Coastal Zones: Remote Sensing Perspectives

By: Debashis Mitra
A coastal zone is one of the most fragile ecosystems on earth. Managing coastal resources sustainably calls for up-to-date knowledge, cutting edge planning and trained human resources. Satellite remote sensing provides synoptic and unbiased content in a multi-temporal domain that can help planners put suitable management policies in place.
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India has a 7516.6 km coastline spread over nine coastal states with a 2.02 million sq km exclusive economic zone (EEZ). The peninsular region of India has the Arabian Sea on the west, the Bay of Bengal in the east and the Indian Ocean in the south.

The coastal zone is a unique environment where land, ocean and atmosphere interact and produce a highly dynamic and important ecosystem. Estuaries, mangroves, coral reefs, sea grass  beds, mud flats and sand beaches are the diverse habitats that comprise the coastal environment and provide valuable benefits to human and marine lives.

Eric Bird points out, in his book Coastal Geomorphology: An Introduction, that the total coastline of the world is 3,56,000 km, with coastal zones comprising around 10 per cent of the earth’s surface. The population density in the world’s coastal zones is much higher than that in non-coastal areas because of the economic benefits and livelihood opportunities that the coastal ecosystem bestows to the people. Coastal habitats, especially mud flats, mangroves, coral reefs, sea grasses and salt marshes are highly productive and serve important ecological functions, besides protecting populations against coastal erosion. However, the world’s coastal zones are under tremendous stress owing to natural and anthropogenic factors. Critical coastal habitats, are rapidly being cleared for urban, industrial, and recreational growth and aquaculture.

Ecologically sustainable development of coastal habitats requires crucial knowledge about the natural variability of marine ecosystems and the dynamics of the coastal environment. Remote sensing, which can be defined as the acquisition of information from an object or an event without physical contact, can help in collecting crucial data on tidal wetland conditions, mangrove degradation, coastal land forms, shoreline changes, tidal boundaries, brackish water areas, suspended sediment dynamics, coastal currents and oil pollution. The data thus collected can help in inventory, monitoring and management of natural resources in the coastal areas, and also develop strategies to exploit coastal resources sustainably.

Major habitats of the Coastal System

Mangroves are important to coastal zones as they produce detritus, organic matter and help in recycling of nutrients in coastal waters (Balasco & M., 1977). The world’s mangroves are spread over 30 countries in tropical and sub-tropical regions. The 2015 State of Forest Report by the Forest Survey of India, estimates a mangrove area coverage of 4,740 sq km. However significant decline in the mangroves along the Gulf of Kachchh and East Godavari has been noticed. At many places, mangrove forests have been degraded for use as fuel, fodder and conversion of mangrove regions for aquaculture cultivation and industry.

Remote sensing enables assessment of mangroves in terms of extent, density of community, health, diversity, habitat and heterogeneity in ecologically rich areas (Fig. 1). Multi-temporal remote sensing data also helps in estimating changes in mangrove forest extent, status of degradation and reasons for deforestation.

Coral reefs are found all around the tropical and sub-tropical oceans. They live in shallow, warm and clear water, and are among the most diverse ecosystems in the world comprising tens of thousands of marine species.

Southeast Asia is home to 30 per cent of the world’s coral reefs; however unfortunately, 60 per cent of the existing reefs are already destroyed or on the verge of getting wiped out. In India, fringing reefs inhabit the Gulf of Kachchh, Gulf of Mannar and the Andaman and Nicobar Islands. The Lakshadweep Islands have mostly atolls with few coral heads, a platform reef and sand cays. The coral reefs of the Gulf of Kachchh and some reefs in the Andaman and Nicobar are degraded, as is clearly evident from the mud deposits on them (Desai et al., 1991). Besides, the felling of mangroves and clearing of forests has increased sedimentation and affected the live coral and species diversity. While global warming and rising ocean temperatures continue to bleach corals across the world, destructive techniques employed in catching fish, such as dynamite blasting, as also pollution of our seas and oceans through oil spills and other effluents have accelerated the destruction of coral reefs.

Fig. 1: Mangrove forest as seen in Odisha coastal belt using satellite imagery
Fig. 1: Mangrove forest as seen in Odisha coastal belt using satellite imagery

Multispectral remote sensing data can identify the various reef features and help map coral reefs along the Indian coast in different scales (Fig. 2). Recent advances in image processing techniques and high resolution satellite imagery have increased the accuracy of data and help identify smaller reefs, besides noting degradation and destruction in the remotest zones.

Mud flats or tidal flats are regions in between high and low tide. They are composed of silt/clay sized particles and are one of the most important ecological elements of the coastal environment. Mud flats usually support a large population of coastal crocodiles, crustaceans, snakes, mudskippers and other creatures. They are the nurseries for fish, tortoise and various other animals. Most mangroves thrive along mud flats (Fig. 3).

Fig. 2: Coral reef in Andaman and Nicobar Islands
Fig. 2: Coral reef in Andaman and Nicobar Islands
Fig. 3: Gulf of Khambhat, Gujarat showing Mudflat regions
Fig. 3: Gulf of Khambhat, Gujarat showing Mudflat regions

Maintenance of mud flats is important for protecting coastal erosion. However, mud flats worldwide are under threat from sea level rise due to global warming, reclamation of mud flats for development, salt production, aquaculture, dredging for shipping purposes and chemical pollution.

Remote sensing data helps monitor the health of mud flats and helps study the reasons for degradation. Upcoming salt firms, aqua cultural activities on mud flats can be closely monitored from high resolution satellite data and quantitative analysis.

Endnote

At a time when our coastal zones are under severe threat due to natural and anthropogenic factors, remote sensing data collected through satellite imagery can help keep track of the health of some important elements of our coastal ecosystem; such as mangroves, coral reefs and mud flats. It can hence help in charting out plans for sustainable development of our coastal belts, with little or no damage to the fragile coastal ecosystem.

References

Bird, Eric. (2011). Coastal Geomorphology: An Introduction. John Wiley & Sons Limited.

Blasco, F., & M. Aizpuru. (1997). Classification and evolution of the mangroves of India. Tropical Ecology, 38, 357-374.

Desai, P.S., Narain, A., Nayak, S.R., Manikiam, B., S. Adiaga, & Nath, A.N. (1991). IRS-1A application for coastal and marine resources. Current Science, 61, 204-208.

ENVIS. (1997). Estuaries of India: State of the Art Report. ENVIS Publication Series, 2(97).

Govt. of India. (1997). Mangroves in India-Status Report, Ministry of Environment and Forests, 156.

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