Estuaries are crucial feeding, nursery and resting sites for fish but can also be subject to the impacts of severe flooding. The environmental features of estuaries can mediate how they respond to ...these impacts. For example, the size, configuration, and context of estuarine habitats across seascapes affects the value of patches for fish, and so fish assemblages at sites with a greater habitat extent or closer to the mouth of an estuary may rebound more quickly from flooding. We investigated how a once in 100-year flood event affected fish assemblages at approximately 600 sites across 13 estuaries and six estuarine habitats (bare sediments, log snags, mangrove forests, rocky structures, saltmarsh and seagrass meadows) in southeast Queensland, Australia, and determined whether flood impacts were mediated by the position of sites within the broader estuarine seascape. Sites were surveyed annually in 2020/2021 (pre-flood) and 2022 (6 months post-flood) using underwater videography. Flooding modified the structure of the fish community and reduced the abundance of fish targeted by local fisheries in all six habitats. Crucially, flood effects on fish were greater at sites near more expansive urbanisation in some ecosystems, but lower at sites nearer to the estuary mouth. Maximising the extent of natural habitats across estuaries can mediate the effects of floods and should be priorities for restoration and management plans seeking to maintain biodiversity and fisheries productivity in the face of increasing climate-related disturbances.
Predation is important in maintaining the community structure, functioning and ecological resilience of estuarine seascapes. Understanding how predator community structure, seascape context and ...habitat condition combine to influence predation is vital in managing estuarine ecosystems. We measured relationships between predator species richness, predator abundance and individual species abundances as well as seascape context and habitat condition, on relative predation probability in mangrove forests, seagrass meadows and unvegetated sediment across 11 estuaries in Queensland, Australia. Predation was quantified using videoed assays of tethered invertebrates (i.e. ghost nippers,
Trypaea australiensis
) and fish assemblages were surveyed using remote underwater video systems. Yellowfin bream (
Acanthopagrus australis
) dominated predation in all three habitats; however, predation was not correlated with yellowfin bream abundance. Instead, predation increased fourfold in mangroves and threefold in unvegetated sediment when predatory species richness was highest (> 3 species), and increased threefold in seagrass when predator abundance was highest (> 10 individuals). Predation in mangroves increased fourfold in forests with a lower pneumatophore density (< 50/m
2
). In seagrass, predation increased threefold at sites that had a greater extent (> 2000 m
2
) of seagrass, with longer shoot lengths (> 30 cm) and at sites that were closer to (< 2000 m) the estuary mouth. Predation on unvegetated sediment increased threefold when more extensive salt marshes (> 15000 m
2
) were nearby. These findings demonstrate the importance of predator richness and abundance in supplementing predation in estuaries, despite the dominance of a single species, and highlight how seascape context and habitat condition can have strong effects on predation in estuaries.
Connectivity between land and sea through the movement of species, energy and nutrients means that land-based impacts can affect the structure and functioning of nearby coastal ecosystems. As the ...interface between land and sea, estuaries are often faced with increasing pressures from catchment modifications (e.g. the removal of terrestrial vegetation) which can alter the overall health of estuaries (e.g. the degradation of coastal water quality due to an increase in terrestrial runoff) and change the value of habitat for many marine species. These landscape-scale impacts can, however, be mediated through variations in the context and connectivity of seascapes (e.g. greater extent of vegetated ecosystems help to filter nutrients). We surveyed fish across five estuaries over four years using underwater videography and sought correlations between fish biodiversity and abundance with variables indexing catchment land use, seascape connectivity, and coastal water quality. Fish assemblages were more abundant and diverse at sites which had lower chlorophyll-a concentrations and were nearer to the estuary mouth, in conjunction with catchments containing higher percent of natural land and heterogenous seascapes. Sites with lower concentrations of chlorophyll-a supported indicator species from more diverse functional groups that had greater fisheries values, in comparison to indicator species from sites with high concentrations of chlorophyll-a. This research can help direct coastal management to better prioritise management in coastal ecosystems, thereby enhancing fish richness and abundance, functional group richness and fisheries value.
•Estuaries connect land to sea and are facing impacts from multiple spatial scales.•Coastal management requires quantitative data to disentangle multi-scaled impacts.•Sites with lower chlorophyll-a concentrations had more abundant and diverse fish.•Catchments with higher nature and conservation land had more diverse fish species.•Disentangling combined multi-scaled impacts can help prioritise coastal management.
