Cochin Backwaters Research Articles

Eutrophication induced changes in benthic community structure of a flow-restricted tropical estuary (Cochin backwaters), India

The influence of anthropogenic loading on the distribution of soft bottom benthic organisms of a tropical estuary (Cochin backwaters) was examined. The industrial activities were found to be high in the northern and central part of the estuary, where dissolved inorganic nitrogen (DIN > 210 μM) and phosphorus (DIP > 6.5 μM) have caused high abundance of chlorophyll a (up to 73 mg m(-3)) and accumulation of organic carbon in sediments (up to 5%). Principal component analysis distinguished three zones in the estuary. The central zone (Z1) was characterized by organic enrichment, low species diversity, and increased number of pollution tolerant species. Long-term deterioration of the estuary is indicated by an increase in the nutrients and chlorophyll a levels by sixfold during the last few decades. Flow restrictions in the lower estuary have lead to a fourfold increase in sediment organic carbon over the period of three decades. The reduced benthic diversity followed by an invasion of opportunistic polychaetes (Capitella capitata), are indicative of a stress in the estuary.

Distribution, reproductive biology and biochemical composition of Rhopalophthalmus indicus (Crustacea: Mysida) from a tropical estuary (Cochin backwater) in India

Distribution, reproductive biology and biochemical composition of Rhopalophthalmus indicus Pillai were investigated base on samples collected over a period of one year from Cochin backwater. Rhopalophthalmus indicus Pillai was recorded through out the year with peak abundance during pre-monsoon. The population density was influenced by Chlorophyll a, dissolved oxygen, salinity and water temperature. The species showed periodicity in the abundance and produce more than one generation per year. The number of embryos carried by a single female ranged from 6-13, and was correlated with female body length (P>0.05), tending to increase with the size of the female. Egg size varies between 0.42-0.47 mm, and was independent of female size. Both males and females attain sexual maturity at a length of 8.4 mm. Seasonality is observed in biochemical composition, as mature males and females had higher protein contents, immature stages contained high carbohydrate content and brooding females accumulated more lipid.

Seasonality, reproductive biology and ecology of Mesopodopsis zeylanica (Crustacea: Mysida) from a tropical estuary (Cochin backwater) in India

Mysids from a tropical estuary (Cochin backwater) in India were studied based on samples collected over a period of one year. Four species belonging to three genera) were represented: Mesopodopsis orientalis, Mesopodopsis zeylanica, Rhopalophthalmus indicus and Kochimysis pillaii, among which Mesopodopsis zeylanica was the most dominant species, recorded throughout the year with its peak abundance observed during the monsoon period (June to September). The wide range of fluctuation in their population density was considered to be mainly due to their heterogeneous distribution. Reproduction of M. zeylanica in Cochin backwater is continuous throughout the year. The number of embryos carried by a single female ranged from 7 to 12, and was correlated with female length (p<0.05), tending to increase with increasing the size of the female. Egg size varied between 0.38 and 0.43 mm, with no correlation with length of the female, and size differences were observed in the same brood. Males and females attain sexual maturity after reaching a total length of 5 mm and 4.5 mm respectively. The environmental parameters, salinity and chlorophyll a, have much influence on the population density of mysids.

Short-term variability of water quality and its implications on phytoplankton production in a tropical estuary (Cochin backwaters—India)

