Blue Carbon in the Persian Gulf: Evidence of Phytoplankton Contribution to Carbon in Sediments

Blue carbon ecosystems, such as mangroves, seagrasses, and tidal marshes, are critical for carbon sequestration and climate change mitigation to ensure environmental sustainability. This study provides a review of the limited inventories of blue carbon habitats in the Persian/Arabian Gulf, highlighting limited spatial and temporal coverage as well as the uncertainties in estimates that are quantified using inconsistent methodologies and satellite resolution limitations. The main focus of this paper is a discussion on the consideration of phytoplankton in blue carbon dynamics, which remains understudied, in the Gulf. To underpin the evidence of phytoplankton permanent burial in marine sediments, shotgun metagenomic sequencing was used and 26 phytoplankton species were identified in sediment cores, showing the dominance of Aureococcus anophagefferens and Thalassiosira pseudonana, and underscoring their potential role in carbon sequestration in the northern Gulf, though their inclusion in blue carbon frameworks is complicated by taxonomic diversity and uncertain sequestration pathways. The permanent burial of phytoplankton in these shallow marine and coastal areas brings an important discussion on their inclusion in blue carbon estimates. The use of remotely sensed data for blue carbon habitat mapping needs standardisation and the use of high spatial and spectral resolution remote sensing to improve blue carbon assessments in the region. This study provides firm evidence of phytoplankton presence using eDNA calls for refining the carbon accounting frameworks in the Gulf and beyond, underscoring the importance of refining blue carbon assessments to support evidence-based environmental sustainability and climate action. By integrating phytoplankton contributions into carbon sequestration, more realistic and inclusive frameworks can be developed, enhancing regional strategies for climate change mitigation and coastal ecosystem conservation.