Marmion Marine Park management Plan - Department of ...

present, little wind transport except in the areas where human activity has degraded dune vegetationor the dune scarp behind the beach. The presence of large, vegetated and stabilised transgressivedunes, however, is evidence of previous periods of major wind transport.Seasonal recycling of beach and foredune material to an offshore bar also occurs, especially alongthe sandy coast between Hillarys and Mullaloo.Longer-term (hundreds of years) changes in coastal processes and sand supply, have led to periodsof erosion or stability during the long-term progradation of the Whitford Plain. Whether thesechanges are cyclical or random is not clear, nor are the periods between each change. Long-termevolution of the sandy coastal landforms is leading to major changes in shoreline position. It isevident that the sandy Whitford Plain prograded, until about 1000 years ago, when the southern flankcommenced eroding. As this is probably related to a long-term decline in sand supply, this process islikely to continue. Although this process is slow, it must, as demonstrated by beach erosion atSorrento and Mullaloo, be taken into account in planning for coastal structures which have designlives of a decade or more (Semeniuk and Searle, 1985).ActionConsider the long-term effects of coastal processes, in particular beach erosion, whenplanning for coastal structures which have design-lives of a decade or more.16.0 MARINE BIOTAThe Park has a high habitat diversity due to the variation in geomorphology, substrate, water depth,and exposure to wave energy and light.These habitats may be classified into five broad categories2:(i) Lagoon Subtidal Sandy Sea FloorThe predominant substratum in this habitat consist of calcareous sand plains, stabilised by seagrassesand interspersed with areas of bare sand. The seagrass meadows (mainly Posidonia spp, Amphibolisantarctica and Halophila ovalis) support a diverse assemblage of animals, and are important as afood source, refuge and nursery for echinoderms, molluscs, crustacea and fish.(ii) Lagoon Subtidal Limestone Pavement29