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Importance of Seagrass Management for Effective Mitigation of Climate Change
C H A P T E R
14 Importance of Seagrass Management for Effective Mitigation of Climate Change R. Ramesh, K. Banerjee, A. Paneerselvam, R. Raghuraman, R. Purvaja, Ahana Lakshmi National Centre for Sustainable Coastal Management (NCSCM), Ministry of Environment, Forest and Climate Change, Anna University Campus, Chennai, India
1 INTRODUCTION Human activities have resulted in increased atmospheric carbon dioxide (CO2) concentrations from 280 ppmv in the preindustrial era to 408 ppmv (CO2 Earth) currently; this in turn has led to a positive radiative forcing of climate. Currently, climate change is an important concern, and several governments worldwide are giving top priority toward mitigating climate change. Climate change mitigation refers to any actions or efforts taken to reduce or prevent the long-term risks of climate change on human life and property by reducing the sources or enhancing the sinks of greenhouse gases emissions. As a part of India’s Intended Nationally Determined Contribution (INDC), an additional carbon sink of 2.5–3 billion tons of CO2 equivalent is expected to be created through additional forest and tree cover by 2030. The National Mission for Green India (GIM) aims at restoring India’s green cover as well as wetlands and other critical habitats, along with carbon sequestration as a cobenefit (MoEF, 2013). More than 0.1 mha of wetlands alone are to be restored as part of this program. India is in a transition to a low-carbon economy, adopting several atmospheric CO2 removal strategies. Among them, biosequestration by coastal ecosystems has gained much attention as this is known for its large biological carbon pools. Carbon accumulation in vegetated coastal sediments provides long-term storage of organic carbon, referred to as “blue carbon” (Mcleod et al., 2011), whereas storage in living biomass takes place over shorter timescales. With a coastline of about 7500 km, India has a fairly large area under coastal
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wetlands. Among various blue carbon ecosystems, seagrass meadows provide high-value ecosystem services such as supporting fisheries and other habitats, regulating water quality, nutrient cycling, sediment stabilization, provisioning of fodder, green manure, medicines, and aesthetic values (Waycott et al., 2009). However, seagrasses at present are under direct threat from a host of anthropogenic influences as well as by the impacts of climate change and ecological degradation (Orth et al., 2006; Duffy, 2006; Waycott et al., 2009). Rapid loss of seagrass beds interrupts the important linkages between seagrass meadows and other habitats (Heck et al., 2008), which in turn creates a long-term impact on themselves. Hence, there is an urgent need to increase the resilience of this important ecosystem to ensure its survival into the future. In this chapter, we look at the status of seagrasses in India, their importance, and their role in mitigating climate change in terms of the quantities of carbon that they sequester. It is clear that seagrass ecosystems need to be managed well for the varied ecosystem services they provide and specifically, for their contribution to climate change mitigation. Methods of seagrass management, including techniques for restoration of seagrass meadows, are discussed as it is essential to increase the area under seagrass meadows for the above mentioned reasons.
2 SEAGRASSES AND THEIR DISTRIBUTION IN INDIA Seagrasses are considered one of the most important coastal habitats, as they support a wide range of keystone and ecologically important marine species from different trophic levels (Orth et al., 2006). They are marine-flowering plants that thrive fully submerged in shallow oceanic and estuarine habitats, colonizing soft substrates, especially in wave-sheltered conditions (Barbier et al., 2011). Global coverage of seagrass is estimated to be 3.45 105 km2 (UNEP-WCMC and Short, 2016), which represents about 0.1%–0.2% of the ocean floor (Fourqurean et al., 2012; Greiner et al., 2013). In India, the total seagrass cover is estimated to be 517 km2 (Geevarghese et al., 2017) with 14 reported species. The overall distribution of seagrass meadows in India occurs from the intertidal zone to a maximum depth of 15 m with varying species diversity. Recent estimates suggest that 471.25 km2 of seagrass meadows (Fig. 1) are distributed along the mainland coast of India, the Andaman and Nicobar Islands (Ganguly et al., 2017), and the Lakshadweep. The Gulf of Mannar and Palk Bay along the southeast coast of India comprise the largest seagrass meadows in India ( Jagtap et al., 2003), covering an area of 76–85.5 and 320 km2, respectively (Umamaheswari et al., 2009; Mathews et al., 2010; Ganguly et al., 2017). The meadows of Palk Bay are more luxuriant due to ideal topography and sediment texture, extend up to 9–10 km from the shore (Mathews et al., 2010; Geevarghese et al., 2017), and are rich in biodiversity. A substratum with sand, silt, and mud with thin layers of sand in Palk Bay/Gulf of Mannar supports the growth and establishment of seagrasses (Thangaradjou and Kannan, 2005, 2007). The Ramsar site os Chilika Lagoon in Odisha State also has seagrass meadows that have expanded from 20 km2 to 80 km2 after the opening of the new bar mouth (Kumar and Patnaik, 2010; Priyadarsini et al., 2014; Singh et al., 2015). Both Geevarghese et al. (2017) and Samal (2014) found changes in the areal distribution pattern of seagrasses during different seasons. On the west coast of India, the Gulf of Kachchh Marine National Park has 17–24 km2 of
2 SEAGRASSES AND THEIR DISTRIBUTION IN INDIA
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FIG. 1 Major seagrass ecosystems along the Indian coast.
seagrass beds distributed mainly in Bhural, Mundika, and Sikka reefs as well as Pirotan Island (Kamboj, 2014; Geevarghese et al., 2017). Very sparse/rare patches of seagrass meadows have been reported from the other coastal states of India such as Kerala, Karnataka, Goa, Maharashtra, Andhra Pradesh,and West Bengal ( Jagtap et al., 2003). Apart from the mainland coast, the atolls of Lakshadweep (12–25 km2) and the islands of the Andaman and Nicobar archipelago (8.3–29 km2) have seagrass meadows (Nayak and Bahuguna, 2001), which were found to be reduced in extent during the recent observations by Geevarghese et al. (2017). Of the 72 globally existing species of seagrass descending from four evolutionary lineages (Short et al., 2011), 14 species belonging to six genera are known to occur in peninsular India and the archipelagos (Ganguly et al., 2017). Species diversity in major seagrass beds in India follows the order Gulf of Mannar > Palk Bay > Andaman and Nicobar Islands> Lakshadweep > Gulf of Kachchh¼ Chilika Lagoon. A detailed overview of the seagrass species distribution in India is given in Table 1, which indicates the wide heterogeneous species distribution. Both the Gulf of Mannar and Palk Bay have 13 tropical seagrass species compared to the 19 species recorded from insular Southeast Asia (Short et al., 2007). Thalassia and Cymodocea are the dominant seagrass genera in the Gulf of Mannar and Palk Bay (Mathews et al., 2010). A salinity regime change in the Chilika lagoon after 2000 introduced new species such as Haloduleuninervis, Halodule pinifolia, and Halophila ovate (Patnaik, 2003; Kumar and Patnaik,
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TABLE 1 Distribution of Major Seagrass Meadows in India East Coast No
Seagrass Species
Reef (R)/Coastal (C)/Estuary (E)
GoM (14)
PB (13)
1
Cymodocea rotundata
R,C
x
2
Cymodocea serrulata
R,C
3
Enhalus acoroides
4
CH (5)
West Coast GoK (5)
Islands A and N (9)
LK (8)
x
x
x
x
x
x
x
R,C
x
x
x
Halodule pinifolia
R,C,E
x
x
x
5
Halodule uninervis
R,C,E
x
x
x
x
6
Halodule wrightii
R
x
7
Halophila stipulacea
R,C
x
x
8
Halophila beccarii
R,C,E
x
x
x
x
9
Halophila decipiens
R,C
x
x
10
Halophila ovalis
R,C,E
x
x
11
Halophila ovalis sub sp: ramamurthiana
R,C
x
x
12
Halophila ovata
R,C,E
x
x
13
Syringodium isoetifolium
R,C
x
x
14
Thalassiahemprichii
R,C
x
x
x
x
x
x
x x
x
x
x
x
x
x
x
x
x
x
x
GoM, Gulf of Mannar; PB, Palk Bay; CH, Chilika Lagoon; GoK, Gulf of Kuchchh; A and N, Andaman and Nicobar Islands; LK, Lakshadweep Islands; “x” indicates presence. K. Ravikumar, R. Ganesan, A new subspecies of halophilaovalis (R. Br.) J.D. Hook. (Hydrocharitaceae) from the eastern coast of peninsular India, Aquat. Bot. 36 (4) (1990) 351–358; T.G. Jagtap, Distribution of seagrasses along the Indian coast, Aqua. Bot. 40 (1991) 379–386; L. Kannan, T. Thangaradjou, P. Anantharaman, Status of seagrasses of India, Seaweed Res. Util. 21 (1&2) (1999) 25–33; V. Nair, Status of Flora and Fauna of Gulf of Kachchh. National Institute of Oceanography, Goa, 2002; A.K. Patnaik, Phyto-diversity of Chilika Lake, Orissa, India. PhD Thesis, Utkal University, 2003, pp. 1–105; T. Thangaradjou, R. Sridhar, S. Senthilkumar, S. Kannan, Seagrass resource assessment in the Mandapam coast of the Gulf of Mannar biosphere reserve, India. Appl. Ecol. Environ. Res. 6 (1) (2007) 139–146; R. Umamaheswari, S. Ramachandran, E.P. Nobi, Mapping the extend of seagrass meadows of gulf of Mannar biosphere reserve, India using IRS ID satellite imagery, Int. J. Biodivers. Conserv. 1 (5) (2009) 187–193; G. Mathews, K. Diraviya Raj, T. Thinesh, J. Patterson, J.K. Patterson Edward, D. Wilhelmsson, Status of seagrass diversity, distribution and abundance in Gulf of Mannar Marine National Park and Palk Bay (Pamban to Thondi), Southeastern India, South Indian Coast, Mar. Bull. 2 (2) (2010) 1–21; T. Thangaradjou, K. Sivakumar, E.P. Nobi, E. Dilipan, Distribution of seagrasses along the Andaman and Nicobar Islands: a post tsunami survey, in: Recent Trends in Biodiversity of Andaman and Nicobar Islands. ZSI, Kolkata, 2010, pp. 157–160; A.F. Newmaster, K.J. Berg, S. Ragupathy, M. Palanisamy, K. Sambandan, S.G. Newmaster, Local knowledge and conservation of seagrasses in the Tamil Nadu state of India, J. Ethnobiol. Ethnomed. 7 (2011) 37; R. Kumar, A.K. Patnaik, “Chilika” – The Newsletter of Chilika Development Authority and Wetlands International – South Asia, vol. 5 (2010) pp. 1–28; P.M. Priyadarsini, N. Lakshman, S.S. Das, S. Jagamohan, B.D. Prasad, Studies on seagrasses in relation to some environmental variables from Chilika lagoon, Odisha, India, Int. Res. J. Environ. Sci. 3 (11) (2014) 92–101; R.D. Kamboj, Biology and status of seagrasses in gulf of Kachchh marine National Park and sanctuary, India, Indian Ocean Turtle Newslett. (2014) 8–11; D. Ganguly, G. Singh, P. Ramachandran, A.P. Selvam, K. Banerjee, R. Ramachandran, Seagrass metabolism and carbon dynamics in a tropical coastal embayment, Ambio. (2017) 1–13.
