Shallow-water seagrasses capture and store globally-significant quantities of organic carbon (OC), often referred to as ‘Blue Carbon’; however, data is lacking on the importance of deep-water (>15 m) seagrasses as Blue Carbon sinks. We compared OC stocks from deep-, mid- and shallow-water seagrasses at Lizard Island within the Great Barrier Reef Lagoon. We found deep-water seagrasses (Halophila species) contained similar levels of OC as shallow-water species (e.g Halodule uninervis) (0.64 ± 0.08% and 0.9 ± 0.1 mg C cm3, 0.87 ± 0.19% and 1.3 ± 0.3 mg C cm3, respectively), despite being much sparser and smaller in stature. Deep-water seagrasses sediments contained significantly higher levels (~9-fold) of OC than surrounding bare areas. Inorganic carbon (CaCO3) levels were relatively high in deep-water seagrass sediments (8.2 ± 0.4%), and if precipitated from epiphytes within the meadow, could offset the potential CO2-sink capacity of these meadows. The δ13C signatures of sediment samples varied among depths and habitats (-10.9 and -17.0), reflecting contributions from autochthonous and allochthonous sources. If the OC stocks reported in this study are similar to deep-water Halophila meadows elsewhere within the GBR lagoon (total area 31,000 km2), then OC bound within this system is roughly estimated at 27.4 million tonnes.

The dataset published in Dryad Digital Repository (doi:10.5061/dryad.kj239), has been updated with the corrected data values for mg C_org cm⁻³.

Please use the corrected data set file:

York_Macreadie_and Rasheed_2018_Lizard_Island_Blue_Carbon_Corrected_Data_Biology Letters