J. mar. biol. Ass. India, 19%, 38 (1 & 2) : 25 - 33 DESTRUCTION OF TIMBER STRUCTURES IN THE ESTUARINE SYSTEMS OF THE SOUTR WEST COAST OF INDIA, THE KALLAYI AND BEYPORE BACKWATERS N. BALAKRISHNANNAIR Department of Aquatic Biology and Fisheries, University of Kerala, Trivandrum, 695 007. ABSTRACT The nature. of destruction of timber structures in the Kallayi and Beypore backwaters of'the South-West mast of India has been examined. Five species of shipworms namely Dicyathifet manni, Lyroduspedicellatus, Teredo furcifera, Nausitora hedleyi and Banhia carinata, two species of pholads Martesin striata, Martesia (Pam'coma) nairi and three species and a variety of sphaeromatids Sphaeroma terebrans, S. annandalei, S. a. travancorensis and S. walkeri constituted the boring community. The incidence, and relative abundance of these borers in relation to the salinity profile of the estuary have been reported. where large quantities of wood are exposed to their attack. The present paper describes the nature of distribution of wood borers in two TIMBERis extensively used all along our backwater systems of Kerala. coastal zone for harbour structures, waterfront installations, different types of fishing crafts and aquaculture implements. Mangrove forests fringe the shore line, more especially the Collections wCre camed out of sheltered areas and are exposed to wood-boring organisms from Kallayi and submergence and emergence during the tidal Beypore backwater systems during the cycles. All these are subject to the attack of pre-monsoon period February-May of 1988. timber boring organisms. The total damage The availability of infested wooden samples inflicted is indeed great, but very difficult to and the area of the system from the bar-mouth assess, yet it is estimated that in India, the to the upper reaches were taken into fishing industry alone suffers an annual loss consideration while selecting sampling sites. of nearly 96 million rupees owing to the Five representative sites in Kallayi covering an ravages on wooden fishing implements by area of 4 krn and 10 sites in Beypore covering these pests (Qasim, 1988). a distance of 7 km from the bar-mouth to the upper reaches were selected for the study. The While a large volume of information is infested samples of wood (chiefly the stem of available on the different aspects of the Cocos nltcifera) were first preserved in neutral taxonomy and biology of these pests (Nair, 5% formalin, packed in polythene bags and at 1984, 1988, 1994) our information is still the laboratory, a fixed volume (1000cc of wood incomplete regarding the incidence and relative measured by displacement volume of water) of abundance of these in the estuarine systems the sample, cleaned of surface fouling, was 26 N. BAJAKRISHNAN NAIR examined for the relative abundance of different for retting. This along with the logs kept in species of borers. The total number of bore-holes the water for conditioning all through the year of the respective species was checked, counted foul the water considerably. The tidal currents and recorded. Then, the samples were dissected enter upstream into the river up to about 18 to remove the borers. Besides salinity, related to 20 km and hence the water is saline during parameters such as temperature, pH and oxygen most of the months. content of water have also been recorded using THE BEYPOREESTUARY (Fig. 2) standard procedures (Martin, 1970). The Chaliyar is one of the major rivers THEKAUAn BACKWATERSYSTEM (Fig. 1) of the West Coast of India and joins the The Kallayi river is connected with the Arabian sea at Beypore near Calicut. At its Chaliyar on the south by a man-made canal. Iower reaches it is known as the Beypore river forming the Beypore backwater before if joins the sea. The Beypore estuary enters the sea in a ~~~th-we~t&l~direction. There is a horse-shoe shapped bar at the entrance and the depths over it vary from 1.5 m to 1.9 m. The sea bed slope at Beypore, is comparatively flat FIG. 1. Map of Kallayi Backwater system The river passes through Olavanna, Manava and Kallayi before finally joining the sea near FIG.2. Map of Baypore estuary Calicut. This backwater is tidal in character and divides the Calicut town into two before with a 9m contour at a distance of 3.5 km its confluence with the sea. The world's second from the river mouth. The tides at Beypore biggest timber depot and a large number of are semidiurnal with a period of 