2010; Priyadarsini et al., 2014). Halophila beccarii, the most commonly distributed species reported from all the coastal states except the Islands, acts as a pioneer species in the succession process of mangrove formation ( Jagtap et al., 2003). Cymodocea serrulata was dominant in the Lakshadweep islands (Nobi et al., 2011). Of the 14 species recorded in India, Halophila
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beccarii has been identified as “vulnerable” under the IUCN Red List (Criterion B2) because of its intertidal habitat, which is under high anthropogenic stress (Patro et al., 2017).
3 IMPORTANCE OF SEAGRASS ECOSYSTEMS
g rtin o p
Pr o
ning sio vi
Su p
Ecosystem services are the benefits people obtain from ecosystems. These include provisioning services such as food, shelter, and medical applications; regulating services that affect climate change, carbon sequestration, wave modification, and water quality; cultural services that provide recreational and aesthetic benefits; and supporting services such as habitats for fishery, turtles, and dugongs (MEA, 2005). The importance of seagrass ecosystems can be seen to derive from the various ecosystem services they provide (Fig. 2).
C u lt u ra
l Re g u l a ti
FIG. 2 Ecosystem services from seagrasses.
ng
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Provisioning services largely relate to goods such as food and fodder from an ecosystem. Apart from these, different species of seagrasses are reportedly used for treating a variety of diseases (NISCAIR, 2013). The NISCAIR report also provides the results of the chemometric analysis of each seagrass species, indicating the potential for pharmaceutical and nutraceutical products in the future. The various traditional uses of different seagrass species are given in Table 2. In India, Newmaster et al. (2011) observed that local knowledge systems consisted of a complex classification of seagrass diversity that considered the role of seagrass in the marine ecosystem, including the use of seagrass for medicine (e.g., treatment of heart conditions, seasickness, etc.), food (nutritious seeds), fertilizer (nutrient rich biomass), and livestock feed (goats and sheep). Recently, a study has shown the presence of various biological metabolites in some Indian seagrass that can be used effectively in the food and pharmacological industries. Specifically, Halodule pinifolia and Cymodocea rotundata exhibited predominant growth-inhibitory activity against all the urinary tract infection (UTI) bacteria (Kannan et al., 2012). With respect to supporting services, as shallow coastal habitats, seagrasses provide key fishing grounds as they offer a complex habitat for a variety of fish and other marine organisms. Seagrass-based fisheries are globally important and are present wherever seagrass exists, supporting subsistence, commercial, and recreational activity (Nordlund et al., 2017). Their high rates of primary production result in well-oxygenated waters that support complex food webs. During photosynthesis, they release oxygen into the water and also pump oxygen into the sediments through their roots, thus creating an oxic environment that promotes nutrient
TABLE 2 Traditional Uses of Various Seagrass Species by Coastal Communities Species
Parts Used
Traditional Uses
Thalassiahemprichii
Leaf, rhizome, whole plant
Fertilizer, fever, malaria, skin diseases, blood pressure, substrate for bait
Cymodocearotundata
Leaf, whole plant
Fertilizer, tranquillizer for babies, cough, malaria, wounds, fodder
Cymodoceaserrulata
Leaf, whole plant
Fertilizer, tranquillizer for babies, cough, malaria, wounds, fodder
Enhalusacoroides
Root, rhizome, seed
Fertilizer, handicrafts, stings of fishes, seasickness, skin diseases
Syringodiumisoetifolium
Leaf, branches
Fodder, green manure
Thalassodendronciliatum
Leaf, whole plant
Green manure, fever, malaria, smallpox
Halophilaovalis
Leaf
Green manure, skin ailments, burns, boils
Halodulepinifolia
Leaf, branches
Fodder
Haloduleuninervis
Leaf, branches
Fodder
Based on A.F. Newmaster, K.J. Berg, S. Ragupathy, M. Palanisamy, K. Sambandan, S.G. Newmaster, Local knowledge and conservation of seagrasses in the Tamil Nadu state of India, J. Ethnobiol. Ethnomed. 7 (2011) 37.
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uptake. While fresh seagrasses are the direct food source for animals such as turtles, dugongs, ducks, fish, sea urchins, and fish, insect larvae and amphipods feed on their decomposed fragments. Among the regulating services, the role played by seagrass ecosystems in reducing the energy of waves and thus protecting the seashore as well as their role in carbon cycling are important. Seagrasses act as ecosystem engineers as they alter water flow, stabilize sediments, and regulate nutrient cycling and food web structure (Hemminga and Duarte, 2000; Gutierrez et al., 2011). By reducing flow velocities in their canopies, seagrass beds promote sedimentation and reduction of grain size (Bos et al., 2007). Carbon sequestration potential is a key aspect of climate regulation and seagrass meadows have shown high carbon sequestration potential as they accumulate from both in situ production and sedimentation of particulate carbon from the water column. So far, studies on the valuation of seagrass ecosystems are sparse in India, covering only a small fraction of different types of wetlands. Most of the studies focus on valuation of provisioning services while regulating services have seldom received attention (Parikh et al., 2012). Cultural services provided by seagrass ecosystems require further research (Nordlund et al., 2017). Seagrass beds along with mangroves and salt marshes account for up to 70% of the organic carbon in the marine realm. Of the various noteworthy ecosystem services, the carbon sequestration potential of seagrasses to combat climate change by mitigating anthropogenic CO2 emissions is of growing importance (Hejnowicz et al., 2015). A discussion on recent research in India on carbon sequestration by seagrasses is presented in the next section.
4 CARBON SEQUESTRATION POTENTIAL OF SEAGRASSES Seagrasses capture carbon dioxide through photosynthesis and incorporate it within their biomass, both above ground and below ground. The extent to which plant biomass accumulates as decay-resistant refractory matter depends on the extent of grazing, export, and burial. Most seagrass ecosystems are net autotrophic as their gross primary production exceeds respiration (Duarte et al., 2010). The proportion of seagrass biomass that accumulates as organic carbon (Corg) stored in sediment depends on a low decomposition rate (Breithaupt et al., 2012). In addition, seagrass leaves also trap suspended particulate matter and promote their sedimentation, thus adding to the sedimentary storage component. Thus, seagrass meadows have the capacity to accumulate large carbon pools in the sediment and store it over millennial time scales (Kennedy et al., 2010; Fourqurean et al., 2012; Duarte et al., 2013; Greiner et al., 2013; Serrano et al., 2016). Global seagrass ecosystems are believed to store between 4.2 and 8.4 PgC (Fourqurean et al., 2012). Recent studies have indicated that these ecosystems also contribute to marine carbon sequestration by exporting 24 Tg of carbon per year (30% of the 80 Tg y1 carbon sequestered annually in meadows) to deeper layers of the sea, that is, the mixing layer, shelf, and deep sea (Duarte and Krause-Jensen, 2017). Fig. 3 depicts the biomass variation in the root-to-shoot ratio of different seagrass species recorded from Palk Bay (Purvaja et al., 2017). A recent study from the Indian seagrass
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14. IMPORTANCE OF SEAGRASS MANAGEMENT
FIG. 3 Biomass variation in root-to-shoot ratio recorded from Palk Bay seagrass species. R. Purvaja, R.S. Robin, D. Ganguly, G. Hariharan, G. Singh, R. Raghuraman, R. Ramesh, Seagrass meadows as proxy for assessment of ecosystem health, Ocean Coast. Manag. 159 (2017) 34–45. doi:10.1016/j.ocecoaman.2017.11.026.
ecosystem of Palk Bay indicates that the below ground biomass (rhizome) of seagrass acts as a major compartment in carbon storage, and that the stored carbon is finally sequestered in the sediments (Ganguly et al., 2017). Another species-specific study from Palk Bay and Chilika seagrass meadows from India reported sedimentation rates ranging between 6.2 and 6.9 mm yr1 (Fig. 4) and mass accumulation rates between 0.84 and 1.12 g cm2 yr1 (Fig. 5), with an organic carbon burial rate between 6.97 and 8.99 mol C m2 yr1 (Banerjee et al., 2015). Preliminary carbon stock assessment by Ganguly et al. (2017) indicates that 1 km2 of a healthy seagrass meadow in India’s coastal waters can store as much as 13.96 Gg C in the top 1 m of the sediment. Similarly, 1 km2 of a healthy seagrass meadow can sequester 0.44 Gg Cyr1. The comparison of net community production (NCP) between Indian (Palk Bay) seagrass meadows (Ganguly et al., 2017) and the global average (Duarte et al., 2010) shows that production in Indian systems is at least three times higher. Higher growth rates in seagrass ecosystems are translated into an increased accumulation of carbon into both the above-ground biomass (leaves and stem) and the below-ground biomass (root systems and rhizomes) (Russell et al., 2013; Duarte and Krause-Jensen, 2017). Recent estimates indicate that mean above-ground biomass (AGB) from the near-shore region of the Indian Palk Bay (Ganguly et al., 2017) is comparable with the global mean seagrass biomass (224 18 g dwt m2) (Duarte and Chiscano, 1999). It is evident from the results presented above that seagrass ecosystems are storehouses of carbon and are capable of capturing atmospheric CO2 through very efficient sequestration mechanisms. Carbon (Corg) is preserved for millennia because seagrass sediment is largely anaerobic. Although extensive literature is available on seagrass carbon sequestration and storage around the globe, research is in its infancy in India. It would be particularly important to estimate the sequestration capacity of dominant seagrass species in India such that conservation efforts of such important seagrass species can be enhanced.
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8.00 Rate of sedimentation (mm yr–1)
7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 Halodule*
Halophila*
Cymodocea # Mixed seagrass # Andaman
Seagrass ecosystems
Sundarbans
Pristine mangrove ecosystems
FIG. 4 Comparison of rate of sedimentation between different seagrass species from Chilika Lagoon and Palk Bay and pristine mangrove ecosystems (Banerjee et al., 2012, 2015).
