Ecological connectivity of seagrasses with mangroves increases the carbon storage of tropical seagrass meadows of an island ecosystem

Abstract

Ecologically connected ecosystems are considered more resilient to climate change mitigation by storing increased amounts of carbon than individual ecosystems. This study quantified the carbon storage capacity of seagrass (Thalassia hemprichii) meadows that are adjacent to mangroves (MG; Rhizophora apiculate) and without mangroves (WMG) at three locations in tropical Andaman and Nicobar Islands (ANI) of India. The sediment organic matter (OM) carbon (Corg) content was 2-fold higher at the MG sites than WMG sites of all three locations within the top 10 cm. The Corg in the total biomass was higher at MG sites than the biomass at WMG sites. The sediment grain size positively influenced the sediment OM and Corg content. The canopy height of T. hemprichii showed a better relationship with sediment OM and Corg at MG sites. In contrast, the shoot density of T. hemprichii showed a better relationship with sediment OM and Corg at WMG sites. The total carbon in 144 ha of T. hemprichii meadows of all three MG sites was 11031± 5223 Mg C, whereas the carbon in 148 ha of WMG sites was 4921±3725 Mg C. These T. hemprichii meadows of ANI store around 40487±19171 ton of CO2 in the MG sites and 18036 ±13672 ton of CO2 at WMG sites. The social cost of these carbon stored in these T. hemprichii meadows is around US$ 34.82 and 1.5 million at the MG and WMG sites, respectively. This study points out the efficiency of seagrass ecosystems of ANI as carbon sinks and the potential of these connected seascapes in increasing the efficiency of seagrass carbon storage. Therefore, this connectivity approach should be further explored to include these connected ecosystems of India as a nature-based solution for climate change mitigation and adaptation plans.