Recovery times for a damaged Posidonia australis bed in south eastern Australia

A seismic survey of southern Jervis Bay (NSW, Australia) carried out in the late 1960s resulted in 11 bare circular areas, or 'holes', within an otherwise continuous Posidonia australis seagrass meadow. The area of these holes were mapped using a series of historical aerial photographs, to determine horizontal spreading rates and to estimate recovery times for P. australis. Between the years 1972 and 1997 the total area occupied by the 11 holes decreased by 56%, from 7606 to 3307 m(2), due to the spread of P. australis rhizomes from the surrounding bed. Recovery was slow but consistent, although further damage to some bare areas was evident between 1981 and 1989. Spreading rates varied between time periods and between holes, ranging from negative estimates during the period of damage, to a maximum rate of 58 cm per year. Mean spreading rate (+/-SE) estimated for the 11 holes over the 25-year period was 21(+/-2)cm per year. Assuming that this mean rate of spreading continues and that there is no further damage to the holes, we estimate that the holes should be completely revegetated at various times over the next century, the earliest being 2034 and the latest 2071. (C) 2000 Elsevier Science B.V. All rights reserved.