Spatial Inventory and Ecological Status of Coral Reefs of the Central Indian Ocean Using Resourcesat-1

Indian Journal of Geo-Marine Sciences Vol. 42(6), October 2013, pp. 684-696

Spatial inventory and ecological status of coral reefs of the Central Indian Ocean using Resourcesat-1

Bahuguna A., Ray Chaudhury N., Bhattji N., Ajai & Navalgund R. R. Space Applications Centre (ISRO), Ahmedabad – 380015, India [Email: [email protected]] Received 8 February 2012; revised 14 September 2012

Spatial inventory of coral reef habitat at eco-morphological level has been carried out for the Central Indian Ocean (CIO) using Resourcesat-1 satellite data. CIO covers India, Sri Lanka, Bangladesh, Maldives and the British Indian Ocean Territory. A comprehensive classification system has been evolved and standardized to map the coral reefs of CIO. Coral reefs of the CIO occupy 18,252.13 sq km area. Maldivian and Indian reefs cover 79.63% (14533.60 sq km) and 13.06% (2383.87 sq km) of CIO reef area respectively. Coral reefs of British Indian Ocean Territory enjoy pristine ecological status among the CIO reefs. In India, Lakshadweep followed by Andaman and Nicobar islands have certain reefs which may be termed as pristine with the rest being in vulnerable condition. Gulf of Kachchh reefs are in degraded condition. Sri Lankan reefs are also in vulnerable condition. Banladesh has a single reef which is in degrading condition. This inventory is the first of its kind providing baseline data not only for management and conservation but also forms an important input for climate change studies.

[Keywords: Coral reefs, Central Indian Ocean, Resourcesat -1, Habitat Mapping]

Introduction Reef conservation and management plans call for

Coral reefs, the rain forests of the tropical seas, are monitoring of reef health as well as identifying critical habitats. Worldwide, detailed coral reef maps are considered to be one of the “keystone ecosystems” 2 with reference to global climate change1. As an essentially nonexistent. Spalding et al. has brought ecosystem, coral reefs are sensitive enough to display out a World Atlas of Coral Reefs providing a any kind of changes occurring within the very narrow summary of the geographic distribution and status of range of biophysical parameters of their common world coral reefs. Though the coral reefs have been marine habitats i.e., the shallow, tropical seas of the mapped at global level, the details in terms of geomorphic and ecological categories are not world as well as changes occurring even at small scale 2,3 in the global and local climate. In fact they are available . Worldwide remote sensing studies of coral reefs have focused on mapping the referred to as ‘harbingers’ of climate change. In 4,5 addition to being high in biological productivity they geomorphological classes . Mapping of ecological are also sources of huge deposits of calcium components of coral reefs have not been attempted using satellite data6. Indian coral reefs have been carbonate. Coral reefs are also sites of CO2 sink. They also ensure coastal protection, are centers of scientific mapped at habitat level using Indian Remote Sensing (IRS) satellite data7. research, provide natural raw materials for deriving pharmacological products especially the life saving Looking at the paucity of information on the coral drugs. Coral reefs have an important ecological reefs extent, its various habitats, ecological and function by serving as habitat, nursery, and feeding geomorphological zones worldwide, spatial inventory areas for many marine species. They represent crucial of coral reefs for the Central Indian Ocean (CIO) at sources of income and resources for the coastal eco-geomorphic level has been carried out using the population through their role in fishing and tourism. data from RESOURCESAT-1 (IRS-P6) satellite. Despite their persistence and importance over Central Indian Ocean covers the countries of India, geological time, coral reefs appear to be one of the Sri Lanka, Bangladesh, Maldives and British Indian most vulnerable marine ecosystems. Ocean Territory. Reefs in Pakistan could not be BAHUGUNA et al.: SPATIAL INVENTORY & ECOLOGICAL STATUS OF CORAL REEFS 685

