Library

Notes: Abstract 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.

Notes: Abstract The filtration rate has been determined for Electra pilosa and Conopeum reticulum, acclimated at 4 constant temperatures (6°, 12°, 18°, 22°C). Cryptomonas sp. was used as the test food-organism. Temperature affects filtration rate in both bryozoans. Clearance rate, measured at hourly intervals during the course of the experiment, was never uniform. Possibly, temporary reductions in ciliary activities were induced by the artificial conditions under which the experiments were carried out. The results obtained compare well with those reported by Bullivant (1968) on Bowerbankia imbricata, a cosmopolitan ctenostome. Rate of food passage through the alimentary canal is affected by temperature. The present study is the first to demonstrate the effect of temperature on the rate of filtration in bryozoans.

Notes: Abstract A comprehensive study of the fouling organisms encountered at the New Mangalore Port at Panambur and the Fish Landing Jetty on the Nethravati-Gurpur estuary near the old Mangalore Port, India, was made. Barnacles, oysters, bryozoans, polychaetes and hydroids are the dominant groups of foulers encountered in this region. Barnacles are by far the most important foulers. Distinct seasonal abundance in settlement was noticed in the different groups. The major peak settlement of barnacles occurs in November and December. Continuous settlement of this group in the harbour indicates the presence of larvae throughout the year in the marine locality. The absence of freshly settled spat in the estuarine locality shows that these larvae do not foul structures in the Fish Landing Jetty during the monsson period. The pattern of oyster settlement indicates that the spat of Crassostrea madrasensis and c. cucullata settle during January, March, May and October in this region. This group remains in the fouling community throughout the year. Only typical marine bryozoans are harboured in abundance in the fouling community. Polychaetes occur in great numbers during April and December.The differences in the quality and quantity of the fouling communities are controlled by their breeding periodicity,seasonal fluctuations in the hydrographical conditions, and the species composition of the sedentary community of this region.

Notes: Abstract An extensive study was conducted on the settlement and seasonal succession of fouling bryozoans in and around Cochin Harbour during the period 1965 to 1966; it was the first study of its kind performed in Indian waters. A total of 14 species was recorded from localities which were ecologically dissimilar. A distinct succession of species, mainly of a seasonal character, was observed. Seasonal succession usually occurs in localities where seasons are well marked, and where different species of animals with short life spans settle during particular times of the year. The study has shown that a distinct seasonal succession of bryozoans occurs in this locality; out of the 14 species which appeared on the panels not one species settled throughout the year. This was due to seasonal differences in the ecological conditions which prevailed in the area investigated. The significant seasonal influences on the incidence of bryozoans led to a categorisation of the species into the following patterns (a) typical brackish-water forms not encountered in purely marine localities; (b) typical brackish-water forms which may occur in marine localities; (c) typical marine forms never found in localities where low salinity conditions prevail.

Notes: Abstract Nine bryozoan species have been illustrated and described for the first time from Indian waters: Parasmittina signata (Waters), P. tubula (Kirkpatrick), P. elongata (Okada and Mawatari), P. parsevalii (Audouin), P. aviculata (Mawatari), P. egyptiaca (Waters), P. tropica (Robertson), P. california (Robertson), P. projecta (Okada and Mawatari) A comparison of the important morphological characteristics with illustrations and descriptions of these species, published in previous papers, has revealed a considerable degree of variability. My findings extend the geographical distribution of 5 species to the Indian Ocean. They demonstrate that the representatives of the genus Parasmittina Osburn in Indian waters are Indo-Pacific in character.

Notes: Abstract Three species of bryozoans—Membranipora membranacea (L.), Electra pilosa (L.) and Conopeum reticulum (L.) — are capable of acclimating to elevated temperatures, above the normal range experienced in nature, when exposed to a gradual increase in ambient temperature. Conspicuous differences in LD 50 values, as a consequence of acclimation, occur between representatives of the same species acclimated and grown at constant temperatures in the laboratory. The tolerance range of these species is influenced by their thermal history in the laboratory. While increased ambient temperatures accelerate growth rate, final colony size attained after prolonged exposure declines at higher temperatures. The size of zooecia attained is inversely proportional to the test temperature. Colonies of E. pilosa maintained at 22°C develop erect branches. Hence, it is probable that E. pilosa forma erecta is only a growth form of normally encrusting colonies of E. pilosa. Temperature affects rate of regeneration.

Notes: In this article, we demonstrate the effect of magnetic linear dichroism (MLD) in electron energy loss spectroscopy (EELS), as applied to the antiferromagnetic compound α-Fe2O3. The experiments were performed in a high resolution scanning transmission electron microscope (STEM), capable of producing a nanoscale electron probe. The resultant difference spectrum is consistent with the MLD observed in x-ray absorption spectroscopy and the known magnetic structure of Hematite, suggesting that MLD in EELS, coupled with the high spatial resolution attainable in STEM, is a useful technique in the study of magnetic microstructure. © 1997 American Institute of Physics.

Notes: Kurzfassung In Zooiden der marinen BryozoaElectra pilosa (L.) wurden zahlreiche Exemplare des freilebenden NematodenPelagonema obtusicauda Filipjev gefunden. Die Nematoden besiedeln offensichtlich die noch jungen Kolonien, in denen sie auch zur Fortpflanzung gelangen. Die Art der Beziehung zwischen den beiden Organismen bedarf noch weiterer Klärung.