Interrelation Among Coral Reef and Sea-Grass Habitats in the Gulf of Mannar

Full Length Research Paper

Interrelation among coral reef and sea-grass habitats in the Gulf of Mannar

R. Uma Maheswari1*, V. Naganathan2 and J. K. Patterson3

1Arulmigu Palaniandavar, Arts College for Women, Chinna Kalayamputtur, Palani – 624 601, Tamil Nadu, India. 2District Forest, Atthur District, Salem – 636121, Tamil Nadu, India. 3SDMRI, Tuticorin, Tamil Nadu, India.

Accepted 29 April, 2011

The Gulf of Mannar consists of ecologically sensitive important habitats such as: coral reef and seagrass. Though each has its own function and importance, two are closely interrelated and supporting each others in function. The majority of the reefs are formed around the 21 islands, while vast sea grass beds are seen in the shoreward side of each islands. In most cases the seagrasses bordering the coral reefs play important role in limiting sedimentation on the coral reefs and help in protection. The coral reefs help in controlling erosion of islands and thereby protecting destruction. These habitats are highly productive and so economically important. The physical, chemical and biological data collected from Manoli Island of Mandapam group of the Gulf of Mannar clearly reveal the interrelationship in enhancing the associated resources, particularly fishes and other invertebrates due to constant supply of nutrients and other favourable environmental factors. The ‘transient’ coral and seagrass associated fishes use these habitats for shelter, food and breeding. During windy and turbulent period in the Gulf of Mannar (April to August), the water is highly turbid and most dense seagrass beds are disturbed because of strong wave action and this period the nearby reefs act as major shelter point to the associated fish resources of seagrass areas. The ecological and economical use of these two important habitats stresses the need for their proper conservation and management to sustain the benefits.

Key words: Gulf of Mannar, interrelation among coral reef and sea-grass habitats, physical, chemical and biological data.

INTRODUCTION

India has a coastline of about 7500 km including that of et al., 1995). A number of coastal areas along the Indian island territories and comprises 60 coastal districts. The coast are rich in marine biodiversity and have unique coastal environment is very dynamic with much cyclic flora and fauna that needs to be preserved as live natural and random process owing to a variety of resources and heritage. Marine environment accounts for 71% of the habitats. Further the coastal ecosystems are the most earth’s surface and play an important role in the productive ecosystems on earth. India is one of the sustenance of life. Vegetation growing along the coast twelve – mega biodiversity areas of the world with 4500 such as: mangroves, macro algae, seagrass and sand wild species of plants and over 7700 wild species of dune plants play an important ecological role in the animals. There are about 448 wildlife sanctuaries, 8 maintenance of the coastal ecosystem and their biosphere reserves and 85 national parks in India. Three productivity. In the first instance, the organic matter biosphere reserve, three national parks and 13 wild life produced by such vegetation enhance the biological sanctuaries are located on the coastline (Krishnamoorthy, productivity of the coastal ecosystem (Wafar, 1988). Many food webs include components that encompass multiple habitats, implying spatial and tropic linkages between these habitats. Tropic linkages between spatially *Corresponding author. E-mail: [email protected]. discrete habitats can occur due to movement of food