Changes in the phytoplankton biomass (chlorophyll a), production rate, and species composition were studied over two seasons using the time series measurements in the northern limb of the Cochin estuary in relation to the prevailing hydrological conditions. The present study showed the significant seasonal variation in water temperature (F=69.4, P<0.01), salinity (F=341.93, P<0.01), dissolved inorganic phosphorous (F=17.71, P<0.01), and silica (F=898.1, P<0.01) compared to nitrogen (F=1.646, P>0.05). The uneven input of ammonia (3.4-224.8 μM) from upstream (Periyar River) leads to the inconsistency in the N/P ratio (range 6.8-262). A distinct seasonality was observed in Si/N (F=382.9, P<0.01) and Si/P (F=290.3, P<0.01) ratios compared to the N/P ratio (F=1.646, P>0.05). The substantial increase in chlorophyll a (average, 34.8±10 mg m(-3)) and primary production (average, 1,304±694 mg C m(-3) day(-1)) indicated the mesotrophic condition of the study area during the premonsoon (PRM) and it was attributed to the large increase in the population of nanoplankton (size<20 μ) such as Skeletonema costatum, Thalassiosira subtilis, Nitzschia closterium, and Navicula directa. In contrast, during the post monsoon (PM), low chlorophyll a concentration (average, 9.3±9.2 mg m(-3)) and primary production (average, 124±219 mg C m(-3) day(-1)) showed heterotrophic condition. It can be stated that favorable environmental conditions (optimum nutrients and light intensity) prevailing during the PRM have enhanced the abundance of the nanoplankton community in the estuary, whereas during the PM, the light limitation due to high turbidity can reduce the nanoplankton growth and abundance, even though high nutrient level exists.

Mortalities caused by the crustacean isopod,Cirolana fluviatilis, in tropical, cage-cultured Asian seabass,Lates calcarifer: a case study from the southwest coast of India

Recurring mortalities inflicted by the cirolanid isopod Cirolana fluviatilis in the juveniles of the Asian seabass, Lates calcarifer, stocked in a cage farm in the Cochin backwaters, from November 2006 to May 2007, were investigated. Hatchery-reared fingerlings (size 8–12 cm) were cultured in floating cages and mortalities were observed after a rearing period of 1 month. The fish were found dead in the cages, with only the remnants of fish skeleton and all the flesh eaten away. Investigations revealed a very high abundance of isopods, identified as C. fluviatilis (Crustacea, Malacostraca, Isopoda and Ciroloanidae). During the first 2 months of stocking, 35% of the fingerlings died, and the cumulative mortality reached 45% in 6 months, considerably reducing the profits from the venture. Management measures for the control of the isopods are discussed. This is the first report on the isopod, C. fluviatilis, inflicting serious mortalities in a tropical cage-rearing system in the southwest coast of India.

Seasonal abundance, ecology, reproductive biology, and biochemical composition of Mesopodopsis orientalis W. M. Tattersall (Mysida) from a tropical estuary (Cochin backwater) in India

Seasonal abundance, life history, and biochemical composition of Mesopodopsis orientalis Tattersall were investigated based on samples collected over a period of one year in tropical estuary, i.e., Cochin backwater. M. orientalis was recorded throughout the year and its peak abundance was observed during the monsoon period. The species produced more than one generation per year. The number of embryos carried by a single female ranged from 7 to12, and was correlated with female length (P<0.05), tending to increase with the size of the female. Egg size varied between 0.39 and 0.47 mm, with no correlation with length of the female, and size difference was observed in the same brood. Males and females attain sexual maturity after reaching the total length of 5 mm and 4.5 mm respectively. With the exception of chlorophyll a, the environmental parameters, dissolved oxygen, salinity, pH and water temperature do not have much influence on population density. The biochemical composition of the species reveals its high nutritional quality. Matured males and females showed higher protein contents than other stages, while carbohydrate content was high in immature stages, and lipid content was high in brooding females.

FRESH WATER INFLUENCE ON NUTRIENT STOICHIOMETRY IN A TROPICAL ESTUARY, SOUTHWEST COAST OF INDIA

Cochin backwaters, a micro tidal estuary, undergo a characteristic transformation from a river-dominated system during summer monsoon to a tide-dominant system during pre-monsoon season. The present study observes that as the river flow weakens after monsoon, the flushing of the estuary diminishes and the nitrogen and phosphorous loadings through anthropogenic activities (industries) and sediment re-suspension alter the nutrient stoichiometry substantially. The increased tidal activity during pre-monsoon changes the estuary into a vertically mixed, eutrophic and flow-restricted system supporting an enhanced organic production. This implies that monsoon-induced hydrology plays an important role in regulating the nutrients, secondary production and even the migrant fauna of the estuary. The system is delicately poised, as continuous release of pollutants including nutrients into this estuary would suppress fish and shell fish production, where only pollution tolerant species can exist.

