Studies on these fragile ecosystem are scanty and the few available w ere relatively of recent attempts . But the far sighted and the intelligent local elders transplanted the sea grass beds to many of the Northern islands for controlling the erosion in the 1950s itself. The elderly locals even now call them Kavarattipullu as it was introduced from Kavaratti lagoon

Kaladharan, P

Koya, K P Said

Kunhikoya, V A

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SEA GRASS ECOSYSTEM - A LAKSHADWEEP PERSPECTIVESaid K o y a .K .R .V .A .  K u nhikoya and P. KaladharanCa licu t R e sea rch  Centre o f  CM FRI., Kozh ikode  - 673005IntroductionThe L IT .o f Lakshadw eep  , the  little specks  in the  A rab ian  Sea .scattered between 8 °00' N and 12 °30' N La titude and 71 °00 ’ E and  74 °00 ’ E Long itude  located on the L a c c a d iv e -C h a g o s  A rch ipe lago is a un ique m agnificent, but very fragile cora! ecosystem . These Islands are believed to  be fo rm ed  ( F ig -1 ) on the  subm erged portions o f Aravali m ounta in  cliffs rising from  1 5 0 0 -4 0 0 0  m deep  r id g e s  as a result o f m illions o f years of reef build ing process of w id e  ve rie ties  o f  co ra ls  and  due  to  the  pro longed geological changes taken p lace during  the  period  .) • • .s V  .  < ,•’ *w '" '  ' > -i( Fig-1) - P ic to ria l rep resen ta tion  o f  Is land form ationThe Lakshadw eep g roup  o f Is lands  (F ig  -2) (cons is ts  o f 11 inhab ited Islands , 0.58-  4.8 S q.Km  s izes ) ,13 un inhab ited  Is lands/Is le ts  , 6  subm erged  banks  and 3 coral reefs), spread in 12 atolls are s itua ted  on the  S ou th  W e s t C oas t o f India. T h e  total land availability including the inhab ited and  the un inhab ited  Island toge ther is 32 Sq.Km  (28.5Sq.Km for revenue p u rp o s e ) only. Except A ndro th , all o the r Is lands are protected by a nearly crescent sh aped  leng thy  'ree f w a ll ’ w ith  m ore  than tw o  boat channels . The enchanting greenish w a te r  a rea  { Fig -3) extrem ely  rich in flora & fauna, between the land ( Is la n d s )a n d th e 're e fw a ir  w h ich  ge ts  exposed  during  low tide  is known as lagoon .It’s depth varies betw een 0 .4  -  15 m during h igh  t ide  . These  lagoons are getting filled up rapidly due to the pe riod ic  accum u la tion  o f  dead corals, coral sand .m olluscan shells etc, Apart from 4 ,200  S q .K m  o f b iod ivers ity  rich lagoons and 20,000 Sq.Km  o f Territorial waters im pregm ent w ith  h igh va lue  fishe ry  resou rces  , it holds 4 lakhs Sq.Km  of EEZ also. Thus it becom es one  o f the  la rgest te rr ito ry  o f our Country .L.ikshaciueep-’I ''*vf'( *’i'............a a a s i s i B a ' 'Fig -3 Typical Lagoon( S u h e li)Fig -2 Lakshadw ee p  Is lands DiscussionA balanced hea lthy  lag o o n  ecosys tem  is a com p lex  chain o f d iffe ren t corrimunities at equilibrium . Sea g ra s s e s  fo rm  th e  m os t im portan t p roducer com m unity  around which others depend fo r  th e ir  surv iva l and g row th . Sea grass m eadow s o f Lakshadweep coral lagoons are know n  to  h a rb o r  dense  and rich invertebrate assem blage ( A nzan et a/.,1991). Sea g rasses  a re  su b m e rg e d  m arin e  m a c r o s c o p i c  f low enng  p lants .belongs to Potomogetanaceae and  H yd rocha r itace ae  f a m i l y  w i t h  well deve loped rh izom e beanngbranched or un b ranched  roo ts  at each node and e rec t shoots bearing several leave ( stolon) which serves as s e d im e n t traps  . T h e y  are  also involved in cycling of nutrients from water as well as se d im e n ts . T h e  c apac ity  o f sea  grasses b s ° r b ^ f  is quiet high and one S q .K m  sea g rass  can absorb  equal quan tity  o f CO ,50 Sq.Km of the trop ica l fo res ts . The sea  g ra ss  ecosysterns are  the ^productive ecosystem s