Primary productivity of two seagrass beds and one algal

bed in the Gulf of Mannar was studied by diurnal curve method.

The sea grass bed close to Mandapam Camp was found to be autotrophic,

with P/R ratios ranging from 1.65 to 3.90. The seagrass

and algal beds around Kurusadai island were heterotrophic.

Production of oxygen by individual sea grasses equalled or exceeded

their consumption

Balasubramanian, T

Wafar, M V M

CMFRI Digital Repository

NOT~S PRIMARY PRODUCTIVITY OF SOME SEA GRASS BEDS IN THE GULF OF MANNAR T. BALASUBRAMANIAN' AND M. V. M. WAFAR2 Regional Centre of CMFRI, Mandapam Camp ABSTRACT Primary productivity of two seagrass beds and one algal bed in the Gulf of Mannar was studied by diurnal curve method. The sea grass bed close to Mandapam Camp was found to be auto-trophic, with P/R ratios ranging from 1.65 to 3.90. The seagrass and algal beds around Kurusadai island were heterotrophic. Production of oxygen by individual sea grasses equalled or exceeded their consumption. Chlorophyll a values in the waters over the ' seagrass bed ranged from 0.893 to 9.49 mg/m3. Benthic algal communities, con-dered as specialised marine environ_ ments, show organic productivity many times higber than those of oceanic waters (0.01 - 0.03 gC I m2 I day) or coastal shallow waters (1-2 gC /m2/day). High values of both gross photosyn-thesis and community respiration have been reported in these environments (Odum, 1956; Qasim and Bhattathiri, 1971). However, a considerable portion or even the entire organic matter pro-duced is lost by way of community respiration. Thus, these environments are not always autotrophic - in fact, some of them are heterotrophic. The present study was taken up to investi-gate the community metabolic state of two seagrass beds and one seaweed bed in the Gnlf of Mannar. The first seagrass bed (A in Fig. I) studied lies in the Gulf of Mannar (Manda pam peninsula), near the jetty of Central Marine Fisheries Research Institute. It covers a distance of about 3 Km from Mandapam Camp to Vedalai, a nearby fishing village. The average width of the bed is about 200 m and the average depth over the bed is about 2 m. The seagrasses found in this bed are Cymodocea isoetifolia, C. serru/afa, Halophyla ovalis, H. slipulacea and Dip-lanthera uninervis. Of these, C. isoetifolia is the dominant species. The second seagrass bed lies north of Kurusadai island (B in Fig. I). This bed is largely composed of Enhalus sp. The algal bed studied (C in Fig. I) lies in the lagoon along tbe southern side of the island. It is enclosed by the reef. Tbe seaweeds found in this bed include species of Halimeda, Caulerpa, Padina and Hypnea. Present address: 1. Regional Centre of NIO, P. B. No. 1913, Cocbin - 682018 2. National Institute of Oceanography. Dona Paula, Goa 403 004 Balasubramanian and Waf": Productivity of Some Seagrass Beds 20r----r--------~--------~ ~10L-~~--------~--------~~ 79' 10 15 -Map showing the location of the seagrass and algal beds. Diurnal curve method of Odum Gross production and respiration were and Hoskin (1958) was employed to calculated foHowing the method of study the community metabolism. Odum and Hoskin (1958). Measure-Duplicate samples for the determina- ments of community metabolism of the tion of dissolved 'oxygen were taken Mandapam bed were made in July, o.ver a fixed station at 3hr intervals for October and December of 1972 and in a period of27 hours and the measure- February, 1,973 and those of the beds on ments were averaged to get an oxygen Kurusadai island in November, 1973. value representative of the waterroass. A curve fOT tbe rate of change of oxygen Gross production and respiration was computed from these values after values (Table 1) and community meta-correcting the diffusion loss or gain. bolism curves (Fig. 2) show that tbe TABLE I. Gross production and community respiration in the algal beds studied. Location of tbe bed Gross Production Respiration and month of study gC/m2/day gC 'm' 'day Mandapam bed July, 1972 8:04 3.25 October, 1972 11.56 2.96 December, 1972 8.35 3.72 February, 1973 8.64 5.24 Kurusadai Island November, 1973 Sea grass bed 2.40 2.95 Seaweed bed 4.30 5.90 88 P(R 2.47 3.'10 2.24 1.65 0.81 0.74 I I ( MQ1l7l~aitlil": Vot. 8' NOs. l ' &' 2, MtJrcir- Jurte 1975 If) , , ; ~ ~--~--~--~~--~--~~--~--~~--~--~~~~. (e) . / 0" Id) E. ai: <0 ,. x , 0 "-o .... '" ,. Ii . ~ 'i 04 08 12 16 20 24 04 04 OB 12 IS 20 24 ()-4 HRS Community metabolism curves a·d: Mandapam bed in July. October, December. ilfii krtd Fel1lu;u'Y. 19'il e-f: 'S<agtass aDd Seaweed beds respectively around Kurusadai Island. in November. 