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

Studies to determine the ecological significance of seagrasses in Owen Anch orage, Western Australia, have been undertaken to allow government to asses s the effects of dredging proposals that result in the removal of seagrasse s. Ecological significance was broadly defined to include physical, chemica l, biological and cultural attributes. The study area (Owen Anchorage) is c haracterised by a mosaic of bare sand and patchy assemblages of a mixture o f seagrass species. These seagrass meadows are quite unlike the more promin ent monospecific meadows in more sheltered waters. Previously, seagrass res earch in Western Australia had focused almost exclusively on these monospec ific meadows. To assess the effects of short-, medium- and long-term dredgi ng on the ecological significance of the study area, a large study was impl emented, with tasks based on the attributes used in the definition. These i ncluded detailed spatial and temporal investigations of the primary produce rs (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 rel ative to the areas left after dredging, Stochastic processes were introduce d using @RISK software, with values based on extensive and intensive field measurements. Linkage with an interactive geographic information system dat abase was developed to better represent seagrass dynamics. The second invol ved defined beneficial uses (i.e. the way society uses or values an area) o f the study area. Preliminary results specific to the individual tasks and more general modelling results are presented to show the value of this mult idisciplinary approach in addressing the ecological significance of seagras ses. (C) 2001 Elsevier Science B.V. All rights reserved.