Author Identifier (ORCID)
Nicole Said's ORCID record 
Chanelle Webster’s ORCID record Kathryn McMahon’s ORCID record Charlie Melissa Phelps’s ORCID record Ankje Frouws’s ORCID record Jack Robinson’s ORCID record Simone Strydom’s ORCID record
Abstract
Executive Summary: Quantifying interactive effects among multiple stressors is important for understanding cumulative impacts on seagrasses, which is imperative for informing the appropriate management of marine ecosystems. To date, many thresholds used to understand seagrass response to dredging are based on singular stressors, such as light reduction or burial, but these pressures often occur simultaneously. Understanding the impacts of multiple stressors, which may act additively, synergistically or antagonistically, could require adjustment of existing single pressure derived thresholds. Furthermore, the recovery time of seagrasses to individual and multiple pressures has been identified as a major gap in literature. Improving our understanding of recovery time is important for impact prediction and management of seagrasses under anthropogenic pressures. Cockburn Sound is a highly industrialised embayment in Perth, Western Australia (WA), where seagrass has been heavily impacted (~75 % decrease; Kendrick et al. 2002). Future dredging activities are currently proposed and threshold information data is a critical component for Environmental Impact Assessment and Management process (EIA&M). This report presents findings from an in situ experiment on the Kwinana Shelf in Cockburn Sound, addressing the cumulative impacts of, and recovery from, sediment burial and reduced light on the seagrass Posidonia sinuosa. To inform the environmental impact assessment for Westport and other future developments, the in situ experiment comprised of an impact (4 months) and recovery (12 months) phase to align with the EPA (2021) zonation scheme (zone of influence, moderate impact, and high impact). This study simulated the cumulative impacts of reduced light (~2 mol photons m-2 d-1 compared to ambient) and sediment burial (0 cm, 4 cm, 8 cm) on P. sinuosa. Sublethal and lethal response variables from the rhizosphere, physiology, plant, and meadow scale were assessed. We hypothesised that the cumulative impacts of reduced light and burial would be greater than a single stressor.
Keywords
seagrass, Posidonia sinuosa, multiple stressors, cumulative impacts, sediment burial, light reduction, dredging impacts, seagrass recovery, environmental impact assessment, marine ecosystems, anthropogenic pressures, recovery thresholds, ecological thresholds, seagrass resilience, sedimentation, coastal management, Cockburn Sound, Kwinana Shelf, Western Australia
Non-Traditional Research Output
Report for External Body
Document Type
Non-Traditional Research Output
Date of Publication
2025
Type of File
Publisher
Western Australian Marine Science Institution (WAMSI)
School
School of Science / Centre for People, Place and Planet
RAS ID
100633
Funding Information
The $13.5 million WAMSI Westport Marine Science Program was funded by the Western Australian Government, Department of Transport. WAMSI partners provided significant in-kind funding to the program to increase the value to >$22 million.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
First Page
1
Last Page
52
Included in
Environmental Indicators and Impact Assessment Commons, Marine Biology Commons, Terrestrial and Aquatic Ecology Commons