Monsoonal impact on planktonic standing stock and abundance in a tropical estuary (Cochin backwaters – India)

Environmental studies in the Cochin backwaters (CBW), a tropical estuary along the southwest coast of India showed that seasonal fluctuations in salinity created by the monsoonal rainfall and associated run off is a major factor controlling the distribution and abundance of micro- and mesozooplankton. During premonsoon season, the CBW was characterized by warm waters (av. 32.6 ± 0.6 °C) with relatively high salinity (>23; except in the lower estuary). On the other hand, fresh water was found to dominate the entire area during monsoon and postmonsoon seasons. The enormous input of nutrients (nitrate, phosphate and silicate) into the estuary from various sources (industries, agriculture and domestic) was responsible for the high phytoplankton biomass (av. 10.4 ± 10.1 mg m −3) irrespective of seasons. The phytoplankton community was, in general, dominated by diatoms (av. 88 ± 12%), and proliferation of multiple species of diatoms ( Skeletonema costatum, Thalassiosira subtilis and Nitzschia closterium – 1600 × 10 3 cells L −1) at different locations were observed especially during high saline condition. In case of zooplankton (micro- and meso), high standing stocks (micro av. 81.4 ± 48.1 mg C m −3; meso av. 88 ± 125 mg C m −3, respectively) were recorded during the premonsoon season. Copepods (e.g. Calanoids) formed the abundant group (av. 75 ± 18%) in the mesozooplankton community irrespective of seasons. The ratio of carbon content between phytoplankton and zooplankton ( P: Z) was quite high (>100) during monsoon and postmonsoon seasons, but became low during premonsoon season (<5). Hence, it is suggested that during the periods of fresh water dominance, the trophic food web of Cochin estuarine system is characterized by substantial amount of unconsumed carbon at primary level owing to the reduction in phytoplankton grazers (zooplankton).

Bioaccumulation of Toxic Metals by Fish in a Semi-Enclosed Tropical Ecosystem

Concentrations of Zn, Cd, Pb, and Mn in different tissues of 17 species of fish from a tropical estuary (Cochin backwaters) are presented. The metal selectivity index (MSI) was found to be a better tool compared with the tissue selectivity index (TSI) for explaining bioaccumulation. Regardless of the tissue type, accumulation was maximum for Zn and minimum for Cd. A distinct metal accumulation capacity for each species was noteworthy. The low variability in metal content in the gills indicated its inertness towards bioaccumulation compared with muscle or liver. The high positive correlation between Zn and Pb in tissues is indicative of the anthropogenic impact in the estuary. Conclusions are that, in a weakly polluted area, the organ of choice for estimating bioaccumulation potential is the liver, whereas in a heavily polluted area, the tissue of choice is the gill. The data presented here may be of help for forensic investigations in tropical ecosystems, for evaluation of contaminant impact, and for assessing past contamination events. Fish are good indicators of contamination, and the composition of bioaccumulative data for different species can serve in establishing a bioaccumulation database for that area, useful as a starting point (background) in forensic investigations.

Impact of freshwater influx on microzooplankton mediated food web in a tropical estuary (Cochin backwaters – India)

The diversity, abundance and biomass of microzooplankton in Cochin backwaters were studied for the first time during pre-summer monsoon to peak of summer monsoon (April–July 2003) to understand the impact of large freshwater influx. Microzooplankton abundance and biomass were highest during pre-summer monsoon (av. 3817 ind. L −1 and 146 μg C L −1) that declined with the onset (av. 2052 ind. L −1 and 45 μg C L −1) and peak (av. 409 ind. L −1 and 10 μg C L −1) summer monsoon. Species diversity, richness and evenness of microzooplankton also showed similar trends as that of abundance and biomass. Grazing experiment showed that microzooplankton consumes 43 ± 1% of the daily phytoplankton standing stock during the high saline condition (27.5). Low abundance of microzooplankton during summer monsoon period (1/8 of the pre-summer monsoon value) along with the concomitant occurrence of low mesozooplankton (1/8 times of pre-summer monsoon value) suggests that there could be a general lack of planktonic grazers. This would result in a weak transfer of primary and bacterial carbon to higher trophic levels, eventually leaving behind much unconsumed basic food in the estuary during summer monsoon. Thus a major portion of the primary carbon either settles down or gets transported to the coastal regions during monsoon. High flushing of Cochin backwaters also facilitates faster removal of primary producers to the coastal regions during monsoon.