Mass accumulation rate ( g cm–2 yr–1)
1.20 1.00 0.80 0.60 0.40 0.20 0.00
Halodule*
Halophila*
Cymodocea # Mixed seagrass #
Seagrass ecosystems
Andaman
Sundarbans
Pristine mangrove ecosystems
FIG. 5 Comparison of mass accumulation rate between seagrass ecosystems (Chilika Lagoon and Palk Bay) and pristine mangrove ecosystems. K. Banerjee, B. Senthilkumar, R. Purvaja, R. Ramesh, Sedimentation and trace metal distribution in selected locations of Sundarbans mangroves and Hooghly estuary, northeast coast of India, Environ. Geochem. Health 34 (1) (2012) 27–42; K. Banerjee, A. Paneer Selvam, K. Arumugam, R. Purvaja, R. Ramesh, Seagrass ecosystems as effective sediment stabilizers. In: Presentation on Past and Present Geochemical Process – Impacts on Climate change at JNU, New Delhi, India (2015).
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All this clearly highlights the important role played by seagrass ecosystems in climate change and therefore the importance that needs to be given to the preservation and conservation of seagrass ecosystems, especially in terms of blue carbon. Recently, Ganguly et al. (2017) estimated that the economic values ranged between $1.02 million and $3.65 million per year, based on the regulatory ecosystem services provided from the total seagrass cover in India. Additionally, the monetary values of the stored carbon in the top 1 m sediment of seagrass meadows ranged between $109 million and $146 million.
5 THREATS TO SEAGRASS ECOSYSTEMS While it is well accepted that ecosystem services provided by seagrass meadows are important, a number of threats to these meadows have been reported. Globally, seagrass habitats have declined in area and several species are threatened due to multiple natural and anthropogenic stressors (Waycott et al., 2009; Short et al., 2011). Natural stressors of seagrass habitat include cyclones, heavy rainfall, coastal uplift and subsidence, grazing herbivores, and diseases, whereas anthropogenic stressors include physical damages due to boating activities, oil spills, and turbidity due to urban, agricultural, and aquacultural runoff (Short and Wyllie-Echeverria, 1996). The leading stressors of Indian seagrass meadows are mainly human-related activities, both in coastal waters and watershed areas, which lead to subsequent loss in both seagrass area and diversity (Prabhakaran, 2006; Thangaradjou et al., 2007; Singh et al., 2015). Key anthropogenic activities that threaten Indian seagrasses that were identified from the literature include: (i) commercial fishing and trawling activities, (ii) boat activities for recreational purposes, (iii) runoff from coastal aquaculture and agriculture, and (iv) shell harvesting/seaweed cultivation. The ranking among the above activities varies between the systems; however, fishing using trawl/gill nets and boating activities are seen as the most important threats to seagrass in India (Thangaradjou and Nobi, 2009; Mathews et al., 2010). Other prolonged disturbances such as continuous loading of nutrients/fresh water often result in the phase shift of seagrass meadows to macroalgae beds, as seen in the Palk Bay region (Thangaradjou et al., 2013). Alteration in the salinity conditions produced a shift in seagrass species in Chilika Lagoon, with colonization by new species (Kumar and Patnaik, 2010). Natural disturbances that are responsible for seagrass loss in these regions include cyclones, storms, coastal uplift, grazing by herbivores, and diseases ( Jagtap et al., 2003; Mathews et al., 2010; Ragavan et al., 2013). Thangaradjou and Nobi (2009) reported the decrease in seagrass area in the Andaman archipelago as a consequence of the tectonic movement/coastal uplift and sediment dumping on seagrass after the 2004 Indian Ocean tsunami. Increase in rainfall intensity and cyclones have damaged the seagrass meadows in various locations by uprooting the plants and affecting the seawater clarity through high suspended matter inputs. Recently, the leaf-reddening disease was found in species such as Halophila ovalis and Thalassia hemprichi, which might have an impact on their productivity and distribution (Ragavan et al., 2013). Thangaradjou and Nobi (2009) reported localized effect on
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reduced leaf cover and biomass distribution in the seagrass meadows of Lakshadweep and Andaman Islands by the grazing of sea turtles. Major threats to different Indian seagrass meadows are summarized in Table 3.
TABLE 3
Threats to Indian Major Seagrass Ecosystems
Location
Major Threats
Impacts
Reference
Palk Bay
High precipitation during northeast monsoon, cyclones
Physical damage to seagrass and reduced light penetration due to high turbidity
Thangaradjou and Nobi (2009)
Anchoring of boats, propeller damage
Uprooting of seagrass
Thangaradjou and Nobi, (2009) and Mathews et al. (2010)
Use of push nets, trawl nets, bottom set gill nets
Physical damage to the seagrasses by uprooting the plants and removing the healthy leaves
Thangaradjou and Nobi (2009), Sridhar et al. (2010), Mathews et al. (2010), and D’Souza et al. (2013)
Nutrient enrichment from aquaculture wastes and proliferation of macroalgae
Eutrophication, growth of algae/ seaweed which competes with seagrass. Diminish light availability and sediment quality
Sridhar et al. (2010) and Thangaradjou et al. (2013)
Exotic seaweed cultivation
Affects light penetration and seagrass die off
Mathews et al. (2010)
Southwest monsoonal winds, northeast monsoon, cyclones
Physical damage to seagrass and reduced light penetration due to high turbidity
Thangaradjou and Nobi (2009)
Shell harvesting of Tellina angulata
Physical destruction of seagrass rhizomes and roots
Thangaradjou et al. (2007) and Thangaradjou and Nobi (2009)
Anchoring of boats, propeller damage
Uprooting of seagrass
Thangaradjou and Nobi (2009) and Mathews et al. (2010)
Use of push nets, trawl nets, bottom set gill nets
Physical damage to the seagrasses by uprooting the plants and removing the healthy leaves
Thangaradjou and Nobi (2009), Mathews et al. (2010) and D’Souza et al. (2013)
Natural hazards such as storms, floods
Physical damage to seagrass and reduced light penetration due to high turbidity
Priyadarsini et al. (2014)
Dredging, inappropriate fishing, anchoring, coastal constructions
Uprooting of seagrass
Priyadarsini et al. (2014)
Coastal aquaculture wastes
Eutrophication, growth of algae which competes with seagrass. Diminished light availability and sediment quality
Priyadarsini et al. (2014)
Gulf of Mannar
Chilika Lagoon
(Continued)
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TABLE 3 Threats to Indian Major SeagrassEcosystems—cont’d Location
Major Threats
Impacts
Reference
Gulf of Kachchh
Industrial and domestic pollution
Eutrophication and formation of algal blooms
Kamboj (2014)
Development of ports and harbors
Increase in sedimentation, solid waste and marine pollution
Kamboj (2014)
Fishing and boat activities
Physical damage to the seagrass leaves and rhizomes
Kamboj (2014)
Intense boating and tourism activities
Physical damage to the seagrasses roots/rhizomes and leaves
Thangaradjou and Nobi (2009)
Diseases – Leaf Redding
Decoloring of leaves leading to seagrass mortality
Ragavan et al. (2013)
Tsunami, cyclones, storms
Physical damage, sediment dumping on seagrass and increase turbidity
Thangaradjou and Nobi (2009) and Danielsen et al. (2005)
Grazing by green turtles (protected species)
Grazing pressure can modify the species composition
Lal et al. (2010) and Kaladharan et al. (2013)
Boating and tourism activities
Physical damage to the seagrasses roots/rhizomes and leaves
Thangaradjou and Nobi (2009) and Nobi et al. (2013)
Sea erosion and siltation
Affects light penetration and seagrass die off
Nobi et al. (2013)
Disposal of fish waste and untreated solid waste
Localized eutrophication and seagrass damage
Thangaradjou and Nobi (2009)
Andaman and Nicobar Islands
Lakshadweep
6 MANAGEMENT OF SEAGRASS ECOSYSTEMS Sea level rise and an increase in the intensity of cyclones are potential consequences of climate change. In this context, the ability of seagrasses to protect coastlines through mitigation of wave energy assumes importance. However, their other important contribution—the ability to sequester carbon—can be considered to be of higher importance because it is also known that considerable amounts of carbon (that were buried) are released when such ecosystems are degraded. Hence, it is obvious that existing areas under seagrass cover have to be protected and overall, areas under seagrass have to be increased. There are a number of legislative and policy options that can be used to protect seagrass ecosystems (Ramesh et al., 2018) in India. Of these, the Coastal Regulation Zone Notification 2011 (CRZ, 2011), issued under the Environmental (Protection) Act, 1986, which classifies seagrass meadows as CRZ-Ia (Ecologically Sensitive Areas), is the only explicit legislation that protects seagrasses by prohibiting development activity in their vicinity. Efforts are also being made in marine spatial planning as part of the development of integrated coastal management plans whereby the locations of these important ecosystems are mapped so that they become areas for conservation and protection.
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A decline in seagrass beds has prompted the implementation of numerous restoration programs in different parts of the world. In addition, blue carbon sequestration has been found to be enhanced with seagrass restoration (Greiner et al., 2013) which has prompted restoration attempts globally. However, the success of these attempts has been hampered by the difficulties in reducing the causes of disturbance (Paling et al., 2009). Techniques for restoration include natural restoration, transplants, and seeding. The cost of restoration may vary depending on the selection of sites for restoration, techniques, degradation intensity, follow-up measures, and surrounding environmental conditions. According to Bergstrom (2006), the lower end of the global seagrass restoration range is between $83,363 and $244,530 per hectare whereas the higher end is between $1,900,000 (McNeese et al., 2006) and $3,387,000 per hectare (Lewis III. et al., 2006; Paling et al., 2009). The only study on seagrass restoration in the Palk Bay and adjacent Gulf of Mannar with a total cost of INR1,426,750 ($22,000 ha1) reported from India showed an average survival rate (after nine months of transplantation) of 81.5% (Thalassia hemprichii), 85.7% (Cymodocea serrulata), and 78.6% (Syringodium isoetifolium), for three major seagrass species, respectively. The activity carried out in pilot mode covered 200 m2 in each location (Patterson and D’Souza, 2015). Three techniques—sprigs (Quadrate), plugs, and saplings—were attempted, of which sprigs were the most successful. Nearly one square kilometer was rehabilitated and another area of equal size is under restoration; both attempts are off the coast of Thoothukudi in the Gulf of Mannar. Considering the elevated cost of seagrass restoration, the conservation of seagrass habitats (e.g., $1400 per hectare as per Stowers et al., 2006) is far more cost effective than the restoration of degraded seagrass meadows.
