Blue gems: carbon storage in seagrass meadows is determined by spatial and temporal variability in environmental and biological conditions

Seagrass meadows are one of three habitats that serve as marine carbon sinks, with a veneer of living tissue preserving up to thousands of years of carbon stored in their sediments. However, seagrass meadows are also highly... [ view full abstract ]

Seagrass meadows are one of three habitats that serve as marine carbon sinks, with a veneer of living tissue preserving up to thousands of years of carbon stored in their sediments. However, seagrass meadows are also highly threatened and are continuing to decline worldwide. Seagrass management and conservation initiatives require adequate understanding of the ecological factors determining carbon content in seagrass meadows, which is currently limited. This project aimed to identify how varying environmental and biological conditions influence spatial and temporal variability of carbon storage in subtropical seagrass meadows. Seagrass biomass and shallow sediment cores were collected at multiple seasons from various locations across a water quality gradient and within an area of high water quality in Moreton Bay, Australia. Sediment carbon content and seagrass structural complexity were determined for each location. Environmental variables were determined from field data (water quality) and modeled data (wave height). There was clear spatial variability in sediment carbon across the study area, mainly influenced by seagrass canopy complexity, water turbidity, depth and wave energy. Seasonal variability was limited and overshadowed by spatial variability. The highest carbon stocks were found in riverine seagrass meadows, while there was lower carbon in meadows at oceanic conditions and riverine areas of seagrass loss. Understanding the physical and biological conditions for seagrasses to thrive and most importantly for the maximum amount of carbon to be stored is of key importance to conservation and management initiatives, for which it is paramount to not only focus on carbon storage but encompass the multitude of ecosystems services that seagrass provide.