Salinity-induced survival strategy of Vibrio cholerae associated with copepods in Cochin backwaters

The occurrence of Vibrio cholerae in water, sediment and copepods was studied over a wide range of salinity using conventional and polymerase chain reaction (PCR) techniques in the Cochin backwaters. V. cholerae occurred either as culturable or non-culturable form in this tropical estuary. During the pre monsoon period when high salinity prevailed (35.5 psu) V. cholerae was associated with copepods only in non-culturable form, but with the onset of monsoon when lower salinity prevailed, copepod-associated- V. cholerae reverted back to culturable form. The optimum salinity range for culturability was found to be 15–20 psu. This points to the fact that salinity is a major factor that which influences V. cholerae’s culturability and its association with copepods in Cochin backwaters.

HYDRODYNAMICS AND SALINITY TRANSPORT MODELLING OF COCHIN ESTUARY

ABSTRACT Understanding the hydrodynamics and transport process in coastal water bodies is very important in the design, construction and maintenance of various structures such as ports, harbours, jetties etc. and the protection of these water bodies against environmental degradation. The solution to coastal water or estuary problems can be obtained through physical models, analytical solutions or numerical models. In the numerical modelling, the hydrodynamics and transport information are obtained by solution of shallow water and transport equations. Backwaters at Cochin, south India, constitutes long and narrow water bodies lying parallel to the coast but separated from it by an equally narrow stretch of land, being open to the sea only at Cochin. In this paper, the hydrodynamics and salinity transport process of Cochin backwaters have been simulated using numerical models considering it as a branched estuary.

Concentrations of suspended particulate organic carbon in the tidal Yorkshire Ouse River and Humber Estuary

Data are presented for particulate organic carbon (POC) and particulate nitrogen (PN) concentrations in the Humber Estuary and tidal River Ouse Estuary. The POC data were derived from approximately monthly surveys and are consistent with data reported for suspended particulate matter (SPM) in the non-tidal River Ouse (the freshwater river) and with SPM, or bed sediments, in estuarine ecosystems such as the Mississippi, Delaware, San Francisco Bay, Tolo Harbour, the Vellar Estuary and Cochin Backwater, as well as the Loire, Gironde, Ems and Tamar Estuaries. Relative to the dry weight of SPM, the Humber-averaged organic carbon and nitrogen percentages during the year February 1995–March 1996 were 2.6±0.6% (mean and S.D.) and 0.21±0.04%, respectively. The ratio of Humber-averaged POC to Humber-averaged PN was 13±3. Higher POC levels were observed near the Humber’s mouth and in the adjacent coastal zone during ‘bloom’ conditions, and in the upper estuarine reaches during large, winter and springtime freshwater inflows. At these times of high runoff, the POC content of SPM increased progressively up-estuary from the coastal zone to the tidal River Ouse. When inflows became very low, during late spring to early autumn of 1995, both the freshwater–saltwater interface (FSI) and the strengthening turbidity maximum (TM) moved further up-estuary and the POC content of SPM in the upper reaches of the Ouse became lower compared with that immediately down-estuary. This led to a poorly defined POC maximum near the confluence of the Humber, Ouse and Trent, before POC eventually decreased again towards the coastal zone. The lower POC contents in the upper estuarine reaches of the tidal Ouse may have been partly due to POC respiration by heterotrophic bacteria attached to SPM within the TM, consistent with the severe oxygen depletion observed there during high turbidity, summertime spring tides.

