Towards ecologically relevant targets: impact of flow and sediment discharge on seagrass communities in the Great Barrier Reef

Lambert, V., Adams, M.P., Collier, C., Carter, A., Saunders, M., Brodie, J., Bainbridge, Z., Rasheed, M., Turner, R., and O'Brien, K.R. (2019) Towards ecologically relevant targets: impact of flow and sediment discharge on seagrass communities in the Great Barrier Reef. In: Proceedings of the 22nd International Congress on Modelling and Simulation. pp. 624-630. From: 23rd International Congress on Modelling and Simulation, 1-6 December 2019, Canberra, ACT, Australia.

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Catchment degradation causing increased sediment flow is one of the key stressors facing Great Barrier Reef (GBR) habitats. Ecologically relevant targets (ERTs) for sediment and nutrient loads have been previously proposed based on seagrass light requirements, the next step is to connect these to ecological response. The overarching goal of the present work is to recommend preliminary thresholds that can be used in the development of more refined ERTs. To achieve this, we perform statistical analysis on datasets for catchment flows and sediment loads and condition of the adjacent seagrass habitat, to identify what might be the direct impacts of catchment discharge on seagrass and the associated timescales of ecological response. Our case study focuses on Cleveland Bay, which is located in the central GBR, and has important seagrass habitat that is affected by discharge from the Burdekin River. Annual monitoring of seagrass biomass and area has been undertaken since 2007. We compare these ecological time-series with data for Burdekin River annual flow and total sediment load from 2005 onwards. Annual Burdekin River flow varied by nearly 40-fold within the 2005-2018 study period, and declines in biomass and area of both subtidal and intertidal seagrasses were associated with high flows and loadsfrom the Burdekin. Subtidal seagrasses appeared more sensitive to changes in catchment discharges than intertidal seagrasses, exhibiting a 3 year timeframe for recovery, following high annual flows and loads. Based on our results, a linear model relating change in seagrass biomass to Burdekin River metrics was used to calculate predicted thresholds below which seagrass biomass was likely to increase, and above which biomass was likely to decline. For seagrass area, a growth threshold, below which seagrass area expanded; and a decline threshold, above which seagrass area fell, were defined for annual Burdekin River flow, and sediment load. Overall these thresholds provide the first steps towards refining ERTs based on ecological condition, which can directly inform the management of the GBR to protect its iconic seagrass habitats and associated communities. The next step is to examine whether the relationship between river discharge and sediment load was the primary cause of seagrass decline.

Item ID: 70930
Item Type: Conference Item (Research - E1)
ISBN: 978-0-9758400-9-2
Keywords: Seagrass, sediment, ecologically relevant target, catchment loads
Copyright Information: These proceedings are licensed under the terms of the Creative Commons Attribution 4.0 International CC BY License (, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you attribute MSSANZ and the original author(s) and source, provide a link to the Creative Commons licence and indicate if changes were made. Images or other third party material are included in this licence, unless otherwise indicated in a credit line to the material. Individual MODSIM papers are copyright of the Authors and Modelling and Simulation Society of Australia and New Zealand Inc. (MSSANZ). MSSANZ is the publisher of the MODSIM Proceedings.
Funders: National Environmental Science Program (NESP) Tropical Water Quality (TWQ) Hub, Great Barrier Reef Foundation
Projects and Grants: NESP 3.2.1
Date Deposited: 22 Nov 2021 23:20
FoR Codes: 41 ENVIRONMENTAL SCIENCES > 4104 Environmental management > 410402 Environmental assessment and monitoring @ 100%
SEO Codes: 18 ENVIRONMENTAL MANAGEMENT > 1802 Coastal and estuarine systems and management > 180201 Assessment and management of coastal and estuarine ecosystems @ 100%
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