delineated from the current satellite data and therefore from the reef-scape. For selecting the low tide image, have not been included in this study. Main objectives we have referred to the predicted tide data of major of the study were: i) To evolve a classification system and minor ports for Indian reefs given by the for mapping coral reefs at geomorphological level Maritime Board. For other regions we have carefully with broad ecological zones, ii) Generate coral reef browsed and selected the data based on the exposure habitat maps at eco-geomorphic level using of reefs. Data of October to April months were Resourcesat-1 data, iii) To infer the ecological status selected to take care of the seasonal vegetation like of the CIO reefs. algae on the reef. Algal growth peaks from October to March in most of these areas. Materials and Methods Study Area Methodology Coral reefs in the CIO occur within the Using the classification system for mapping Indian 7,8   reefs as a base along with intensive literature geographical limits of 23 North to 8 South latitudes 4,5,9,10,11 and 69 East to 94 East longitudes. In the CIO survey we have evolved a common, region, the major reef formations are present in the comprehensive classification system (Table 1) to map Indian sub-continent and the Maldives. As an the CIO coral reefs. Ecological components are oceanographic ecotone this region epitomizes the bio- limited to assemblages of plants (algae and seagrass) geographical transition observed over the entire and the inhabited substrata. In order to map the live Indian Ocean from its west to the east. CIO serves as corals very high resolution data 1m or better is a ‘critical link’ between the robust, endemic reefs required, therefore this study is limited to mapping found in the enclosed seas of the Middle East geomorphological zones having the probability of live (Arabian Gulf and the Red Sea) marking the north coral occurrence (like outer reef crest, shallow pools, western continental margin of the Indian Ocean and etc.). After frequent ground checks using GPS, areas the Southeast Asian reefs: the region of highest reef having live corals along with other categories like biodiversity in the world. To the west, the reefs from algae or shallow pools have been labelled in maps as south India (Lakshadweep) to the British Indian algae with live corals or shallow pools having live Ocean Territory or the Chagos Archipelago include corals etc. An interpretation key was generated which certain elements of more typically Indian Ocean helped in identifying and mapping different reef species, as well as small number of species which features based on optical characteristics along with locational-attributes. characterize the Western Indian Ocean. According to Spalding et al.2, maximum reef diversity in the Methodology to map and monitor the Indian coral Central Indian Ocean is restricted to a “narrow path” reefs at eco-morphological level evolved earlier8,12,13,14 –centred to the southern Maldives and Chagos has been used for mapping the CIO reefs. Standard Archipelago. digital as well as visual analysis procedures such as pre-processing of images (image corrections and Data used image enhancements), georeferencing, subset CIO reefs have been mapped using data from generation, delineation of reef boundary and high tide RESOURCESAT-1 (IRS-P6) satellite launched on line, visual interpretation of satellite data for reef October 17, 2003. This satellite has three sensors: an classification, etc., were employed to generate the Advanced Wide Field Sensor (AWiFS) having spatial coral reef map using ERDAS Imagine software. resolution of 56 m and two Linear Imaging and Self Geographic projection and Modified Everest datum Scanning Sensors LISS-III and LISS-IV having 23 m have been chosen for the geo-referencing of satellite and 5.8 m spatial resolutions respectively. images. Due care has been taken to ensure geo- Primarily, LISS-IV data pertaining to 2004 to 2007 referencing with Root Mean Square Error (RMSE) to has been used in the present study. However, in case be less than one pixel. Regions having coral reefs of non-availability of cloud-free and low tide (subsets) were extracted from the full image to get exposure of coral reefs in LISS-IV data, LISS-III and maximum details of the reef region. Digital imagery AWiFS data have been used. Data acquired at low displayed as colour composite image by combining tides and clear sky conditions were carefully selected green, red and near-infra red band (or the standard as high tides modify and reduce the signature coming False Colour Composite Combination) was processed 686 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013

Table 1  Classification System for Mapping the CIO Reefs

Reef Type Geomorphological Geomorphological Ecological Zone Zone Sub-zone

Fringing/Platform/Patch/ Reef Front/Windward Reef Edge* Pinnacle Reef Front* Reef Slope* Reef Crest* Algal Ridge/Algal Pavement* Macro and Micro Algae* Moat* Live Corals, Algae* Reef Flat* Outer Reef Flat* Coral Zone/ Mixed Coral Zone, Algae* Inner Reef Flat* Macroalgae, Seagrass, less corals* Reef Flat (Degraded)* Macroalgae* Sanded Reef Flat* Macroalgae, Seagrass* Muddy Reef Flat* Macroalgae dense* Sandy Muddy Reef* Algae, Seagrass* Boulder Zone* Algae* Rubble Zone* Algae* Shallow Tidal Pools* Algae (matty)* Exposed Reef Flat Algae (dense), Seagrass* (After-Tsunami) Eroded Reef Area (After Tsunami) Backwash/Detritus Deposit (After-Tsunami) Sand Deposition (After-Tsunami) Sand Patches* Sand Cay* Sandy Ridge* Algae* Rocks* Coralline Shelf* Barrier/Ribbon Reef Atoll/Faros Atoll Outer Rim Lagoon Shallow sandy lagoon (Depth 1-5 meters) Lagoon of Intermediate Depth (Depth 5-20 meters) Deep Lagoon (Depth > 20 meters) Lagoonal Reef Slope Lagoonal Reef Patches Coral Knoll Lagoonlet

Submerged Reef* Submerged Reef (After-tsunami)

Coral Head* Live Coral* Beach* Dune Vegetation* Island*

Mudflat Sub-tidal Mudflat Inter-tidal Mudflat High-tidal mudflat Mangroves Jetty High Tide Line

*:The Geomorphological Zones/Sub-zones & Ecological Zones marked with asterisk are common to all Types of reefs. BAHUGUNA et al.: SPATIAL INVENTORY & ECOLOGICAL STATUS OF CORAL REEFS 687