7 CONCLUSIONS AND RECOMMENDATIONS It is clear that seagrasses are extremely important in the current context of climate change, as these systems are highly efficient in both sequestering and long-term storage of carbon. To increase the area under seagrass meadows, two plans of action may be considered. In the first case, the effective implementation of available legislation may help in the reduction of threats. Ensuring that the provisions of protection accorded to CRZ-I are strictly followed can prevent further degradation and promotion of self-restoration of seagrass meadows. The sequestration capacity of dominant seagrass species in India needs to be estimated so that conservation efforts of such important seagrass species can be enhanced. Research also needs to be undertaken on the use of seagrasses by local communities to determine if protection of seagrass meadows could be enhanced by declaration of such areas as Critically Vulnerable Coastal Areas (CVCA), which are to be managed with the involvement of local communities including fishers (CRZ, 2011). Simultaneously, mapping of areas with potential for growth of seagrasses needs to be accomplished. Action is necessary to increase the area under seagrass, either by natural expansion or by planting. For the former, areas such as the Chilika lagoon where natural expansion of seagrass meadows has been reported must be studied so as to enable replication in other potential areas. For the latter, trials that have been carried out in Palk Bay and the Gulf of Mannar could help in strengthening this activity. This needs to be supported by research into techniques for seagrass transplantation.
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It is also recommended to bring local communities, scientists, resource managers, and government officials together in designing an action plan for seagrass conservation. Such a strategy would be in accordance with Chapter 17 of Agenda 21 of the 1992 Earth Summit at Rio de Janeiro, Brazil, which states that government agencies charged with coastal zone protection must integrate traditional ecological knowledge (TEK) and sociocultural values with management agendas (Wyllie-Echeverria et al., 2002). Ultimately, more awareness needs to be created among all stakeholders about the various ecosystem services provided by seagrasses, especially their role in carbon sequestration.
References Banerjee, K., Senthilkumar, B., Purvaja, R., Ramesh, R., 2012. Sedimentation and trace metal distribution in selected locations of Sundarbans mangroves and Hooghly estuary, northeast coast of India. Environ. Geochem. Health 34 (1), 27–42. Banerjee, K., Paneer Selvam, A., Arumugam, K., Purvaja, R., Ramesh, R., 2015. In: Seagrass ecosystems as effective sediment stabilizers.Presentation on Past and Present Geochemical Process – Impacts on Climate change at JNU, New Delhi, India. Barbier, E.B., Sally, D.H., Kennedy, C., Koch, E.W., Stier, A.C., Silliman, B.R., 2011. The value of estuarine and coastal ecosystem services. Ecol. Monogr 81 (2), 169–193. https://dx.doi.org/10.1890/10-1510.1. Bergstrom, P., 2006. In: Treat, S.F., Lewis III, R.R. (Eds.), Species selection, success, and costs of multi-year, multispecies submerged aquatic vegetation (SAV) planting in Shallow Creek, Patapsco River, Maryland. Seagrass Restoration: Success, Failure, and the Costs of Both. Selected Papers Presented at a Workshop, Mote Marine Laboratory, Sarasota, Florida, 11–12 March 2003. Lewis Environmental Services, Valrico, Florida, pp. 49–58. Breithaupt, J.L., Smoak, J.M., Smith, T.J., Sanders, C.J., Hoare, A., 2012. Organic carbon burial rates in mangrove sediments: strengthening the global budget. Glob. Biogeochem. 26(3). Bos, A.R., Bouma, T.J., de Kort, G.L., van Katwijk, M.M., 2007. Ecosystem engineering by annual intertidal seagrass beds: sediment accretion and modification. Estuar. Coast. Shelf. Sci. 74 (1), 344–348. https://dx.doi.org/10.1016/ j.ecss.2007.04.006. Danielsen, F., Sørensen, M.K., Olwig, M.F., Selvam, V., Parish, F., Burgess, N.D., Hiraishi, T., Karunagaran, V.M., Rasmussen, M.S., Hansen, L.B., Quarto, A., 2005. The Asian tsunami: a protective role for coastal vegetation. Science 310 (5748), 643. D’Souza, N., Patterson, J.K., Ishwar, N.M., 2013. Survey and assessment of seagrass beds in the Gulf of Mannar and Palk Bay to support strategy to conserve and manage seagrass habitats. SDMRI, Tamil Nadu, pp. 1–29. Duarte, C.M., Marba, N., Gacia, E., Fourqurean, J.W., Beggins, J., Barron, C., Apostolaki, E.T., 2010. Seagrass community metabolism: assessing the carbon sink capacity of seagrass meadows. Glob. Biogeochem. Cycles 24, 1–8. Duarte, C.M., Chiscano, C.L., 1999. Seagrass biomass and production: a reassessment. Aquat. Bot. 65 (1), 159–174. https://dx.doi.org/10.1016/S0304-3770(99)00038-8. Duarte, C.M., Krause-Jensen, D., 2017. Export from seagrass meadows contributes to marine carbon sequestration. Front. Mar. Sci. 4. https://dx.doi.org/10.3389/fmars.2017.00013. Duarte, C.M., Sintes, T., Marba, N., 2013. Assessing the CO2 capture potential of seagrass restoration projects. J. Appl. Ecol. 50 (6), 1341–1349. Duffy, J.E., 2006. Biodiversity and the functioning of seagrass ecosystems. Mar. Ecol. Prog. Ser. 311, 233–250. Fourqurean, J.W., Duarte, C.M., Kennedy, H., Marba, N., Holmer, M., 2012. Seagrass ecosystems as a globally significant carbon stock. Nat. Geosci. 5, 505–509. https://dx.doi.org/10.1038/ngeo1477. Ganguly, D., Singh, G., Ramachandran, P., Selvam, A.P., Banerjee, K., Ramachandran, R., 2017. Seagrass metabolism and carbon dynamics in a tropical coastal embayment. Ambio, 1–13. Geevarghese, G.A., Akhil, B., Magesh, G., Krishnan, P., Purvaja, R., Ramesh, R., 2017. A comprehensive geospatial assessment of seagrass distribution in India. Ocean Coast. Manag. https://dx.doi.org/10.1016/j. ocecoaman.2017.10.032. Greiner, J.T., McGlathery, K.J., Gunnell, J., McKee, B.A., 2013. Seagrass restoration enhances “blue carbon” sequestration in coastal waters. PLoS ONE 8 (8), e72469. https://dx.doi.org/10.1371/journal.pone.0072469.
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Nobi, E.P., Dilipan, E., Thangaradjou, T., Dinesh Kumar, P.K., 2013. Restoration scaling of seagrass habitats in the Oceanic Islands of Lakshadweep, India using geospatial technology. Appl. Geomat. 5 (2), 167–175. Nordlund, L.M., Unsworth, R.K.F., Gullstrom, M., Cullen-Unsworth, L.C., 2017. Global significance of seagrass fishery activity. Fish Fish., 1–14. https://dx.doi.org/10.1111/faf.12259. Orth, R.J., Carruthers, T.J., Dennison, W.C., Duarte, C.M., Fourqurean, J.W., Heck, J.K.L., Hughes, A.R., Kendrick, G.A., Kenworthy, W.J., Olyarnik, S., Short, F.T., 2006. A global crisis for seagrass ecosystems. Bioscience 56 (12), 987–996. Paling, E.I., Fonseca, M., van Katwijk, M.M., van Keulen, M., 2009. Seagrass restoration. In: Coastal Wetlands: An Integrated Ecosystem Approach., pp. 687–713. Parikh, K.S., Ravindranath, N.H., Murthy, I.K., Mehra, S., Kumar, R., James, E.J., Vivekanandan, E., Mukhopadhyay, P., 2012. The Economics of Ecosystems and Biodiversity-India: Initial Assessment and Scoping Report. Working Document, p. 157. Patnaik, A.K., 2003. Phyto-diversity of Chilika Lake, Orissa, India. PhD, ThesisUtkal University, pp. 1–105. Patro, S., Krishnan, P., Samuel, V.D., Purvaja, R., Ramesh, R., 2017. Seagrass and salt marsh ecosystems in south asia: an overview of diversity, distribution, threats and conservation status. In: Wetland Science. Springer, India, pp. 87–104. Patterson, J.K., D’Souza, N., 2015. Rehabilitation of degraded seagrass area in Tuticorin coast of Gulf of Mannar, Tamil Nadu, to support long term conservation of seagrass habitats. SDMRI, Tuticorin, Tamil Nadu, pp. 1–12. http:// www.sdmri.in/index.php/seagrass-rehabilitation. Prabhakaran, M.P., 2006. Community shift in seagrass ecosystem Minicoy atoll (India). Seagrass Watch News 27, 15. Priyadarsini, P.M., Lakshman, N., Das, S.S., Jagamohan, S., Prasad, B.D., 2014. Studies on seagrasses in relation to some environmental variables from Chilika lagoon, Odisha, India. Int. Res. J. Environ. Sci. 3 (11), 92–101. Purvaja, R., Robin, R.S., Ganguly, D., Hariharan, G., Singh, G., Raghuraman, R., Ramesh, R., 2017. Seagrass meadows as proxy for assessment of ecosystem health. Ocean Coast. Manag. 159, 34–45. https://dx.doi.org/10.1016/ j.ocecoaman.2017.11.026. Ragavan, P., Saxena, A., Mohan, P.M., Coomar, T., Ragavan, A., 2013. Leaf reddening in seagrasses of Andaman and Nicobar Islands. Trop. Ecol. 54 (2), 269–273. Ramesh, R., Banerjee, K., Paneerselvam, A., Lakshmi, A., Krishnan, P., Purvaja, R., 2018. Legislation and policy options for conservation and management of seagrass ecosystems in India. Ocean Coast. Manag. https://dx.doi.org/ 10.1016/j.ocecoaman.2017.12.025. Russell, B.D., Connell, S.D., Uthicke, S., Muehllehner, N., Fabricius, K.E., Hall-Spencer, J.M., 2013. Future seagrass beds: Can increased productivity lead to increased carbon storage? Mar. Pollut. Bull. 73 (2), 463–469. https:// dx.doi.org/10.1016/j.marpolbul.2013.01.031. Samal, R.N., 2014. In: Applications of RS and GIS in Wetland management: case study of Chilika lagoon.User Interaction Meet Proceedings, US4, 20–21 January NRSC, India. Serrano, O., Lavery, P.S., Lopez-Merino, L., Ballesteros, E., Mateo, M.A., 2016. Location and associated carbon storage of erosional escarpments of seagrass Posidonia mats. Front. Mar. Sci. 3, 42. Short, F., Carruthers, T., Dennison, W., Waycott, M., 2007. Global seagrass distribution and diversity: a bioregional model. J. Exp. Mar. Biol. Ecol. 350 (1–2), 3–20. Short, F.T., Polidoro, B., Livingstone, S.R., Carpenter, K.E., Bandeira, S., Bujang, J.S., Calumpong, H.P., Carruthers, T.J., Coles, R.G., Dennison, W.C., Erftemeijer, P.L., 2011. Extinction risk assessment of the world’s seagrass species. Biol. Conserv. 144 (7), 1961–1971. https://dx.doi.org/10.1016/j.biocon.2011.04.010. Short, F.T., Wyllie-Echeverria, S., 1996. Naturalandhuman-induceddisturbancesofseagrass.Environ.Conserv.23,17–27. Singh, G., Ganguly, D., Paneerselvam, A., Kakolee, B., Purvaja, R., Ramesh, R., 2015. Seagrass ecosystem and climate change: an Indian perspective. J. Clim. Change 1 (1, 2), 67–74. https://dx.doi.org/10.3233/JCC-150005. Sridhar, R., Thangaradjou, T., Kannan, L., Astalakshmi, S., 2010. Assessment of coastal bio-resources of the Palk Bay, India, using IRS-LISS-III data. J. Indian Soc. Remote Sens. 38, 565–575. Stowers, J.F., Fehrmann, E., Squires, A., 2006. In: Treat, S.F., Lewis III, R.R. (Eds.), Seagrass scarring in Tampa Bay: impact analysis and management options. Seagrass Restoration: Success, Failure, and the Costs of Both. Selected Papers presented at a workshop, Mote Marine Laboratory, Sarasota, Florida, March 11–12, 2003. Lewis Environmental Services, Valrico, FL, pp. 69–78. Thangaradjou, T., Kannan, L., 2005. Marine sediment texture and distribution of seagrasses in the Gulf of Mannar biosphere reserve. Seaweed Res. Util. 27, 145–154.