Disentangling natural and anthropogenic effects on ecosystem condition can uncover bright spots in urban landscapes that are performing above expectations and so are potential sites for conservation ...or benchmarking, as well as sites performing below expectations that should be the focus of management. In this study, we tested for correlations between metrics indexing ecological condition (focusing on habitat-forming species) and a suite of spatial and environmental variables at 373 sites across four ecosystems (mangroves, seagrass, saltmarsh and rocky outcrops) and 13 estuaries in southeast Queensland, Australia. Ten condition metrics across the four ecosystems correlated with variables indexing the seascape context of sites, with condition metrics typically higher at sites more connected to natural features including the estuary mouth and mangroves. Urbanisation affected only two metrics, with rocky outcrop oyster cover being 75% lower at sites near extensive urbanisation and algae cover being highest at sites with intermediate urbanisation. We identified patterns in at least two variables from each ecosystem, meaning that decisions need to be made regarding optimal ecosystem states. Overall, management sites were more common than bright spots, with 50% more management sites in mangroves, 42.8% more in seagrasses, 38.5% more in saltmarshes and no bright spots in rocky outcrops (however, 10.3% of rocky outcrop sites were bright spots under an alternate ecosystem state model). We found that patterns in habitat condition across coastal seascapes can be predicted using spatial modelling approaches, and that these models can be readily used to prioritise management actions across the entire regions.
Ecosystems are increasingly degraded, fragmented and lost because of human activities globally. These impacts cause changes in the distribution of biodiversity and key ecological functions, ...modifications to food webs and reductions in ecosystem condition and seascape connectivity. Understanding whether, and how, the spatial context (i.e. extent, position) and condition (i.e. structure and condition of patches, including habitat forming species) of ecosystems coalesce to support their function as animal habitats is critical for effective and cost efficient coastal management. These potential combined, or interactive, effects of spatial context and habitat condition on fish assemblages are, however, rarely quantified. We sampled fish assemblages from six different ecosystems (mangrove, seagrass, saltmarsh, log snag, rocky outcrop and unvegetated sediment) across 13 estuaries in eastern Australia and quantified the relative importance of spatial context and habitat condition variables for fish assemblage composition. Spatial context variables were consistently more important than habitat condition in structuring fish abundance and diversity. Sites that were closer to smaller vegetated habitats (i.e. mangrove and seagrass) and key seascape features (i.e. estuary mouth and intertidal flats) typically supported diverse fish assemblages in high abundance. While the composition of fish assemblages was primarily linked to spatial context variables, habitat condition variables that index food availability were also important for fish in mangroves, seagrass and rocky outcrops. Our results show that fish abundance and diversity are intimately linked to seascape connectivity and heterogeneity, and have important implications for conservation planning and fisheries management decisions in coastal ecosystems. We highlight the importance of quantifying the influence of the combined effects of habitat condition and spatial context for biodiversity across multiple ecosystems, and expect the outcomes to lead to more efficient and effective management planning.
Fish assemblages are considered valuable monitoring targets for coastal and marine ecosystems because their populations can reflect ecosystem condition. Human impacts to coastal seascapes are ...pervasive, necessitating management and restoration actions that are assessed against quantitative targets. Relationships between metrics of habitat condition and animal assemblages can be used to identify where management interventions should aim to maximise outcomes for key functions and services. In this study, we surveyed fish assemblages (using underwater videography) and habitat condition (focusing on the size, composition and complexity of habitats) of five estuarine ecosystems (mangrove forests, seagrass meadows, saltmarsh, log snags and rocky outcrops) across 13 estuaries over two years (for n = 981 sites) in southeast Queensland, Australia. We used generalised additive models to quantify relationships and identify thresholds between metrics indexing habitat condition and key metrics of fish assemblages (species richness and abundance), and used these models to calculate optimal habitat condition values that maximise habitat value for fish and fisheries. We also identified indicator fish species whose abundance correlated with these optimal values. Metrics of habitat condition that index food availability for fish (such as algae and oyster cover) or broader habitat complexity (such as seagrass height or mangrove canopy cover) were consistently important for fish biodiversity and abundance. Relationships were readily translated into optimal values for key metrics of habitat condition for four of the five ecosystems surveyed. We propose that incorporating optimal values of habitat condition into management would maximise the abundance of key indicator fish species, including several which are important fisheries targets. The findings of this study will help managers to identify the optimal condition requirements of coastal ecosystems, thereby maximising the effectiveness and efficiency of often sparse management resources.
