Seagrass for Swimmers – Leschenault Estuary, WA

Learning about the Leschenault

The Leschenault Estuary (Derbal Elaap) stretches for 13 kms northwards from the city of Bunbury in Wadandi Country and is well known as a great place to catch a feed of blue swimmer crabs over the warmer months. Seagrass in the estuary is essential habitat for crabs and fish, it also feeds the local black swan colony. There have been significant seagrass losses in the past and although much has returned, it is not in the healthy state it once was.

Trialling restoration methods

With support from the Water Corporation,  OzFish collaborated with seagrass researchers from the University of Western Australia and the Bunbury Dolphin Discovery Centre to test the viability of restoration work using beach cast seagrass root material in Geographe Bay.

Seagrass was grown successfully in the tanks for four months providing hope for using this method in future WA projects. After investigating the possibilities for a rhizome-based restoration project in Geographe Bay and consultation with researchers, DPIRD, DWER and local agencies, it was concluded that there is a greater need for an estuary-based seagrass project in the Southwest region.

New seagrass species for restoration

Halophila ovalis is one of the smaller species of seagrass, it keeps a low profile and has paddle shaped leaves, hence its common name paddleweed or spoongrass. Leaves of up to 7cm grow from branched rhizomes spreading through the sediment, but paddleweed can also colonise new areas by seed. Just like Posidonia, Halophila seagrass produces flowers, fruit and seeds but they are much smaller. The tiny fruits can hold up to 20 seeds each which look like grains of sand.

Activating citizen scientists

In early 2024, OzFish and project partners began a thorough examination of existing seagrass meadows in the Leschenault with community citizen scientists, including students from Manea College. Students worked with scientists to process seagrass samples from different sites within the estuary. They learned how to identify seagrass fruit and flowers while collecting real data.

Information gathered will help direct the next stage of the project which will involve developing a process for the community to collect and disperse the seeds into trial plots for seagrass restoration in the estuary.