Galaxea, Journal of Coral Reef Studies 12: 65-75（2010）

Original paper

Reef status in the Mandapam group of Islands, Gulf of Mannar

N. MARIMUTHU1, *, J. Jerald WILSON2, and A.K. KUMARAGURU3

1 Andaman & Nicobar Centre for Ocean Science and Technology, National Institute of Ocean Technology (Ministry of Earth Sciences, Govt. of India), Dollygunj, Port Blair 744103, Andaman and Nicobar Islands, India 2 Marine Studies Unit, Department of President’s Affairs, P.O. Box 27613, Abu Dhabi, UAE 3 Department of Marine and Coastal Studies, School of Energy, Environment and Natural Resources, Madurai Kamaraj University, Madurai 625021, India

* Corresponding author: N. Marimuthu E-mail: [email protected]

* Communicated by Hiroya Yamano (Environment and Conservation Editor)

Abstract Manoli Reef Complex (MRC) and Kurusadai The environmental conditions of Gulf of Mannar are Reef Complex (KRC) of the Gulf of Mannar, southeast unique, mainly because of the coral reefs, seagrass beds coast of India were taken for this study to estimate the and mangroves, which act as spawning and feeding biophysical status of the coral reef ecosystems. This study grounds and shelters for many species of economically was conducted between the years 2006 and 2008. About important finfish and shellfish (Kumaraguru et al. 2006). 25 sites all around the islands were chosen for this study. Hence they are protected under the Gulf of Mannar Marine Among them, good Live Coral (LC) cover was recorded Biosphere Reserve. There are different types of reefs in fourteen sites. The other categories like Dead coral with observed in the Gulf of Mannar such as shore, platform, algae, Exposed reef and Rubble, Seagrass, Algal assem­ patchy and fringing type (Muley et al. 2000). The islands blage, Muddy flat and Sandy flat were also considered in in the Gulf of Mannar contain fringing and patch reefs this study. The estimated sedimentation rate of this area around them. The corals of Gulf of Mannar have already was higher in seaward sides than the shoreward sides. faced two catastrophic bleaching events, one in 1998 and the other in 2002 (Kumaraguru 1999; Kumaraguru et al. Keywords Manoli Reef Complex (MRC), Kurusadai Reef 2003) and have recovered slowly. The major issue causing Complex (KRC), coral reef, sedimentation rate concern for the coral reefs were backwash of mud and other sedimentation-related stress created after recession of the tsunami. The 21 islands in the Gulf of Mannar can be classified into 4 groups namely, Mandapam group, Introduction Keelakarai group, Vembar group and Tuticorin group. In this study, the ground truthing analysis of coral reef was The Gulf of Mannar reefs are situated around a chain of performed in the Mandapam group of islands (Fig. 1). 21 islands along 140 km stretch from Rameswaram to This Mandapam group of islands possesses two major Tuticorin in the southeast coast of India. This reef eco­ reef complexes known as Manoli Reef Complex (MRC) system is endowed with a rich variety of marine organisms. and Kurusadai Reef Complex (KRC). The main objective 66 Marimuthu et al.: Reef status of Mandapam

Fig. 1 Map showing the Manoli (MRC) and Kurusadai Reef Complexes (KRC).

of this study was to assess the status of corals of these two mentation of silt. Among them, two traps were in the sea­ reef complexes. ward side and another two were in the lagoon side. Ac­ cumulation of sediments was analyzed on monthly basis in terms of mg/cm2/d. Materials and methods ARMDES package V1.6 (Data Entry Program) Line Intercept Transect method The collected raw data were sorted and assessed using The sessile benthic community of corals was estimated AIMS Reef Monitoring Data Entry System (ARMDES using, Line Intercept Transect (LIT) method (English et V1.6 Data Entry Program - Long term reef monitoring al. 1997). About 25 study sites were chosen (Table 1) in project, Australian Institute of Marine Sciences). The the MRC and KRC and were marked in GARMIN model percentage cover was calculated for benthos, life forms GPS-12XL for continuous monitoring. A 20-meter long and also for the total Acropora and non-Acropora cate­ flexible underwater tape was laid on the reefs roughly gories. The cumulative percentage of hard coral cover, parallel to the shore with five replicates at each site. The algae and abiotic forms were also estimated using this benthos coming under the transition points were recorded package. using international codes.