and enhanced digitally. Image enhancement, was Results & Discussion solely done to improve the appearance of the imagery to assist in visual interpretation and analysis. As the Indian Reefs coral reefs often occur in submerged conditions, care was taken to enhance the coral reefs by softening the In the Indian coast, major coral reef regions are land pixels (contrast and brightness stretching) from Gulf of Kachchh (Gujarat), Malvan in Maharashtra, the image. Lakshadweep, Palk Bay and Gulf of Mannar (Tamil Nadu) and the reefs of the Andaman and Nicobar Visual interpretation of intra-reef geomorphic Group of Islands. Resourcesat-1 satellite images features, ecological and litho-substrates was done to depicting the coral reefs for the four major reef classify the reefs using the interpretation key evolved regions of India are shown in Fig. 1. Field photographs during this study. Same were labelled and a map was of common corals found in these regions are given in composed for each subset. Unsupervised Fig. 2. The total area under coral reefs mapped for the Classification based on Iterative Self-Organising Data Indian coast is 2383.87 sq km. There is a unique linear Analysis (ISODATA) clustering algorithm available ribbon reef connecting India and Sri Lanka. The details in ERDAS IMAGINE image processing software has for the above regions are discussed below: been used for pixel level area estimation. Digital classification accuracies from ISODATA algorithm Gulf of Kachchh reefs, occupying 352.5 sq km on Indian reefs have been between 77-92% at 90% area, are northernmost of the Indian reefs, mostly confidence level8. consisting of dead coral boulders and pebbles. They comprise fringing, platform and patch type of reefs along with some coral pinnacles. Well defined reef Maximum visible reef edge seaward on the image slope and reef front mainly occurs in the northern and is discerned as the reef boundary. Since satellite data western regions. Algal/Reef ridge follows the reef of low-tide exposure was preferred, hence it became crest in the north and is the most distinct feature of the easier to discern the upper limit of tidal reach and island reefs like Bural Chank (Fig. 1A), Kalubhar, accordingly the High Tide Line was delineated. Major Paga, etc. Ridge is markedly absent on the eastern or reef typology and intra-reef geomorphic features were the leeward side of the reefs. On certain reefs a clear delineated with reference to the elements of location, distinction between outer and inner reef flat is association, size and shape whereas the ecological and observed from the satellite data. Outer reef flat here is litho-substrates were discerned with reference to their narrow and the percentage of live corals is more. On tone and texture and also according to their spatial the outer reef flats of Bural Chank, Paga, Ajad and occurrence. Main typology of reef is decided with Kalubhar, live corals are found to co-habit with dense reference to its association and distance to other land algae (mapped as Algae Dense with Live Corals) or features. sometimes even under dense cover of algae. Inner reef flat has lesser percentage of live corals and has more It is important to mention here extensive ground of dead coral boulders, shallow pools, algae truthing/reef surveys of Indian reefs was carried out, (calcareous as well as fleshy algae; Sargassum is however the reefs of Sri Lanka, Bangladesh, Maldives found in abundance here) and sparse seagrass. and British Indian Ocean Territory were not surveyed. Recently, increase in macro algae has been observed, The signatures and knowledge of Indian reefs were particularly of the fleshy algae like Ulva. Muddy reef extrapolated to these reefs for visual interpretation, flat or thick mud depositions (thickness of mud varies e.g., the coral reefs of Lakshadweep are similar to from few centimeters to more than a meter) are Maldivian reefs, therefore, the signatures of observed on almost all the reefs in the leeward or the Lakshadweep reefs were extended to reefs of eastern side. An encrusting alga belonging to Maldives. The Gulf of Mannar and the fringing reefs Vaucheria family (carpet or matty algae) grows of Sri Lanka are similar. Reefs of British Indian profusely on this muddy zone. Area of the sanded reef Ocean Territory have similarity with the flat varies within the inner reef flat, sometimes Lakshadweep. We have also taken help from experts adjoining the linear beach. Seasonal cover of in the field and the available literature2,10,15 for vegetation is observed during October-April months, interpreting the unsurveyed reefs. mainly consisting of algae and species of Ipomoea. 688 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013

Periodic monitoring using multitemporal satellite (for e.g., the Pirotan reef which lies in the core Marine data has given insight on the ecological status of these National Park, Jamnagar, Gulf of Kachchh). Temporal reefs. Sand deposition is one of the major cause of satellite images of Pirotan Island for a period of 20 reef degradation. At many places, the degradation of years (1986-2006) shown in Fig. 3 reveals successive coral reefs due to bleaching has also been observed degradation of Pirotan reef from a coral dominated

Fig. 1  Resourcesat-1 LISS images showing coral reef habitats of A) Bural Chank Reef, Gulf of Kachchh; B) Bangaram Island, Lakshadweep; C) Krusadai Reef Complex, Gulf of Mannar and D) Interview Island, Andaman.

Fig. 2  Field photographs of different types of corals in India a) Bural Chank Reef, Gulf of Kachchh b) Bangaram Island, Lakshadweep c) Krusadai Reef Complex, Gulf of Mannar and d) Interview Island, Andaman. BAHUGUNA et al.: SPATIAL INVENTORY & ECOLOGICAL STATUS OF CORAL REEFS 689

habitat to a macroalgae dominated habitat. It is due to reef is a very small reef having an area of 0.28 sq km. mass coral bleaching following anomalous rise in sea Coral reef is well defined in the eastern part of the surface temperatures; effect of sedimentation (both Malvan Island. Inspite of the corals remaining sand as well as mud) as well as anthropogenic submerged even at very low tides, it was possible to pressures. Pirotan reef covers an area of 12.90 sq. km. delineate this zone using LISS IV data. This reef lacks A comparison between 1996 and 2002 IRS data proper reef zones. Windward reef front, reef crest and revealed that mud on Pirotan reef rose from 3.7 sq. outer reef flat are not present here. Reef flat is broader km to 7.7 sq. km while algae cover on muddy reef flat on the west and northwest. Submerged corals are increased from 6.3 sq. km to 10.9 sq. km. Deposition present in the northeast. Seagrass is observed to be of both silt and sand effectively hinders the occupancy linearly distributed along the sandy beach in the east. of live corals on reef flat. Fringing reefs of Dhani bet Lakshadweep archipelago consists of a chain of have significantly degraded with more mud well developed coral reefs, lying about 200-470 km depositions. Areas having live corals are almost non- off the Kerala coast. Southernmost island of Minicoy existent here. It can also be inferred that the fringing is separated from rest of the islands by a 180 km wide type of reefs have degraded the most due to more stretch of sea. Coral formations built up on the anthropogenic pressure. Laccadive-Chagos submarine ridge rising steeply Malvan coast in Maharashtra forms a part of the from a depth of about 1500 m to 4000 m form an Western Ghats where the Sahyadri mountain ranges interrupted chain covering a distance of over 2000 km gradually meet the Arabian Sea. A chain of along with the Maldives and the Chagos submerged and exposed rocky islands extend Archipelago3. Coral reefs of Lakshadweep, covering southwards comprising several islands at the southern 933.7 sq km area are atoll type except for Pitti tip and the Sindhudurg fort at the northern tip. (Submerged Bank), and Androth (Platform reef). Sindhudurg is a low fortified island on the coastal The growth of reefs is widest on the western side reef, which is joined to the mainland by a dying reef. presumably because the growth is facilitated by the During low tide, the exposed area of the bay has large continuous supply of the nutrients on the western side. rock pools with rocks partially exposed and the corals Along with well developed atolls, there are are generally seen attached to the rocks. Corals occur submerged coral growth and coral heads. Reef front is here in spite of the region being highly turbid. Malvan mapped in the western, southwestern and northern

