Impact of mooring activities on carbon stocks in seagrass meadows.

O Serrano,P S Lavery,G A Kendrick,P Masqué,A Steven,R Ruhon,A Arias-Ortiz,C M Duarte,S Hickey

doi:10.1038/srep23193

Abstract

Boating activities are one of the causes that threaten seagrass meadows and the ecosystem services they provide. Mechanical destruction of seagrass habitats may also trigger the erosion of sedimentary organic carbon (Corg) stocks, which may contribute to increasing atmospheric CO2. This study presents the first estimates of loss of Corg stocks in seagrass meadows due to mooring activities in Rottnest Island, Western Australia. Sediment cores were sampled from seagrass meadows and from bare but previously vegetated sediments underneath moorings. The Corg stores have been compromised by the mooring deployment from 1930s onwards, which involved both the erosion of existing sedimentary Corg stores and the lack of further accumulation of Corg. On average, undisturbed meadows had accumulated ~6.4 Kg Corg m−2 in the upper 50 cm-thick deposits at a rate of 34 g Corg m−2 yr−1. The comparison of Corg stores between meadows and mooring scars allows us to estimate a loss of 4.8 kg Corg m−2 in the 50 cm-thick deposits accumulated over ca. 200 yr as a result of mooring deployments. These results provide key data for the implementation of Corg storage credit offset policies to avoid the conversion of seagrass ecosystems and contribute to their preservation.

Highlights

Boating activities are one of the causes that threaten seagrass meadows and the ecosystem services they provide
The interpretation of the aerial imagery within this study showed that moorings led to the loss of 1.3 ha and 0.9 ha of seagrass meadows at Thomson Bay and Stark Bay, respectively (Table 1)
Mechanical destruction of seagrass meadows by moorings at Rottnest Island from the 1930s onwards has led to the loss of their Corg sequestration capacity by precluding further accumulation of Corg, and through the erosion of the centenary Corg stores underneath seagrass meadows

Summary

Introduction

Boating activities are one of the causes that threaten seagrass meadows and the ecosystem services they provide. ‘Blue carbon’ strategies build on the opportunity to avoid or mitigate CO2 emissions through the conservation and restoration of seagrass meadows, which rank among the most threatened habitats in terms of global loss rates. Loss of seagrass meadows results in erosion of sediments and, potentially, the re-mineralization of the sedimentary Corg accumulated over millennia, which may contribute to increasing atmospheric CO26. Marbá et al.[6] reported that loss of a seagrass meadow in Oyster Harbor (SW Australia), led, within two decades from the loss, to the loss of the Corg stored in the preceding 60 years This is, to the best of our knowledge, the only estimate far available on the loss of Corg stocks following seagrass loss. Fate of Corg stores following disturbances to seagrass meadows, a critical step for seagrass conservation efforts to be assigned carbon mitigation credits[8]

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Conclusion