Development and application of single beam acoustics and underwater videography in marine benthic habitat assessment and mapping
Creators: name: Macmillan-Lawler, M
Publisher: name: University Of Tasmania
Year: 2023

description: In marine habitat mapping, single beam echo sounders are widely used to derive information about the geophysical properties of the seabed, while underwater video can provide supplementary information about the physical structure of the seabed and associated marine biological communities. In this thesis, data from both systems are integrated and used to classify seabed habitats. The habitat classification is based on categories within a hierarchical system that is conducive to information from different instruments or collected at different spatial scales. The classification of single beam echo sounder data at different levels of the hierarchical classification is the focus of the first half of the thesis. The first data chapter examines the effect of depth, bottom slope, prevailing weather conditions, and vessel speed on measured acoustic return from the seabed, and the subsequent capacity to classify this data at the substrate level. The following three chapters are case studies that progressively develop techniques for classification of single beam acoustic data at lower levels of the hierarchical classification including identification of soft sediment habitats in commercial scallop fishing grounds; mapping the distribution of urchin barrens on rocky reefs; and detection and mapping of sub-surface giant string kelp, Macrocystis pyrifera. Each of the case studies develops analysis and classification techniques that are applicable for mapping at levels below substrate in the hierarchical classification. At lower levels of the hierarchical classification, biological communities and species distributions are commonly used as habitat descriptors. The second half of this thesis focuses on extracting information from video for the classification of biological communities. In the first of these chapters, methods are compared for extracting estimates of algal cover on temperate rocky reef substrates from towed underwater video. The algal cover data is then used to examine the capacity of a towed video to detect changes in algal community structure at two spatial scales. The following chapter describes the design, construction and evaluation of a stereo video system developed to measure sponge morphological metrics. These metrics are then used to establish a quantitative classification of sponge functional morphology. Differences in sponge functional morphology are examined between sponge communities in two different regions with differences detected in both the composition of functional groups and the size of those functional groups. The thesis presents a framework and methodologies for extracting both physical and biological information from single beam echo sounder and underwater video systems. These methods can easily be incorporated into existing seabed mapping programs, and provide information that will improve our understanding of the spatial distribution of subtidal habitats. This information is directly beneficial to marine resource management, including marine protected area planning and fisheries management, and will allow baseline documentation of habitats for future climate change research.