Fig. 3  IRS LISS sequel of Pirotan Reef, Gulf of Kachchh, India 690 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013

reef regions of Lakshadweep reefs. Outer reef flat has Some of the Lakshadweep reefs (Bitra, Perumal a prominent boulder zone or the algal ridge on the Par, Baliyapaniyam, Cheriyapaniyam) are in near western seaward side. Porites and Favia are pristine ecological status. Lagoons have clear waters commonly found here. Sandy Ridge and Rubble Zone harbouring rich coral patches along with other fauna occur on certain reefs on the seaward side after the like Green turtles, Sting rays, Sea Cucumber, and a reef front. Reef flat of Lakshadweep is an aligned plethora of fish. The reefs are rich in diversity. coral zone comprising dense coral growth. Live corals However, reefs like Kadmat, Kavaratti, Agatti, and like Acropora and Pocillopora dominate in this zone Minicoy are in vulnerable conditions. These reefs along with sporadic occurrence of Favites and have seagrass cover that has significantly increased Heliopora. Sand, coral rubbles and shingles and algae within a span of 5 years. The increase is mainly are also present. Seagrass occupies the shallow attributed to eutrophication due to human pressure. lagoonal area landwards along the beach on many Bangaram islands too are being surrounded by reefs. Shallow western lagoon of the Kadmat inhabits seagrass (an activity observed only in last 5 years). extensive seagrass beds apart from seaweeds and Sand deposition has also increased here. This reef corals. All the atolls have centrally or westerly located otherwise harbours rich corals in the lagoonal and reef lagoons with clear waters. Shallow lagoon on certain areas and also has coral knolls having dominant cover reefs (Baliyapaniyam, Cheriyapaniyam, Bitra, Perumal of live corals. In view of this, the islands need to be Par, Suheli Par, Minicoy, Chetlat, Bangaram and Agatti) managed effectively to stall degradation and improve harbour lagoonal patch reefs comprising massive coral their ecological status. colonies of mainly Porites, Acropora and Pocillopora Gulf of Mannar has a number of offshore platform with sporadic presence of Acropora. These patch reefs reefs, patch reefs and coral pinnacles, lying along the are found at depths of 1.5-5 m. The most conspicuous 140 km stretch from south of the Pamban Pass to feature of the coral reefs of Bangaram (Fig. 1B), Bitra, north-east of Tuticorin. The islands lie at an average Cheriyapaniyam, Baliyapaniyam and Minicoy is the distance of 8 km from the mainland. presence of a number of coral knolls in the lagoonal A linear Ribbon reef situated between 79º27′- region. On an average, knolls posses about 70-80% live 79º42′ E longitudes and 09º04′-09º09′ N latitudes coral cover. There are more than 100 such knolls in extends from south-eastern tip of the Rameswaram Bangaram, Cheriyapaniyam and Bitra. Minicoy has 11 Island going up to the northwest of Sri Lanka. This is and Baliyapaniyam has 12 coral knolls. Extensive a spectacular landform connecting the two countries Coralline shelf is present near Agatti-Bangaram, Pitti and is known as Adam’s Bridge16. Spalding et al.2 and Kalpeni atolls and the platform reef of Androth. mentioned Adam’s Bridge as a string of reefs Among all the Lakshadweep islands, the coralline stretching Sri Lanka. Distinctly visible reef crest lies shelf joining the two reefs, Bangaram and Aggati, is between the back reef and fore reef zones. There are a most unique. From the north of Aggati, the shelf total of 25 sand cays along the reef out of which 9 fall extends northwards and joins the western portion of in the Indian side and the remaining are part of Sri the Bangaram reef. The shelf is wider on the western Lanka. Adam’s Bridge reefs are now being region and is linear and parallel in the rest of the increasingly subjected to heavy sedimentation round regions and could be differentiated clearly using the year. Sedimentation has resulted in excessive sand satellite data. The shelf as such has not been earlier deposition and degradation of the reefs. Percentage of live corals is negligible. charted. Bathymetric charts show the contour of 30-40 m (area which has been marked by coralline shelf in The fringing reef in the Palk Bay lies in an the present study). In the north of Lakshadweep east-west direction along the mainland from the islands, two atolls, namely, Cheriyapaniyam and Pamban channel at the Pamban end of the bridge to Baliyapaniyam which were not charted earlier in the Rameswaram Island. The reef flat is relatively broad Survey of India topographical maps or Naval from Pamban channel to southern end near Ramnad Hydrographic bathymetric charts have been mapped and narrow from Pamban to south of Rameswaram. using satellite data. Sandy beach/storm beaches (12 sq Reef flat is followed by sandy beach on the landward km) characteristically make up the coast of all the side. Live coral percentage is less here, as these reefs Lakshadweep islands, comprising coralline sand, dead are also subjected to excessive sedimentation coral boulders and sandstone. particularly in the monsoon. BAHUGUNA et al.: SPATIAL INVENTORY & ECOLOGICAL STATUS OF CORAL REEFS 691

