Salt marsh vegetation in India: Species composition, distribution, zonation pattern and conservation implications
Graphical abstract
Introduction
Salt marshes are coastal wetlands in the upper tidal zones and are subjected to tidal inundation at regular or seasonal intervals. They are recognized as one of the most productive coastal ecosystems due to their diverse ecosystem services such as storm protection, coastal erosion control, carbon sequestration, and maintenance of fisheries (Barbier et al., 2011). The global extent of salt marshes varies from 2.2 to 40 Mha (Pendleton et al., 2012) and is mostly confined to low-energy coasts in temperate and high latitude regions. Salt marshes are colonized by salt-tolerant vegetation (halophytic macrophytes). The dominant vegetation in the salt marsh areas are herbs, shrubs, grasses and sedges which differ from their associates by growing well only when they are supplied with salt water (Beeftink, 1977; Dijkema, 1984; Abeywickrama and Arulgnanam, 1993). Salt marsh vegetation is classified into different biogeographical types such as arctic, boreal, temperate, West Atlantic, dry coast and tropical types (Adam, 1990). Salt marshes in the temperate regions are widespread, while salt marshes are generally substituted by mangroves in the tropical and sub-tropical regions and appear in patchy distribution nearby mangroves (Allen and Pye, 1992; Pennings and Bertness, 2001; Reis et al., 2019). However, herbaceous salt marshes are developed in the muddy environments of the tropics, where mangrove communities have been unsuccessfully established (Nayak and Bahuguna, 2001). Studies on tropical salt marshes are less compared to temperate salt marshes, particularly in Asia (Zedler et al., 2009; Reis et al., 2019).
In India, salt marshes are categorized as one of the Ecologically Sensitive Areas (ESA) under the Coastal Regulation Zone (CRZ) Notification 2019 issued under section 3 of the Environment (Protection) Act, 1986, due to their ecological sensitivity and their role in maintaining the integrity of the coast (MoEFCC, 2019). Salt marsh vegetation is often considered as halophytes, mangroves, mangrove associates and/or coastal vegetation (Untawale and Jagtap, 1991; Mandal and Naskar, 2008; Pattanaik et al., 2008; Swain et al., 2008; Balachandran et al., 2009; Lokhande et al., 2009; Rao and Dora, 2009; Bhatt et al., 2011; Ashokbhai, 2013) and therefore there are disparities in the number of salt marsh species reported in India. Recently, Patro et al. (2017) published a checklist of 14 species of salt marsh along the Indian coast. Studies related to the salt marsh ecosystem in India are found to be scarce (Patro et al., 2017; Gopi et al., 2019) and the few conducted are species-specific, mainly confined to plants with pharmaceutical, biotechnological and bioremediation significances, plant-microbe interactions, habitat characterization and nutritional assessments (Jagtap et al., 2002, 2006; Ravindran et al., 2005; Eganathan et al., 2006; Jagtap et al., 2006; Bharathkumar et al., 2008; Stanley, 2008; Nabikhan et al., 2010; Joseph et al., 2013; Ghosh and Mitra, 2015; Raju and Kumar, 2016; Rathore et al., 2016; Singh et al., 2016; Begam et al., 2017). In addition, SAC (2011a) has mapped salt marshes in India that include natural or semi-natural halophytic grassland and dwarf brushwood along the tidally or non-tidally influenced saline water bodies. The overall area of salt marshes is estimated to be about 1611 km2 with 1443 km2 in Gujarat, 61 km2 in Tamil Nadu, 60 km2 in Andaman and Nicobar Islands, 40 km2 in Andhra Pradesh, six km2 in Maharashtra, 0.7 km2 in Puducherry and 0.6 km2 in Daman and Diu (SAC, 2011a). However, vegetation features such as species diversity, abundance and zonation pattern of salt marshes in India have not been extensively dealt with.
The present study, which is part of a nationwide research conducted on mapping of ESA along the Indian coast (including mangroves, salt marshes, coral reefs and seagrasses), attempts to assess the status of salt marsh vegetation along the Indian coast in terms of its species composition, density and zonation pattern, which also adds insight into the tropical salt marshes.
Section snippets
Mapping of salt marshes
Due to inaccessible settings and structural patchiness, field observations alone would often preclude the complete spatial appraisal of salt marshes and remote sensing based mapping serves as a promising alternative. Satellite images of IRS P6 LISS IV (spatial resolution - 5.8 m) for the year 2010–2011 were used as the base data. Other satellite images such as IRS P6 LISS III (23.5 m), Landsat 8 OLI (30 m) and high resolution images (<4 m) available through Google Earth were also consulted for
Mapping of salt marshes
Vectorization of salt marsh patches across the coastal states of India on IRS P6 LISS IV images (2010–2011) resulted in an area of 290.49 km2. The state of Gujarat sustains the maximum extent of salt marsh (157.94 km2) commensurate with its coastline of about 1600 km, the longest among all the states. The areal extent in each of the coastal states/UTs is presented in Fig. 1.
Species composition
The results of benthic and literature surveys on the Indian coast revealed that the richness of true salt marsh species is
Salt marsh extent
High spatial resolution data from satellite sensors are widely used for identifying and demarcating coastal vegetation which helps to create maps of the areas, measure changes and augment management efforts. A recent estimate of the global salt marsh extent has been about 54951 km2 (Mcowen et al., 2017). Therefore, the current estimate of the salt marsh cover in India (about 290 km2) accounts for about 0.53% of the global salt marsh cover. Salt marsh extent of India was estimated as about
Conclusion
The recognition of salt marshes as an ESA and the need of its conservation have started since the issue of CRZ Notification, 2011. In the midst of such efforts, salt marshes are under tremendous pressures due to a lack of better understanding of their biological, ecological and socio-economic significance, and therefore this study is timely in attracting attention to conservation of salt marshes. This study provides baseline information on the pattern of distribution, density, and zonation of
CRediT authorship contribution statement
C. Viswanathan: Formal analysis, Investigation, Writing - original draft, Writing - review & editing, Visualization. R. Purvaja: Conceptualization, Methodology, Resources, Supervision, Project administration. J. Joyson Joe Jeevamani: Formal analysis, Investigation, Writing - review & editing, Visualization. V. Deepak Samuel: Investigation, Writing - review & editing. R. Sankar: Investigation. K.R. Abhilash: Writing - review & editing. Gejo Anna Geevarghese: Methodology, Formal analysis,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study is part of the grant-in-aid project of Ministry of Environment, Forest and Climate Change (MoEFCC), Government of India on "Mapping of Ecologically Sensitive Areas (ESA) and Critically Vulnerable Coastal Areas (CVCA) along the Coast of India" (F.No.22–29/2008-WBICZM-IA-III). The authors acknowledge the financial and technical support of MoEFCC and the World Bank under the India ICZM Project. We also thank Dr. R. Soundararajan, NCSCM for his critical review, Mr. R. Raghuraman, NCSCM
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