in the  w orld  and have ve ry  high ratesmatter of about 300-600g dry  w t /m ^ /y r (  H a r to g ,1970; Thayer e f a/ 1975)  ^Seahave shown decis ive ro le in the  p roduc tiv ity  and  oxygen budget o f coral atoll {Qasim  &B h a tta th ir i, 1971; N a ir&  Pillai ,1972; K a ladha ran  & D av id  Raj ,1989). D e g ra d a tio n  o f th^ key stone com m unity  in an ecosys tem  leads to  the  b reakage  o f the  co m p le x  bu t balanced web and tr iggers the total co llapse  o f  the  eco sys tem  .Lakshadw eep sea grass -  B r ie f  h is toryStudies on these frag ile  e co sys te m  are  scan ty  and the fe w  ava ilab le  w e re  relatively of recent a ttem pts  . But the  fa r  s igh ted  and the  in te ll igen t loca l e lders  transp lan ted  the sea g rass beds to m any o f the  N o rthe rn  is lands fo r  con tro lling  the e ro s io n  in the  1950s itself. The e lderly  locals even  n o w  call them  K avara tt ipu llu  as it w as  in troduced  from Kavaratti lagoon. Sea g ra sse s  th u s  tra n sp la n te d  e s tab lished  itse lf in to  a healthy ecosystem  in short t im e  ex tend ing  to  40 - 60 m w id e  a rea  from  the  t ida l line to the deeper zone. Until the  last decade, th e  centra l 2 /3  o f  e ach  lagoons w e re  covered  with dense g row ths  o f sea g rasses  m ixed  w ith  rich b io m a s s  o f d iffe ren t sea  w e e d  species, particu larly  Gracila ria  spp. T he  sea grass leaves and sea  w eed  fra g m e n ts  regularly fo rm ed ‘cush ion beds ' all a long the  beach w h e n  th e y  w e re  seasona lly  w a s h e d  ashore . The shoots  o f sea grass beds, es tab lished  in the  lagoons, trapped  th e  sed im en ts  and the rh izom es & roots held the sand  partic les  f irm ly  a nd  e ffec tive ly  a rres ted  the  erosionMoreover, they helped in es tab lish ing  a ve ry  hea lthy  critica l habitat by supporting  the m ultip lication and es tab lishm ent o f w ide  verities  o f  b e n th ic  co m m un it ie s  . F urthe rm ore , the 'sediment trappe rs ’ p ro tec ted  the  frag ile  co ra l po lyps  from  ge tt in g  killed by e sediments . T he  recent large sca le  cora l m orta lit ies  reported  from  Lakshadweep cou ^ be due to  the  sea grass des truc tion  and  its resu ltan t sed im en ta tion . T he  removal o f  sea grass shoots leads  to  s tir r in g  up o f sa n d s  &  sed im en ts . S uch  partic les tra n sp o rte d  by th e  w a v e s  and cu rren t, s e tt le d  on th e  live  po lyps  instantaneously kill them . T he  dead  corals, particu la rly  the  branch ing co ra ls , j|^gsmall p ieces ( sh ing les ) tra nspo rted  by cu rren t & w a v e  actions get d e p o s ite  relatively deeper parts o f the  lagoons. T h is  accretion and seasonal filling u p  O' ^ticularly reduces the dep ths at v a ry in g  leve ls. T he  re su lta n t w a rm ing  o f lagoo '^ ' andduring low  tides fu rthe r w o rse n s  th e  cond itions  o f  th e  vu lne rab le  c o m m  acce lera tes the im ba lances in the  ecosys tem . ■, ,,rseryg ''° 'J '^°Apart from  these the sea g ra ss  m eadow s acted as the  b reed ing a nd  nu  gxtent not only fo r  the  m ajority  o f the  re s id e n t s tocks  o f  th e  a n im a ls  but a lso  ® W ealthy to the non res ident stocks w h ich  seaso na lly  v is it the  lagoons. A lso , th e  li'/® year, productive lagoons intern suppo rted  the  needy loca ls  w ith  g ood  ca tches  Till 15-20 years back, a lm os t the  en tire  fresh  fish  re qu irem en ts  d u r in g   ^ p resen tly  months ( July -  August) o f e ach  Is lands  w ere  m et b y  the  respective  proba^'.