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Thangaradjou, T., Kannan, L., 2007. Nutrient characteristics and sediment texture of the seagrass beds of the Gulf of Mannar. J. Environ. Biol. 28 (1), 29. Thangaradjou, T., Nobi, E.P., 2009. Seagrass – Watch, Threats to the Seagrasses of India. vol. 39, pp. 20–21. Thangaradjou, T., Sridhar, R., Senthilkumar, S., Kannan, S., 2007. Seagrass resource assessment in the Mandapam coast of the Gulf of Mannar biosphere reserve, India. Appl. Ecol. Environ. Res. 6 (1), 139–146. Thangaradjou, T., Subhashini, P., Raja, S., 2013. Macroalgae competition-challenging seagrass survival. Seagrass – Watch Threats Human Impacts and Mitigation 47, 50–51. Umamaheswari, R., Ramachandran, S., Nobi, E.P., 2009. Mapping the extend of seagrass meadows of gulf of Mannar biosphere reserve, India using IRS ID satellite imagery. Int. J. Biodivers. Conserv. 1 (5), 187–193. UNEP-WCMC, Short, F.T., 2016. Global distribution of seagrasses (version 4.0). In: Fourth update to the data layer used in Green and Short (2003). UNEP World Conservation Monitoring Centre, Cambridge, UK. http://data. unepwcmc.org/datasets/7. Waycott, M., Duarte, C.M., Carruthers, T.J., Orth, R.J., Dennison, W.C., Olyarnik, S., Calladine, A., Fourqurean, J.W., Heck, K.L., Hughes, A.R., Kendrick, G.A., 2009. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Proc. Natl. Acad. Sci. 106 (30), 12377–12381. Wyllie-Echeverria, S., Gunnarsson, K., Mateo, M.A., Borg, J.A., Renom, P., Kuo, J., Schanz, A., Hellblom, F., Jackson, E., Pergent, G., Pergent-Martini, C., Johnson, M., Sanchez-Lizaso, J., Boudouresque, C.F., Aioi, K., 2002. Protecting the seagrass biome: Report from the traditional seagrass knowledge working group. Bull. Mar. Sci. 71 (3), 1415–1417.
Further Reading Jagtap, T.G., 1991. Distribution of seagrasses along the Indian coast. Aqua. Bot. 40, 379–386. Kannan, L., Thangaradjou, T., Anantharaman, P., 1999. Status of seagrasses of India. Seaweed Res. Util. 21 (1&2), 25–33. Nair, V., 2002. Status of Flora and Fauna of Gulf of Kachchh. National Institute of Oceanography, Goa. Ravikumar, K., Ganesan, R., 1990. A new subspecies of halophilaovalis (R. Br.) J.D. Hook. (Hydrocharitaceae) from the eastern coast of peninsular India. Aquat. Bot. 36 (4), 351–358. Thangaradjou, T., Sivakumar, K., Nobi, E.P., Dilipan, E., 2010. Distribution of seagrasses along the Andaman and Nicobar Islands: a post tsunami survey. In: Recent Trends in Biodiversity of Andaman and Nicobar Islands. ZSI, Kolkata, pp. 157–160.
14 Importance of Seagrass Management for Effective Mitigation of Climate Change R. Ramesh, K. Banerjee, A. Paneerselvam, R. Raghuraman, R. Purvaja, Ahana Lakshmi National Centre for Sustainable Coastal Management (NCSCM), Ministry of Environment, Forest and Climate Change, Anna University Campus, Chennai, India
1 INTRODUCTION Human activities have resulted in increased atmospheric carbon dioxide (CO2) concentrations from 280 ppmv in the preindustrial era to 408 ppmv (CO2 Earth) currently; this in turn has led to a positive radiative forcing of climate. Currently, climate change is an important concern, and several governments worldwide are giving top priority toward mitigating climate change. Climate change mitigation refers to any actions or efforts taken to reduce or prevent the long-term risks of climate change on human life and property by reducing the sources or enhancing the sinks of greenhouse gases emissions. As a part of India’s Intended Nationally Determined Contribution (INDC), an additional carbon sink of 2.5–3 billion tons of CO2 equivalent is expected to be created through additional forest and tree cover by 2030. The National Mission for Green India (GIM) aims at restoring India’s green cover as well as wetlands and other critical habitats, along with carbon sequestration as a cobenefit (MoEF, 2013). More than 0.1 mha of wetlands alone are to be restored as part of this program. India is in a transition to a low-carbon economy, adopting several atmospheric CO2 removal strategies. Among them, biosequestration by coastal ecosystems has gained much attention as this is known for its large biological carbon pools. Carbon accumulation in vegetated coastal sediments provides long-term storage of organic carbon, referred to as “blue carbon” (Mcleod et al., 2011), whereas storage in living biomass takes place over shorter timescales. With a coastline of about 7500 km, India has a fairly large area under coastal
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wetlands. Among various blue carbon ecosystems, seagrass meadows provide high-value ecosystem services such as supporting fisheries and other habitats, regulating water quality, nutrient cycling, sediment stabilization, provisioning of fodder, green manure, medicines, and aesthetic values (Waycott et al., 2009). However, seagrasses at present are under direct threat from a host of anthropogenic influences as well as by the impacts of climate change and ecological degradation (Orth et al., 2006; Duffy, 2006; Waycott et al., 2009). Rapid loss of seagrass beds interrupts the important linkages between seagrass meadows and other habitats (Heck et al., 2008), which in turn creates a long-term impact on themselves. Hence, there is an urgent need to increase the resilience of this important ecosystem to ensure its survival into the future. In this chapter, we look at the status of seagrasses in India, their importance, and their role in mitigating climate change in terms of the quantities of carbon that they sequester. It is clear that seagrass ecosystems need to be managed well for the varied ecosystem services they provide and specifically, for their contribution to climate change mitigation. Methods of seagrass management, including techniques for restoration of seagrass meadows, are discussed as it is essential to increase the area under seagrass meadows for the above mentioned reasons.
2 SEAGRASSES AND THEIR DISTRIBUTION IN INDIA Seagrasses are considered one of the most important coastal habitats, as they support a wide range of keystone and ecologically important marine species from different trophic levels (Orth et al., 2006). They are marine-flowering plants that thrive fully submerged in shallow oceanic and estuarine habitats, colonizing soft substrates, especially in wave-sheltered conditions (Barbier et al., 2011). Global coverage of seagrass is estimated to be 3.45 105 km2 (UNEP-WCMC and Short, 2016), which represents about 0.1%–0.2% of the ocean floor (Fourqurean et al., 2012; Greiner et al., 2013). In India, the total seagrass cover is estimated to be 517 km2 (Geevarghese et al., 2017) with 14 reported species. The overall distribution of seagrass meadows in India occurs from the intertidal zone to a maximum depth of 15 m with varying species diversity. Recent estimates suggest that 471.25 km2 of seagrass meadows (Fig. 1) are distributed along the mainland coast of India, the Andaman and Nicobar Islands (Ganguly et al., 2017), and the Lakshadweep. The Gulf of Mannar and Palk Bay along the southeast coast of India comprise the largest seagrass meadows in India ( Jagtap et al., 2003), covering an area of 76–85.5 and 320 km2, respectively (Umamaheswari et al., 2009; Mathews et al., 2010; Ganguly et al., 2017). The meadows of Palk Bay are more luxuriant due to ideal topography and sediment texture, extend up to 9–10 km from the shore (Mathews et al., 2010; Geevarghese et al., 2017), and are rich in biodiversity. A substratum with sand, silt, and mud with thin layers of sand in Palk Bay/Gulf of Mannar supports the growth and establishment of seagrasses (Thangaradjou and Kannan, 2005, 2007). The Ramsar site os Chilika Lagoon in Odisha State also has seagrass meadows that have expanded from 20 km2 to 80 km2 after the opening of the new bar mouth (Kumar and Patnaik, 2010; Priyadarsini et al., 2014; Singh et al., 2015). Both Geevarghese et al. (2017) and Samal (2014) found changes in the areal distribution pattern of seagrasses during different seasons. On the west coast of India, the Gulf of Kachchh Marine National Park has 17–24 km2 of
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FIG. 1 Major seagrass ecosystems along the Indian coast.
