Biotic carbon stocks across trophic levels in the shallow littoral zone – the role of biodiversity and environmental drivers

Carbon storage is an important ecosystem service that marine ecosystems provide. Shallow vegetated habitats are a hotspot for carbon cycling, having high benthic productivity due to high solar irradiation and nutrient inputs from land. Quantification of the carbon stocks on an ecosystem level has rarely been done in the very shallow littoral (∼1 m) zone. In this study, we quantified biotic carbon stocks of primary producers to predators at 20 relatively exposed coastal sites in the northern Baltic Sea, where the dominant seafloor habitats were submerged mixed vegetation and bare sediment. There was high spatial variability in the total biotic carbon stock, ranging from 0.13 to 45.95 g C m⁻². Most of the carbon in the studied soft-sediment habitats was bound in vegetation (on average 5.14 g C m⁻²), followed by infauna (on average 4.96 g C m⁻²), while the carbon stocks of epifauna and fish were much smaller. Biodiversity, here represented by taxon richness, and sediment properties (i.e., fine sediment and organic matter content) were the most important drivers of variation in the different compartments of the biotic carbon stock. Our study shows that shallow, littoral ecosystems are important in capturing carbon and sustaining biodiversity, which should be considered in management and conservation strategies.