Sedimentation rate Results Sediment traps were custom made, following the English et al. (1997). Each traps containing 4 plastic con­ Biophysical status of coral reef ecosystem tainers measuring 11.5 cm in height. Four traps were MRC 16 and KRC 7 had the maximum live coral cover placed in the Manoli Reef Complex to assess the sedi­ as 65.5±3.5% and 64±5.9% respectively. The lowest live Marimuthu et al.: Reef status of Mandapam 67

Table 1 Study sites at MRC and KRC SITE GPS COORDINATES SITE GPS COORDINATES MRC01 N 09°13.211′E 79°04.174′ MRC14 N 09°12.141’ E 79°09.170’ MRC02 N 09°12.325′E 79°04.534′ MRC15 N 09°13.042’ E 79°09.597’ MRC03 N 09°11.476′E 79°04.269′ MRC16 N 09°12.340’ E 79°10.284’ MRC04 N 09°11.086′E 79°04.019′ MRC17 N 09°12.149’ E 79°10.159’ MRC05 N 09°11.071′E 79°04.240′ MRC18 N 09°11.439’ E 79°08.093’ MRC06 N 09°11.263′E 79°04.461′ MRC07 N 09°11.307′E 79°05.258′ KRC01 N 09°14.978’ E 79°13.267’ MRC08 N 09°11.439′E 79°05.435′ KRC02 N 09°15.029’ E 79°12.790’ MRC09 N 09°10.465′E 79°05.295′ KRC03 N 09°15.052’ E 79°12.724’ MRC10 N 09°13.137′E 79°06.328′ KRC04 N 09°14.973’ E 79°10.955’ MRC11 N 09°12.126′E 79°06.233′ KRC05 N 09°14.752’ E 79°11.091’ MRC12 N 09°13.071′E 79°07.280′ KRC06 N 09°14.734’ E 79°13.148’ MRC13 N 09°11.241′E 79°07.141′ KRC07 N 09°14.683’ E 79°12.924’

coral cover was observed in MRC 18 (22.5±3.1%) and The quantity of silt collected during this study was KRC 2 (14.3±4%). The live coral percentage of all the significantly varied from seaward side to shoreward side. study sites is represented in the Fig. 2. The highest per­ The minimum level of sedimentation (2 mg/cm2/d) was centage of DCA was observed in the KRC 6 and KRC 2 observed in the shoreward side in the month of January sites (Fig. 2). No live coral cover was observed in MRC 2007 and the maximum of 15.6 mg/cm2/d was observed in 01, 02, 04, 05, 11, 12, 13, 14, 17, KRC 1 and 5 transects. the month of April 2008. In the case of Seaward side, the In the case of MRC 14, the entire reef was always exposed minimum of 2 mg/cm2/d was observed in January 2007 (50.7±1.9%) above sea level. The seagrass was dominant and the maximum of 30 mg/cm2/d was in May 2007 in the in MRC 12 (87.2±1.6%) followed by MRC 02 (83.8± seaward side. A test of ANOVA on the quantity of sedi­ 3.2%) and KRC 5 (77.7±0.3%) and moderate in other ments in these study sites indicated that the sedimentation sites (Fig. 3). rates were significantly varied (P＜0.05). The composition of mud (Fig. 3) was more in MRC 11 Based on the coefficient of determination value (r2 with the percentage of 89±2.3% followed by MRC 04 ＝0.702), it was evident that almost 70% of the variance in (88.9±0.4%). When compare to the Manoli Reef Complex, the dependent variable (i.e. percentage live corals) is the mud composition of the Kurusadai Reef Complex was explained by the derived regression equation (y＝−1.796x at the lower end, among them the maximum percentage of ＋72.92), and mere 30% is unexplained (Fig. 5). A signifi­ mud was recorded in KRC 5 (13.4±1.9%). The highest cant negative correlation of the % live corals with the sand cover in Manoli Reef Complex was observed in sedimentation rate is observed from the collected data and MRC 17 (91.4±3.4%) similarly in Kurusadai Reef Com­ the summary of the results is shown in the following plex, the highest sand cover was observed in KRC 4 (Fig. tabulation. 3). The algal cover (Fig. 3) was dominantly noticed in MRC 14 with a percentage of 32.1±2.1 followed by the MRC 15 (30.7±3.8%). In Kurusadai Reef Complex, the Discussion highest algal composition was observed in KRC 3 (13.9±4.4%). This study was carried out roughly parallel to the shore from shallow to deeper part (up to 42 feet) of the Manoli Sedimentation rate and Kurusadai Reef complexes. In this study, the seasonal The sedimentation rate of Manoli Reef Complex (Fig. analysis indicated that there was no significant variation 4) was estimated for two years period at monthly intervals. (P＞0.5) in the live coral cover in the study sites of MRC 68 Marimuthu et al.: Reef status of Mandapam