^'^^many of the lagoons has becom e barren & non productive. !t is believed w ith  hi9 ^,^g||abili^y- that the sea grass habitat des truc tion  is respons ib le  fo r  the  reduction  if  ^ ^It is high time that immediate rem edia l m easures are w o rked  out fo r  theSpecies &  s ta tusA total of 6 species of sea grasses , Cymodocea rotundata, C. serrulata, Haiodule uninervis, Halophila ovata, Syringodium isoetifolium  and Thalassla hemprichii occurred in the Islands (Kaliaperumal et a/.,1989 ). V ictor et a/., ("ISSS) has reported relatively dense growth of sea grasses in almost all the Islands. Structure of dominant sea grass vegetation from three coral atolls o f Lakshadweep was described by Jagtap (1998). Anzari et ai, ('1991) reported a sea grass vegetation cover of 0.05 Km^ with 895 g / wet biomass in Agatti atoll & 0.34 Km^with 720 g /m ^ wet biomass in Kavaratti atoll. All these studies conducted 15-25 years back on a nearly virgin habitat with minimal disturbances were mostly aimed at som e specific problems only . Subsequently, Jagtap { 1998) has reported a sea grass vegetation cover o f 0.005 Km^ only with dry biomass of 0.74 tonnes at Agatti a to ll. This shows a drastic reduction in the sea grass vegetation in Agatti atoll This is the case with m any o ther islands like Kavaratti .Minicoy .Kiltan etc. The recen t, 2009-11, observations at Agatti,Kavaratti & Minicoy lagoons revealed decline in the sea grass vegetation cover in these lagoons at an alarming proposition. Drastic changes such as exponential increase in the turtle population in recent years has occurred due to increased anthropogenic activities and conservation policies. This necessitates a through detailed study on a holistic basis. The investigations should necessarily look in to the aspects like present status, level o f sea grass destruction, coral mortality rate, lagoon filling (accre tion) rate, productivity, community assemblage, fish species diversity and catch rates from the lagoon as well as from  the open sea around each atollSea grass destructionsSea grass habitat destructions are known to be caused mainly due to the increased anthropogenic activities , foraging by sea urchins and • turtles. Historical decline in sea grass beds of Maho & Francis Bays, St.john,Vergin Islands has been attributed to heavy boat traffic & grazing by green turtles (W iliams ,1988). Over grassing by sea urchins & resultant destructions has been reported from Jamaica (Cam pefa/., 1973), Florida UbA(R o s e  e t a!.. 1999), G u lf  o f M exico  & C a r ib b e a n  (G reen  w ay, 1995; H eck & Valentine ,1995) and Kenya (Alcoverro &Fig -4 Turtle dung Fig -5 Kavaratti LagoonMariani ,2002). Deraniya gala (1 9 6 1 ) ;  Frazier (1971 ); Agasthesapillai &Thiagarajen (1979) have recorded C ym odocea  & Haloph ila  in the turtle stomach. Mortimer (1979) has reported Thalasia hem pe rch i i  favoritism by C/ie/o/i/a myc/as. Kar (1980) recorded Posidonia ocean ic  & Syr ingod iyum  sp. along with som e sea weeds in turtle stomach ,( Fig -4)Personal observations from 1987 -88 onwards at 4 important lagoons (Agatti. Kavaratti,M in icoy & Kalpeni) and one artif ic ia l bay at Andro th  showed that the anthropogenic activities and sea urchin caused destruction were almost uniform in all theses lagoons & the bay. However, the turtle densities varied w ide ly . The turtle densities were relatively very high at Agatti (Highest, 205 -250 / Sq.Km in 2008-09) Minicoy & Kavaratti (Fig -5 ), the sea grass destruction too was very high in these lagoons . Whereas, sea grass habitat at Kalpeni lagoon (Fig -  6), where turtle population is scarce , remained intact with extensive coverage and profuse growth . In the recent years Kalpeni Dweep Panchayath was forced to divert the ir labour forces to clean the beaches due to the characteristic foul smell emitted from  the dead and decaying (Fig- 7) hick deposits of sea grass /seaweed foliages on the beaches. The Androth Bay (Fig -8) which has experienced maximum anthropogenic activities am ong the Islands in recent years on account of