In view of the significance of the mangrove areas for coastal aquaculture, a reconnaissance survey of the mangrove areas in the Cochin estuarine system was undertaken during 1976-78. The mangroves of Cochin are formative, mostly developing on small reclaimed or natural islands. Environmental characters showed considerable seasonal fluctuations, especially the salinity which in some of the natural ponds in the mangrove area varied from freshwater condition to high saline, mainly due

to the monsoonal and tidal influence. The rate of primary production ranged from 0.02 to 2.0 gC/m'/ day which fluctuated from the ambient waters of the estuary

Aboobaker, P M

Gopinathan, C P

Kanagam, A

Pillai, C S G

Pillai, P P

Rajagopalan, M S

Selvaraj, G S D

CMFRI Digital Repository

PROCEEDINGS OF THE SYMPOSIUM ON COASTAL AQUACULTURE Held at Cochin From January 12 to 18, 1980 PART 4 : CULTURE OF OTHER ORGANISMS, ENVIRONMENTAL STUDIES, TRAINING, EXTENSION AND LEGAL ASPECTS (Issued in December 1986 ) ^^iA0 t,^ftV^P9^9^f^9 MARINE BIOLOGICAL ASSOCIATION OF INDIA POST BOX NO. 1023, COCHlN-682 031, INDIA Price : Rs. 400.00 EDITORIAL BOAtlD DR. E. G. SILAS DR. P . V. RAO DR. P . V. RAMACHANDRAN NAIR DR. K . RENGARAJAN MR. T. JACOB DR. K . J, MATHEW DR. R. PAUL RAJ DR. S. KULASEKHARAPANDIAN DR. A. G. PONNIAH MARINE BIOLOGICAL ASSOCIATION OF INDIA COCHIN-682 031, INDIA SYMPOSIUM SERIES 6 Abbreviation Proc. Symp. Coastal AquacuUure, Pt. 4. PRINTED IN INDIA BY A. D. THOMAS STEPHEN AT THE DIOCESAN PRESS, MADRAS 7 AND PUBUSHED BY E. G. SILAS ON BEHALF OF THE MARINE BIOLOGICAL ASSOCIATION OF INDIA, COCHIN-682 031 Proc. Symp. Coastal Aquacutture, 1986, 4 : 1068-1073 AN APPRAISAL OF THE BIOTIC AND ABIOTIC FACTORS OF THE MANGROVE ECOSYSTEM IN THE COCHIN BACKWATER, KERALA M. S. RAJAGOPALAN, C. S. GOPINADHA PILLAI, C. P. GOPINATHAN, G. S. DANIEL SELVARAJ, P. PARAMESWARAN PILLAI, P. M. ABOOBAKER AND A. KANAGAM Central Marine Fisheries Research Institute, Cochin-6%2 031, India ABSTRACT In view of the significance of the mangrove areas for coastal aquaculture, a reconnaissance survey of the mangrove areas in the Cochin estuarine system was undertalcen during 1976-78. The man-groves of Cochin are formative, mostly developing on small reclaimed or natural islands. Environ-mental characters showed considerable seasonal fluctuations, especially the salinity which in some of the natural ponds in the mangrove area varied from freshwater condition to h i ^ saline, mainly due to the monsoonal and tidal influence. The rate of primary production ranged from 0.02 to 2.0 gC/m'/ day which fluctuated from the ambient waters of the estuary. The dominant mangrove vegetation is constituted by species oiAcanthus, Excoecaria, Clerodendrum, Aegiceras, Avicemia and Rhizophora. Most of the resident fauna include typical mangrove forms such as Uca spp. in the upper littoral zone, hermit crabs and Nautica spp. in the mid-littoral zone, Cerethidium sp. and Terebralia sp. on the mud-flats and on the trunks and leaves of mangroves the gastropods Littorina sp. are also common. Wood boring organisms such as Sphaeroma sp. among crustaceans and teredinids and bivalves were observed to cause damage to the dead roots and trunks of mangrove trees. In tidal pools and creeks of mangroves, concentration of larvae and juveniles of prawns and fishes was observed during certain seasons in conjunction with thick growth of fila-mentous algae. These seeds are usually collected by local people for the stocking of perennial and seasonal culture fields in and around the area. INTRODUCTION Further, mangrove vegetations colonise on muddysea shores along the borders of the IN RECENT YEARS there has been a growing estuaries and typically comprise of highly interest and awareness of the mangrove eco- specialised