seagrass beds distributed mainly in Bhural, Mundika, and Sikka reefs as well as Pirotan Island (Kamboj, 2014; Geevarghese et al., 2017). Very sparse/rare patches of seagrass meadows have been reported from the other coastal states of India such as Kerala, Karnataka, Goa, Maharashtra, Andhra Pradesh,and West Bengal ( Jagtap et al., 2003). Apart from the mainland coast, the atolls of Lakshadweep (12–25 km2) and the islands of the Andaman and Nicobar archipelago (8.3–29 km2) have seagrass meadows (Nayak and Bahuguna, 2001), which were found to be reduced in extent during the recent observations by Geevarghese et al. (2017). Of the 72 globally existing species of seagrass descending from four evolutionary lineages (Short et al., 2011), 14 species belonging to six genera are known to occur in peninsular India and the archipelagos (Ganguly et al., 2017). Species diversity in major seagrass beds in India follows the order Gulf of Mannar > Palk Bay > Andaman and Nicobar Islands> Lakshadweep > Gulf of Kachchh¼ Chilika Lagoon. A detailed overview of the seagrass species distribution in India is given in Table 1, which indicates the wide heterogeneous species distribution. Both the Gulf of Mannar and Palk Bay have 13 tropical seagrass species compared to the 19 species recorded from insular Southeast Asia (Short et al., 2007). Thalassia and Cymodocea are the dominant seagrass genera in the Gulf of Mannar and Palk Bay (Mathews et al., 2010). A salinity regime change in the Chilika lagoon after 2000 introduced new species such as Haloduleuninervis, Halodule pinifolia, and Halophila ovate (Patnaik, 2003; Kumar and Patnaik,
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TABLE 1 Distribution of Major Seagrass Meadows in India East Coast No
Seagrass Species
Reef (R)/Coastal (C)/Estuary (E)
GoM (14)
PB (13)
1
Cymodocea rotundata
R,C
x
2
Cymodocea serrulata
R,C
3
Enhalus acoroides
4
CH (5)
West Coast GoK (5)
Islands A and N (9)
LK (8)
x
x
x
x
x
x
x
R,C
x
x
x
Halodule pinifolia
R,C,E
x
x
x
5
Halodule uninervis
R,C,E
x
x
x
x
6
Halodule wrightii
R
x
7
Halophila stipulacea
R,C
x
x
8
Halophila beccarii
R,C,E
x
x
x
x
9
Halophila decipiens
R,C
x
x
10
Halophila ovalis
R,C,E
x
x
11
Halophila ovalis sub sp: ramamurthiana
R,C
x
x
12
Halophila ovata
R,C,E
x
x
13
Syringodium isoetifolium
R,C
x
x
14
Thalassiahemprichii
R,C
x
x
x
x
x
x
x x
x
x
x
x
x
x
x
x
x
x
x
GoM, Gulf of Mannar; PB, Palk Bay; CH, Chilika Lagoon; GoK, Gulf of Kuchchh; A and N, Andaman and Nicobar Islands; LK, Lakshadweep Islands; “x” indicates presence. K. Ravikumar, R. Ganesan, A new subspecies of halophilaovalis (R. Br.) J.D. Hook. (Hydrocharitaceae) from the eastern coast of peninsular India, Aquat. Bot. 36 (4) (1990) 351–358; T.G. Jagtap, Distribution of seagrasses along the Indian coast, Aqua. Bot. 40 (1991) 379–386; L. Kannan, T. Thangaradjou, P. Anantharaman, Status of seagrasses of India, Seaweed Res. Util. 21 (1&2) (1999) 25–33; V. Nair, Status of Flora and Fauna of Gulf of Kachchh. National Institute of Oceanography, Goa, 2002; A.K. Patnaik, Phyto-diversity of Chilika Lake, Orissa, India. PhD Thesis, Utkal University, 2003, pp. 1–105; T. Thangaradjou, R. Sridhar, S. Senthilkumar, S. Kannan, Seagrass resource assessment in the Mandapam coast of the Gulf of Mannar biosphere reserve, India. Appl. Ecol. Environ. Res. 6 (1) (2007) 139–146; R. Umamaheswari, S. Ramachandran, E.P. Nobi, Mapping the extend of seagrass meadows of gulf of Mannar biosphere reserve, India using IRS ID satellite imagery, Int. J. Biodivers. Conserv. 1 (5) (2009) 187–193; G. Mathews, K. Diraviya Raj, T. Thinesh, J. Patterson, J.K. Patterson Edward, D. Wilhelmsson, Status of seagrass diversity, distribution and abundance in Gulf of Mannar Marine National Park and Palk Bay (Pamban to Thondi), Southeastern India, South Indian Coast, Mar. Bull. 2 (2) (2010) 1–21; T. Thangaradjou, K. Sivakumar, E.P. Nobi, E. Dilipan, Distribution of seagrasses along the Andaman and Nicobar Islands: a post tsunami survey, in: Recent Trends in Biodiversity of Andaman and Nicobar Islands. ZSI, Kolkata, 2010, pp. 157–160; A.F. Newmaster, K.J. Berg, S. Ragupathy, M. Palanisamy, K. Sambandan, S.G. Newmaster, Local knowledge and conservation of seagrasses in the Tamil Nadu state of India, J. Ethnobiol. Ethnomed. 7 (2011) 37; R. Kumar, A.K. Patnaik, “Chilika” – The Newsletter of Chilika Development Authority and Wetlands International – South Asia, vol. 5 (2010) pp. 1–28; P.M. Priyadarsini, N. Lakshman, S.S. Das, S. Jagamohan, B.D. Prasad, Studies on seagrasses in relation to some environmental variables from Chilika lagoon, Odisha, India, Int. Res. J. Environ. Sci. 3 (11) (2014) 92–101; R.D. Kamboj, Biology and status of seagrasses in gulf of Kachchh marine National Park and sanctuary, India, Indian Ocean Turtle Newslett. (2014) 8–11; D. Ganguly, G. Singh, P. Ramachandran, A.P. Selvam, K. Banerjee, R. Ramachandran, Seagrass metabolism and carbon dynamics in a tropical coastal embayment, Ambio. (2017) 1–13.
2010; Priyadarsini et al., 2014). Halophila beccarii, the most commonly distributed species reported from all the coastal states except the Islands, acts as a pioneer species in the succession process of mangrove formation ( Jagtap et al., 2003). Cymodocea serrulata was dominant in the Lakshadweep islands (Nobi et al., 2011). Of the 14 species recorded in India, Halophila
3 IMPORTANCE OF SEAGRASS ECOSYSTEMS
287
beccarii has been identified as “vulnerable” under the IUCN Red List (Criterion B2) because of its intertidal habitat, which is under high anthropogenic stress (Patro et al., 2017).
3 IMPORTANCE OF SEAGRASS ECOSYSTEMS
g rtin o p
Pr o
ning sio vi
Su p
Ecosystem services are the benefits people obtain from ecosystems. These include provisioning services such as food, shelter, and medical applications; regulating services that affect climate change, carbon sequestration, wave modification, and water quality; cultural services that provide recreational and aesthetic benefits; and supporting services such as habitats for fishery, turtles, and dugongs (MEA, 2005). The importance of seagrass ecosystems can be seen to derive from the various ecosystem services they provide (Fig. 2).
C u lt u ra
l Re g u l a ti
FIG. 2 Ecosystem services from seagrasses.
ng
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14. IMPORTANCE OF SEAGRASS MANAGEMENT
Provisioning services largely relate to goods such as food and fodder from an ecosystem. Apart from these, different species of seagrasses are reportedly used for treating a variety of diseases (NISCAIR, 2013). The NISCAIR report also provides the results of the chemometric analysis of each seagrass species, indicating the potential for pharmaceutical and nutraceutical products in the future. The various traditional uses of different seagrass species are given in Table 2. In India, Newmaster et al. (2011) observed that local knowledge systems consisted of a complex classification of seagrass diversity that considered the role of seagrass in the marine ecosystem, including the use of seagrass for medicine (e.g., treatment of heart conditions, seasickness, etc.), food (nutritious seeds), fertilizer (nutrient rich biomass), and livestock feed (goats and sheep). Recently, a study has shown the presence of various biological metabolites in some Indian seagrass that can be used effectively in the food and pharmacological industries. Specifically, Halodule pinifolia and Cymodocea rotundata exhibited predominant growth-inhibitory activity against all the urinary tract infection (UTI) bacteria (Kannan et al., 2012). With respect to supporting services, as shallow coastal habitats, seagrasses provide key fishing grounds as they offer a complex habitat for a variety of fish and other marine organisms. Seagrass-based fisheries are globally important and are present wherever seagrass exists, supporting subsistence, commercial, and recreational activity (Nordlund et al., 2017). Their high rates of primary production result in well-oxygenated waters that support complex food webs. During photosynthesis, they release oxygen into the water and also pump oxygen into the sediments through their roots, thus creating an oxic environment that promotes nutrient
TABLE 2 Traditional Uses of Various Seagrass Species by Coastal Communities Species
Parts Used
Traditional Uses
Thalassiahemprichii
Leaf, rhizome, whole plant
Fertilizer, fever, malaria, skin diseases, blood pressure, substrate for bait
Cymodocearotundata
Leaf, whole plant
Fertilizer, tranquillizer for babies, cough, malaria, wounds, fodder
Cymodoceaserrulata
Leaf, whole plant
Fertilizer, tranquillizer for babies, cough, malaria, wounds, fodder
Enhalusacoroides
Root, rhizome, seed
Fertilizer, handicrafts, stings of fishes, seasickness, skin diseases
Syringodiumisoetifolium
Leaf, branches
Fodder, green manure
Thalassodendronciliatum
Leaf, whole plant
Green manure, fever, malaria, smallpox
Halophilaovalis
Leaf
Green manure, skin ailments, burns, boils
Halodulepinifolia
Leaf, branches
Fodder
Haloduleuninervis
Leaf, branches
Fodder
Based on A.F. Newmaster, K.J. Berg, S. Ragupathy, M. Palanisamy, K. Sambandan, S.G. Newmaster, Local knowledge and conservation of seagrasses in the Tamil Nadu state of India, J. Ethnobiol. Ethnomed. 7 (2011) 37.
