Seagrass loss associated with boat moorings at Rottnest Island, Western Australia

Abstract

The loss of seagrasses caused by mooring damage at Rottnest Island, Western Australia is studied using aerial photographs taken between 1941 and 1992. The study is conducted by comparing areal coverage of seagrasses and sand patches, and increases in the length of the exposed seagrass edge within the seagrass beds. The study focuses on Rocky Bay and Thompson Bay. Results show that the loss of seagrasses associated with moorings in Rocky Bay is dramatic, with 18% of seagrass area lost between 1941 and 1992, and 13% between 1981 and 1992. The exposed edge of the beds increased by 230% between 1981 and 1992. Meanwhile, the areal loss recorded from Thompson Bay is less than 5%, yet the exposed edge of the seagrass beds doubled between 1941 and 1992. Fragmentation of the bed is visible near heavy use areas.