The Use of Remote Sensing and Field Validation For Mapping Coral Communities Of Hervey Bay and the Great Sandy Strait And Implications for Coastal Planning Policy

Coral reefs are under threat from stressors at various scales from the global to regional and local scales. Nearshore reefs are most at threat from land-based runoff and other human-induced disturbances which may result in ‘phase-shift’ from coral to another substrate or benthic cover type. Maintaining connectivity between reefs and related ecosystems of mangroves and seagrass enhances reef health via fluxes of nutrient and detritus and the movement of organisms that maintain substrate ‘phase’. This study within Hervey Bay, an estuarine coastal embayment in the Burnett Mary region of southern Queensland, eastern Australia, investigated three topics. (1) An integrated approach was developed, using field, ecological and remote sensing techniques. This was used to map the composition of turbid water nearshore reefs south of the Great Barrier Reef. Part of this work also implemented a comparison of the accuracy of different image data sets, image classification techniques and field-survey data analysis techniques. (2) The context, biodiversity and geomorphic values of nearshore reefs were examined within the mapped areas. Regional connectivity between reefs and functionally-related communities of seagrass and mangroves was measured by spatial analysis. (3) The spatial and strategic planning policy implications of nearshore reef values and connectivity were evaluated in the national and regional context of marine spatial planning. Benthic living and non-living substrates of Hervey Bay’s nearshore reefs were mapped with an integrated approach using field, ecological and remote sensing techniques. Benthic substrate field data were analysed quantitatively to produce homogeneous substrate groups. These groups were used to train supervised classification of Quickbird images, enabling mapping of dominant substrate phase, including hard coral (>85% cover) to 60% accuracy and above. The classification also differentiated hard coral from soft coral, macro-algae, turf-algae and heterogeneous back-reef rubble and sand. The findings from this section indicated that manual habitat delineation and spatially-referenced Rapid Ecological Assessment methods were suitable for unconsolidated, low density/high diversity, deep water habitats; and/or patchily distributed habitats e.g. Acropora. Further work is required on accuracy measures suited to marine survey; spatially integrating REA surveys; sample design for spatial and ecological analysis; water column effects; and mapping of low density soft bottom biota. The context, ecological values and connectivity assessment demonstrated that Hervey Bay’s nearshore reefs have substantial values and connectivity. The mainland reefs were found to resemble turbid water reefs of the Great Barrier Reef. Both are dominated by reef-building genera Turbinaria, Goniopora and patchy Acropora but with significantly absent Montipora. High latitude species and brain corals dominant in Moreton Bay were a subdominant component. Areas exhibiting high ecological values, in terms of rarity, range limits, local morphs, reef forming species and large massive form were located at points or sheltered bays which were well-connected to seagrass and mangroves. The connectivity analysis identified chains of reefs, connected seagrass meadows and mangroves throughout the Burnett-Mary region. The Hervey Bay reef – seagrass –mangrove network is the southernmost of three mainland reef networks of the Burnett-Mary region and one of two which connect both latitudinally and across-shelf. Maintaining high ecological values and connectivity against likely impacts from flood plumes and sediment deposition was identified as a key consideration for management activities across the region. The spatial and strategic policy study identified maintenance of connectivity between the Hervey Bay shallow water system and equivalent ecosystems of the GBR and Tweed-Moreton bioregions as a management priority. The study showed that disconnects between and within federal and state jurisdictions and terrestrially-focussed local government plans, severed connectivity within marine ecosystems. In particular this severed connectivity between estuarine and reef wetlands, which are essential for maintaining the resilience of these reefs. Solutions to challenges of increased sedimentation and loss of connectivity may lie in the implementation of integrated legislation and policy that requires the maintenance of riparian corridors, wetlands and estuarine connectivity of these reefs. Overall, this study showed that the integrated field, ecological and image analysis method enabled differentiation of hard coral reefs, possessing characteristics of both tropical and high latitude reefs. Spatial datasets revealed reefs previously unknown to marine park management agencies; and regional connectivity between reef, seagrass and mangroves. A Marine Spatial Planning approach was advocated to maintain genetic connectivity of nearshore reefs with the GBR and with high latitude reefs. This approach would integrate mapping and assessment with policy and management of land and sea connected ecosystems.