the construction o f break waters , passenger berths and jetties in a relatively very small area. The boats /vessels traffic in the limited ( small) Bay area is the highest among all Islands. However, there  is very litt ie turtle  sighting records at Androth. The sea grass beds here have in fact expanded in rapid speed inside the Bay as well as the reef (Fig -9 ) around the Island.Turtle S tatusT h e  com m on  species o f  m arine  tu rt les  viz. C i ie io n ia  m y d a s  ,L^p i '^oc lie it^s  o livacea .E re tm oche iys  im b r ica te  & D e rm o ch e lys  co r iacea  are known to occur m Lakshadweep Islands (Bhasker ,1978;1979;, S ilas,1984). Lai IVIohan (1989) r e c o r d e d  sightings and nesting of 4 species . L a te r , the Wild life Institute of India conducted extensivesurvey (Triphathy e ta l.2002 ).  Declined predation, d ue  to  the  decline in the  p redators  liketiger sharks, the legal protection by categorizing them in the endangered group ,its longe' '^^V and confinement into relatively smaller (lagoons) areas has led to proliferation sod exponential increase of turtle density in many of the lagoons in recent years. While  studying the implications of conserving an ecosystem m o d if ie r : Lai Aparna e ta l.  f2010) caut'O^® that the increasing green turtle {C he lon ia  m ydas)  densities substantially alters sea meadows. The study was conducted in Agatti lagoon. The turtle density in Agatti in 2008 -09 period was about 205-250 /Km^ (Persona l observation). Subsed'^®^ observations in 2010 & 2011 has shown considerable reduction in numbers inside lagoon, due to their tem porary regular migration to the western side, where patches o sea grass beds exists, of the Island during high tides. Simultaneously due to the pressure and competition at Agatti some of the turtles migrated to Bangaram,Thinna'^^'^^^ Parali lagoons and probably to Kavaratti lagoons in search of new pastures and the invasion these lagoons also are almost com plete ly defoliated (Fig -10). ^biomass of rhizomes and roots in an unit area in Agatti -  Bangaram lagoons were found to be considerably more compared to shoots. In spite of the migrations the density at Agatti is very high .ConclusionThe sea grass habitats o f Lakshadweep islands is the most important l<ey stone critical habitat in the lagoon ecosystem. The health and very survaiva! of the various communities ( assemblage ) of the lagoon ecosystem depends on the existence of the sea grass beds. Mainly 3 factors viz. anthropogenic activities, sea urchin foraging and turtle grazing affect the survival o f sea grass habitats. In the case of Lakshadweep turtle (grazing) seems to be the most important ecosystem modifier. The rapid increase in the turtle densities, particularly in the Northern Islands & Minicoy, had a very damaging and deleterious impact on the sea grass beds in the respective lagoons.The alterations in the ecosystem, large scale coral mortality and resultant reduction in the lagoon depths .resultant increase in the sea w ater temperature in side the lagoon and the open sea (Average temperature increase was highest in Arabian/Lakshadweep Sea in recent years-  Vivekanthan, 2011.) m ight have adversely affected the availability of the fishery resources. This might be one of the reasons fo r the collapse of life line tuna (pole & line) fishery in Lakshadweep in general and the Northern Islands and Minicoy in particular. In fact, fish landing in Kalpeni has shown remarkable increase in recent years and the decline in the catches at Androth was relatively very less ? . The socio economic impacts on account of the collapse of the Lakshadweep pole & line fishery in recent years has to be looked in to properly. Any further alterations in the habitats has to be prevented immediately, to maintain the equilibrium o f  t h e  habitats. It is