Griffith University: Poor water quality and trawling take toll on seagrass

Ecosystems under the sea, such as seagrass, cannot be easily observed like forests or prairies on the land.

A team of researchers led by Griffith University used data from the places where seagrass trends have been assessed to calculate for all the world’s oceans where risks to this ecosystem are greatest.

This will help to target monitoring geographically and ultimately focus conservation actions where they are most needed.

The researchers found that poor water quality and destructive fisheries practices such as trawling are contributing to the global decline of seagrass meadows, which are vital habitats and food sources for marine species and act as climate regulators.

Published in PNAS, researchers from the Australian Rivers Institute and Coastal and Marine Research Centre modelled the trajectories of seagrass meadows in response to anthropogenic pressures at 395 sites around the world between 2000 and 2010.

Seagrass meadows off Australian coastlines were among these sites, where meadows ranged from being increasing to rapidly declining.

The authors assessed the impacts of eight factors and predicted the regions at greatest risk of seagrass meadow decline. The results suggest that water quality and destructive trawl and dredge fishing had the strongest associations with rapid seagrass meadow decline.

“Seagrasses are critical coastal marine habitats that provide ecosystem services including climate regulation and fisheries production,” Dr Mischa Turschwell said.

“With fisheries for example, seagrasses provide nursery habitat for juvenile fish and foraging grounds for about 25% of the world’s biggest fisheries.

“We identified associations between pressures and measured changes in seagrass extent and found that seagrasses are especially under threat from poor water quality and destructive fisheries like trawling.

“We gap-fill and predict risk of seagrass loss in regions where no long-term monitoring exists, highlighting where urgent monitoring and management is required.”

Most recent estimates suggest that seagrass meadows cover around 160,000 km2 globally.

Seagrasses with different life histories had variable trajectories, and persistent seagrass species exhibited the most stable trajectories.

The authors identified areas at high risk of seagrass loss, including in the North Sea, the Baltic Sea, the northern British Isles, the western North Atlantic, the Gulf of Saint Lawrence, the northeast Pacific Ocean, Japan, and several hotspots in Southeast Asia.

“The results suggest the need for improved monitoring and targeted management actions to reverse seagrass loss,” Dr Turschwell said.

“Seagrasses face multiple anthropogenic pressures, but a lack of monitoring renders the assessment of risks of seagrass decline challenging.

“By identifying likely hotspots of change, we provide a stepping-stone to guide future monitoring efforts to support the protection of seagrass meadows.”

The research ‘Anthropogenic pressures and life history predict trajectories of seagrass meadow extent at a global scale’ has been published in PNAS.

Researchers from Simon Fraser University, the University of British Columbia, Swansea University and James Cook University contributed to the study.

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