Fig. 2 Live coral, dead coral with algae and exposed reef and rubble cover of MRC and KRC Marimuthu et al.: Reef status of Mandapam 69

Fig. 3 Sea grass, mud, sand & silt and algal cover of MRC and KRC 70 Marimuthu et al.: Reef status of Mandapam

Table 2 Correlation coefficient table Correlation coefficient (r) Student’s ‘t’ value p df N −0.838 −11.284 ＜0.0001 54 56 p＝significance level; df＝degrees of freedom; N＝sample size

Fig. 4 Sedimentation rate of MRC

But, in the seaward side strong wave action was noticed all the times especially during the natural disturbances (Kumaraguru et al. 2005). In this case, the water becomes more turbid and inundation was occurred. The sediment­ ation rate observed in this island was correlated and re­ sulting that the seaward side is more prominent to sedi­ mentation than the shoreward side. The southeast coast of India is getting two kinds of monsoons namely Southwest and Northeast monsoons. The Southwest monsoon lasts for six months i.e. from Fig. 5 Regression analysis of live coral cover (%) with the April to September which makes Gulf of Mannar waters sedimentation rate (mg/cm2/d) at Manoli Reef Complex more rough and turbid. On the other hand, the Northeast during 2007-2008 monsoon makes Palk Bay (an adjacent coast demarcates by the Mandapam peninsula) waters murky. The highest percentage of the sedimentation was observed in the and KRC. It might due to the gradual growing nature of seaward side (site-4) in the month of May 2007 due to the the Scleractinian corals (Barnes and Lough 1999). As the Southwest monsoon period. Similarly, the lowest percent­ islands of Gulf of Mannar are lying parallel to the shore, age of silt was observed in the pre-monsoon period. the lagoon waters are most of the time observed confined. In some cases the northeast monsoon which commonly Marimuthu et al.: Reef status of Mandapam 71 disturbing the Palk Bay waters may also having its impact na checklist has been prepared (Table 3 and Figs. 6, 7). on Gulf of Mannar. This may due to the strong sediment About 48 species of Scleractinian corals of 8 families exchange from the Palk Bay to the Gulf of Mannar through were identified in this study and verified (Venkataraman the Pamban via duct (Wilson 2010). It evidenced in the et al. 2003; Veron 2000; Pillai, 1986). Among them, the higher sediment accumulation in the months of October Acropora muricata, Acropora cytherea and Pocillopora and November 2007. damicornis were dominating the reefs. The Favia pallida, A comparison study indicated that the highest sedi­ F. favus, Favites abdita, Porites lichen and P. mannarensis mentation rate observed in the MRC was two third (42 were other widely noticed corals. In the case of soft corals, mg/cm2/d) of the Palk Bay (Wilson et al. 2005) and four the Sinularia sp. and Lobophytum sp. were observed more. times lesser than the (124.49 mg/cm2/d) Lakshadweep is­ Echinoderms and Holothurians were the other forms ob­ lands (Suresh 1991). The minimum sedimentation rate served in these transects. observed was similar to Lakshadweep islands (2.69 mg/ Sedimentation rate was observed higher in seaward cm2/d) but one fold higher than that of the Palk Bay (1 mg/ side of the island, particularly during the southwest mon­ cm2/d). soon period which makes the Gulf of Mannar waters Regarding the coral cover, the study sites MRC 16 rough. The ground truthing results from this study hope­ (Shoreward side) and KRC 7 (Seaward side) of the cor­ fully helped to know the current scenario of the live coral responding islands possess the highest live coral cover. cover of the Mandapam group. This study also helped to This may due to the massive corals lying on the wave calibrate the GIS imagery of the coral reef ecosystem of breaking zone, provides a barrier like protection from the Mandapam group of islands. sedimentation to the branching corals like Acropora. Most of the branching corals were observed in the shallow waters and were exposed during low tides. But the massive Acknowledgments corals like Porites were found mostly in the deeper waters. The authors are thankful to ISRO-SAC, Ahmedabad, In overall, the lowest live coral cover was observed in India for funding and to IATCB (India-Australia Capacity MRC 2 which is located in the seaward side. It may pos­ Building Project, Dept. of Environment and Forests, Port sibly due to that it was directly lying on the wave breaking Blair) for providing training and monitoring methods zone, which was always turbid. The area lying between pertaining to Coral reef ecosystem. We thank Mr. Dilip Manoli and Manoli putti Islands was muddy where Kumar Jha, Project Scientist-1, National Institute of Ocean seagrass Halophylla ovalis predominantly observed. The Technology, Port Blair, India for his help in the prepara­ algal cover was noticed diversely in all the study sites but tion of map. Thanks are due to statistical sug­gestions ren­ dominantly observed in the MRC 14 and KRC 3. The dered by Dr. T. Ganesh, Pondicherry University, Port Blair, Caulerpa racemosa, green algae formed a velvete kind of India. sheath on the dead corals for a long stretch and giving a greenish appearance to that area. The other associated algae observed were Sargassum wightii, Ulva lactuca, U. reticulata, Gracilaria corticata and Padina sp. The abiotic forms like sand, rubble were observed more in the intertidal regions and were more in MRC 18 and MRC 14. Particularly in the case of MRC 14 the entire reef was exposed all the time and acting as a nesting and resting ground for birds. In Krusadai reef complex, the KRC 3 consists of more abiotic cover than the others. During this study the available Scleractinian coral fau­ 72 Marimuthu et al.: Reef status of Mandapam