194 Int. J. Biodvers. Conserv.

resources (for example, nutrients, detritus and prey) and and fin fishes were carried out. The assessments on the movement of consumers (Polis et al., 1997). These cross benthic categories are also discussed subsequently. habitat linkages can have important ecological consequences, especially by increasing productivity in the recipient area. In some cases, this maintains higher METHODOLOGY populations of consumers than would otherwise be supported (Bustamante et al., 1995). The filter feeders The Gulf of Mannar is one of the coral reefs rich areas of India situated in the southeast coast of India. The coral reef needs the create extra levels in aquatic food chains that tends to be following for their perfect growth. They are: constant salinity, warm more complex than terrestrial ones (Margulis and water between 27 and 30°C, clear and clean water and sufficient Schwartz, 1988; UNEP, 1992). nutrient levels. The highest atmospheric temperature recorded was Nearly 60% of the human population which occupy the 32°C and the lowest was 30°C. Due to rains, land run – off and coastal zone, exploit the coastal resources (Kathiresan sewage input, salinity level at Rameswaram showed the lowest level of 28%. The highest level of salinity was observed in places and Rajendran, 1996). Among the islands of Gulf of were land drainage was limited. The pH level was similar in all the Mannar, only the Manoli Island shows rich diversity and selected locations. The study was carried out in Manoli Island of the density of coral. The Hare Island supports extensive Gulf of Mannar. A permanent monitoring site has been fixed for the corals on the southern west end, but not as much in monitoring. The site was selected according to the presence of all comparison to Manoli Island (Jeyabaskaran and Lyla, two habitats nearby. The Manoli Island (N 09013.300’E 1996; Kannaipar, 1997). Coral reef fish in tropical waters 079008.592’) is rich in corals and seagrass beds. In the permanent monitoring site, physic - chemical and biological parameters were can move between different marine habitats in close analyzed separately for reef area and nearby seagrass area. proximity, including mangroves and seagrasses The chemical analysis was carried out by following APHA (1992). (Cocheret de la Moriniere et al., 2002). Acid and double distilled water washed ploythene plastic bottles Coral reefs and seagrasses are fundamentally were used for collection of water. Temperature and PH was connected ecosystems. Seagrasses provide spawning measured in situ. Dissolved oxygen and salinity were estimated in and nursery ground for many of the species of animals the laboratory immediately after collection on the same day. Measurement of nitrite, nitrate, phosphate were made by who spend their adult lives on the reefs. In return, the Colorimetry methods using HITACHI U – 2000 UV – VIS coral reefs provide shelter for the sea grasses and their Spectrophotometer within 24 h period. The water samples were inhabitants, while the calcium carbonate eroded from the collected every month and the physico-chemical parameters such reef provides sediment from which the sea grasses grow. as: temperature, salinity, transparency, pH, dissolved oxygen, TSS, However, the reciprocity of these linked ecosystems is turbidity and nutrients were analyzed using standard methods. Plankton samples were collected from surface water using plankton not limited to benefits, threats to one have consequences nets, biomass, density and primary productivity were measured to both. using standard methods. Macro benthos was collected from the Tropical seagrasses are important in their interactions bottom using grab and the densities of the major groups were with coral reefs. All these systems exert a stabilizing analyzed. The aforesaid parameters were analyzed separately in effect on the environment, resulting in important physical coral and seagrass areas. and biological support for the other communities The benthic cover assessment was carried out in October 2007, January 2008, April 2008 and July 2008. The benthic cover around (Amesbury and Francis, 1988). Barrier reefs protect the islands was assessed by Line intercept transect (LIT) method coastlines, and the lagoon formed between the reef and (English et al., 1997). The fish diversity and abundance was the mainland is protected from waves, allowing the assessed visually through belt transect method. Before, starting the seagrass communities to develop. Seagrasses trap in-depth study, a general preliminary survey was conducted to sediment and slow water movement, causing suspended assess and observe the benthic community using manta tow method (Done et al., 1982). The assessment in the seagrass area sediment to fall out. This trapping of sediment benefits 2 was carried out with the use of 0.5 x 0.5 m quadrates (Saito and coral by reducing sediment loads in the water. Atobe, 1970).

Study area RESULTS

The Gulf of Mannar (GoM) is one of the four major coral Physico-chemical parameters reef areas of India, covering an area of approximately 10,500 sq. km from Rameswaram to Kanyakumari (Map In Manoli Island, temperature level was between 27.1 1). The area includes a chain of 21 coral islands and 32.6°C in the reef area and between 27.3 and 32.8°C surrounded by fringing reefs and patch reefs rising from in the seagrass area with the maximum in June 2008 and the shallow sea floor. The interrelationship between these minimum in January 2008. Salinity did not show much two potentially dynamic habitats was studied in Manoli difference as it ranged between 34.7 and 36% during the Island of Mandapam group of the Gulf of Manna. The study period. pH was between 7.8 and 8.2 in all the physico-chemical parameters of the sea water around the months in both the habitats. Turbidity ranged between 2.9 islands were analyzed, qualitative and quantitative and 11.6 NTU with the maximum record in July 2008 and analyses of plankton, primary productivity, macro benthos minimum in October 2007 in both reef and seagrass

Maheswari et al. 195

Figure 1. Temperature.