very essential for the very existence of the assemblages including the ecosystem modifier turtles.Herding the turtles ,confinem ent in the "link mesh" cages /enclosures and the development of the turtle watch tourism would prevent /restrict the free run This will support in the restoration of the ecosystem as well as promote ecotounsm. A link mesh protected lagoon based pen culture extended up to 12-15 feet (during high tide) deep lagoon areas, with fin fishes , lobsters etc, is another option for the ecosystem restoratioa T h i s  would instantaneously enable the growth of the shoots (extensive grazing /nibbl ng has mainly effected the foliages (shoots) only and rhizome biomass with roots remains almost intact). This would also indirectly ensure the increased fresh fish availability as well as employment opportunities to the locals.Apart from these. It is also suggested that a detailed investigations on a holist^^c basis may be under taken immediately in order to understand various ^spects hke ^  present status of habitats, level of destruction, coral mortality rates,rates, productivity, community assemblage, fish species diversity and catches from lagoon as well as the open sea around each atoll.Fig -6 -Ka lpen i lagoon F ig - 7 - Dead & decaying Sea grassFig -8 -A ndro th  Bay with luxurious growth Fig -9 -A n d ro th  reef with sea grassF ig - 1 0 - Grazed m eadow in the  lagoonSuggested  Read ingAnsari, Z.A., Rivonker, C.U.. Ramani. R and A. H. Parulekar. 1991 . S eag rass  hat)ita^ complexity and macrcinvertebrate in Lakshadweep coral reef lagoons Arabian Sea Reefs, 10: 127-131.Bjorndal, K. A. 1980. Nutrition and grazing behavior o f the green turtle Chelonia  Marine Biology 56: 147-154.Camp, D. K., S. P. Cobb and J.V. Breedfield. 1973. Overgrazing of seagrasses by a regular urchin. Lytech inus variegatas. B ioScience  23: 37-38.Greenway, M. 1995. Trophic relationship of macrofauna within a Jamaican seagrass meadow and the role of the echinoid Lytech inus variegatus  (Lamarck). Bulletin o f  Marine Science, 17 (3): 719-736.Hartog den. C. 1970. The seagrasses  o f  (he world. North Holland. Amsterdam, 275PPJagtap, T.G.1998. S tructure of major seagrass from three coral reef atolls of Lakshadweep, Arabian Sea India. Aqua t .Bat.. 60 (4): 397-408.Kaladharan, P. and I. David Raj. 1989. Primary production of seagrass Cymodocea  serrulata and its contribution to the productivity of Amini atoll, Lakshadweep islands, Indian J. mar Sci., 18; 215-216.Kaladharan, P, K.A. Navas and S. Kandan, 1998. Seagrass production in Minicoy atoll of Lskshadweep Archipelago. Indian J  .Fish., 45  7 9 - Q3.Kaliaperumal, N., P  Kaladharan and S. Kalimuthu. 1989. Seaweed and Seagrass Resources, Bull. cent. mar. Fish. Res. Inst., 43:162-175.Kar, C. S. 1980. The Gahirmatha Turtle Rookery along the coast of Onssa, India. lUCN/SSC M ar Tuiiie Newsletter. No. 15: 2-3.Lakshmanan, K.K. and S. Rajeswari. 1982. The new record of Thalassla hemprichii Ehrenb.) Aschers. from the main coast of India. C urr  Sci., 51; 373- 374.Qasim, S.Z. and PM .A. Bhattathiri. 1971, Primary productivity of a seagrass bed in Kavaratti atoll (Laccadives), l-lydrobiol., 38; 29-38.Rose C D W  C. Sharp and W. J. Kenworthy. 1999. Overgrazmg of a large seagrass bed by the sea urchin Lytechinus ariegatus  in Outer Florida Bay. Marine Eco gy Progress Series, 190: 211-222.Thayer, G.W., D A. W o lf and R B. Williams. 1975 T h e  i m p a c t  of man on seagrass system, American Sociologist, 63: 288-296.Wlliams, S.L, 1988. Thatassia tes tud inaum  producWiiV  and grazing by greenturtles in a highly d is tu rbed seagrass bed, M a r  S/o/., 98 (3). 447

Sea grass Ecosystem - A Lakshdweep perspective

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Sea grass Ecosystem - A Lakshdweep perspective

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