trees and shrubs mostly belonging systems as evidenced in the proceedings and to the families, Acanthaceae, Avicenniaceae, deliberations of International and regional Euphorbiaceae, Myrsinaceae, Rhizophoraceae symposia and seminars. The mangrove eco- and Verbenaceae. This vegetation is morpho-system usually harbours a characteristic faunal logically and physiologically adapted to with-assemblage consisting of resident and migratory stand vide fluctuations in salinity and hence animals. It also serves as a breeding and referred to as ' Halophytes '. The root system nursery groimd for many finfishes and shell- of these plants serve to bind the deposited fishes. In many parts of the Indo-Pacific, estuarine mud together and stabilize the sub-the mangrove areas are proved to be potential strata and prevent erosion. The area con-sites for culture of fishes, crustaceans and sequently becomes a region of acowtion and molluscs. h i ^ production. The bacterial and fungal BIOTIC AND ABIOTIC FACTORS OF MANGROVE ECOSYSTEM 1069 dtooomposition of the litter fall in the system in considerable quantity results in the high primary production which in turn leads to dense population of secondary and tertiary producers. A preliminary survey of the mangrove eco-systems was taken up during the years 1976 to 1978 and as the first step, the backwater areas around Cochin was studied and the findings are enumerated in this account. The authors wish to express their grateful thanks to Dr. E. G. Silas, Director, Central AREA OF STUDY The area of present survey extended from the vicinity of Cochin Harbour in the north, to Perumt^lam in the south and the stations, mostly islets were located in the Cochin Back-water system connected to the Vembanad Ufee (Fig. 1). Station 1 Pambaimoola (Local name) is located about 5 km south of Poohin in the backwater system and is mainly a shallow muddy bay which COCHIN E^TUARINE SYSTEA1 I MANOROVE AREAS STATfONS 1 - 4 -i>~ Fig, 1. Codtin Estuarim System with stations surveyed. Marine Fisheries Research Institute for the extends to about 800 sq. metres. In swampy encouragement and guidance given in carrying pools, dense patdies of Acanthus ilicifoHus out this survey and also to Dr. P. V. Rama- dominate and on the shoreward side patches Oh^dran Ns^ ir for helpful su^stions ^ven. • of Avicemin Q^tcimlis o<iqwx, 1070 M. S. RAJAGOPALAN AND OTHERS Station 2 This is a sniall island near Perumbalam Island in the Vembanad Lake. The mangrove here consists of low wooded shrubs mostly belonging to genera Clerodendrum, Aegkeras, Excoecaria and Rhizophora. During low tide, half of the island is exposed with muddy and sandy flats. Station 3 This is also a small island (opposite to Chenthuruthu) covered with Acanthus ilici-folius in patches, along the fringes. Most part of the island which has a clayey soil has been utilised for paddy-cum-prawn culture by the local people. Station 4 It has fairly a vast area in the mainland opposite to station 3 and is covered by more terrestrial vegetation due to man-made changes. The mangrove vegetation could be seen inter-mingled with terrestrial trees and also coconut plantation. A number of shallow ponds occur which serve as good nursery grounds for prawn and estuarine fish larvae. Routine data were collected every fortnight on the mangrove vegetation, physico-chemical factors of the water such as temperature, salinity, oxygen content, nutrients and primary productivity. Qualitative data on fauna were also collected. Dissolved oxygen content in the mangrove creeks showed seasonal changes and ranged from 1.03 to 5.03 ml/1 (station 1); 2.02 to 5.6 ml/1 (station 2); 3.15 to 6.33 ml/1 (station 3) and 2.91 to 5.6 ml/1 in station 4. Nutrients Stn. 1 Stn. 2 Stn. 3 Stn. 4 Nitrite N 0.74-0.85 0.35-0.85 0.40-0.59 0.43-0.82 (/igat/1) Phosphate 1.0-1.52 0.00-1.68 0.00-2.27 0.00-1.59 (/tgat/1) Carbon (mgC/g) 21.2-27.69 16.0-26.30 21.8-31.84 15.2-1.82 Primary produc tion Primary productivity was estimated by both oxygen technique and " C technique. In general, the values ranged from 240-2150 mgC/mVday in different months of the year. The seasonal variation in production is presented below. Pre-monsoon (Jan-April) Monsoon (May-Aug.) Postmonsoon (Sept.