Table 3 Checklist of Scleractinian coral fauna of MRC and KRC S.No. FAMILY CORAL FAUNA 1. I. Pocilloporidae Pocillopora damicornis (Linnaeus, 1758) 2. Pocillopora verrucosa (Ellis and Solander, 1786) 3. Stylophora pistillata (Esper, 1797) 4. II. Acroporidae Acropora digitifera (Dana, 1846) 5. Acropora muricata (Linnaeus, 1758) 6. Acropora humilis (Dana, 1846) 7. Acropora hyacinthus (Dana, 1846) 8. Acropora gemmifera (Brook, 1892) 9. Acropora intermedia (Dana, 1846) 10. Acropora cytherea (Dana, 1846) 11. Acropora valenciennesi (Edwards and Haime, 1860) 12. Montipora digitata (Dana, 1846) 13. Montipora hispida (Dana, 1846) 14. Montipora foliosa (Pallas, 1766) 15. Montipora exserta (Quelch, 1886) 16. Montipora aequituberculata (Bernard, 1897) 17. III. Poritidae Porites lichen (Dana, 1846) 18. Porites lobata (Dana, 1846) 19. Porites lutea (Edwards and Haime, 1860) 20. Porties mannarensis (Pillai, 1969) 21. Porites compressa (P. harrisoni in Veron (2000)) 22. Goniopora stutchburyi (Wells, 1955) 23. IV. Oculinidae Galaxea fascicularis (Linnaeus, 1767) 24. Galaxea astreata (Lamarck, 1816) 25. V. Mussidae Symphyllia recta (Dana, 1846) 26. Symphyllia radians (Edwards and Haime, 1849) 27. Lobophyllia hemprichii (Ehrenberg, 1834) 28. VI. Merulinidae Hydnophora microconos (Lamarck, 1816) 29. Hydnophora exesa (Pallas, 1766) 30. Hydnophora grandis (Gardiner, 1904) 31. VII. Faviidae Favia favus (Forskal, 1775) 32. Favia pallida (Dana, 1846) 33. Favia speciosa (Dana, 1846) 34. Favites abdita (Ellis and Solander, 1786) 35. Favites complanata (Ehrenberg, 1834) 36. Goniastrea retiformis (Lamarck, 1816) 37. Goniastrea pectinata (Ehrenberg, 1834) 38. Platygyra lamellina (Ehrenberg, 1834) 39. Platygyra daedalea (Ellis and Solander, 1786) 40. Platygyra sinensis (Edwards and Haime, 1849) 41. Leptastrea purpurea (Dana, 1846) 42. Leptastrea transversa (Klunzinger, 1879) 43. Leptoria Phrygia (Ellis and Solander, 1786) 44. Cyphastrea microphthalma (Lamarck, 1816) 45. Cyphastrea serailia (Forskal, 1775) 46. Echinopora lamellosa (Esper, 1795) 47. VIII. Dendrophylliidae Turbinaria crater (T. mesenterina in Veron (2000)) 48. Turbinaria peltata (Esper, 1794) Marimuthu et al.: Reef status of Mandapam 73

Fig. 6 Scleractinian corals of MRC and KRC 74 Marimuthu et al.: Reef status of Mandapam

Fig. 7 Scleractinian corals of MRC and KRC Marimuthu et al.: Reef status of Mandapam 75

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