Seagrass restoration in Oyster Harbour, Western Australia

Geoff Bastyan AND Marion Cambridge  

UNIVERSITY OF WESTERN AUSTRALIA

The decline of seagrass meadows is a common and widespread problem throughout the world, but strong recovery seems to be happening in the Albany Harbours region on the south coast of Western Australia. Almost 90% of the seagrass disappeared in just a few years in the early 1980’s in Oyster Harbour, coinciding with a buildup of masses of green algae after extensive changes in land use within the catchment area. 

Aerial photograph (October 2001) showing details of the Posidonia seagrass transplant plots in Oyster Harbour, Albany, after 3.6 years growth. Transplant plots were 10 x 10m and approximately 10m apart. Individual transplant units were planted 1m apart. The regular circles are seagrass approx. 12 years old that grew back from remnants of the original meadow. 

Aerial photograph (October 2001) showing details of the Posidonia seagrass transplant plots in Oyster Harbour, Albany, after 3.6 years growth.

Transplant plots were 10 x 10m and approximately 10m apart. Individual transplant units were planted 1m apart. The regular circles are seagrass approx. 12 years old that grew back from remnants of the original meadow. 

Aerial photograph (March 2011) showing progress over a decade. Individual plants spaced 1m apart were still visible after 3.6 years, but by 7 years, plants in each plot had grown together to form a continuous dense meadow. The rectangular shape of the 10x10m plots was still evident but by 11.5 years, even the spaces between some of the plots, originally spaced 10m apart, were being vegetated.

Aerial photograph (March 2011) showing progress over a decade. Individual plants spaced 1m apart were still visible after 3.6 years, but by 7 years, plants in each plot had grown together to form a continuous dense meadow.

The rectangular shape of the 10x10m plots was still evident but by 11.5 years, even the spaces between some of the plots, originally spaced 10m apart, were being vegetated.

 

By the mid 1990’s, there seemed to be some improvement. Geoff Bastyan began a small study in 1994 to assess the feasibility of transplanting the seagrass, Posidonia australis, into areas once vegetated by seagrass meadows. The success of the pilot study prompted a second, more comprehensive series of trials at the same site two years later in 1996, to assess whether results for survival and growth were repeatable and to compare growth of planting units taken from the edges versus centres of seagrass meadows. Observations of P. australis suggested that most growth occurred during spring and summer, so the trial in Oyster Harbour was extended in the following spring to examine the effect of planting at the beginning versus the middle of the growing season. 

These restoration activities have now been running for 20 years. The original 10 x 10 meter plots of transplanted seagrass, which showed up so clearly in aerial photos taken 3.5 years later in 2001, have now coalesced into a continuous dense meadow. Fruit were produced from the transplants four years after planting, and together with natural horizontal growth of the transplants, have resulted in the infill and expansion of the original transplant plots. 

Results for survival and growth, and a comparison of growth of planting units taken from the edge versus centre of seagrass meadows, were described for the first 10 years in Bastyan & Cambridge (2008), and now after the first tentative pilot trial 20 years ago, broad scale recovery seems to be well underway and will be reported on in the near future. The successful seagrass restoration at Oyster Harbour highlights the time, dedication, and commitment required for restoring ecological systems.

Recognition of Geoff Bastyan’s commitment and determination
was finally acknowledged in 2014 with the UWA Oceans Institute ‘Southseas Oceans Hero’ Award,

followed by the Great Southern Development Commission medal in 2016.

Details of the transplanting technique were published in 2013: Transplanting Posidonia seagrass in temperate Western Australian waters: A practical ‘How To’ Guide. Available at: http://www.bmtoceanica.com.au/products/seagrass-transplanting-manual/

Reference

Bastyan GR, Cambridge ML (2008) Transplantation as a method for restoring the seagrass Posidonia australis. Estuarine, Coastal and Shelf Science, 79: 289-299.