North Marine Region benthic environmental classification

The dataset is a map of a benthic environmental classification of the North Marine Region (NMR). The aim of the classification was to summarise the way the physical environment near the seabed varies across the NMR. In particular, we were interested in variation within and across bioregion boundaries. The analysis was performed for the Department of the Environment and Water Resources for use in profiling of the NMR during the development of a marine bioregional plan for the region. The environmental classification process comprised laying a grid of cells over the NMR and sorting the cells into clusters on the basis of their physical environmental attributes. The classification method was unsupervised, model-based clustering with a Gaussian mixture model, and was performed with the MCLUST package for R. With this method, the statistical distributions of the clustering variables are modelled as a mixture of multivariate normal distributions. Clustering is a two-step process. First, the parameters of the mixture model are fitted by maximum likelihood. Second, the model is used to assign grid cells to clusters. The clustering variables were bathymetry, median current stress, sediment gravel percentage and average bottom salinity. The environmental characteristics of the nine clusters were (1) deep; (2) deep; (3) low stress, low gravel, low salinity; (4) average for the region; (5) average for the region; (6) shallow, low stress, high salinity; (7) shallow, low salinity; (8) shallow, high stress, gravel; and (9) shallow, high stress, high salinity.