1973. Mandapam bed is autotrophtc. The seagrass and algal beds of Kurusadai island are heterotrophic . Tsolated sea-grass beds are generally autorrophic., Oduin (1956) observed a production of 10.63 gC/m2 /day in a turtle grass community . Qasi m and Bhattathiri (1971) recorded a productivity of 11.97 gC/m2/day in Tha/assiti and Cymodocea bed oil 'Kavaratti atoll. The luxurious g row,th of the seagrllsses in the Manda-pam bed accounts for the high primary productivity observed here. Rao (19i73) has estimated the mean density of sea-grasses in the Malldapam area as 558 tonnes/sq. Km . The ecological impli-cations of a high productivity in sea-grass beds has been dealt with in detail by 'Qasim and Bhattathiri (1971 ). The productivity of both the algal como. Inunities around Kurusadai islaod Jlre low and in addition, they are hetero-_ ... Bala.ubramanian and Wafer: Productivity of Some St!agra6. Beds trophic. Tbe limited expanse of tbese two beds and the low density of 0.67 Kg of fresh Wt of algae/m as observed by Rao (1972) migbt probably account for the low productivity and hetero-tropbic state of these two beds. Furtber, tbe possibility of a seasonal minimum of production cannot be rnled out as seasonal differences in the growth and attrition of marine algae are well known. Odum er al., (1959) observed that the consumption in two Thalaosia beds in Puerto Rico waters exceeded tbeir production. Studies on the photosyntbetic and respiratory rates of tbe individual seagrasses found in tbe Mandapam bed indicate that tbese are autotrophic individually with P/R ratios equalling or exceeding I, (Table 2). Kanwisher (1966) has shown that under optimum temperature and light conditions the photosynthesis is very high in several species of seaweeds. Qasim and Bhattathiri (1971) observed that many of the seagrasses and seaweeds found on Kavaratti atoll produce more oxygen ' than they consume. Thus tbe higb " production rates of the individual species make the algal beds highly productive in spite of the combined respiratory demands of the algae and the organisms associated with them. Chlorophyll a values obtained for one year from the waters over the sea-grass bed at Mandapam ranged from 0.893 to 9.49 mgjm 3 • Unfortunately, tbere is no other data on the pigment values of seagrass bed waters elsewhere for a comparison. Chlorophyll a values from this bed are several times higher than those obtained from the coral reef waters in tbe Palk Bay side of Manda-pam (0.177 to 0.695 mg/m3 ). However, the extent of contribution. by free phytoplankton to the overall producti-vity of the seagrass bed is yet to be ascertained. ACKNOWLEDGEMENTS Our thanks are due to Dr. S. Z. Qasim, Di rector, National Institute of Oceanograpby, for his guidance and suggestions. We are grateful to the Ministry of Education and Social Wel-fare, Government of India, for the award of Senior Research scholarships. T ABLE II. Rates of production and consumption in some of the seagrasses found in the seagrass beds of Gulf of Mannar. Species Cyrnodocea i.oetifolia Cymodocea serrulata Diplanthera uninervis Halophyla ovalis Halophyla .tipulacea Production gCjgmjhr 0.6012 0.3261 0.4084 0.2650 0.4910 90 Respiration gCjgmjhr 0.6012 0.3260 0.1880 0.1130 0.1880 PjR 1.00 1.00 2.17 2.35 2.61 Mahasagar, Vol. 8 Nos. 1 & 2, March - June 1975 REFERENCES Kanwisher. J. W., 1966. Photosynthesis and respiration in some seaweeds. In: Some contemporary studies in marine scienc, George AlI~n & Unwin, London: 407·420. Odum, H. T., 1956. Primary productivity in flowing waters. Limnol. Oceanogr., 1: 102-117. Odum, H . T. and C. M. Hoskin , 1958. Comparative studies on the metabolism of marine waters. Pub!. Inst. Mar. Sci. Univ. Texas 5: 16-46. Odum, H. T ., Burkholder, P. R. and J. Rivero, 1959. ductivity of turtlegrass flats, reefs and the Southern Puerto Rico. Ibid. , 6: 159-170. Measurements of pro-Bahia Fosforescente of Qasim, S. Z., and P. M. A. Bhattathiri, 1971. Primary production of a seagrass bed on Kavaratti atoll (Laccadives). Hydrohiologia, 38: 29-38. Rao, M. U., 1972. Coral reef flora of the Gulf of Mannar and Palk Bay. Proc. Symp. corals and coral reefs. C. Mukundan and C. S. Gopinadba Pillai (Ed), Mar. Bioi. Ass. India, Mandapam Camp : 217-230. Rao, M. U., 1973. The seaweed potential of the seas around India . Proceedings of the Symposium onLiving Resources of the seas around India: 687~692., Central Marine Fisheries Research Institute, Cochin . • " 91 

Primary productivity of some sea grass beds in the Gulf of Mannar

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Primary productivity of some sea grass beds in the Gulf of Mannar

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