-December) Production mgCjm^lday Stn. Stn. Stn. Stn. 1 2 3 4 900 450 620 665 1370 510 610 370 805 560 630 455 RESULTS Physico-chemical features Average monthly surface temperature varied from 25 to 30°C in station 1; 28.2 to 38.3°C in station 2 ; 24.2 to 36.5°C in station 3 and 31.2 to 41.0'*C in station 4. Monthly average values of surface salinity varied from 0.77 %o to 29.0 %o (station 1), 0.21 to 29.21 % (in station 2), 0.68 to 30.26 %o (Station 3) and 0.90 %» to 29.0%, in station 4. Distribution and zonation of mangrove flora and fauna The mangrove flora in the tidal zone of station 1 was dominated by Acanthus ilictfolius and the rest consisted of Clerodendrum inerme, Rhizophora mucronata and Avicennia officianalis. The upper zone is colonised by typically ter-restrial trees such as Thespesia pupulnea. The muddy outpocket which is often exposed during low tide, was inhabitated by TerebraJia BIOTIC AND ABIOTIC FACTORS OF MANGROVE ECOSYSTEM 1071 with a density of 15-25 no./sq.m. This area is used for soaking timber and is highly polluted. At the upper fringe of the swampy area Nerita and Littorina could be found on hard substrata and Crassostrea and barnacles in the lower zone. Burrowing polychaetes and egg case of Marphysia were also common. Occasionally Modiolus sp. were observed as attached to Terebralia. A few nudibranch were collected from the leaves of Acanthus. Above the intertidal zone crabs belonging to the families Portunidae, Ocypodidae and Grapsidae are commonly found. Juveniles of Hcplocheilus, TTtercpon, Ambassis and of the prawns Penaeus and Metcpenaeus occur com-monly in the swampy pools. The southern side of station No. 2 is populated by low shrubs Clerodendmm etierme, Aegiceras corniculatttm, Excoecaria agallocha and occasional stands of Rhizophbra mucronata. Hydromedusae such as Eiivne sp. were collected in good numbers during summer months. In the sandy flat^, tube dwelling polychaetes could be observed. Young ones -of mussels and Modiolus occurred on dead mangrove trunks. Wood boring bivalves and crustaceans were noticed on certain occasions on mangrove stumps and breathing roots. Ceretheditm usually occur in large numbers during March-May. Juveniles of Therapon Ambassis and prawns occur in good numbers in ihe tidal pools among mangrove vegetation. The 3rd station was dominated by the follow-ing vegetation; Acanthus iticifolius, Aegiceros comiculatum, Clerodendrum inernie and Mizo-phora mucronata. This was backed by terres-trial forms like Vitex sp:, Ipomea Mloba, Phyllanthus sp. and Acrostichum aureum. Ilobium sp. audits egg masses could be observed in the exposed muddy areas. Juveniles of Penaeus indicus, Metapenaeus dobsoni and M. monoceros were usually observed in the creeks of mangrove area. During summer months, when the salinity is high, prawn culture is practised in this island. The station 4 has a good compliment of mixed, mangroves such as Rhizophora mucrO' nata, Bruguiera cylindrica, Aegiceros comi-culatum, Clerodendrum inerme, Excoecaria agallocha and Acrostichum aureum. Terrestrial forms such as Calophyllum inophyllum, Ipomea bilaba and Eriocolon sp. also occur. In general, the mangrove vegetation exhibit luxurient growth in the post-monsoon months with flowering in September to December" period. In station 4 species of Terebralia occur only