Context Landscape modification alters the condition of ecosystems and the structure of terrain, with widespread impacts on biodiversity and ecosystem functioning. Seafloor dredging impacts a diversity of flora and fauna in many coastal landscapes, and these processes also transform three-dimensional terrain features. The potential ecological significance of these terrain changes in urban seascapes has, however, not been investigated. Objectives We examined the effects of terrain variation on fish assemblages in 29 estuaries in eastern Australia, and tested whether dredging changes how fish associate with terrain features. Methods We surveyed fish assemblages with baited remote underwater video stations and quantified terrain variation with nine complementary metrics (e.g. depth, aspect, curvature, slope, roughness), extracted from bathymetry maps created with multi-beam sonar. Results Fish diversity and abundance were strongly linked to seafloor terrain in both natural and dredged estuaries, and were highest in shallow waters and near features with high curvature. Dredging, however, significantly altered the terrain of dredged estuaries and transformed the significance of terrain features for fish assemblages. Abundance and diversity switched from being correlated with lower roughness and steeper slopes in natural estuaries to being linked to features with higher roughness and gentler slopes in dredged estuaries. Conclusions Contrasting fish-terrain relationships highlight previously unrecognised ecological impacts of dredging, but indicate that plasticity in terrain use might be characteristic of assemblages in urban landscapes. Incorporating terrain features into spatial conservation planning might help to improve management outcomes, but we suggest that different approaches would be needed in natural and modified landscapes.

Coastal wetlands are restored to regenerate lost ecosystem services. Accurate and frequent representations of the distribution and area of coastal wetland communities are critical for evaluating restoration success. Typically, such data are acquired through laborious, intensive and expensive field surveys or traditional remote sensing methods that can be erroneous. Recent advances in remote sensing techniques such as high-resolution sensors (<2 m resolution), object-based image analysis and shallow learning classifiers provide promising alternatives but have rarely been applied in a restoration context. We measured the changes to wetland communities at a 200 ha restoring coastal wetland in eastern Australia, using remotely sensed Worldview-2 imagery, object-based image analysis and random forest classification. Our approach used structural rasters (digital elevation and canopy height models) and a multi-temporal technique to distinguish between spectrally similar land cover. The accuracy of our land cover maps was high, with overall accuracies ranging between 91 and 95%, and this supported early detection of increases in the area of key ecosystems, including mixed she-oak and paperbark (10 ha), mangroves (0.91 ha) and saltmarsh (4.31 ha), over a 5-year monitoring period. Our approach provides coastal managers with an accurate and frequent method for quantifying early responses of coastal wetlands to restoration, which is essential for informing adaptive management in the regeneration of ecosystem services.

No abstract

No abstract

Mangroves and seagrasses are important nurseries for many marine species, and this function is linked to the complexity and context of these habitats in coastal seascapes. It is also connected to bathymetric features that influence habitat availability, and the accessibility of refuge habitats, but the significance of terrain variation for nursery function is unknown. To test whether seafloor terrain influences nursery function, we surveyed fish assemblages from mangrove and seagrass habitats in 29 estuaries in eastern Australia with unbaited underwater cameras and quantified the surrounding three-dimensional terrain with a set of complementary surface metrics (that is, depth, aspect, curvature, slope, roughness) applied to sonar-derived bathymetric maps. Terrain metrics explained variability in assemblages in both mangroves and seagrasses, with differing effects for the entire fish assemblage and nursery species composition, and between habitats. Higher depth, plan curvature (concavity or convexity) and roughness (backscatter) were negatively correlated with abundance and diversity in mangroves and positively linked to abundance and diversity in seagrass. Mangrove nursery species (6 species) were most abundant in forests adjacent to flats with concave holes, rough substrates and low-moderate depths, whereas seagrass nursery species (3 species) were most abundant in meadows adjacent to deep channels with soft mounds and ledges. These findings indicate that seafloor terrain influences nursery function and demonstrate contrasting effects of terrain variation in mangroves and seagrass. We suggest that incorporating three-dimensional terrain into coastal conservation and restoration plans could help to improve outcomes for fisheries management, but contrasting strategies might be needed for different nursery habitats.