Indian Journal of Geo-Marine Sciences Vol. 40(5), October 2011, pp. 624-634 Distribution and biology of seagrass resources of Lakshadweep group of Islands, India Nobi. E.P, E. Dilipan, K. Sivakumar & T.Thangaradjou* Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences Annamalai University, Parangipettai - 608 502, Tamilnadu, India *[Email: [email protected]] Received 8 April 2010; revised 26 October 2010 Present study explains the diversity, distribution, biomass and productivity of seagrasses in the Lakshadweep group of Islands. Seven seagrass species under five genera were recorded from nine islands and no seagrass was found at Bitra island. Out of seven seagrass species, Cymodocea serrulata was found to be dominant in the Lakshadweep group of islands whereas Halophila decipiens was found only in Kalpeni island. Biomass varied widely from 72+9 to 944+99 gfr.wt.m-2 among all the species of seagrasses. Productivity also showed clear variation within the species and between the species at different stations. Productivity of the species varied from 2.76+0.17 mgCm-2day-1 to 95.53+10.06 mgCm-2day-1 and it was in the following order of increase: H. decipiens< H. pinifolia< H. uninervis< T. hemprichii< C. rotundata< S. isoetifolium < C. serrulata. The spatial cover of seagrasses in Lakshadweep Island is more and are healthy in almost all the islands. [Keywords: Seagrass biomass, Diversity, Productivity, Lagoon, Lakshadweep] Introduction Andaman and Nicobar and Lakshadweep islands7-8. Seagrass ecosystem is one of the most widespread Unfortunately, seagrasses of these regions significantly coastal vegetation types when compared to coral and declining in their coverage and density9-11. mangrove ecosystems. Seagrasses comprise <0.02% Health of the seagrasses is usually evaluated based of the angiosperm flora, represented by sixty odd on shoot morphology, productivity, density and species1 but occur in all the coastal areas of the world biomass12-15 of persistent meadows in similar except the polar regions because of ice scouring2. It geographical areas15-17. Present study was conducted represents one of the highly productive coastal to find out the distribution and biology of the ecosystem of the world and protects the shorelines seagrasses of nine islands of the Lakshadweep by against erosion in the middle and lower intertidal and recording distribution, biomass and productivity of subtidal zones3. This ecosystem is conspicuous and the seagrasses of the Lakshadweep Islands. often a dominant habitat in shallow coastal waters and well known for its higher primary and secondary Material and Methods productivity and supports diverse floral and faunal Study area communities by generating vast quantity of detritus. Lakshadweep group of islands are scattered in the Seagrass ecosystem in the tropics and particularly Arabian Sea about 200 to 400 km off the west coast of in India has always been given with low priority in Kerala, situated between the latitudes 8°- 12° N and research by the scientific communities and longitudes 71°-74° E (Fig.1). It consists of 36 islands, environmentalists4. But, in the late nineties and early 12 atolls, 3 reefs and 5 submerged coral banks. The 2000’s, the scenario has changed slowly and started to present study was carried out in 9 different islands gain momentum. Indian seagrass habitats are mainly (Table 1) of the Lakshadweep, among them, 7 are limited to mud flats and sandy regions. It extend from inhabited (Kalpeni, Kavarathi, Agathi, Amini, the lower inter tidal zone to a depth of 10-15 m along Kadamath, Kilthan and Chethlath) and 2 are the open shores and in the lagoons around the uninhabited (Bangaram and Thinnakkara). islands5-6. Seagrass flora of India is represented by For understanding the seagrass diversity, 6 genera and 14 species, Gulf of Mannar and distribution, biomass and productivity in Palk Bay harbour the maximum species followed by Lakshadweep group of islands, field surveys were NOBI et al.: SEAGRASS RESOURCES OF LAKSHADWEEP 625 carried out in 27 marine locations, falling in 9 islands Seagrass diversity (3 sampling locations/island) during January and Sampling was carried out during low tide at inter February, 2009. Mean of the values recorded from and subtidal regions by skin diving method. Line different sampling locations in each island were transects of (100 m) were made perpendicular to the computed and presented. coastline randomly (5 numbers) at each sampling locations. Presence of different species of seagrasses along transects was recorded. Seagrass samples were identified by following the field guide18 and were confirmed in the laboratory by referring to standard literatures7,19. Seagrass biomass and productivity For biomass estimation, a quadrate (0.25 m2) was placed ten times at random and all the seagrass materials found in the quadrate were collected and washed thoroughly with the habitat