We would like to invite you to attend the Final Thesis Presentation of Hayden Borland, a Doctor of Philosophy candidate in the School of Science, Technology and Engineering.
Estuarine fish ecology in three-dimensions: The ecological consequences of terrain and dredging on fish assemblages, ecosystem processes and habitat functions.
The structural complexity of habitats has pervasive ecological effects on the diversity of fish assemblages and the functioning of ecosystems within coastal and marine seascapes. Studies have typically recorded more fish species and larger fish populations in structurally complex habitats, such as coral reefs, seagrass meadows and mangrove forests. Most studies have, however, only quantified the structural complexity of habitats at small spatial scales, using in-situ measures of complexity (e.g. chain and tape rugosity). Recent advancements in marine habitat mapping technology (e.g. aerial imagery, LiDAR, echo-sounders) have allowed researchers to map the bathymetry (i.e. topography in the sea) of coastal and marine seascapes at much higher resolutions, and this means that we can now test for the possible effects of three-dimensional terrain complexity on fish assemblages over much wider spatial scales. This thesis reviewed the global literature linking fish assemblages to terrain variation and shows that the relief, class, complexity and morphology of terrain features shape the abundance and diversity of fish populations and assemblages, and the health and functioning of ecosystems, within most coastal and marine seascapes. It demonstrates that fish respond to terrain variation in different always within distinct seascapes and that the ecological consequences of terrain complexity, morphology and composition, have never been tested within shallow coastal seascapes, such as estuaries. Estuarine seascapes contain a diversity of structurally complex ecosystems (e.g. mangrove forests, seagrass meadows) and habitats (e.g. rock-bars, intertidal flats, subtidal channels, rock-walls), that provide important habitat functions (e.g. foraging grounds, reproduction sites, juvenile nurseries) for coastal fishes. This thesis demonstrates that the ecological value of two important nursery habitats, mangrove forests and seagrass meadows, is modified by variation in seafloor terrain, and that the abundance, diversity and assemblage composition of nursery species, are strongly associated with distinct terrain features within these coastal ecosystems. Estuarine seascapes are, however, also hot-spots for human recreation, commerce and development, and in urban estuaries, the seafloor is dredged to improve the navigability of estuarine shipping channels, and this typically results in the modification and simplification of seafloor terrain features. This thesis shows that the ecological significance of terrain is fundamentally altered by dredging, that fish abundance, composition, and functional diversity (i.e. variation in the physiological morphological and behavioural traits of species) associate with terrain in contrasting ways within natural and dredged estuaries, and that variation in the spatial extent and terrain of dredged channels are correlated with functional shifts in urban seascapes. This thesis highlights the importance of terrain variation for fish assemblages and ecosystem functioning in coastal and marine seascapes and details the ecological consequences of seafloor modification by dredging in estuarine seascapes. Furthermore, this thesis advocates for the inclusion of terrain into coastal management and spatial conservation plans that aim to improve the health and functioning of ecosystems and fisheries productivity, and outlines how dredging operations and urban planning could be optimised to reduce impacts upon biodiversity and ecosystem functioning in urban seascapes.