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289
uptake. While fresh seagrasses are the direct food source for animals such as turtles, dugongs, ducks, fish, sea urchins, and fish, insect larvae and amphipods feed on their decomposed fragments. Among the regulating services, the role played by seagrass ecosystems in reducing the energy of waves and thus protecting the seashore as well as their role in carbon cycling are important. Seagrasses act as ecosystem engineers as they alter water flow, stabilize sediments, and regulate nutrient cycling and food web structure (Hemminga and Duarte, 2000; Gutierrez et al., 2011). By reducing flow velocities in their canopies, seagrass beds promote sedimentation and reduction of grain size (Bos et al., 2007). Carbon sequestration potential is a key aspect of climate regulation and seagrass meadows have shown high carbon sequestration potential as they accumulate from both in situ production and sedimentation of particulate carbon from the water column. So far, studies on the valuation of seagrass ecosystems are sparse in India, covering only a small fraction of different types of wetlands. Most of the studies focus on valuation of provisioning services while regulating services have seldom received attention (Parikh et al., 2012). Cultural services provided by seagrass ecosystems require further research (Nordlund et al., 2017). Seagrass beds along with mangroves and salt marshes account for up to 70% of the organic carbon in the marine realm. Of the various noteworthy ecosystem services, the carbon sequestration potential of seagrasses to combat climate change by mitigating anthropogenic CO2 emissions is of growing importance (Hejnowicz et al., 2015). A discussion on recent research in India on carbon sequestration by seagrasses is presented in the next section.
4 CARBON SEQUESTRATION POTENTIAL OF SEAGRASSES Seagrasses capture carbon dioxide through photosynthesis and incorporate it within their biomass, both above ground and below ground. The extent to which plant biomass accumulates as decay-resistant refractory matter depends on the extent of grazing, export, and burial. Most seagrass ecosystems are net autotrophic as their gross primary production exceeds respiration (Duarte et al., 2010). The proportion of seagrass biomass that accumulates as organic carbon (Corg) stored in sediment depends on a low decomposition rate (Breithaupt et al., 2012). In addition, seagrass leaves also trap suspended particulate matter and promote their sedimentation, thus adding to the sedimentary storage component. Thus, seagrass meadows have the capacity to accumulate large carbon pools in the sediment and store it over millennial time scales (Kennedy et al., 2010; Fourqurean et al., 2012; Duarte et al., 2013; Greiner et al., 2013; Serrano et al., 2016). Global seagrass ecosystems are believed to store between 4.2 and 8.4 PgC (Fourqurean et al., 2012). Recent studies have indicated that these ecosystems also contribute to marine carbon sequestration by exporting 24 Tg of carbon per year (30% of the 80 Tg y1 carbon sequestered annually in meadows) to deeper layers of the sea, that is, the mixing layer, shelf, and deep sea (Duarte and Krause-Jensen, 2017). Fig. 3 depicts the biomass variation in the root-to-shoot ratio of different seagrass species recorded from Palk Bay (Purvaja et al., 2017). A recent study from the Indian seagrass
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14. IMPORTANCE OF SEAGRASS MANAGEMENT
FIG. 3 Biomass variation in root-to-shoot ratio recorded from Palk Bay seagrass species. R. Purvaja, R.S. Robin, D. Ganguly, G. Hariharan, G. Singh, R. Raghuraman, R. Ramesh, Seagrass meadows as proxy for assessment of ecosystem health, Ocean Coast. Manag. 159 (2017) 34–45. doi:10.1016/j.ocecoaman.2017.11.026.
ecosystem of Palk Bay indicates that the below ground biomass (rhizome) of seagrass acts as a major compartment in carbon storage, and that the stored carbon is finally sequestered in the sediments (Ganguly et al., 2017). Another species-specific study from Palk Bay and Chilika seagrass meadows from India reported sedimentation rates ranging between 6.2 and 6.9 mm yr1 (Fig. 4) and mass accumulation rates between 0.84 and 1.12 g cm2 yr1 (Fig. 5), with an organic carbon burial rate between 6.97 and 8.99 mol C m2 yr1 (Banerjee et al., 2015). Preliminary carbon stock assessment by Ganguly et al. (2017) indicates that 1 km2 of a healthy seagrass meadow in India’s coastal waters can store as much as 13.96 Gg C in the top 1 m of the sediment. Similarly, 1 km2 of a healthy seagrass meadow can sequester 0.44 Gg Cyr1. The comparison of net community production (NCP) between Indian (Palk Bay) seagrass meadows (Ganguly et al., 2017) and the global average (Duarte et al., 2010) shows that production in Indian systems is at least three times higher. Higher growth rates in seagrass ecosystems are translated into an increased accumulation of carbon into both the above-ground biomass (leaves and stem) and the below-ground biomass (root systems and rhizomes) (Russell et al., 2013; Duarte and Krause-Jensen, 2017). Recent estimates indicate that mean above-ground biomass (AGB) from the near-shore region of the Indian Palk Bay (Ganguly et al., 2017) is comparable with the global mean seagrass biomass (224 18 g dwt m2) (Duarte and Chiscano, 1999). It is evident from the results presented above that seagrass ecosystems are storehouses of carbon and are capable of capturing atmospheric CO2 through very efficient sequestration mechanisms. Carbon (Corg) is preserved for millennia because seagrass sediment is largely anaerobic. Although extensive literature is available on seagrass carbon sequestration and storage around the globe, research is in its infancy in India. It would be particularly important to estimate the sequestration capacity of dominant seagrass species in India such that conservation efforts of such important seagrass species can be enhanced.
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8.00 Rate of sedimentation (mm yr–1)
7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 Halodule*
Halophila*
Cymodocea # Mixed seagrass # Andaman
Seagrass ecosystems
Sundarbans
Pristine mangrove ecosystems
FIG. 4 Comparison of rate of sedimentation between different seagrass species from Chilika Lagoon and Palk Bay and pristine mangrove ecosystems (Banerjee et al., 2012, 2015).
Mass accumulation rate ( g cm–2 yr–1)
1.20 1.00 0.80 0.60 0.40 0.20 0.00
Halodule*
Halophila*
Cymodocea # Mixed seagrass #
Seagrass ecosystems
Andaman
Sundarbans
Pristine mangrove ecosystems
FIG. 5 Comparison of mass accumulation rate between seagrass ecosystems (Chilika Lagoon and Palk Bay) and pristine mangrove ecosystems. K. Banerjee, B. Senthilkumar, R. Purvaja, R. Ramesh, Sedimentation and trace metal distribution in selected locations of Sundarbans mangroves and Hooghly estuary, northeast coast of India, Environ. Geochem. Health 34 (1) (2012) 27–42; K. Banerjee, A. Paneer Selvam, K. Arumugam, R. Purvaja, R. Ramesh, Seagrass ecosystems as effective sediment stabilizers. In: Presentation on Past and Present Geochemical Process – Impacts on Climate change at JNU, New Delhi, India (2015).
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All this clearly highlights the important role played by seagrass ecosystems in climate change and therefore the importance that needs to be given to the preservation and conservation of seagrass ecosystems, especially in terms of blue carbon. Recently, Ganguly et al. (2017) estimated that the economic values ranged between $1.02 million and $3.65 million per year, based on the regulatory ecosystem services provided from the total seagrass cover in India. Additionally, the monetary values of the stored carbon in the top 1 m sediment of seagrass meadows ranged between $109 million and $146 million.
5 THREATS TO SEAGRASS ECOSYSTEMS While it is well accepted that ecosystem services provided by seagrass meadows are important, a number of threats to these meadows have been reported. Globally, seagrass habitats have declined in area and several species are threatened due to multiple natural and anthropogenic stressors (Waycott et al., 2009; Short et al., 2011). Natural stressors of seagrass habitat include cyclones, heavy rainfall, coastal uplift and subsidence, grazing herbivores, and diseases, whereas anthropogenic stressors include physical damages due to boating activities, oil spills, and turbidity due to urban, agricultural, and aquacultural runoff (Short and Wyllie-Echeverria, 1996). The leading stressors of Indian seagrass meadows are mainly human-related activities, both in coastal waters and watershed areas, which lead to subsequent loss in both seagrass area and diversity (Prabhakaran, 2006; Thangaradjou et al., 2007; Singh et al., 2015). Key anthropogenic activities that threaten Indian seagrasses that were identified from the literature include: (i) commercial fishing and trawling activities, (ii) boat activities for recreational purposes, (iii) runoff from coastal aquaculture and agriculture, and (iv) shell harvesting/seaweed cultivation. The ranking among the above activities varies between the systems; however, fishing using trawl/gill nets and boating activities are seen as the most important threats to seagrass in India (Thangaradjou and Nobi, 2009; Mathews et al., 2010). Other prolonged disturbances such as continuous loading of nutrients/fresh water often result in the phase shift of seagrass meadows to macroalgae beds, as seen in the Palk Bay region (Thangaradjou et al., 2013). Alteration in the salinity conditions produced a shift in seagrass species in Chilika Lagoon, with colonization by new species (Kumar and Patnaik, 2010). Natural disturbances that are responsible for seagrass loss in these regions include cyclones, storms, coastal uplift, grazing by herbivores, and diseases ( Jagtap et al., 2003; Mathews et al., 2010; Ragavan et al., 2013). Thangaradjou and Nobi (2009) reported the decrease in seagrass area in the Andaman archipelago as a consequence of the tectonic movement/coastal uplift and sediment dumping on seagrass after the 2004 Indian Ocean tsunami. Increase in rainfall intensity and cyclones have damaged the seagrass meadows in various locations by uprooting the plants and affecting the seawater clarity through high suspended matter inputs. Recently, the leaf-reddening disease was found in species such as Halophila ovalis and Thalassia hemprichi, which might have an impact on their productivity and distribution (Ragavan et al., 2013). Thangaradjou and Nobi (2009) reported localized effect on
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5 THREATS TO SEAGRASS ECOSYSTEMS
reduced leaf cover and biomass distribution in the seagrass meadows of Lakshadweep and Andaman Islands by the grazing of sea turtles. Major threats to different Indian seagrass meadows are summarized in Table 3.
