ABSTRACT1. Mapping of seabed habitats is increasingly being used to identify the distribution and structure of marine ecosystems and as surrogate measures of biodiversity for marine protected area (MPA) planning. In this study, the distribution of seabed habitats to the 3 nmi limit around the Kent Group of islands, south-eastern Australia were mapped using video ground-truthed single-beam acoustics at the mesoscale level (10 m to 1 km) as part of an MPA planning process.2. Six distinct seabed habitat types (continuous reef, patchy reef, sand, hard sand, sparse sponge, and seagrass) were identified based primarily on visual differences in the first and second echo and a further four (low, medium and high profile reef, and sand hills) on variations in seabed profile identified in the echogram. Extensive acoustic and video transects allowed an estimate of the broad-scale spatial distribution of seabed habitats defined at several hierarchical levels and provided information on the cover of the dominant benthic species or assemblages.3. The island group supports a range of consolidated habitats, including rocky reefs of varying profile dominated by the macroalgae Phyllospora comosa and Ecklonia radiata in depths down to around 45 m, adjacent to deeper sponge-dominated reefs containing encrusting, erect and branching forms. Unconsolidated habitats occurred broadly through the island group, with the offshore region dominated by hard sand (sand with scallop shells and/or shell grit) and sparse sponge-habitats (sand interspersed with low cover of sponge-dominated assemblages). The sheltered coves were dominated by sand and seagrass habitats consisting of beds of the seagrasses Halophila australis, Zostera tasmanica and Posidonia australis, with variations in species composition, patchiness and percentage cover evident within and between coves.
Radiation frosts during clear and calm weather can damage crops in the growing season. In complex topography, large spatial variations in near surface temperatures occur, which makes it more difficult to predict frost events and plan preventive actions. One approach followed in this study is to embark on detailed measurements of temperatures at high spatial and temporal resolution. Data were collected in a small vineyard (0.5 km2) in north‐eastern Tasmania, Australia. Mobile measurements were used to register temperatures five times each night at two levels. A digital elevation model and a GIS (geographical information system) were used to create descriptive landscape parameters. Multiple linear regression was used to model temperatures and cooling rates as a function of topography. Between 50% and 60% of the variation in temperature was explained by the model. Variability in cooling rates was more difficult to describe. The efficiency of using wind machines for frost prevention was studied during one night. Due to topography, they were only efficient in parts of the property that were higher than the fans. At lower elevations, ground frost was not prevented. Proper location of wind machines is therefore important.
A single beam acoustic ground discrimination system (AGDS) was used to survey 1.25 km 2 of shallow (< 20 m depth) seabed on the northeast coast of Tasmania, Australia. This paper investigates the uncertainties associated with the qualitative interpretation of real time and post-processed acoustic signal, and the effect of track spacing on the mapping of rocky reef distribution. The survey was repeated with different track spacing (50 m, 100 m, 200 m and 50 × 200 m shore normal) to investigate the influence of data density and 'knowledge based interpolation' validated against direct measurements made with an underwater video camera. Habitat area calculations varied substantially only with the 50 × 200 m transect. These results have important implications for the qualitative assessment and application of AGDS technology in shallow water marine habitat mapping.
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