water to remove debris. Moisture from the samples was removed using adsorbent paper and weighed to get the total biomass. The mean of ten quadrate samplings was considered for computing the seagrass biomass per square meter and the mean values have been expressed in terms of gram fresh weight per square meter (g.fr.wt.m-2). Changes in dissolved oxygen concentration in the water surrounding a plant community was used by several workers as measurements of the products of photosynthesis. Dissolved oxygen was measured20 and productivity of seagrasses was estimated18,21. Results Seagrass distribution During the survey on seagrass resources of the Fig. 1 Map showing the study areas. Lakshadweep islands, 7 seagrass species under Table 1 Distribution of seagrasses in the study areas. Island Latitude Longitude Salient features Kavaratti 10o32’ - 10o35’N 72o35’ - 72o40’E Located between Agatti island on the west and Andrott island on the east. Major coral reefs around island, with sandy beaches and seagrass meadows in the lagoons Agatti 10o48’ - 10o53’N 72o09’ - 72o13’E Located on the west of Kavaratti Island bestowed with 70 species of corals. Bangaram, Thinnakara 10o55’ - 10o58’N 72o17’ - 72o20’E Though the island is small the combined lagoons and Parali of these islands is large Amini 11o06’ - 11o08’N 72o42’ - 72o45’E Located between Kavaratti island in the south and Kadmat island in the north. Kadmat 11o15’52” - 11o15’26” N 72o45’41” - 72o47’29”E It is surrounded by Chethlath and Kilthan on the north, Thinnakara and Amini on the south. Kiltan 11o28’ - 11o30’N 72o59’ - 73o01’E Lies 51 km north-east of Amini Chetlat 11o41’ - 11o43’N 72o41’- 72o43’ E Lies 56 km on the north of the Anini Bitra 11o36’ N 72o11’ E The smallest inhabited island in the territory but has more than 45 sq km lagoon Kalpeni 10o03’ - 10o07’N 73o37’ - 73o39’E Isolated from the other islands lying between Androth on the north and Minicoy on the south. Corals are mainly confined to the intertidal, reef flat and slope extends up to 35 m depths 626 INDIAN J. MAR. SCI., VOL. 40, NO. 5, OCTOBER 2011 5 genera were recorded in the 9 islands (Table 2). Out Kadamath, whereas the biomass values of of 7 species, Cymodocea serrulata was found to be C. serrulata ranged from 204+77 to 944+99 gfr.wt.m-2 dominant in the Lakshadweep islands whereas recording the minimum at Kavarathi and maximum at Halophila decipiens was found only in Kalpeni Kadamath islands. island. Higher seagrass diversity was found in Agathi H. uninervis, biomass values ranged between island (6 species) and the lower diversity, in Kilthan 97+17 and 169+22 gfr.wt.m-2 recording the island (1) probably transplanted by the local NGOs. minimum at Amini and maximum at Kavarathi, whereas H. pinifolia, the biomass values ranged Biology of seagrasses between 83+7 and 100+9 gfr.wt.m-2 and was found Biomass only in Agathi and Thinnakkara islands. The biomass Seagrass biomass values varied highly with respect of S. isoetifolium varied between 104+28 and 860+3 to the species in different stations (Fig. 2). H. decipiens gfr.wt.m-2 recording the lower biomass at Kavarathi was recorded only at Kilthan with a biomass of and the higher biomass at Kadamath island. -2 79+1 gfr.wt.m . The biomass of T. hemprichii varied -2 between 106+9 and 441+99 gfr.wt.m registering the Productivity minimum at Agathi and the maximum at Kadamath Productivity values showed clear variation within island. The minimum biomass of 72+9 gfr.wt.m-2 of the species and between the species at different C. rotundata was recorded at Kilthan and the stations (Fig. 3). Productivity of H. decipiens was maximum of 880+ 107 gfr.wt.m-2 was recorded at 2.76+0.17 mgCm-2day-1 at Kalpeni. The productivity Table 2 Distribution of seagrasses in the study areas. St.1. Kavarathi; St.2. Agathi; St.3. Bangaram; St.4. Thinnakkara; St.5. Amini; St.6. Kadamath; St.7. Kilthan; St.8. Chethlath; St.9. Kalpeni Seagrass St.1 St.2 St.3 St.4 St.5 St.6 St.7 St.8 St.9 Monocotyledonae Helobiae Hydrocharitaceae Halophila decipiens Ostenf. - - - - - - - - + Thalassia hemprichii (Ehrenb.) Asch. + + - - + + - - + Cymodocea rotundata Ehrenb. and Hempr. Ex Asch + + + + + + + + + Potamogetonaceae Cymodocea serrulata (R.Br) Asch. and Magnus + + + + + + - + + Halodule uninervis (Forsk.) Asch + + - - + + - + - Halodule pinifolia (Miki) Hartog - + - + - - - - - Syringodium isoetifolium (Asch.) Dandy + + - - - + - + - Total 5 6 2 3 4 5 1 4 4 Fig. 2 Biomass of different species of seagrasses recorded in the Lakshadweep islands. NOBI et al.: SEAGRASS RESOURCES OF LAKSHADWEEP 627 Fig. 3 Productivity of different species of seagrasses recorded in the Lakshadweep islands. values of T. hemprichii varied between 7.71+0.66 and earlier from these islands25 and are not been recorded 31.99+7.16 mgCm-2day-1 with the minimum at Agathi during the study period. However, our recent survey and maximum at Kadamath islands respectively.