The effect of catchment land management on seagrass habitat in the Great Barrier Reef

The ecological health of the Great Barrier Reef (GBR) is affected by water quality, which is impacted by catchment land use. The Reef Water Quality Improvement Plan 2017-2022 aims to improve GBR water quality, and ecologically-relevant targets can be used to prioritise investments and optimise costeffectiveness of activities under the plan. The Queensland Government and CSIRO have modelled the effects of improvements to land management practices in GBR catchments on river sediment and nutrient loads, that will potentially improve marine water quality. We combined the outputs of these models together with seagrass distribution models to assess how the extent of five seagrass species could potentially change. The models indicate that improving land management practices will increase the area of suitable seagrass habitat and improve the quality of existing habitat for both shallow-water and deepwater specialists. The potential improvement is largest for the species Halophila decipiens and Halophila spinulosa, which can grow throughout deep waters of the lagoon. There are also regional differences, with the largest potential improvements in the Mackay-Whitsunday and Fitzroy NRM regions and the smallest improvement in Cape York, which receives relatively small river loads under current conditions. These findings build upon complementary assessments of current and predicted future risk to seagrass habitat. This can assist with prioritising land management interventions, spatial planning within the GBR, and to communicate the benefits of future investment in catchment management.

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