Changes to the distribution of Posidonia seagrass communities of James Point, in response to the development of Cockburn Sound, Western Australia
Australia’s oceans provide many economic and environmental benefits both nationally and regionally, and are of particular social, recreational and cultural importance. Western Australia's most intensively used marine embayment is Cockburn Sound, is Cockburn Sound, it supports one of the most extensive Posidoni seagrass communities in Western Australia. The protected coastal waters off the southern metropolitan coastline of Perth arc utilised intensively for industrial, commercial and recreational purposes. Over the past 50 years, wastes have been routinely discharged into Cockburn Sound causing extensive phytoplankton and epiphyte blooms, particularly during the 1960's and 1970's. The development of industrial and naval facilities and the intensification of landuses in the surrounding catchments over the past 50 years have together contributed to major losses of seagrass meadows in Cockburn Sound. Along with the contamination of biota, sediments and water, raising many concerns particularly for the future uses of the area. The Environmental Protection Authority (EPA) has expressed the view that industrial developments should not be considered in isolation, either from each other or existing activities but should be integrated in Cockburn Sound. Since the late 1970's, there have been reductions in the quantities of wastes discharged, however continued monitoring and the implementation of environmentally sustainable policies must continue, as Cockburn Sound remains in a delicate state of ecological balance. This study involved a detailed examination of the industrial development of Cockburn Sound since it began in 1953, and how this development significantly reduced Posidonia seagrass meadows. Original aerial photographs of Cockburn Sound in 5 year intervals since 1948 were used, and the study area of James Point was mapped to establish spatial and temporal patterns in Posidonia seagrass meadows. These patterns were further defined by grouping them into 5 distinct 10 year periods. These 5 periods grouped spatial and temporal patterns which were found to be most pronounced between 1960 and 1975 This destructive period accounted for 85 % of seagrass loss in Cockburn Sound, mainly from the combined physical (man-made) and chemical effects. These losses immediately commenced with the industrialisation of Kwinana in 1953, and as a consequence the physical destruction of large inshore seagrass meadows for the construction of groynes, jetties and marina's resulted. The 1960's and 1970's decades are characterised by the chemical (particularly nutrient) discharges into Cockburn Sound as a result of heavy industries which had been established in the Kwinana lndustrial Area during the 1950's. Large amounts of nitrogen and phosphorous entered the Sound from the slow release of sediments and heavily impacted upon seagrass meadows. From this study Posidoni seagrass meadows were found to be lost due to the destructive effects of the industrialisation, and that by the end of the 1970's almost all seagrass meadows had been effected. Dramatic seagrass movements occurred and the expanding industrial and residential sectors greatly impacted upon their distributions. The further loss of whatever seagrass meadows that still occur in Cockburn Sound may seem inevitable, but once meadows have been lost they do not easily recolonise, if at all. Therefore incorporating ecologically sustainable development measures should be an immediate priority in such an already heavily degraded marine environment.
Seagrasses, Posidonia oceanica, Western Australia, Cockburn Sound., Terrestrial and Aquatic Ecology
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Edith Cowan University, Research Online, Perth, Western Australia