An integrated study of the Gladstone marine system

The overarching goal of the GISERA marine environmental research program has been to make possible more accurate prediction and understanding of impacts and trends in water quality as well as ecological responses in primary producers (seagrass) and grazers (turtles) that have been assessed as being vulnerable due to expansion of development in the Port of Gladstone. In doing this is has also been the aim of the GISERA marine research program to develop tools that can be used to determine management options that may lead to the reduction of impacts on these key ecological assets in the future, well beyond the Port Curtis and the current phase of development. The GISERA Marine project has made significant progress in integrating environmental and ecological knowledge and towards providing tools, notably a re-locatable seagrass growth model, and a turtle shipping-risk assessment model, that provide for a synoptic picture of conditions within the harbour as well as risks to its key ecological elements. The two major sub-components in the project, 1) Sustaining turtles, dugongs and their habitat - an integrated marine observation system, and 2) Integrated modelling, are presented in five chapters, starting with observations of the biophysical properties of the water column (Chapter I) and seagrasses (Chapter II) that are brought together in a biogeochemical model of seagrass growth (Chapter III), moving up the food web to studies of turtle movements (Chapter IV)and modelling of turtle habitat use and risk from shipping (Chapter V). The optical data detailed in Chapter I has been vitally important for the development and validation of modelling of coastal waters in Gladstone Harbour, as well as more widely. The data provides confidence in both the use of GISERA optical samples for terrestrially-sourced fine sediment parameterisation in the optical model, as well as in the calculations for converting total suspended solids to remotely-sensed reflectance. The improved confidence in the performance of the model in terms of water column optical properties also means increased confidence in the performance of the model for predicting benthic processes such as seagrass growth. Seagrass cover and biomass (Chapter II) was low in most areas as expected, confirming the results of other studies which have documented declines in the region since 2010-2011. The exception to this was Pelican Banks where cover of Zostera reached as high at 70%. Seagrass biomass estimates were pivotal to the parameterization of the seagrass growth model and surveys of maximum depth range throughout the harbour provide strong validation of the seagrass growth model and indicate that maximum depth of seagrass beds corresponded to approximately 13% of surface irradiation which was similar to the levels shown to be required to sustain seagrass growth. The actual depth of this point varied throughout the harbour according to water quality. Biogeochemical modelling of seagrass growth has developed efficient new algorithms for the growth of seagrasses that take into account self-shading effects and competition between seagrasses (Chapter III). In Gladstone Harbour, the model was able to produce results that closely reflected the observed values for seagrass depth range and distribution. The model includes two seagrasses, Zostera and Halophila, and also reflects well the historical distribution of seagrass throughout the harbour. The model has provided an invaluable platform for the development of operational modelling of water quality and seagrass growth in Gladstone Harbour as part of the Gladstone Healthy Harbours Program. Innovations developed in the GISERA seagrass model will also provide a basis for predicting the effects of future impacts on the harbour’s natural assets. The model will also have a broader impact through adoption of these innovations into other ecological models in the region. The iconic fauna of Gladstone Harbour depend on its continued heal...