Ashley Rummell

Restoration projects are increasingly widespread and many promote habitat succession and the diversity and abundance of faunal communities. These positive effects on biodiversity and abundance may extend to enhancing the ecological functioning and resilience of previously degraded ecosystems, but this is rarely quantified. This study surveyed a 200‐ha restoring coastal wetland and three control wetlands in the Maroochy River, eastern Australia to compare the effects of wetland restoration on the consumption of carrion and the biodiversity, abundance, and functional diversity of functionally important fish and crustaceans. Carrion consumption by fish and crustaceans was measured every 6 months from spring 2017 until spring 2021 for nine events using a combination of baited cameras and scavenging assays. We found restoration improved rates of carrion consumption and the biodiversity, functional diversity, and abundance of scavenger species. Despite positive effects on the diversity of scavengers and carrion consumption, the abundance of two species, longfin eels ( Anguilla reinhardtii ) and mud crabs ( Scylla serrata ), was the most important predictors of carrion consumption rates. The spatial distribution of carrion consumption was concentrated in areas with high saltmarsh extent, moderate to high mangrove extent, and high salinity, which also resembled the distribution of both longfin eels and mud crabs. We show that restoration can promote the rates of key ecological functions but that increases to functions are likely to be characterized by low functional redundancy and greater complementarity. Therefore, maintaining or increasing the abundance of functionally important species should become a key objective in future restoration projects.

Coastal wetlands are communities of mangroves and saltmarshes that provide numerous ecosystems services and functions, including carbon storage, nutrient cycling, fisheries benefits and biodiversity. However, mangroves and saltmarshes are amongst the world’s most degraded ecosystems which have been depleted of the services and functions they provide. For this reason, wetland restoration projects are becoming more widespread with greater investment that focuses on the regeneration of focal ecosystems and their associated ecological co-benefits. Providing accurate assessments of recovery, selecting and measuring suitable indicators to detect benefits of restoration, and adopting appropriate approaches for site selection that are informed by principles from landscape ecology and spatial conservation prioritization, are essential for supporting wetland restoration projects to deliver positive outcomes for the recovery of target ecosystems and ecological co-benefits. This thesis used a restoring coastal wetland in eastern Australia as a model system to fill a sizable gap in our knowledge and understanding of remote sensing science, restoration ecology and spatial and seascape ecology, and examine how the learnings from these disciplines might be integrated to improve the effectiveness of wetland restoration projects in delivering positive outcomes for target ecosystems and ecological co-benefits. It pioneered an accurate and reliable approach (i.e. 90 to 95% overall accuracy) for monitoring the recovery of target ecosystems, identified the viability of fish and crustacean assemblages as early indicators of positive recovery trajectories in restoration, demonstrated the strong effects of connectivity and habitat context in influencing the recovery of ecological co-benefits in restoration, and illustrated the significance of functional complementarity and landscape heterogeneity for promoting ecological functions across restoring seascapes. These results highlight the need for coastal managers to use more robust methods to quantify the succession of target ecosystems, adopt fish and crustacean communities as early success indicators for biodiversity and fisheries targets co-benefits, prioritise restoration sites to enhance ecological co-benefits and widen the diversity and availability of ecological niche space to promote ecological functioning. Incorporating these approaches into the planning and management of wetland restoration projects can provide numerous performance indicators of restoration success, support informed and adaptive management decisions, and ensure restoration programs are sited, designed and monitored to maximise potential ecological co-benefits and functions from ecosystem recovery.

Early indicators of restoration success can inform adaptive management strategies and maintain community interest and financial investment. Coastal wetland restoration projects prioritize monitoring the succession of habitat forming communities. However, these communities often expand slowly. In contrast, fish and crustaceans can quickly occupy newly available habitats and therefore, may be early indicators of restoration success. Here, we compared the short-term responses of fish and crustacean communities and landcover area to restoration actions at a restoring wetland and three reference wetlands in the Maroochy River in eastern Australia. Fish and crustacean communities and landcover area were surveyed every 6 months between Spring 2017 and Spring 2019 (n = 5), with two sampling events conducted before restoration actions commenced in May 2018 and three after. Fish and crustaceans were surveyed using baited underwater video stations and fyke nets. Landcover was remotely sensed using a combination of Worldview-2 satellite imagery, object-based image analysis, and random forest classification. Fish and crustaceans make viable indicators for early restoration success, as our findings show the composition, diversity, and abundance of species targeted in fisheries of these communities can resemble assemblages at reference sites within 1 year of restoration actions. The area of tidal inundation significantly increased overtime, but the recovery of mangroves and saltmarsh communities did not. These findings support the notion that coastal wetland restoration can promote immediate recruitment by fish and crustacean communities, thus making these taxa useful indicators for communicating early success of restoration projects.

Connectivity and landscape context are common considerations in the spatial prioritisation of conservation actions. Similar spatial principles can also be used to inform the selection, prioritisation and monitoring of sites for restoration, but it is not clear whether these variables consistently shape the delivery of benefits from restoration. This study aimed to determine whether, and how, seascape connectivity and landscape context combine to influence the recovery of fish and crustacean communities at a restoring coastal wetland. We measured changes to biodiversity (fish species richness), fisheries benefits (fisheries harvested abundance) and functioning (fish functional diversity) bi-annually at a 200 ha restoring wetland, and three control sites, in eastern Australia between 2017 and 2021. Connectivity and landscape context were quantified using a combination of in-field measurements, remote sensing techniques and least-cost path analysis. Biodiversity, fisheries benefits, and functional diversity increased at the restoration site over time, but these metrics did not change significantly at any of the control sites over the same time period. The delivery of each of the three co-benefits at the restoration site was also positively linked to increased wetland connectivity, larger areas of mangroves and higher salinity levels in the recovering seascape. These results support tighter integration of connectivity and landscape context to optimise and inform spatial planning in restoration, and we suggest that this is essential for supporting the delivery of multiple benefits from recovering habitats and seascapes. Adopting similar approaches to understand the drivers of restoration success would improve the ecological and economic outcomes of actions.

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.