Gulf of Mannar has a number of offshore platform, and the Southeast Asian centre of biodiversity than to patch reefs, coral pinnacles and atoll. Reefs having a Indian reefs. Coral species diversity of these reefs is total area of 75.93 sq km, are present from south of the maximum (219 species) among all Indian reefs. the Pamban Pass to Tuticorin. Windward Reef Front Windward reef front comprising live corals surrounds covers the southern area from the seaward edge that the entire reef on the seaward side followed by non- slopes into deeper water to the landward edge of the aligned coral zone shoreward. Live corals of various shelf platform. In north the signature of the windward species (mixed coral zone) including Porites, reef front was not distinct due to excessive turbidity Goniopora, Pocillopora, Acropora (Fig. 2D), of water. It is conspicuously absent in the northern Symphyllia Fungia, Echinopora and Goniastrea sp region. The ecological components of Reef Flat occupy the zone. The reef flat comprises sandy include live corals, algae and seagrass. Live corals are substrate with intermittent rocks, live massive coral represented by Acropora, Montipora, Pocillopora, colonies (20 cm to > 1 m in diameter) of Porites, Porites, Favia, Favites, Goniastrea, Echinopora, Acropora, Symphyllia, Lobophyllia, Goniopora, Leptastrea, Platygyra, Galaxea, Goniopora, etc. Heliopora and Montipora (covering 50-70% area) Micro-atolls were observed on this zone (in the field) and algae. Patchy algae are dominated by Sargassum, especially in the northern region. Major portion of the Padina, Halimeda and Caulerpa. Turbinaria reef flat is occupied by algal growth comprising increases in percentage as we move seaward. mainly Turbinaria sp. Other species are Padina, Turbinaria is observed to dominate the outer reefs Halimeda, Sargassum and Gracilaria. Central part of where the wave energy is high whereas, Sargassum, the reef [mainly Krusadai Reef Complex (KRC) (Fig. Halimeda and Padina dominate the inner reef flat 1C) and Manouli Reef Complex (MRC)] makes a portions. Cymodocea and Halophyla seagrass were shallow lagoonal environment covering an area of also found on the reef flat. Shallow pools on the about 1.2 sq. km. Bottom of the lagoon is mainly sanded reef flat have corals like Porites, Acropora sandy. The sea grass ecosystem dominates the MRC and Pocillopora. Jolly Boys is the only reef, which with 87% cover. It is represented by Cymodocea has large sanded reef flat making up almost 70-80 % rotundata, Cymodocea serrulata, Halodule, of the reef system. Rock exposures occur within the Halophila ovalis, Halophila ovata, Enhalus reef system north of the Belle reef, Tarmugli reef, etc. acoroides, Thalassia hemprichii, etc. The Andaman group occupies reef area of 968.44 sq

Presence of macroalgae, seagrass in major portions km while the Nicobar Islands cover an area of 53.02 of the reef and high level of sedimentation is sq km of coral reefs. indicative of degrading ecological condition of the th The coral reefs of the Andaman and Nicobar reef. Tsunami of 26 December, 2004 has also islands were in near pristine condition prior to rendered damages to the northeastern reefs of the th 17 17 tsunami of 26 December, 2004 . When giant Gulf . Coral blocks were found to be uprooted tsunami waves smashed onto shores, the coral in during a ground survey carried out after the tsunami. nearby shallow areas were destroyed, crushed and Reefs near Tuticorin are also in a degrading condition shrouded in debris. Massive backwash returned to sea due to thermal ash deposits. Gulf of Mannar reefs are carrying a deadly cargo of detritus material and also subjected to illegal quarrying. deposited on coral reef. Erosion due to breakage has Andaman and Nicobar group of islands are resulted in loss of 54% of Andaman reefs (covering separated by the 160 km wide Ten Degree Channel. 227 sq km area). The subsidence (for e.g., in the north The western side of the Andaman Islands has coral and middle Andaman the subsidence has resulted in reefs of fringing type running intermittently for about increase of water level to the extent of 1.2 m) along 350 kilometers. Earlier study7 using satellite data with the high intensity waves have caused physical revealed that reefs are in good condition with broad damage to these reefs. Earthquake has caused about reef flat in the west. Eastern side has narrow fringing 15 – 60 cm wide and 80 – 100 m long cracks in the reefs in certain places. The east coast is a sheltered outer reef flat and the reef slope (ground observation). type with creeks and monsoonal river estuaries and Earthquakes have also resulted in elevation of areas bays. As the Andaman and Nicobar reefs are closer to wherein the reefs have become exposed. Significant Indonesia and Southeast Asia, the reef diversity in this erosion is observed in the easterly-located Havelock region is therefore closer and similar to the Indonesian group of reefs (comprising 5 reef complexes). A total 692 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013