12 hours and wood-based industries are also situated along 40 minutes. The maximum flows occur during its banks. The entire stretch is shallow. the months of June-August, and during this Considerable amount of coconut husks are period the tidal limits come down to the fisheries deposited in this estuary by coir industry units wharf downstream of the Feroke bridge for a DESTRUCTION OF TIMBER STRUCTURES IN THE ESTUARINE SYSTEMS 27 , river discharge of 500 m3/sec. The least causing severe damage to the water quality and discharge is found to occur during the latter fishery prospects of the estuary. The Beypore half of April and first half of May, during backwater is connected to Kallayi river and which period the tidal limit is observed to be large quantities of timber are floated down to at a distance of 26 km upstream of the mouth Kallayi through the Beypore river from the near the confluence of the two major tributaries Nilambur valley. This part of the backwater is joining the estuary. an important link of the westcoast inland navigation system. KALLAYI @ HYDROGRAPHY RESULTS AND DISCUSSION The results of the study conducted at Kallayi are presented in Table 1 and fig. 3. and those of Beypore in Table I1 .and Fig. 4. The most notable features of the study ate - SALINITY indicated below. BEVPORE =r - ATMOSPHERIC 0-4 WATER C1 SEDIMENT 30 @ WOOD-BORING ORGANISMS -03 0,C L 0 SHIPWORMS a0 PHMADS m sPH,aERoMATIos FIG. 3. Hydrography and distribution of wood borers in Kallayi backwater Beypore estuary has been subjected to severe pollution due to the effluent discharge FIG.4. Hydrography and distribution of wood borers from the Mavoor Gwalior Rayons Factory in the Beypore estuary 3 28 N. BALAKRISHNAN NAIR At Kallayi, the atmospheric temperature the value of this parameter was negligible. The fluctuated between 31 - 33°C. The minimum values ranged between 33.2 x 1u3 - 33.8 x values of atmospheric (31°C) and water (30.5"C) The distribution of salinity in the different TABLE1 Abundance of wood-boring organisms in ';~eKallayi estuary during pre-monsoon period (No. of organisms/1000 cc of wood) - 1 2 3 4 5 Total SHIPWORMS D. mnnni 5 10 4 9 10 38 (8.3) (34.50) (3.7; (40.9) (47.6) (15.8) L. pedicellntus 41 6 7 4 5 3 134 (68.3) (2O.7) (73.2) (z2.7) (14.3) (55.8) T. furcfirn 11 13 23 8 8 63 (18.3) (44.8) (21.3) (46.4) (38.1) (26.3) B. cnrinntn 3 - 2 - 5 (5.0) (1.9) (2.1) Total 60 29 108 22 21 240 (17.0) (9.9) (36.4) (4e4) (28.0) (15.8) PHOLADS M. strinta 17 13 - 1- 4 12 63 (25.0) 43.3 (25 .O) (3.8) (22.2) (19.4) M. (P.) nniri 5 1 17 -51 101 42 262 (75.0) (56.7) (75.0) (96.2) (77.7) (80.6) Total 68 30 68 105 54 325 (19.3) (10.2) (22.9) (20.9) (72.0) (21.4) SPHAEROMATIDS S. terebrnns - 130 55 47 - 222 (55.3) (45.5) (12.5) (24.2) S. anr ,uidnlei 225 105 66 329 - 725 (100) (44.7) (54.6) (87.5) + (75.8) Total 225 235 121 376 - 957 (63.7) (79.9) (40.7) (74.8) (62.9) Grand Total 353 294 297 503 75 1522 Species of borers in parenthesis; *Percentage of groups temperatures were noted at station 1 and the regions of the estuary from the bar mouth to maximum values 33°C (atmosphere), 335°C the rivenne zone of the estuary at station 5 (water) at station 5. At Beypore, atmospheric was rather homogeneous. temperature varied between 30.5 to 33°C with Permanently connected to the adjoining the minimum at station 1 and the maximum sea, the Beypore estuary is influenced by tidal at station 6, 7 and 10. Surface water temperature currents, the limit of which is observed at a fluctuation had a range of 1.5"C, the maximum distance of about 28 km upstream of the mouth of 33.5"C was recorded at stations 7 and 8 during the summer months o'f April and May and the minimum of 32°C at station 1. when the river discharge is the lowest (James The salinity maintained high values at all et al. 1983). The minimum salinity of 18.8 the study sites in Kallayi. The difference in x lo9 was recorded in the interior of the DESTRUCTION OF TIMBER STRUCTURES IN THE ESTUARINE SYSTEMS 29 h h hh '9 a oq h Ah- 1 -2 4% 1 -2 a~ 9: 1 VW VW ww wwz hcn h" n hhh I 2 I modrr) ;;g" rnZ 2z "'4 I I I I s ww www h G - hhh I s2rg I 26 a$ -2 39.::; I I I I rr) o?) w VW WWV- h h "! h hhh I =, wN I 3: gz hzrr) 09 1 gF9z 1 I VW w"z%g -I% 30 N. BALAKRISHNAN NAIR estuary at station 5 while the maximum of average concentration of 6.5 mlA was noticed 34.4 x 10'~was noted at station 10 near the whereas in the middle and riverine zones the bar mouth region.