Cochin Backwaters Research Articles

Sediments of the Cochin Backwaters [western India] in relation to pollution: Remani, K. N., P. Venugopal, K. Sarala Devi, S. Lalitha and R. V. Unnithan, 1980. Indian J. mar. Sci., 9(2): 111–114

Sediments of the Cochin Backwaters [western India] in relation to pollution: Remani, K. N., P. Venugopal, K. Sarala Devi, S. Lalitha and R. V. Unnithan, 1980. Indian J. mar. Sci., 9(2): 111–114

On a New Species of Hexapus De Haan (Decapoda, Goneplacidae) From Cochin

Some stake net collections from Thevara and Mulavukad within the Cochin backwater region (S.W. India) procured five specimens of an undescribed species of Hexapus De Haan, H. (Hexapus) estuarinus n. sp. A perusal of literature has indicated that Alcock (1900) described another species of Hexapodinae from the Bay of Bengal (Lambdophallus sexpe.r). Hexapus sexpes (Fabricius) is also reported to have been collected from India. The substratum at the place of collection is covered with silt and clay and the morphological features such as the reduced eyes and the thick fringes of hairs on either sides of the inhalent opening of the branchial chamber above the base of chelipeds indicate that the species is well adapted to such an environment.

Seasonal changes in the zooplankton population in the Cochin Backwater (a South Indian estuary)

1. The seaward part of the Cochin Backwater accomodates different types of zooplankton communities. 2. Some copepods and meroplanktonic larvae predominate in the plankton. 3. Abundance and diversity of the micro-zooplankton are positively correlated to salinity which indicates the type of water: mixture of fresh with seawater and the origin of the water: river, estuarine or marine. 4. The rain-dependent oligohaline water-community is poor and cannot develop due to short duration of this condition. The “true estuarine” community is the richest and the most diverse containing estuarine and marine and euryhaline marine species. 5. The types of communities present at a given point in the Backwater are transported to this point along with their original water.

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The diversity of brachyuran crabs of Cochin backwaters, Kerala, India was recorded in this study. Sampling was conducted on a monthly basis for a period of 2 years from June 2010 to May 2012 at 15 selected stations of the Cochin backwaters. A total of 24 species of crabs belonging to 16 genera and 8 families were recorded. The highest number of species was from family Portunidae (9 species), followed by Grapsidae (7 species). Six species were found to be commercially important, namely Scylla serrata, Scylla tranquebarica, Scylla sp., Portunus pelagicus, Portunus sanguinolentus and Charybdis feriata. The salinity gradient and the substrate suitability may be the reasons supporting diversity of brachyuran crabs in the Cochin backwaters.

The influence of salinity on a tropical estuarine shipworm Nausitora hedleyi Schepman (Bivalvia - Teredinidae)

Species belonging to the genus Nausitora (Bivalvia - Teredinidae) are generally confined to brackish waters. In the Cochin backwaters, a tidal estuary on the southwest coast of India, this genus is represented by the species N. hedleyi Schepman. Fresh settlement of the species in the area is noticed only during the period of low salinity, though the species of found to exist, throughout the year. Tests conducted to ascertain the effect of salinity changes on the activity of the borer showed that though it can endure a wide range, the optimum salinity range for early development was from 11.24–14.54%.

A preliminary survey of aquatic habitat in the Periyar River - A tributary to the Cochin backwater system.

A preliminary survey of aquatic habitat in the Periyar River - A tributary to the Cochin backwater system.

Application of a model to an estuarine ecosystem

The annual cycles of primary production and plankton succession in the Cochin Backwater, South India, are examined in the context of a model given by Margalef. The increased flushing of the estuary caused by the southwest monsoon is seen as the main driving force behind the changes which take place.Fish production in the estuary is high when compared with primary production; it is suggested that detritus is an important component of the food web.

Growth kinetics and nutrient requirements of two tropical marine phytoplankters

Growth rates of nutrient-depleted cells of Biddulphia sinensis Greville and Ceratium furca (Ehrenberg) Claparede et Lachmann as a function of phosphate and nitrate, follow the hyperbolic expression of the Michaelis-Menten equation. variations in the half-saturation constants (K s) for both species in each nutrient gave an index of their capacity to utilize these two nutrients when available either singly or in combination. The maximum growth rates (μmax) of the two species did not follow the trends shown by K s. Seasonal abundance of the two species in the Cochin Backwater (an Indian tropical estuary) showed that, at low concentrations of nutrients, C. furca becomes predominant; high nutrient concentrations present in the estuary during the monsoon months tend to increase the abundance of B. sinensis. The differences in the K s values of the two organisms seem to reflect their observed seasonal abundance in the estuary.