of 7.5 sq km reef area of Havelock Island has The reef area of Indian coral reef regions under the undergone erosion. Just after tsunami 2.1 sq km area present study has been compared with the previous eroded as observed in the AWiFS data of 16th inventory on Indian coral reefs7 using satellite data of February 2005. The erosion reportedly increased to 1987 to 1991 (Table 2). 7.5 sq km area as mapped using IRS LISS III data in rd 3 August 2005 data. Gradual erosion is indicative of Coral Reefs of Sri Lanka continuing subsidence due to recurring earthquakes. Sri Lanka has almost continuous and well About 22% of the total area occupied by the reef has developed fringing reefs in the north and north-west experienced damage due to backwash (covering 93.9 and patchy reef growth in the east. Reef covers 475.70 sq km area). Sentinel reef located in the western part sq km area. Significant reef systems of Sri Lanka are has undergone damage entirely due to the backwash. Karaitivu, Jaffna Lagoon, Eulaitivu, Andalaitivu, However, significant improvement was noticed after Delft Island, Palitivu and Punkudutivu, Nainativu and 11 months. Backwash like sand and detritus has Bar Reef, the latter happens to be a Marine Sanctuary. washed off significantly. About 41% of reef area was These small island reefs survive in a comparatively restored (i.e. the backwash got washed off), sand high turbid condition. Mud depositions on the reef flat depositions came back to their original extent, and have been noticed on the fringing reef near Nainativu, detritus reduced to 3.7 sq km. Similarly sand that Jaffna lagoon (Fig. 4A) in the north-west. covered 800 m in Havelock just after tsunami was Punkudutivu in the north-west has a significantly observed to have washed off subsequently resulting in large fringing reef system. After tsunami, sand an increase in the sand free shallow reef flat area. deposition appears to have increased on the northern Elevation of the reef flat leading to exposure and reef. Reef Ponnaveli has been exposed significantly dying of corals at a large scale occurred particularly in after the tsunami and earthquake of 26th December the west of the North Andaman where the reef flat 2004. South western reefs of Sri Lankan coast have now stands exposed most of the time and comprises more of the narrow fringing reefs of Bentota, sand, algae and intermittent shallow pools. In the Hikkaduwa Marine Nature Reserve near Galle, Nicobar group of reefs, erosion was more prominent. Weligama, Polhena Reef, and Kalametiya Kalapuwa A total of 69% of reefs have totally broken off and Sanctuary. These reefs have characteristically long eroded. Coral reefs of the entire Little Nicobar Island narrow reef flats, sometimes sanded. In certain cases (earlier covering an extent of 9.8 sq km) have been submerged reefs have also been detected from the eroded. Trinkat and Camorta Reefs have suffered LISS-III images for this region. Reef near Kalpitiya maximum damage. These two islands shared a has a shallow lagoon which shows signs of common reef area (they were joined by the coral reef eutrophication in certain places as well as high growth) and had a total reef area of 60 sq km prior to sediment concentration. South-eastern coast of Sri tsunami. About 50% of its area has eroded totally and Lanka has some offshore prominences of reefs and 49% area has been severely damaged due to submerged coral banks. In the eastern coast fringing backwash. A large extent of Great Nicobar reef reefs occur in Vandeloos Bay, Vellaiyadimadu and (covering 98 sq km and making up 83.8% area) has surrounding area, near Verukal, Seruwila Allai totally eroded. Sanctuary, Kunittivu and surroundings, Great Sober

Table 2  Comparison of coral reef area of India over two Island Sanctuary. Intra-reef zonation pattern could not decades be inferred from the satellite data in the Sri Lankan reef system probably because of narrow fringing Reef Region 1987-91 2004-07 Difference in area reefs. Prominent reef features appearing for these (in sq km) reefs are mostly the long narrow reef flat, reef Gulf of Kachchh 460.20 352.50 107.70 front/reef slope and the adjacent beaches.

Malvan Not mapped 00.28 00.28 Coral reefs of Sri Lanka are in vulnerable Lakshadweep 816.10 933.70 117.60 condition. West coast has coral reefs that are narrow Gulf of Mannar 94.30 75.93 18.37 and fringing and the east coast has sparse distribution of coral reefs. Coral reefs in the north-west of Sri Andaman & Nicobar 959.30 1021.46 62.16 Lanka are in good ecological condition e.g., Delft Total 2329.90 2383.87 53.97 Island, Palitivu & Punkudutivu, Mannar Island. BAHUGUNA et al.: SPATIAL INVENTORY & ECOLOGICAL STATUS OF CORAL REEFS 693

Fig. 4  Resourcesat-1 images showing A) Jaffna Lagoon, Sri Lanka; B) St. Martin’s Island, Bangladesh; C) Felidu Atoll, Maldives and D) Blenheim reef, BIOT. Among the western and south-western coast reefs, the tide exposure is required to obtain in-depth Hikkaduwa Marine Nature Reserve and Bar Reef information on this reef. Marine Sanctuary have coral reefs that are in good ecological condition. However all these reefs have Coral Reefs of Maldives been damaged to some extent due to tsunami. Major Located south of the Lakshadweep islands of India damage has occurred due to the deposition of and running for about 800 kilometers north to south in sand/debris on the reefs. the CIO, the Maldives form a definite sequence of large oceanic atolls. The Maldivian reefs are unique Coral Reef of Bangladesh among CIO reefs. These are the only faros atoll reefs. In Bangladesh, the only coral reef is around the St. They cover an area of 14533.60 sq km. Each reef Martin’s Island (locally known as Jinjiradwip or system forms a chain of individual atolls around a Narikel Jingira) covering 4.0 sq km area. Reef occurs deep central lagoon and each individual atoll has its in the extreme south, off the mainland coast of own lagoon (thus called Faros atoll). These atolls rise Bangladesh in the north eastern Bay of Bengal. Reef steeply from the base of the submerged Chagos- development in this region has occurred in an Laccadive ridge and are aligned in two parallel unfavourable condition as there is continuous chains. Faros are more common in the northern freshwater discharge of mighty rivers like the Ganges, Maldives, but absent at Fua Mulaku atoll in the south. Brahmaputra and Meghna. AWiFS image shows an Fua Mulaku is the only patch reef in Maldives having exposure of a fringing reef around the island (Fig. a small lagoonlet18. Thiladhunmathi atoll in the north 4B). The eastern side of the island shows the reef in is the largest faros atoll occupying 2408.70 sq. km continuity whereas to the western side, the reef area. Makunudu atoll is a uniform atoll with no faros abruptly ends in the central portion. In the atolls. In its central deep lagoon there are a number of northwestern and northern side of the island there is a patch reefs as well as coral knolls. North Male atoll wide reef front area with a narrow reef flat. The flat has more than hundred faros and mini-atolls in the however widens onto the east. Existence of boulders lagoon. Gaa Faru is a small, elliptical, atoll situated to is visible in the northwestern reef front area. Higher the north-west of North Male atoll. Gaa Faru atoll has spatial resolution satellite data obtained during low coral zone lining the entire inner edge of the 694 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013

