Landscape-scale changes in seagrass distribution over time: a case study from Success Bank, Western Australia.

Seagrasses in temperate Australia persist on sand habitats in shallow coastal environments by recruitment from seedlings and lateral spread of rhizomes from existing meadows. These colonizing processes, combined with seagrass loss from physical disturbance, result in a mosaic of sand and seagrass habitats. Here we describe these changing seagrass landscapes on Success Bank, Western Australia over a 20-year period, using aerial photographs.The 4 ha landscape units (LUs), selected from areas of current Posidonia coriacea Cambridge and Kuo and Amphibolis griffithii (Black) Den Hartog meadows, were analyzed for seagrass cover from aerial photographs from 1972, 1982 and 1993. Two LUs for each species;were chosen from three regions (west, central and east) across Success Bank. Changes in landscape features of LUs were then summarized into total area and length of edge to area ratios of seagrass patches and meadows; Seagrass cover in LUs increased by 20,000 to 30,000 m(-2) between 1972 and 1993. Such a large increase in seagrasses has not been documented elsewhere in Australia:for these seagrass genera. Seagrass expansion was observed as an increase in the number and size of seagrass patches (