Coral reef area ) t

p Sea grass area p (

y t

i 35 n i l a S

Figure 2. Salinity.

areas. TSS was highest in June 2008 with 105 mg/l and Biological parameters lowest in October 2007 with 51 mg/l in the reef area and it was between 53 and 115 mg/l in the seagrass area. Phytoplankton density in Manoli Island ranged between Transparency was highest in December 2007 with 3.8 m 53486 and 63542 cells/l, with the maximum in April 2008 and lowest in the month July 2008 with 1.1 m in the reef and minimum in June 2008 in the reef area, and between area and it was between 1 and 3.5 m in the seagrass 54120 and 64250 cells/l in the seagrass area. area. Dissolved oxygen values in all the months ranged Zooplankton density ranged between 10306 and 15245 between 4.65 and 4.96 mg/l in both ecosystems. Calcium cells/l, with the maximum in June 2008 and minimum in values ranged between 400 and 560 mg/l with the November 2007 in the reef area, and between 11240 and highest in July 2008 and lowest in November 2007 in the 15950 cells/l in seagrass area. Plankton biomass ranged reef area and between 440 and 600 mg/l in the seagrass between 2.3 and 4.9 g/m3 with the highest in the month area. Magnesium values between 1140 and 1526 mg/l April 2008 and lowest in June 2008 in reef area and with the maximum in April 2008 and minimum in between 2.5 and 5.2 g/m3 in the seagrass area. Primary November 2007 were obtained in the reef area and productivity ranged between 3.6 and 6.5 g/m3 with the between 1250 and 1612 mg/l in the seagrass area. maximum in April 2008 and minimum in June 2008 in the Phosphate values ranges between 2.15 and 3.28 µg/l reef area, and between 3.9 and 6.7 g/m3 in seagrass with the highest in June 2008 and lowest in January 2008 area. The details of plankton assessments are given in in the reef area and between 2.45 and 3.81 µg/l in the the Figures 13 to 16. seagrass area. Nitrate concentrations ranged between Among the macrobenthic communities, gastropods 0.36 and 0.54 µg/l with the maximum in May 2008 and formed the dominant major group and it was between minimum in June 2008 in the reef area and between 0.42 5.03 and 6.31/m2 in the reef area and between 6.03 and and 0.71 µg/l in the seagrass area. The values of nitrite 7.62 m2 in the seagrass area. This was followed by ranged between 0.02 and 0.08 µg/l in both the habitats. bivalves, with a density of 1.96 and 4.02 m2 in the reef The details of physico-chemical parameters are given in area and between 1.95 and 4.53 m2 in seagrass area. the Figures 1 to 12. The densities of polychaetes, echinoderms, scaphopods

196 Int. J. Biodvers. Conserv.

10.0 Coral reef area Sea grass area

H 8.0 p

6.0

Figure 3. pH

Coral reef area 14.0 Sea grass area

) 12.0 U

T 10.0 N (

y 8.0 t i d

i 6.0 b r 4.0 u T 2.0 0.0

Figure 4. Turbidity.

