Ecological significance of seagrasses: Assessment for management of environmental impact in Western Australia

Studies to determine the ecological significance of seagrasses in Owen Anchorage, Western Australia, have been undertaken to allow government to assess the effects of dredging proposals that result in the removal of seagrasses. Ecological significance was broadly defined to include physical, chemical, biological and cultural attributes. The study area (Owen Anchorage) is characterised by a mosaic of bare sand and patchy assemblages of a mixture of seagrass species. These seagrass meadows are quite unlike the more prominent monospecific meadows in more sheltered waters. Previously, seagrass research in Western Australia had focused almost exclusively on these monospecific meadows. To assess the effects of short-, medium- and long-term dredging on the ecological significance of the study area, a large study was implemented, with tasks based on the attributes used in the definition. These included detailed spatial and temporal investigations of the primary producers (seagrasses and algae), the secondary consumers (invertebrates and fish), and their interactions. Two techniques were used to assess the ecological significance of the study area. The first involved a matrix of biological characteristics that calculated proportional losses of seagrass meadows relative to the areas left after dredging. Stochastic processes were introduced using @risk software, with values based on extensive and intensive field measurements. Linkage with an interactive geographic information system database was developed to better represent seagrass dynamics. The second involved defined beneficial uses (i.e. the way society uses or values an area) of the study area. Preliminary results specific to the individual tasks and more general modelling results are presented to show the value of this multidisciplinary approach in addressing the ecological significance of seagrasses.