Organic detritus of a tropical estuary

Organic detritus of the Cochin Backwater (India) is largely composed of fine silt and sand particles around which organic matter adheres and forms aggregates. In addition to plankton, large quantities of benthic algae, rooted plants, animal matter, suspended soft mud and the material brought down by the rivers and land runoff constitute the main sources of detritus. Detritus sedimentation in the estuary attains its maximum from April to June. Detritus forms a major portion of seston, while phytoplankton productivity constitutes 0.1 to 1.0% of settled detritus. Detrital pigments include degraded chlorophyll (phaeophytin), which has a marked seasonal variation; detrital carbon, phosphorus and nitrogen show little change during the year. The caloric value of detritus, calculated from protein, carbohydrate and lipid fractions and also from total carbon, indicates that sedimented detritus does not have a high nutritional value. However, being a readily available material, its entry into the food chain seems to increase the efficiency of energy transfer from one trophic level to another.

Coexistence of species of Acartiidae (Copepoda) in the Cochin Backwater, a monsoonal estuarine lagoon

A study was made of copepods of the family Acartiidae which form the dominant component of the plankton in the Cochin Backwater (Kerala, India). At least nine species inhabit the backwater at one time or another, more than have been recorded for any other area. Reasons were sought for this diversity. The surface plankton was sampled from the head of the estuary to the mouth and from one season to another. There were large seasonal changes in salinity (0 to 35 ‰), due to monsoonal flooding, and associated changes in species composition. Species diversity was highest during the dry season and lowest in the wet. It is suggested that this annual catastrophic flooding leads, in the long run, to high species diversity by imposing a regular check on interspecific competition.

The ecology of hydromedusae from the Cochin area

A survey has been made of medusae found in plankton samples taken fortnightly over a period of a year at 2 fixed stations in the waters near Cochin, Kerala, India. Twenty two species were identified, 8 of them were recorded for the first time in this region. The 2 stations were found to be controlled by different hydrographical regimes; that at Aroor is entirely characterised by backwater conditions, with salinity afternating from fresh water to 32‰ S according to the monsoon cycle; the station at Fairway Buoy is also dominated by the monsoon cycle, with mixed, low-salinity (11 to 13‰) waters at the surface, and upwelled Arabian Sea water in the bottom layer during the Southwest monsoon Life cycles are discussed and the population dynamics of Eutima commensalis at Aroor are analysed. A mathematical model is proposed for more detailed population dynamics studies of plankton species in the Cochin Backwaters, taking E. commensalis as an example.

The life cycle of Eutima commensalis sp. nov. (Eutimidae, Hydromedusae)

Developmental stages of the medusa Eutima commensalis sp. nov. were obtained from plankton collections made at 2 fixed stations, one at Fareway Buoy and the other at Aroor in the Cochin backwater system. Six stages were arbitrarily assigned and described. The hydroid and the medusa of this form were found to occur in these waters throughout the year, except during the monsoon months from June to September. The hydroid is endocommensalic on wood-boring molluscs such as Nausitora hedleyi, Teredo furcifera and Martesia striata.

Tidal cycle and the environmental features of Cochin Backwater (a tropical estuary)

In the Cochin Backwater the tides are of a mixed, semidiurnal type with a maximum range of about 1 m. Two high and two low water-marks occur each day, with an appreciable difference in range and time. The various environmental features such as temperature, salinity, dissolved oxygen, pH, seston, nutrients, alkalinity and chlorophyll are greatly influenced by the tidal rhythm. The differences in almost all these parameters are more marked at the surface than at the bottom. The magnitudes of variation are not consistent and largely depend upon the time of the year.

Nutrients of the Cochin Backwater in relation to environmental characteristics

The nutrient distribution of the Cochin Backwater was studied at 6 stations throughout the year. The depth profiles of phosphorus (inorganic and organic), nitrogen (nitrate and nitrite) and silicon, showed a marked seasonal rhythm, induced by the local precipitation and land runoff. Changes in other environmental features such as temperature, salinity, dissolved oxygen, pH and alkalinity were small during the premonsoon period when the system remains marine-dominated, and large during the monsoon period when the estuary becomes freshwater-dominated. Seasonal changes in the hydrographical conditions of the adjoining coastal waters of the Arabian Sea which influence the backwater system have been discussed.