100.0 )

l 80.0 / g

m 60.0 (

Coral reef area S

S 40.0 Sea grass area T 20.0

0.0

Figure 5. Total suspended solids (TSS).

and crustraceans were not high. The details of 42.25 and it increased to 43.25% in ten months. The macrobenthos densities are given in the Figures 17 and percentage DCA (Dead coral with algae) was between 18. 12.87 and 16.25%, while the percentage abiotic factors were between 15.23 and 18.44%. The percentage algae was between 12.25 and 13.85 and others were between Benthic community structure of reef area 9.22 and 14.77%. Acropora branching corals were the dominant coral type with around 12% followed by Percentage of live coral cover during October 2007 was massive corals and Acropora foliose corals. The details

Maheswari et al. 197

) 9 m

( Coral reef area

c Sea grass area n 6 e r a p s

n 3 a r T

Figure 6. Transparency.

9 Coral reef area Sea grass area ) l /

g 6 m (

O D 3

Figure 7. Dissolved Oxygen (DO).

550 ) l / g m (

400 Coral reef area m

u Sea grass area i c l

a 250 C

100

Figure 8. Calcium.

are given in Figures 19 and 20. 31.05% followed by T. hemprichii with 20.9%. Shoot density was high for C. serrulata (124.35 shoot/m2) followed by T. hemprichii with 78.62 shoot/m2. Biomass Benthic community structure of seagrass area was also high for C. serrulata with 95.61 g dwt/m2 followed by T. hemprichii with 54.02 g dwt/m2 (Figures 21 In Manoli Island, the percentage of seagrasses near the to 23). permanent study site was 45%. Totally 8 species of seagrasses were recorded, they are as follow: Thalassia hemprichii, Halphila ovalis, Halophila decipiens, Abundance of fish Cymodocea serrulata, Halodule pinifolia, Halodule uninervis, Syringodium isoetifolium and Enhalus The abundance of fish was random and reasonably high acoroides. Among these, C. serrulata was dominant with during the study period. The most abundant fish species

198 Int. J. Biodvers. Conserv.

) l

/ 1600 g m ( 1450 m u i

s 1300 e n

g Coral reef area

a 1150

M Sea grass area

1000

Figure 9. Magnesium.

5 ) l / 4 g µ (

e 3 t a h

p 2 Coral reef area s o h 1 Sea grass area P

Figure 10. Phosphates.

) 4 l /

g Coral reef area µ

( 3

e Sea grass area t a

r 2 t i

N 1

Figure 11. Nitrates.

recorded in the reef area were Lethrinus nebulosus, Chaetodon sp., Scarus, Siganus ghobban, Sardinella Lethrinus microdon, Lethrinus ornatus, Lutjanus gibbosa and Odonus niger. The most common fish lunulatus, Lethrinus lutjanus, Lethrinus malabaricus, species recorded in the seagrass area were Lutjanus Lethrinus fulviflamma, Carangoides malabaricus, lutjanus, L. malabaricus, Terapon sp., Amphiprion sp.,

Maheswari et al. 199

0.1 Coral reef area

) Sea grass area l / g µ (

e 0.05 t i r t i N

Figure 12. Nitrites.

70000

Coral reef area Sea grass area ) l /

s 60000 l l e c (

y t i s n e

D 50000

40000

Figure 13. Phytoplankton density.

18000 Coral reef area Sea grass area 16000 ) l / s l l 14000 e c (

t 12000 i s n

e 10000 D

8000

6000

Figure 14. Zooplankton density.

200 Int. J. Biodvers. Conserv.

6 Coral reef area Sea grass area 5 ) 3 m

/ 4 g (

s 3 a m o

i 2 B 1

Figure 15. Plankton biomass.

8 Coral reef area ) 3 Sea grass area

m 7 / g (

6 y r i

v 5 i t c

u 4 d o r 3 p

r 2 a m i

r 1 P 0

Oct'07 Nov'07 Dec'07 Jan'08 Feb'08 Mar'08 Apr'08 May'08 Jun'08 Jul '08

Figure 16. Primary productivity.

Coral reef area 7 6 5 2 m / 4 y t i s

n 3 e D 2 1 0 Oct'07 Nov'07 Dec'07 Jan'08 Feb'08 Mar'08 Apr'08 May'08 Jun'08 Jul'08

Gastropods Bivalves Polychaetes Echinoderms Scaphopods Crustaceans

Figure 17. Macrobenthos in Coral reef area.