Hydrobiology of the Cochin backwater system – a review

On the south west coast of India, there is an extensive estuarine system of backwaters, of which Vembanad Lake is the largest. The backwaters of Kerala support as much biological productivity and diversity as tropical rain forests. They are responsible for the rich fisheries potential of Kerala. Cochin backwaters situated at the tip of the northern Vembanad lake is a tropical positive estuarine system extending between 9° 40′ and 10° 12′N and 76° 10' and 76° 30′ E with its northern boundary at Azheekode and southern boundary at Thannirmukham bund. The lake has a length of 80 km and the width varies between 500 and 4000 m. A channel, about 450 m wide at Cochin gut and another at Azheekode, make permanent connections with the Arabian Sea. The depth of the estuary varies considerably. While the shipping channels are maintained at a depth of 10–13 m, the major portion of the estuary has a depth range of 2–7 m. Water from two major rivers viz., Periyar and Muvattupuzha drain into this estuary. During south west monsoon, the estuary is virtually converted into a freshwater basin even in areas around barmouth where salt water penetration occurs below 5 m depth only. The major hydrological variable in the Cochin backwaters is salinity, similar to the situations encountered in estuaries with a gradual declension of salinity from 30 at the entrance of the estuary to 0.2 at the point of entry of the rivers. Salinity gradient in the Cochin backwaters supports diverse species of flora and fauna depending on their capacity to tolerate oligohaline, mesohaline or marine conditions. Low lying swamps and tidal creeks, dominated by sparse patches of mangroves with their nutrient rich physical environment, support larvae and juveniles of many economically important species. Backwaters also act as nursery grounds of commercially important prawns and fishes. The fields around the backwater are suitable for aquaculture. These areas support traditional, seasonal and perennial prawn fishery. The changes in the hydrology controlled by the seasons play an important role in regulating the migrant fauna of the estuary. The Cochin backwater supports a well established endemic fauna. The nutrients and pollutants introduced into the estuary control to a great extent the distribution and abundance of less tolerant species in ecologically sensitive areas in the backwaters. Cochin backwaters, widely regarded as one of the polluted estuaries in India, receive contaminated freshwater inputs and discharges of effluents and partially treated sewage from many points throughout its tidally mixed zone. Recently, changes brought about in the estuary like reclamation and consequent shrinkage of the backwaters and the discharge of pollutants have made an adverse impact on the potential of aquatic ecosystems that used to support high levels of bioproductivity and biodiversity. The construction of Thannirmukham bund and Thottapally spillway to prevent salt water penetration into the paddy fields during pre-monsoon has led to serious ecological problems by interrupting the natural ebb and flow of tides. The hydrography, floral and faunal composition – its spatial and temporal variation plus assessments of the impact of the anthropogenic activities are presented in this review. An attempt to critically evaluate the status of the estuary from the biological and pollutional stand point is also done.

Metal concentrations in recently deposited sediments of Cochin backwaters, India

The concentrations of a number of metals (Cd, Cu, Co, Cr, Fe, Mn, Ni, Pb and Zn) were determined in recently deposited sediments before, during and after flood conditions in the lower reaches of two large tropical rivers and in their adjoining estuarine beds of the Cochin backwater system, southwest India. Markedly elevated concentrations (ppm) of some metals, Cd (0.6–1.8), Cr (20–35), Ni (20–45) and Pb (12–18), were observed near the discharge outlets of industrial units. The results show enrichment of metals during post-flood periods in selected regions of the estuary, indicative of accumulation in sedimentary material. There were pronounced seasonal variations in the distribution of trace metals in the sediments which coincided with the flushing of bottom bed material to nearshore coastal plains. This study reveals that the transport of trace metals associated with bottom sediments occurs predominantly during the monsoonal months (flood conditions). Analyses of dissolved and particulate metals in overlying waters revealed that Cu and Cd concentrations consistently covaried, while Zn, Ni and Pb covaried on a seasonal basis with sediment-associated metals. There was no correlation between trace metal concentrations and organic carbon content of the sediments.

