Humans have urbanised and fragmented landscapes across the globe, with detrimental impacts to biodiversity, habitats and food webs in most biomes. Urbanisation might also modify the provision of ecological functions, but these putative effects of landscape transformation are rarely measured. Coastal cities are typically located near estuaries, and we tested for potential impacts of these on ecological functions. Our study used 22 estuaries in eastern Australia as model systems to examine how urbanisation shapes the consumption of carrion by fish, a pivotal ecological function in estuaries. Fish assemblages varied among estuaries according to the extent of shoreline hardening, and this was correlated with changes in the rate of carrion consumption. In estuaries with low levels of shoreline hardening and abundant remnant mangroves, most carrion was consumed by toadfishes (Tetraodontidae). By contrast, in moderately urban estuaries (i.e. where 20–60% of shorelines had been hardened with artificial structures) yellowfin bream (Sparidae) replaced toadfish and performed the bulk of the scavenging function. Bream are particularly effective scavengers that utilize artificial structures as habitat for both foraging and sheltering. We show that by augmenting habitat for an important species of scavenger, the moderate addition of urban structures to estuarine shorelines also helped to supplement a key ecological function in estuaries. Urbanisation impacts diversity in all ecosystems, but many opportunistic species flourish in urban habitats. Identifying and conserving taxa that perform important roles in urban environments is now a critical conservation challenge for maintaining ecological functions across disturbed landscapes.

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Nature reserves are created to conserve biodiversity and restore populations of harvested species, but it is not clear whether this strategy is successful in all ecosystems. Reserves are gazetted in estuaries to offset significant impacts from burgeoning human populations, however, coastal conservation cannot be optimized because their effectiveness is rarely evaluated. We surveyed 220 sites in 22 estuaries in the Moreton Bay Marine Park, Queensland, Australia, which included all six current estuarine marine reserves within the park. Fish were surveyed using one hour deployments of baited remote underwater video stations twice at each site over consecutive days. We show that although the estuarine reserves in Moreton Bay contain a significantly different fish community, they fail to enhance the abundance of harvested fish species. We posit that performance is limited because reserves protect unique spatial features, or conserve narrow estuaries with weak connections to mangrove habitats and the open sea. Seascapes within reserves are, therefore, not representative of estuaries in the region, and reserves primarily support residual estuarine habitats (i.e. expansive intertidal flats or shallow creeks) which are not particularly significant to either fish or fishers. We argue that reserve effectiveness can be improved by conserving deeper estuaries, with diverse habitats for fish and strong connections to both freshwater and the open sea. Without incorporating these critical spatial considerations into estuarine reserve design, estuarine reserves are doomed to fail.

Species surrogates, the use of particular species to index habitat condition or to represent ecological assemblages are commonly identified in many ecosystems, but are less tested, and therefore less employed in estuaries. Estuaries provide important ecosystem goods (e.g. harvestable species) and services (e.g. carbon processing, coastal armouring), but require protection from multiple human activities, meaning that finding surrogates for estuarine condition or faunal assemblages is a significant knowledge gap. In this study, we test the efficacy of the threatened estuary ray Hemitrygon fluviorum, as a suitable indicator of ecosystem condition and management umbrella surrogate species for conservation prioritisation and monitoring purposes within estuaries. We surveyed fish assemblages and ray presence at ten sites within each of 22 estuaries in southeast Queensland, Australia, using one hour deployments of baited video arrays. We then tested for correlations between ray presence, a series of environmental variables considered important to ecosystem management within estuaries (i.e. testing rays as indicator species), and the co-occurring fish species (i.e. testing rays as umbrella species). Estuary rays function as both umbrella species and ecological indicators of habitat status in subtropical Australian estuaries. As umbrellas, ray occurrence concords with elevated species richness. As ecological indicators, ray distribution concords with habitats of good water quality (especially low turbidity) and more natural vegetation remaining in the catchment. These results highlight the potential for other threatened aquatic vertebrates that are both readily detectable and that are reliable proxies for ecosystems status to be become useful management tools in estuaries. The protection of such large, threatened species in coastal seascapes

Connectivity is a pivotal feature of landscapes that affects the structure of populations and the functioning of ecosystems. It is also a key consideration in conservation planning. But the potential functional effects of landscape connectivity are rarely evaluated in a conservation context. The removal of algae by herbivorous fish is a key ecological function on coral reefs that promotes coral growth and recruitment. Many reef herbivores are harvested and some use other habitats (like mangroves) as nurseries or feeding areas. Thus, the effects of habitat connectivity and marine reserves can jointly promote herbivore populations on coral reefs, thereby influencing reef health. We used a coral reef seascape in eastern Australia to test whether seascape connectivity and reserves influence herbivory. We measured herbivore abundance and rates of herbivory (on turf algae and macroalgae) on reefs that differed in both their level of connectivity to adjacent mangrove habitats and their level of protection from fishing. Reserves enhanced the biomass of herbivorous fish on coral reefs in all seascape settings and promoted consumption of turf algae. Consumption of turf algae was correlated with the biomass of surgeonfish that are exploited outside reserves. By contrast, both reserve status and connectivity influenced herbivory on macroalgae. Consumption of macroalgae was greatest on fished reefs that were far from mangroves and was not strongly correlated with any fish species. Our findings demonstrate that landscape connectivity and reserve status can jointly affect the functioning of ecosystems. Moreover, we show that reserve and connectivity effects can differ markedly depending on resource type (in this case turf algae vs. macroalgae). The effectiveness of conservation initiatives will therefore depend on our ability to understand how these multiple interactive effects structure the distribution of ecological functions. These findings have wider implications for the spatial conservation of heterogeneous environments and strengthen the case that the impact of conservation on ecosystem functioning is contingent on how reserves are positioned in landscapes.