Maheswari et al. 201

Seagrass area 9 8 7

2 6 m /

y 5 t i

s 4 n e

D 3 2 1 0 Oct'07 Nov'07 Dec'07 Jan'08 Feb'08 Mar'08 Apr'08 May'08 Jun'08 Jul'08

Gastropods Bivalves Polychaetes Echinoderms Scaphopods Crustaceans

Figure 18. Macrobenthos in Seagrass area.

y 50 t i

n 45 u

m 40 m

o 35 c

i 30 h t

n 25 e b

20 f o 15 r e

v 10 o C

5 % 0 Live coral DCA Algae Abiotic Others

Oct'07 Jan'08 Apr'08 Jul'08

Figure 19. Benthic community structure of reef area.

14 y r o

g 12 e t a c

10 l a r

o 8 c

e v i

l 6

f o

r 4 e v o 2 C

% 0 ACB ACT ACF ACD ACE CM CB CE CS

Oct'07 Jan'08 Apr'08 Jul'08

Figure 20. Coral types.

202 Int. J. Biodvers. Conserv.

Sea grass species composition

10.2 20.9%

16.1% 2.7%

8.15% 7.3% 3.6% 31.05% Thalassia hemprichii Halophila ovalis Halophila decipiens Cymodocea serrulata Halodule pinifolia Halodule uninervis Syringodium isoetifolium Enhalus acoroides

Figure 21. Percentage distribution of seagrass species.

150

120 2 m 90 s t o

o 60 h S 30

0 Thalassia Halophila Halophila Cymodocea Halodule Halodule Syringodium Enhalus hemprichii ovalis decipiens serrulata pinifolia uninervis isoetifolium acoroides

Figure 22. Seagrass shoot density.

120

2 2 m \ m / t t w w 60

y y r r D d 30

0 Thalassia Halophila Halophila Cymodocea Halodule Halodule Syringodium Enhalus hemprichii ovalis decipiens serrulata pinifolia uninervis isoetifolium acoroides

Figure 23. Seagrass biomass.

Maheswari et al. 203

) 2 15 m 0

0 12 1 ( 9 e c

n 6 a

d 3 n u

b 0 a

h . r s p s s a s n s s n n ta e i s a i m . s u u s u . u a o s g s p a u .. t n u m su o t .. c c d a tu a i .. a tu p s F r a n la a ic d a o i c to b a m n . s a a o b b o u tj r m lo ro rn b d lu e b l s ig n l b u a g n lu a la u c o a in o a o u s u a e u m ib r al o u b if b i l h h lic ru n b d n g n p l s la lv e m s a s m g a u o w s n o o m A s u a u n s u m u is C s n h d a u u r la tr s u n f s u in e r u a t rc e x th el n u n ja m s u n r es n e r c n O n a o e l ja t s u n i th e h ca ca e e r r in c e t u u n ri hr e id p p s p p o A d o h u L n a h t L o ru m S u A o U th r g p L ja tj t e g a e n m o a r e t u e L n P a m n S a in u L L a P ig a S p L ar S s ym E C P G

Oct'07 Jan'08 Apr'08 Jul'08

Figure 24. Abundance of fish in the reef area.

) 2 15 m

0 12 0 1 (

9 e

c 6 n a

d 3 n

u 0 b a

h . . s p p . s i s p u s s a n s s n u u .. s F o n s a c s . o p io u tj ri lo o b a r e lu a u ab ib r ip en s b b l g Te h p u la e a a p u n a n m ll m ar ja m s s e A t s u e in P Lu u rin id rd n th o a tja e g S u L an L ar C

Oct'07 Jan'08 Apr'08 Jul'08

Figure 25. Abundance of fish in the reef area.

