No detectable impact of small-scale disturbances on ‘blue carbon’ within seagrass beds
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Seagrass meadows are among the most efficient and long-term carbon sinks on earth, but disturbances could threaten this capacity, so understanding the impacts of disturbance on carbon stored within seagrass meadows—‘blue carbon’—is of prime importance. To date, there have been no published studies on the impacts of seagrass loss on ‘blue carbon’ stocks. We experimentally created several kinds of small-scale disturbances, representative of common grazer and boating impacts, within seagrass (Zostera nigracaulis) meadows in Port Phillip Bay (Australia) and measured the impacts on sediment organic carbon stocks (‘C org’, and other geochemical variables—%N, δ13C, δ15N). Disturbance had no detectable effect on C org levels within seagrass sediments, even for high-intensity disturbance treatments, which remained bare (i.e. no seagrass recovery) for 2 years after the disturbance. These findings challenge the widely held assumption that disturbance and concomitant loss of seagrass habitat cause release of carbon, at least for small-scale disturbances. We suggest that larger (e.g. meadow scale) disturbances may be required to trigger losses of ‘blue carbon’ from seagrass meadows.
KeywordsOrganic Carbon Particulate Organic Carbon Seagrass Meadow Disturbance Treatment Seagrass Habitat
This study was financially supported by a research grant from the Victorian Department of Sustainability and Environment: ‘Seagrass resilience in Port Phillip Bay: aiming to develop better predictions of how seagrass responds to environmental change’ and an Australian Research Council DECRA Fellowship (DE130101084). We thank Marcus Huettel, Daniel Nielsen and three anonymous reviewers for providing feedback that improve this paper.