Solar radiation and its penetration in a tropical estuary

The Cochin Backwater which is an estuarine area on the west coast of India receives maximum solar radiation from December to March and minimum from June to September. During the monsoon months the estuary becomes highly turbid as a result of the inflow of a considerable amount of fresh water. Seasonal changes in the attenuation coefficient showed that light penetration is small throughout the year and least during the monsoon months. No relationship was found between the attenuation coefficient and amount of suspended matter. The upward scattering of light in the estuary ranged from 2–8% of the incident illumination and the transmission of surface light at Secchi depth was about 23%. The compensation depth in the estuary varied from 2.5–5 m and the zone of optimum illumination for maximum photosynthesis lay between 0–1.5 m.

Studies on the benthic fauna of Cochin backwater

Studies on the macrofauna from the five selected stations spread over a distance of about 25 km. in the Cochin backwater showed that the benthic biomass was greater in the regions which were near the sea. The abundance of organisms decreased progressively towards the more estaurine zone. The bivalves, gastropods and polychaetes were the most predominant forms in the sample. The presence of larger bivalve,Meretrix ovum and the polychaete,Diopatra neopolitana at the stations near the sea considerably increased the benthic biomass at these stations. Organisms of lesser importance were crabs, fish, ophiuroids and sea anemones. Studies on meiobenthos which was restricted to the estuarine zone only showed a high degree of abundance of foraminiferans and nematodes. Foraminiferans were more abundant at stations nearer the sea suggesting their preference for marine conditions. The nematodes on the other hand were more dominant at stations away from the sea. An examination of the substrata at five stations showed that the conditions were different from one place to the other. A substratum of fine and coarse sand seems to support a denser benthic population. The distribution and abundance of macro and meiobenthos when compared with the seasonal changes in physico-chemical conditions of the backwater was investigated. It appeared that perhaps the most important factor governing the quantitative distribution of benthos is the salinity. Settling stages of bivalves and gastropods, which are of purely marine origin, though appear in large numbers, do not survive in estuarine conditions. Areas of high salinity in the backwater are those which are rich in nutrients and chlorophyll and were found to support a denser benthic population.

Seasonal cycles of hydrological events in Vellar Estuary : Jacob, J. and K. Rangarajan, 1962. Proc. First All-Ind., Cong. Zool., 1959, Sci. Pap., 2: 329–350. Also in: Annamalai Univ. Mar. Biol. Sta., Porto Novo, S. Ind., Publ. 1961–1962

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.

Observations on the prawn fishery of the Cochin backwaters with special reference to the stake net catches : Krishna Menon, M. and K. Raman, 1961 (Issued Sept. 1962). Ind. J. Fish., 8 (1): 1–23

Observations on the prawn fishery of the Cochin backwaters with special reference to the stake net catches : Krishna Menon, M. and K. Raman, 1961 (Issued Sept. 1962). Ind. J. Fish., 8 (1): 1–23

植物性網糸の耐蝕性の研究

1. Rotting resistance of cotton, sun hemp, Italian hemp, sisal, manila and coir twines immersed in Cochin backwater has been determined. 2. The values of rotting coefficient K in TAUTI'S formula log T/T0-T=-(K log e)+ Const. were calculated from the results obtained by the experiments and it was confirmed that the value of K is inversely proportional to the diameter of twines dipped. The values of K worked out are as follows: and Higher the value of K, the rotting would be quicker. 3. Number of days N till a twine loses half of its original breaking strength is proportional to the diameter of the twine dipped in water, i. e. N=αD. Where a is constant and when D the diameter is in mm, N=6.50 D for cotton =5.75 Dfor sun hemp =2.55 D for Italian hemp =6.00 D for sisal and =7.40 D for coir.

Trimethylamineoxide content of marine prawns occurring in the backwaters and in the sea off Cochin

TRIMETHYLAMINEOXIDE has been reported in most marine fishes and several other marine animals occurring to the extent of l~o while it is absent or present only in very small concentration in freshwater fishes. 1 This distribution suggests the probability of its having a role in the physiology, possibly in the osrnoregulation, of marine fishes. The oxide is also the precursor of trimethylamine which is produced postmortem in seafish through bacterial action. The estimation of trimethylamine in fish muscle has been found useful as an index of spoilage in seafish. 2 The occurrence and distribution of trimethylamineoxide in fishes has thcrcfore drawn the attention of physiologists and fish technologists. In this context the values of trimethylamineoxide content of marine prawns belonging to different species caught from the sea off Cochin and from the Cochin backwaters respectively determined by us recently appear to be significant.