C. malabaricuss, S. gibbosa and Parupeneus sp. The the pH level. The dissolved oxygen concentration was details are given in the (Figures 24 and 25). higher in the coral reef environment. The low level of dissolved oxygen was recoded during summer season due to the higher surface water temperature. The nutrient DISCUSSION level can also have consistent impact on both the coral reef and sea grass ecosystem. The coral reefs are more In the present study, the temperature recorded that the sensitive to the changes in the nutrient level in the summer season was maximum. The increasing trend of ambient environment, especially nitrogen and temperature found confirms that the life of the corals in phosphorous which have limiting nutrient for coral growth. this part of the sea is going to be challenging in the year The seagrass ecosystem is capable of withstanding to come. It was observed in windy and turbulent period higher nutrient levels when compared to the coral reef (April to August) the water is highly turbid and most the ecosystem. dense sea grass beds are disturbed because of strong A dense vegetation of seagrass in Manoli Island wave action and this period, the nearby reefs act as produces a great quantity of organic material, and offers major shelter point to the associated fish resources of a good substrate for epiphytic small algae, micro flora, seagrass areas. There was also no much difference in and sessile fauna. The vegetation plays the role of

204 Int. J. Biodvers. Conserv.

sediment trap, and minute suspended particles, both Roberts, 1996). organic and inorganic, are deposited in this biotope, thus increasing water clarity (Smith, 1984). It also creates unique microhabitats for small animals. In the case of an Conclusion animal assemblage, epifauna attached to the seagrass may have close correlation with the seagrass bed, but The present study showed that Manoli Island is rich in all some infauna may be a part of the benthic community of the two dynamic habitats like coral reef and seagrasses. the surrounding area and not positively correlated with Plankton density, biomass and primary productivity were the seagrass bed. Regarding nekton, some fishes are also high in the seagrass area than the reef area and this permanent residents, some reside there only seasonally, richness can be transported to the nearby reef through and for some the seagrass bed is only a part of their daily consumers. The temperature and the nutrient foraging area. Nevertheless, these various components concentration level have increased compared to the are linked together by tropic interrelationships. The previous year. The temperature would directly affect increasing trend of temperature and nutrient level in both these environments. The increase nutrient level in the the coral reef and seagrass environment has to be coral water would affect the coral skeleton formation and checked otherwise such climatic change, eutrophication causes the micro and macro – algal blooming. The and food web alterations have independent effect and previous process would affect the coral reefs by potential for synergistically enhancing the development of decreasing the light availability to the zooxanthellae. The macro- algae blooms in coastal ecosystem. increase in the nutrient levels in the seagrass The coral reefs and sea grasses are characterized by environment would favour the growth and effect of high biodiversity, productivity and provide a wide epiphytes. It was observed that the fish diversity was high spectrum of services to coastal communities, especially in the reef area than the sea grass area and few common in relation to fisheries and coastal protection. The species were present in both ecosystems indicating seagrasses and mangroves frequently exist in close migration and adaptability. There must be a strong association with coral reefs and often interact through relationship between these two habitats, in exchange of exchanges of biodiversity and productivity. Shallow, nutrients and organisms in this Island. The study coastal areas with coral reefs and sea grasses are concludes that, if these habitats are present near to each among the most diverse and productive in the world other the diversity and abundance of fish and other (Beck et al., 2001; Valiela et al., 2001). organisms will be great because they aid each other. The Coral reef and seagrass habitats are juxtaposed in Gulf of Mannar is rich with these two important habitats many areas of the world. Bensan and Udayasankar and since each habitat is dependent on other, it is (1990) have attempted the colonization and growth of essential to protect these habitats with utmost care. seagrass H. uninervis and H. ovalis in the marine culture ponds of Mandapam. Kannan (1997) and Kannan and Thangaradjou (1999) are the very few attempts made in REFERENCES creation of awareness about the seagrass resources and Amesbury SS, Francis JH (1988). “The Role of Seagrass Communities their need of conservation, have also developed a simple in the Biology of Coral Reef Fishes: Experiments with Artificial economically feasible tank culture technique for E. Seagrass Beds.” Sea Grant Q., 10: 1: 1-6. APHA (American Public Health Association) (1992). 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