experiments in mesocosms to standardise for such local contingencies, this study evaluated the impacts of this invasive species on assemblages in experimental oyster-beds. We deployed experimental oyster-beds among natural oyster-beds in locations within Hawkesbury River, Australia, where C. harfordi was absent, to be colonised by the assemblage of organisms for 2 months. C. harfordi were then introduced to these experimental oyster-beds in mesocosms. Assemblages in invaded experimental oyster-beds were compared to those in non-invaded experimental oyster-beds in mesocosms and in natural oyster-beds in Sydney Harbour. The results showed no change in the structure of assemblages where C. harfordi were introduced, and those assemblages were similar to those in natural oyster-beds, thus supporting the initial patterns observed in the field. The evidence did not support the general assumption that non-indigenous species with high biomass and abundance cause impacts on local assemblages. This quantitative assessment of the potential impact of C. harfordi provides valuable information for managers to decide on control strategies.

Biological introductions can alter the ecology of local assemblages and are an important driver of global environmental change. The first step towards understanding the impact of a non-indigenous species is to study its distribution and associations in the invaded area. In Sydney Harbour, the non-indigenous isopod Cirolana harfordi has been reported in densities up to 0.5 individuals per cm2 in mussel-beds. Abundances of this species have, however, been largely overlooked in other key habitats. The first aim of this study was to evaluate the abundances and distribution of C. harfordi across different habitats representative of Sydney Harbour. Results showed that C. harfordi occurred in oyster and mussel-beds, being particularly abundant in oyster-beds. We also aimed to determine the role of C. harfordi as a predator, scavenger and detritus feeder by investigating the relationships between densities of C. harfordi and (i) the structure of the resident assemblages, and (ii) deposited organic matter in oyster-beds. Densities of C. harfordi were not related to the structure of the assemblages, nor amounts of deposited organic matter. These findings suggested little or no ecological impacts of C. harfordi in oyster-beds. These relationships may, however, affect other variables such as growth of individuals, or be disguised by high variability of assemblages among different locations. Future studies should, therefore, test the impacts of C. harfordi on the size of organisms in the assemblage and use manipulative experiments to control for spatial variation. This study is the first published work on the ecology of the invasion of C. harfordi and provides the starting-point for the study of the impacts of this species in Sydney Harbour.