Protecting meadows under the water by learning how they respond to cumulative pressures  

The seagrass meadows within Cockburn Sound have been recognised as being regionally important as nursery and spawning areas for numerous recreational and commercially fished species (e.g. pink snapper and blue swimmer crab), play a role in mitigating climate change through carbon sequestration and contribute to improved water quality. Seagrass is one of the main sensitive receptors in Cockburn Sound, where increased nutrient pollution from industrialisation is thought to be the main drivers behind a significant loss (~75%) of seagrass in the area; 2920 ha to 721 ha from 1960’s to 2000’s respectively.

Researchers from Edith Cowan University and Department of Biodiversity, Conservation and Attractions are collaborating on a project with support from the Department of Primary Industries and Regional Development within the larger WAMSI Westport Marine Science Program to investigate the cumulative impacts of light reduction and sediment burial on seagrass to mimic dredging impacts. This research will generate thresholds relevant for environmental impact assessment (EIA) to minimise the impact of coastal development on our seagrass meadows. This work is being carried out in Kwinana, Cockburn Sound on the seagrass species Posidonia sinuosa which is the most dominant species.

Researchers set up 24 by 1.3m2 underwater structures (see feature photo) utilising gardening shade cloth to mimic light reduction under dredging conditions, as well as PVC tubing around the seagrass with sediment (see photo 1) to mimic burial conditions that seagrasses are likely to experience during dredging operations. Some critters have made this their new home (see photo 2). To date, many thresholds used to understand seagrass response to dredging are based on singular stressors (i.e. light or burial).  Focusing on cumulative impacts is important to understand as these stressors often occur simultaneously so considering their cumulative impact on seagrasses is highly relevant and can inform impact assessment and management.

Authors: Nicole Said, Chanelle Webster, Natasha Dunham, Simone Strydom, Kathryn McMahon.

Photo credits: Nicole Said, ECU.