TABLE 3
Threats to Indian Major Seagrass Ecosystems
Location
Major Threats
Impacts
Reference
Palk Bay
High precipitation during northeast monsoon, cyclones
Physical damage to seagrass and reduced light penetration due to high turbidity
Thangaradjou and Nobi (2009)
Anchoring of boats, propeller damage
Uprooting of seagrass
Thangaradjou and Nobi, (2009) and Mathews et al. (2010)
Use of push nets, trawl nets, bottom set gill nets
Physical damage to the seagrasses by uprooting the plants and removing the healthy leaves
Thangaradjou and Nobi (2009), Sridhar et al. (2010), Mathews et al. (2010), and D’Souza et al. (2013)
Nutrient enrichment from aquaculture wastes and proliferation of macroalgae
Eutrophication, growth of algae/ seaweed which competes with seagrass. Diminish light availability and sediment quality
Sridhar et al. (2010) and Thangaradjou et al. (2013)
Exotic seaweed cultivation
Affects light penetration and seagrass die off
Mathews et al. (2010)
Southwest monsoonal winds, northeast monsoon, cyclones
Physical damage to seagrass and reduced light penetration due to high turbidity
Thangaradjou and Nobi (2009)
Shell harvesting of Tellina angulata
Physical destruction of seagrass rhizomes and roots
Thangaradjou et al. (2007) and Thangaradjou and Nobi (2009)
Anchoring of boats, propeller damage
Uprooting of seagrass
Thangaradjou and Nobi (2009) and Mathews et al. (2010)
Use of push nets, trawl nets, bottom set gill nets
Physical damage to the seagrasses by uprooting the plants and removing the healthy leaves
Thangaradjou and Nobi (2009), Mathews et al. (2010) and D’Souza et al. (2013)
Natural hazards such as storms, floods
Physical damage to seagrass and reduced light penetration due to high turbidity
Priyadarsini et al. (2014)
Dredging, inappropriate fishing, anchoring, coastal constructions
Uprooting of seagrass
Priyadarsini et al. (2014)
Coastal aquaculture wastes
Eutrophication, growth of algae which competes with seagrass. Diminished light availability and sediment quality
Priyadarsini et al. (2014)
Gulf of Mannar
Chilika Lagoon
(Continued)
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TABLE 3 Threats to Indian Major SeagrassEcosystems—cont’d Location
Major Threats
Impacts
Reference
Gulf of Kachchh
Industrial and domestic pollution
Eutrophication and formation of algal blooms
Kamboj (2014)
Development of ports and harbors
Increase in sedimentation, solid waste and marine pollution
Kamboj (2014)
Fishing and boat activities
Physical damage to the seagrass leaves and rhizomes
Kamboj (2014)
Intense boating and tourism activities
Physical damage to the seagrasses roots/rhizomes and leaves
Thangaradjou and Nobi (2009)
Diseases – Leaf Redding
Decoloring of leaves leading to seagrass mortality
Ragavan et al. (2013)
Tsunami, cyclones, storms
Physical damage, sediment dumping on seagrass and increase turbidity
Thangaradjou and Nobi (2009) and Danielsen et al. (2005)
Grazing by green turtles (protected species)
Grazing pressure can modify the species composition
Lal et al. (2010) and Kaladharan et al. (2013)
Boating and tourism activities
Physical damage to the seagrasses roots/rhizomes and leaves
Thangaradjou and Nobi (2009) and Nobi et al. (2013)
Sea erosion and siltation
Affects light penetration and seagrass die off
Nobi et al. (2013)
Disposal of fish waste and untreated solid waste
Localized eutrophication and seagrass damage
Thangaradjou and Nobi (2009)
Andaman and Nicobar Islands
Lakshadweep
6 MANAGEMENT OF SEAGRASS ECOSYSTEMS Sea level rise and an increase in the intensity of cyclones are potential consequences of climate change. In this context, the ability of seagrasses to protect coastlines through mitigation of wave energy assumes importance. However, their other important contribution—the ability to sequester carbon—can be considered to be of higher importance because it is also known that considerable amounts of carbon (that were buried) are released when such ecosystems are degraded. Hence, it is obvious that existing areas under seagrass cover have to be protected and overall, areas under seagrass have to be increased. There are a number of legislative and policy options that can be used to protect seagrass ecosystems (Ramesh et al., 2018) in India. Of these, the Coastal Regulation Zone Notification 2011 (CRZ, 2011), issued under the Environmental (Protection) Act, 1986, which classifies seagrass meadows as CRZ-Ia (Ecologically Sensitive Areas), is the only explicit legislation that protects seagrasses by prohibiting development activity in their vicinity. Efforts are also being made in marine spatial planning as part of the development of integrated coastal management plans whereby the locations of these important ecosystems are mapped so that they become areas for conservation and protection.
7 CONCLUSIONS AND RECOMMENDATIONS
295
A decline in seagrass beds has prompted the implementation of numerous restoration programs in different parts of the world. In addition, blue carbon sequestration has been found to be enhanced with seagrass restoration (Greiner et al., 2013) which has prompted restoration attempts globally. However, the success of these attempts has been hampered by the difficulties in reducing the causes of disturbance (Paling et al., 2009). Techniques for restoration include natural restoration, transplants, and seeding. The cost of restoration may vary depending on the selection of sites for restoration, techniques, degradation intensity, follow-up measures, and surrounding environmental conditions. According to Bergstrom (2006), the lower end of the global seagrass restoration range is between $83,363 and $244,530 per hectare whereas the higher end is between $1,900,000 (McNeese et al., 2006) and $3,387,000 per hectare (Lewis III. et al., 2006; Paling et al., 2009). The only study on seagrass restoration in the Palk Bay and adjacent Gulf of Mannar with a total cost of INR1,426,750 ($22,000 ha1) reported from India showed an average survival rate (after nine months of transplantation) of 81.5% (Thalassia hemprichii), 85.7% (Cymodocea serrulata), and 78.6% (Syringodium isoetifolium), for three major seagrass species, respectively. The activity carried out in pilot mode covered 200 m2 in each location (Patterson and D’Souza, 2015). Three techniques—sprigs (Quadrate), plugs, and saplings—were attempted, of which sprigs were the most successful. Nearly one square kilometer was rehabilitated and another area of equal size is under restoration; both attempts are off the coast of Thoothukudi in the Gulf of Mannar. Considering the elevated cost of seagrass restoration, the conservation of seagrass habitats (e.g., $1400 per hectare as per Stowers et al., 2006) is far more cost effective than the restoration of degraded seagrass meadows.
7 CONCLUSIONS AND RECOMMENDATIONS It is clear that seagrasses are extremely important in the current context of climate change, as these systems are highly efficient in both sequestering and long-term storage of carbon. To increase the area under seagrass meadows, two plans of action may be considered. In the first case, the effective implementation of available legislation may help in the reduction of threats. Ensuring that the provisions of protection accorded to CRZ-I are strictly followed can prevent further degradation and promotion of self-restoration of seagrass meadows. The sequestration capacity of dominant seagrass species in India needs to be estimated so that conservation efforts of such important seagrass species can be enhanced. Research also needs to be undertaken on the use of seagrasses by local communities to determine if protection of seagrass meadows could be enhanced by declaration of such areas as Critically Vulnerable Coastal Areas (CVCA), which are to be managed with the involvement of local communities including fishers (CRZ, 2011). Simultaneously, mapping of areas with potential for growth of seagrasses needs to be accomplished. Action is necessary to increase the area under seagrass, either by natural expansion or by planting. For the former, areas such as the Chilika lagoon where natural expansion of seagrass meadows has been reported must be studied so as to enable replication in other potential areas. For the latter, trials that have been carried out in Palk Bay and the Gulf of Mannar could help in strengthening this activity. This needs to be supported by research into techniques for seagrass transplantation.
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It is also recommended to bring local communities, scientists, resource managers, and government officials together in designing an action plan for seagrass conservation. Such a strategy would be in accordance with Chapter 17 of Agenda 21 of the 1992 Earth Summit at Rio de Janeiro, Brazil, which states that government agencies charged with coastal zone protection must integrate traditional ecological knowledge (TEK) and sociocultural values with management agendas (Wyllie-Echeverria et al., 2002). Ultimately, more awareness needs to be created among all stakeholders about the various ecosystem services provided by seagrasses, especially their role in carbon sequestration.
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Thangaradjou, T., Kannan, L., 2007. Nutrient characteristics and sediment texture of the seagrass beds of the Gulf of Mannar. J. Environ. Biol. 28 (1), 29. Thangaradjou, T., Nobi, E.P., 2009. Seagrass – Watch, Threats to the Seagrasses of India. vol. 39, pp. 20–21. Thangaradjou, T., Sridhar, R., Senthilkumar, S., Kannan, S., 2007. Seagrass resource assessment in the Mandapam coast of the Gulf of Mannar biosphere reserve, India. Appl. Ecol. Environ. Res. 6 (1), 139–146. Thangaradjou, T., Subhashini, P., Raja, S., 2013. Macroalgae competition-challenging seagrass survival. Seagrass – Watch Threats Human Impacts and Mitigation 47, 50–51. Umamaheswari, R., Ramachandran, S., Nobi, E.P., 2009. Mapping the extend of seagrass meadows of gulf of Mannar biosphere reserve, India using IRS ID satellite imagery. Int. J. Biodivers. Conserv. 1 (5), 187–193. UNEP-WCMC, Short, F.T., 2016. Global distribution of seagrasses (version 4.0). In: Fourth update to the data layer used in Green and Short (2003). UNEP World Conservation Monitoring Centre, Cambridge, UK. http://data. unepwcmc.org/datasets/7. Waycott, M., Duarte, C.M., Carruthers, T.J., Orth, R.J., Dennison, W.C., Olyarnik, S., Calladine, A., Fourqurean, J.W., Heck, K.L., Hughes, A.R., Kendrick, G.A., 2009. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Proc. Natl. Acad. Sci. 106 (30), 12377–12381. Wyllie-Echeverria, S., Gunnarsson, K., Mateo, M.A., Borg, J.A., Renom, P., Kuo, J., Schanz, A., Hellblom, F., Jackson, E., Pergent, G., Pergent-Martini, C., Johnson, M., Sanchez-Lizaso, J., Boudouresque, C.F., Aioi, K., 2002. Protecting the seagrass biome: Report from the traditional seagrass knowledge working group. Bull. Mar. Sci. 71 (3), 1415–1417.
Further Reading Jagtap, T.G., 1991. Distribution of seagrasses along the Indian coast. Aqua. Bot. 40, 379–386. Kannan, L., Thangaradjou, T., Anantharaman, P., 1999. Status of seagrasses of India. Seaweed Res. Util. 21 (1&2), 25–33. Nair, V., 2002. Status of Flora and Fauna of Gulf of Kachchh. National Institute of Oceanography, Goa. Ravikumar, K., Ganesan, R., 1990. A new subspecies of halophilaovalis (R. Br.) J.D. Hook. (Hydrocharitaceae) from the eastern coast of peninsular India. Aquat. Bot. 36 (4), 351–358. Thangaradjou, T., Sivakumar, K., Nobi, E.P., Dilipan, E., 2010. Distribution of seagrasses along the Andaman and Nicobar Islands: a post tsunami survey. In: Recent Trends in Biodiversity of Andaman and Nicobar Islands. ZSI, Kolkata, pp. 157–160.