in small numbers and in a scattered manner. Above the intertidal zone crabs such as JJca, Scylla serrata, Sesarma and Metcipogr(^sus could be found in different months. In the creeks and ponds, juveniles of Haplocheilus, Ambassis, Etroplus, gobiids, Tetradon and Batrachus could be found in different seasons. The distribution of flora and fauna commonly occuring in the different mangrove statiops could be summarised as follows : Habitat Flora Fauna Mid'tidal Acantbus ilkifplius, Scylla serrata, / •zone 'Excoecaria Uca amulipesr, agallocha, • Uca vocans, Aegiceros Sesarma Umatum, : comicidatum Sesarma pUcatum^'.- • • and Clerodendrum Metapagrapsus messor, inerme hermit crabs, ^ burrowing amphi-pods, barnacles, wood boring bivalves, Littorina sp. and Nerita sp. Boring bivalves were commonly observed ,, >, , ~~, j.i. J J i -r ^ '. Upper . Avicenniaoffici-m the dead roots of mangroves. During tidal nedis, certain months anemones and gastropod zone Terebralia sp., Cerethedium sp., small gastropods, 1072 M. S. RAJAGOPALAN AND OTHERS Habitat Flora Fauna Tidal pools & creeks Terrestrial" Rhizophora mucronata and Bruguiera cylindrica Acrosiichum aureum. Eriocolon sp., Cyperus sp. and Ipomea polychaetes and diogenes. Amphipods, alphaeids, small Neptunus, juveniles of P. indicus, M. dobsoni M. monoceros. Etroplus maculatus, E. suratensis, Ambassis dayi and A. commersoni ' Thespesia pupulnea. Vitex sp., Phyllanthus sp. Calophyllum inophyllum and Panicum sp. DISCUSSION The mangroves in the Cochin Backwater system as it is observed now could be described as isolated patches which have undergone degradation due to man made dianges. Blasco (1975) pointed out that out of the estimated 70,000 ha of mangrove areas in India, Kerala Backwaters have only a vestige of less than 100 ha. Although the backwater channels are shallow, narrow and well connected to the sea and the adjacent terrain vtdth copious rainfall annually, mangrove development has been very much restricted. The areas bordering the canals are over populated and what was once a mangrove area has been converted into coco-nut groves and paddy fields or prawn culture fields. Wide seasonal fluctuations in the physico-chemical factors have been noticed in the mangrove areas investigated. The Cochin Backwater where these mangrove stations are located, is also subjected to considerable * The twrestrial zone was completely donunated by terrestrial angiosperms, fluctuations in the above factors (Qasim et al., 1969). Qasim (1970) estimated gross production in the estuary as ranging from 270-295 gC/jn'/ year and the annual consumption of the zoo-plankton herbivores as only about 30 gC/m*. This indicated the availability of large surplus food in the estuary and the connected mangrove area which may perhaps be utilized by other members of the ecosystem such as herbivorous fishes (mullets) and omnivorous detritus feeders such as prawns. Commenting on the faunal characteristics of Asian mangroves Morton (1978) has ob-served, that a wide range of animals including worms (Phascolosoma), snails (Telescopium, Cerethidia and Terebralia), bivalves (Gelonia, Enigmonia, Pharella, Modiolus), crustaceans (,Sesarma,Uca, Ilyoplax,ScyUa, nalassina),&shes (Periopthalmus, Ambassis, Scatophagus, Platy' cephalus) and protochordates (Balanoglossus) are usually foimd in the mangrove habitat and they are capable of tolerating wide fluctuations in saUnity. The mangrove soils and mud are acidic and deficient in calcium salts, so that the back of the mangroves are colonised by Gelonia or by pulmonate snails Ellobium, Melampus and Cassidula. On the trunks and roots of mangroves could be observed re-presentatives of seashore life such as lidiens, littorine snails, barnacles and mangrove bivalve Enigmonia. These assemblages