Seasonal variation of mercury, copper, and zinc in the prawn Metapenaeus dobsoni (Miers) from Cochin backwaters

Seasonal variation of mercury, copper, and zinc in the prawn Metapenaeus dobsoni (Miers) from Cochin backwaters

Development and Ecodisaster: A Lesson from Cochin Backwater System

Kerala, with a unique climate, has rich and varied ecosystems with luxuriant and diverse plant and animal communities. This has led to a high density of human population. The State has resorted to modern technological methods for its economic development which include industrialization and improvement of agricultural production. The establishment of a modern port at Cochin has transformed the region into the industrial capital of the State. Simultaneous with economic progress, the environmental conditions have become deranged due to large scale shipping operations. Of late the environmental problems are increasing in the highly productive backwater system, due to industrial effluents. How developmental programs can undermine the ecological balance and cause deleterious effects as well as unforseen consequences are well illustrated by the deltaic region of Kuttanad - “the rice bowl of Kerala”. Dams, at the upper reaches of the rivers, provide power for industry and water for irrigation. But inadvertent denudation of the forests due to continuous human settlement and related activities will not only damage the dams, the industry and agriculture but also the climate of the region. The high density of population exerts undue pressure on the ecosystem whether it be terrestrial, aerial or aquatic and causes serious imbalances.

Population Dynamics of Estuarine Amphipods in Cochin Backwaters

Population dynamics of 11 gammarid amphipod species (belonging to 9 genera), collected from Cochin backwaters, have been studied for the first time, based on an year round collection. The species are: Corophium triaenonyx Stebbing, Photis digitata Barnard, Grandidierella gilesi Chilton, Melita zeylanica Stebbing, Eriopisa chilkensis (Chilton), Quadrivisio bengalensis Stebbing, Grandidierella bonnieri Stebbing, Cheiriphotis megacheles Walker, Ampelisca zamboangae Stebbing, Perioculodes longimanus (Bate and Westwood) and Ampelisca cyclops Walker The highly varying salinities (0 to 36.20% S) are one of the major limiting factors which govern the numerical density and species diversity of these gammarid populations. Except for the 3 high-saline species A. zamboangae, A. cyclops and P. longimanus, which are recorded during late January, all other species contribute substantially to the ecosystem. C. megacheles and G. bonnieri are estuarine and failed to establish themselves. C. triaenonyx is the most widespread species inhabiting all stations with maximum numerical abundance. The coefficient of correlation of different groups with temperature, salinity, dissolved oxygen, C/N ratio and phosphorus revealed that representatives of the families Arnpeliscidae, Gammaridae and Photidae are negatively correlated with salinity. Members of the family Corophidae showed some positive correlation with salinity. None of the groups exhibited significant correlation with temperature or with dissolved oxygen. The effect of temperature, salinity and dissolved oxygen on the production of gammarid amphipods was studied by multiple regression analysis. Salinity was found to be the prominent factor controlling the abundance of gammarid amphipods, followed by temperature and dissolved oxygen. The fitted regression was found to be significant at the l % level (P < 0.01) only for Station

コチン潟産食用魚の品質に対する発光細菌の影響

コチン潟産食用魚の品質に対する発光細菌の影響

Distribution and seasonal variation of temperature and salinity in Cochin Backwaters [west India] : Lakshmanan, P.T., C.S. Shynamma, A.N. Balchand, P.G. Kurup and P.N.K. Nambisan, 1982. Indian J. mar. Sci., 11(2): 170–172. Nambisan: Dept. of Mar. Sci., Univ. of Cochin, Cochin 682016, India

Distribution and seasonal variation of temperature and salinity in Cochin Backwaters [west India] : Lakshmanan, P.T., C.S. Shynamma, A.N. Balchand, P.G. Kurup and P.N.K. Nambisan, 1982. Indian J. mar. Sci., 11(2): 170–172. Nambisan: Dept. of Mar. Sci., Univ. of Cochin, Cochin 682016, India