lagoonward reef. South Male atoll has eastern faros and the reefs of Western Indian Ocean. BIOT forms atolls with sandy shallow lagoons and sanded reef the southernmost extension of the Chagos-Laccadive flats while the west is devoid of sand depositions. Ari Ridge. These reefs and the islands are highly isolated atoll consists of ring shaped faros reefs that form its – the nearest reef structures are those of Maldives, outer edge and has numerous mini atolls inside its some 500 kilometers to the north. Reefs of BIOT can lagoon. This atoll has only four inhabited small be classified into atolls, faros atolls and submerged islands in the south making the region comparatively coral banks covering 854.96 sq km area. Reef free of anthropogenic pressure. There are no visible structures although resemble the Maldivian atolls but signs of eutrophication and algal growth here. Toddu among all the reefs of BIOT, only Peros Banhos atoll in the north east of Ari atoll has a well defined qualify to become a faros atoll as per its definition. inner reef flat which shows aligned coral zone. Felidu Due to the unavailability of cloud free data of atoll (Fig. 4C) is another beautiful atoll. It is a boot- RESOURCESAT-1 satellite, major portions of shaped atoll with the horizontal arm having shallow Colvocoresses reef, Great Chagos Bank, Cauvin sandy lagoonal floor and sanded reef flat while the Bank, Egmont reef, Pitt Bank, Ganges Bank, vertical arm is devoid of any sand. Huvadhoo atoll in Centurion Bank and Wight Bank could not be the south has number of coral knolls both in its central mapped. Speakers Bank is a large submerged coral deep lagoon as well in the lagoons of mini-atolls. bank. About 50 to 65 m wide reef edge is visible in Addu, the southernmost atoll has well defined reef the satellite data. Certain reef patches in the lagoonal slope and reef crest on the outer side. Reef flat is area are also visible. Another submerged bank that narrow. To the east after the sandy region, a well could be detected from LISS III data is the Victory defined lagoon slope is observed with coral zone that Bank. Due to cloud cover, the western portion of the goes down comparatively gently to the lagoon floor. Bank could not be detected. The Blenheim reef (Fig. Seagrass lines the sandy region in the east. Lagoon 4D) appears to be in good condition. Numbers of has reef patches and is covered with growing corals. small, mostly symmetrical patch reefs with live corals Few Atolls like Addu have visible impacts of are present in its lagoon. Reef flat is narrow but it has anthropogenic pressure. The western arm of the atoll an extensive reef slope plunging deep down into the has more signs of anthropogenic pressure. Southern lagoon. The reef crest however, is fostering the region has extensive areas showing eutrophication and foundation of a juvenile beach. Saloman atoll, lying to algae cover. the east of Blenheim has a deep lagoon with a wide More than any other nation outside the Western reef flat and a comparatively narrow lagoonal reef Pacific, the Maldives is dependent on coral reefs for slope. Reef crest is narrow and filled with sand maintenance of land area, food, export earnings and deposition. This reef has five major islands with foreign currency from revenues. permanent vegetation and five smaller islands are in British Indian Ocean Territory (BIOT) coral reefs the stage of their territorial expansion on the reef flat itself. Lagoonal reef slope is characteristically wide at Coral reefs of British Indian Ocean Territory certain places. Reef of Peros Banhos practically (BIOT) serve to be the link between Maldivian atolls resembles the faros atoll structure of other Maldivian Islands. Circumfering a deep lagoon the main Table 3  Countrywise reef area in CIO structure of faros atoll of Peros Banhos stands to the Sr. No. Country Reef Area east of Saloman Island. This reef however, bears (in sq. km) certain signs of concern for the overall reef health as 1 India 2383.87 algal growth on reef flat is observed. Atoll of Diego 2 Sri Lanka 475.70 Garcia marks the end of linear extension of the axis line of Maldivian Atolls. This reef housed the 3 Bangladesh 04.00 southernmost British base in the Indian Ocean. Even 4 Maldives 14533.60 on the narrow reef flat of Diego Garcia a strip of 5 BIOT 854.96 island with permanent vegetation runs continuously. (mapped so far) Lagoonal reef slope shows two distinct slope profiles: the sandy shallow slope adjacent to the island and the Total 18252.13 relatively deeper slope which plunges down to the BAHUGUNA et al.: SPATIAL INVENTORY & ECOLOGICAL STATUS OF CORAL REEFS 695