constitute a hard shore niche in an otherwise soft shore environment and the principle of inter-tidal zonations could be observed. The tides indeed are responsible for affecting, creating and main-taining the zonation of animal community. Saseekuraar (1978) has pointed out that the detritus foodweb based on mangrove plant material is more complex in the tropical areas due to the presence of more species of crusta-ceans, gastropods and fishes. The examination of gut contents of these fishes, some of them CQonomically important, consisted of mangrove BIOTIC AND ABIOTIC FACTORS OF MANGROVE ECOSYSTEM 1073 detritus and mangrove dwelling invertebrates. In the case of mullet, 40 % of the diet consisted of detritus and in Hes>locheilus melastigma it was over 80%, for Plotosus caninus, the chief food consisted of mangrove snail Ceretkidia. It is interesting to observe that these flnflshes community occur in the Cochin mangroves also. ^ In the course of our observations on the mangrove areas of Cochin, on many occasions, juveniles of prawns were observed in the man-grove creeks and ponds, particularly associated with filamentous algae along the ^ore. It is well known that these areas serve as nursery grounds for the juvenile stages of prawns which feed on detritus rich benthos and flora of micro-algae. Saseekumar (1978) has drawn attention to the fact that the prawn catches in Malaysia Were greater along the mangrove-rich west coast than the east coast. Ife has also drawn attention to similar linear relation between prawn production and aoeage of mangroves akeady established in Indonesia. Though it may not be possibte to establi^ such a relationship in the Codrin Backwater, the contributory factors from mangrove areas cannot be ruled out. The objective of this account is to focus attention on the structure of the mangroves in the Cochin estuarine system and the charac-teristics of resident and migratory fauna. The seasonal fluctuations in the physico-chemical features and general productivity of the man-grove areas are influenced by the general dynamics of the estuarine system of the whole area. Being overpopulated, the coastal areas have gradually been transformed to many productive uses sudi as coconut plantation, paddy-cum-prawn filtration and perennial prawn culture practices. In this process the fragile mangrove ecosystem has suffered depletion, a fact which must be viewed with concern from the point of view of conservation. That the mangrove creeks and swamps are utilised by the local population as the site for collection of seeds of cultivable finfishes and shellfishes, points to the ecological significance of mangroves for coastal aquaculture. R B F B R E N C B S BLASCO, F . 1975. Lts mmgrove de L*inde, Travaux de la section Scientiflque. Tonw XIV, I^Hcieale 1. MORTON, B. S. 1978. Eeolcgy tmd productivity of South East Asian waters. Lecbim t^vm at FAOI SWA workthop on aquatic ponution Maoila, 1977, pp. 288-331. QASIM, S. Z. 1970. Some problems telated to the food chain in a tr<H>ical estuary In: J. H, Steele Oliver and Boyd (Ed.)\Marine Food Chain. Bdinbnrglt, pp.45-51. , S, WoxauHAUs, P. M. A. BHATTATHIRI AND S. A. H. AUDI 1969, Organic production in a tropical estuary. Proc. Indian. Acad. Sd., 69: 51-94. SAoraccMAR, A. 1978. Value of the numgrove ecosysltm and Us poUtMon problems. Proc. FAO/ SIDA workdiop on aquatic poUution in rdation to protection of living resources, Manila, Philippines. 1977. pp. 332-341. 

An appraisal of the biotic and abiotic factors of the mangrove ecosystem in the Cochin backwater, Kerala

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An appraisal of the biotic and abiotic factors of the mangrove ecosystem in the Cochin backwater, Kerala

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