Lack of ecological data hinders management of ecologically important saltmarsh ecosystems: A case study of saltmarsh plant Porterasia coarctata (Roxb.).

Saltmarsh ecosystems though ecologically important are one of the least studied ecosystems in Asia. This study reviewed the published literature from 1988 to 2021 of India to assess the current status of the data deficient saltmarsh species Porterasia coarctata (Roxb.) within its distribution limits. This saltmarsh species inhabits the lower intertidal silty-sandy habitats of India's west coast and silty-clay habitats of the east coast. In the lower intertidal zone, P. coarctata is mostly associated with Myrostachia wightiana, whereas in the upper intertidal zone the highest chance of presence was for Suaeda maritima (18%) and the lowest for Cressa cretica (1%), S. fruticosa (1%) and Scirpus littoralis (1%). The deep root system of P. coarctata helps in sediment accretion and facilitates the formation of mangrove ecosystems. From this study it was evident that most of the research on P. coarctata in India was part of survey of mangrove ecosystems. In India, significant knowledge gap exists on the reproductive ecology and population trends of this species. Most importantly, the genes responsible for salinity and submergence tolerance of P. coarctata are well documented, that can provide solutions for salt and submergence tolerant rice plants in coastal areas prone to sea level rise. The blue carbon storage potential of P. coarctata is higher than other saltmarsh plants, that can be leveraged as a nature-based solution for CO2 emission reductions. The ecosystem services of P. coarctata can also contribute towards achieving various sustainable development goals (SDG-1,2,6,13 and14). Coastal development, mangrove restoration and marine food provisioning are the most important drivers causing the decline of P. coarctata ecosystems across India. This study proposes a long-term coastal monitoring plan for essential conservation and management of existing P. coarctata beds and preventing further degradation and loss of these ecosystems. This study also showcases species-specific valuation of individual saltmarsh plants at regional scale are essential to catalogue the most efficient saltmarsh plants that can play an important role in future climate change scenarios and serve as a global model.

Seagrass ecosystem adjacent to mangroves store higher amount of organic carbon of Andaman and Nicobar Islands, Andaman Sea.

This study quantified the organic carbon (Corg) stocks in Thalassia hemprichii meadows that are (i) adjacent to mangroves (MG), and (ii) without mangroves (WMG), in tropical Andaman and Nicobar Islands (ANI) of India. In the top 10 cm of the sediment, Corg content was 1.8-fold higher at the MG sites than the WMG sites. The total Corg stocks (sediment + biomass) in the 144 ha of seagrass meadows at MG sites (988.74 ± 138.77 Mg C) was 1.9-fold higher than in 148 ha of WMG sites. Protection and management of T. hemprichii meadows of ANI can lead to emission avoidance of around 5447.33 (MG; 3595.12 + WMG: 1852.21) tons of CO2. The social cost of the carbon stocks in these T. hemprichii meadows is around US$ 0.30 and 0.16 million at the MG and WMG sites, respectively, showcasing the importance of ANI's seagrass ecosystems as nature-based solutions for climate change mitigation.

Blue carbon assessments of seagrass and mangrove ecosystems in South and Southeast Asia: Current progress and knowledge gaps.

Coastal blue carbon ecosystems can be an important nature-based solution for mitigating climate change, when emphasis is given to their protection, management, and restoration. Globally, there has been a rapid increase in blue carbon research in the last few decades, with substantial investments on national scales by the European Union, the USA, Australia, Seychelles, and Belize. Blue carbon ecosystems in South and Southeast Asia are globally diverse, highly productive and could represent a global hotspot for carbon sequestration and storage. To guide future efforts, we conducted a systematic review of the available literature on two primary blue carbon ecosystems-seagrasses and mangroves-across 13 countries in South and Southeast Asia to assess existing national inventories, review current research trends and methodologies, and identify existing knowledge gaps. Information related to various aspects of seagrass and mangrove ecosystems was extracted from 432 research articles from 1967 to 2022. We find that: (1) blue carbon estimates in several countries have limited data, especially for seagrass meadows compared to mangrove ecosystems, although the highest reported carbon stocks were in Indonesia and the Philippines with 4,515 and 707 Tg within mangrove forest and 60.9 and 63.3 Tg within seagrass meadows, respectively; (2) there is a high difference in the quantity and quality of data between mangrove and seagrass ecosystems, and the methodologies used for blue carbon estimates are highly variable across countries; and (3) most studies on blue carbon stocks are spatially biased towards more familiar study areas of individual countries, than several lesser-known suspected blue carbon hotspots. In sum, our review demonstrates the paucity and variability in current research in the region, and highlights research frontiers that should be addressed by future research before the robust implementation of these ecosystems into national climate strategies.

Trace metal accumulation in seagrass and saltmarsh ecosystems of India: comparative assessment and bioindicator potential.

Coastal macrophytes serve as bioindicators of coastal trace metal contamination. In this study, trace metal levels in India's seagrass and saltmarsh ecosystems were assessed for their suitability as bioindicators of metal contamination. Trace metal accumulation and bioindicator potential of both seagrasses and saltmarshes were found to be metal and species-specific. Higher concentrations of Cu, Fe, Mg and Mn were found in the tissues of seagrasses, while saltmarshes showed higher accumulation of Cd, Cr, Hg, Ni, Pb and Zn. The leaves of seagrasses are suitable bioindicator of metals in the water column, while the roots and rhizomes of saltmarshes/seagrasses are suitable bioindicators of metals in the sediment. This study proposes the development of a monitoring network using seagrasses and saltmarss as model organisms for short and long-term monitoring of coastal metal contamination. Determining the phytotoxic levels of trace metals in seagrasses and saltmarsh is important for monitoring plant die-offs and loss.