lagoon floor. Coral zones can be easily identified Kamaraj University, Madurai are acknowledged for along with coral knolls present in the lagoon from the providing ground photographs of Gulf of Mannar. Resourcesat-1 image. Probably as a result of their isolation, these reefs References are the most pristine and best protected ones in the 1 Hoegh-Guldberg, O., Climate change, coral bleaching and the future of the world’s coral reefs, Mar. & Freshwater Central Indian Ocean. There are submerged banks Res., 50 (1999) 839-866. which harbour coral reefs and its flora and fauna in 2 Spalding M D, Ravilious C & Green E P, World atlas of good diversity and health. coral reefs, (University of California Press, Berkeley, USA) Country wise reef area of CIO region mapped 2001, pp. 424. under the present study is given in Table 3. 3 Venkataraman, K., Coral reefs in India, NBA Bulletin, No.4, (National Biodiversity Authority, Chennai, India) 2006, pp. 70. 4 Green, E. P., Mumby, P. J., Edwards, A. J. & Clark, C. D., Conclusion A review of remote sensing for tropical and coastal resources Baseline mapping of the Central Indian Ocean reefs assessment and management, Coastal Management, 24 covering India, Sri Lanka, Bangladesh, Maldives and (1996), 1-40. BIOT at ecological as well as geomorphic level has 5 Green E P, Mumby P J, Edwards A J & Clark C D, (Edited by A. J. Edwards), Remote sensing handbook for tropical been carried out for the first time using satellite data. coastal management: Coastal management sourcebooks 3, A comprehensive classification system has been (UNESCO, Paris) 2000, pp. 316. 6 Bainbridge, S. J. & Reichelt, R. E., An assessment of ground evolved to map the coral reefs of the world at eco- th morphological level. Mapping at ecological and truthing methods for coral reef remote sensing data, Proc.6 International Coral Reef Symposium, (Townsville), 1989, pp. geomorphic level has given significant insight on the 439-444. ecological condition of these reefs, highlighting 7 Nayak S & Bahuguna A, Coral reef atlas of India, (Space regions which have undergone degradation, or Applications Centre, Ahmedabad) 1997, pp. 96. vulnerable to degradation and the regions which can 8 Nayak, S. & Bahuguna, A., Eco-morphological zonation of selected coral reefs of India using remotely sensed data, be called pristine or in good ecological conditions. Scientific Note, Space Applications Centre, Ahmedabad, Among the Indian reefs, Gulf of Kachchh and Gulf 2003, pp. 108. of Mannar reefs are in degrading condition. 9 Holthus P F & Maragos J E, Marine ecosystem Lakshadweep and Andaman and Nicobar reefs are in classification for the Tropical island Pacific, in: Marine & vulnerable condition. In Bangladesh the only reef is coastal biodiversity in the Tropical island Pacific region, edited by J. E. Maragos, M. N. A. Peterson, L. G. Eldredgeh, found in St. Martin’s Island (fringing type). Maldives, J. E. Bardach & H. F. Takeuchi, (East-West Centre, the country with largest atolls of the world is closely Honolulu) 1995, pp. 239-278. followed by the British Indian Ocean Territory 10 Hopley D, The geomorphology of the Great Barrier Reef: (BIOT) in terms of similar kind of reefs. Quaternary development of coral reefs, (John Wiley & Sons, New York) 1982, pp. 453. The coral reefs including the lagoonal system 11 Mumby, P. J. & Harborne, A. R., Development of occupy 18,252.13 sq km area in the Central Indian systematic classification scheme of marine habitats to Ocean region. Indian reefs cover 2383.87 sq km area. facilitate regional management of Caribbean coral reefs, Highest reef area excluding the lagoons is occupied Biol. Cons., 88 (1999) 155-163. by the Indian reefs (1734.9 sq km) followed by the 12 Bahuguna, A. & Ray Chaudhury, N., Coral reefs of the world as viewed by Resourcesat satellite, SAC Courier, 31 Maldives reefs (1654 sq km). In CIO, reefs of (2007) 15-18. Maldives and BIOT are found to be in pristine 13 Bahuguna, A., Ray Chaudhury, N., Nayak, S., Sharma, S. & condition compared to the reefs of India, Sri Lanka Bhanderi, R. J., Assessment of coral reef health using and Bangladesh. satellite data, Scientific Note, Space Applications Centre, Ahmedabad, 2008, pp. 14. 14 Deshmukh, B., Bahuguna, A., Nayak, S., Dhargalkar, V. K., Acknowledgements & Jagtap, T. G., Eco-geomorphological zonation of the Authors acknowledge Dr. Shailesh Nayak, Bangaram reef, Lakshadweep, Photonirvachak, Jour. of ISRS, 33 (2005) 99-106. Secretary, Ministry of Earth Sciences, Govt. of India 15 Rajasuriya A, Zahir H, Muley E V, Subramanian B R, and Dr. M.V.M. Wafar, Coral Reef Scientist, National Venkataraman K, Wafar M V M, Khan S M M H & Institute of Oceanography, Goa for their guidance and Whittingham E., Status of coral reefs in South Asia: help in evolving the classification schemes for Bangladesh, India, Maldives & Sri Lanka, in Status of coral reefs of the world:2000, edited by C. R. Wilkinson mapping coral reefs of the Central Indian Ocean. Dr. (Australian Institute of Marine Science, Cape Ferguson, A.K. Kumaraguru and Dr. N. Marimuthu, Madurai Western Australia) 2000, pp. 95-115. 696 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013

16 Bahuguna, A., Nayak, S. & Deshmukh, B., IRS views the using Resourcesat AWiFS data, International Journal of Adams Bridge (bridging India & Sri Lanka) Applied Earth Observation & Geoinformation, 10 (2008) Photonirvachak, Jour. of ISRS, 31 (2003) 237-239. 229-237. 17 Bahuguna A., Nayak S. & Roy D., Impact of the tsunami & 18 Stoddart D. R., Coral reefs of the Indian Ocean in: Biology earthquake of 26th December 2004 on the vital coastal & Geology of coral reefs: Vol.1, edited by O. A. Jones & R. ecosystems of the Andaman & Nicobar Islands assessed Endean (Academic Press, New York) 1973, pp. 51-92.