•Impacts to coastal seascapes by humans affect ecosystem services like fisheries.•We identify threshold relationships between habitat condition and fish assemblages.•We used these to calculate optimal habitat condition values that maximise fisheries.•We identified fish which correlate with optimal values and so should be monitored.•Identifying thresholds in fish metrics can optimise management and restoration.
Nature reserves are often implemented to restore the condition of habitats, protect populations of harvested species and to protect, as well as enhance, ecological functions. It is, however, not ...clear whether and how the spatial context of reserves influences their capacity to promote this ecosystem multifunctionality. We measured how the spatial context of no-take marine reserves and the condition of ecosystems combine to structure animal assemblages and modify rates of two key ecological functions (herbivory, carrion scavenging) in mangrove forests in the Moreton Bay Marine Park, Queensland, Australia. Fish diversity and the abundance of harvested fish species were highest inside reserves, and in mangrove forests nearer to the open ocean and moderate-sized seagrass meadows, and far from coral reefs. The rates of both ecological functions were, however, not elevated inside reserves. The highest rates of carrion scavenging occurred in mangrove forests that were open to fishing, far from the open ocean, and near both large seagrass meadows and coral reefs. Herbivory was highest in mangrove forests that were close to both large seagrass meadows and coral reefs, and with abundant pneumatophores and low mangrove tree canopy cover. We therefore found positive effects of reserves on animal assemblages, but not on ecological functions, and show that ecosystem multifunctionality is not always tightly linked with biodiversity. The results of this study highlight the importance of quantitative conservation goals, and in integrating data on both the ecological condition and spatial context of ecosystems when prioritizing conservation to maximise both biodiversity and ecosystem multifunctionality.
•Ecosystem multifunctionality is the provision of multiple functions and services.•It is not clear how the spatial context of reserves modifies ecosystem multifunctionality.•We quantified the drivers of multifunctionality in reserves protecting mangroves.•Fish diversity and abundance were higher in reserves, but functions were not.•Conservation must consider both the condition and landscape context of ecosystems.
Human impacts lead to widespread changes in the abundance, diversity and traits of shark assemblages, altering the functioning of coastal ecosystems. The functional consequences of shark declines are ...often poorly understood due to the absence of empirical data describing long-term change. We use data from the Queensland Shark Control Program in eastern Australia, which has deployed mesh nets and baited hooks across 80 beaches using standardised methodologies since 1962. We illustrate consistent declines in shark functional richness quantified using both ecological (e.g., feeding, habitat and movement) and morphological (e.g., size, morphology) traits, and this corresponds with declining ecological functioning. We demonstrate a community shift from targeted apex sharks to a greater functional richness of non-target species. Declines in apex shark functional richness and corresponding changes in non-target species may lead to an anthropogenically induced trophic cascade. We suggest that repairing diminished shark populations is crucial for the stability of coastal ecosystems.
Human activities in coastal catchments can cause the accumulation of pollutants in seafood. We quantified the concentration of heavy metals, pesticides and PFASs in the flesh of the fisheries species ...yellowfin bream Acanthopagrus australis (n = 57) and mud crab Scylla serrata (n = 65) from 13 estuaries in southeast Queensland, Australia; a region with a variety of human land uses. Pollutants in yellowfin bream were best explained by the extent of intensive uses in the catchment. Pollutants in mud crabs were best explained by the extent of irrigated agriculture and water bodies. No samples contained detectable levels of pesticides, and only six samples contained low levels of PFASs. Metals were common in fish and crab flesh, but only mercury in yellowfin bream from the Mooloolah River breached Australian food safety standards. High pollutant presence and concentration is not the norm in seafood collected during routine surveys, even in estuaries with highly modified catchments.
•We quantified concentrations of 70 pollutants in the flesh of two fisheries species.•We sampled 13 estuaries in southeast Queensland with a variety of human land uses.•No samples contained pesticides, only six samples contained low PFAS levels.•Metals were common, but only one estuary had fish that exceeded safe mercury values.•High pollutant loads are not the norm in seafood collected during routine surveys.
