P K Abdul Azis

Ecology of Indian estuaries—V: Primary productivity of the Ashtamudi estuary, south-west coast of India

Primary productivity at four representative stations in the Ashtamudi estuary has been presented. The average gross and net productivities in the surface water was maximum at Neendakara, the bar mouth zone and minimum at Kadapuzha, the riverine zone consistently exposed to pollution from paper mill effluents. Ashtamudi, the station directly on the gradient line and Kanjirakode, the station equidistant from Kadapuzha and Ashtamudi presented a transition phase with regard to the primary productivity. In the bottom water also productivity was minimum at the polluted zone. Generally productivity at sub-surface levels was higher than that at the surface. A seasonal pattern, independent of various environmental parameters, was discernible both in the gross and net productivity changes at surface and sub-surface levels. High concentrations of dissolved oxygen, silicate and nitrite helped to maintain higher productivities at Neendakara, Ashtamudi and Kanjirakode on several occasions during the year. The fact that productivity at the polluted Kadapuzha station was the lowest, indicates that the paper mill effluent has considerably disturbed the productivity mechanism of this otherwise healthy ecosystem.

Ecology of biofouling on Crassostrea madrasensis (Preston) (Mollusca:Bivalvia) in a tropical backwater

Ecology of biofouling on the edible estuarine oysterCrassostrea madrasensis (Preston) has been investigated in the Ashtamudi Backwater of the southwest coast of India. Fouling was highly conspicuous throughout the year and dominant groups included barnacles, serpulids, bryozoans and modiolids. Intensity of fouling varied from 73 to 179 % on living oyster valves and 65 to 172 % on dead valves with respective annual averages of 118 and 127%. Substrate selection and settlement of the different groups were mostly opportunistic. Barnacles were the most dominant, living and dead ones collectively contributing to about 26 % of fouling on living valves and 32 % on dead valves. Serpulid fouling was 22 % both on living and dead oyster valves, bryozoans 15 and 12%, modiolids 11 and 12% and the miscellaneous groups formed 27 and 20 % respectively. Availability of free settling space and fouling in relation to substrate size were also investigated. Total fouling was very intense on oysters of 25–35 cm2 size group. Impact of biofouling on oysters and certain earlier studies on the topic are discussed.

Benthic polychaetes in the anoxic sulphide biomes of the retting zones in the Kadinamkulam Kayal

Retting is the basic process serving as the backbone of the Coir industry in Kerala. The shallow fringes of Kayals (estuaries) and channels drawn from them are the traditional sites for the retting of coconut husk. Retting is brought about by the pectinolytic activity of micro‐organisms especially bacteria, fungi and yeasts degrading the fibre binding materials of the husk and liberating large quantities of organic matter and chemicals into the environment, including pectin, pentosan, tannins and polyphenols. Retting of coconut husk has thus led to anoxic conditions along with the increase in hydrogen sulphide and BOD5 with a sharp depletion in the biotic communities. This paper presents the species composition, occurrence, abundance and diversity of the benthic polychaete population in relation to sulphide pollution.

Ecology of Indian estuaries: studies on the zooplankton ecology of kadinamkulam backwater

Ecology of the zooplankton of Kadinamkulam Backwater, a brackish water lake along the south-west coast of India, has been studied from February 1980-January 1981. Seasonal distribution of the zooplankton followed an uniform pattern throughout the backwater. Zooplankton in the Kadinamkulam Backwater is composed of foraminifers, coelenterates, nematodes, rotifers, chaetognaths, polychaetes, cladocerans, ostracods, amphipods, copepods, decapod larvae, insect larvae, bivalves, tunicates, and fish eggs and larvae. Among these, rotifers, copepods and copepod nauplii are the major components which form the bulk of the zooplankton (nearly 98 %). A distinct regional variation is discernible in the dominance of zooplankton components. Copepods constitute the dominant group near the barmouth and middle portion of the backwater, while rotifers are dominant in the upper reaches, where freshwater influx was relatively high. Factors influencing seasonal variation and distribution have also been discussed.

Pollution indicators of coconut husk retting areas in the kayals of Kerala

The coast of Kerala is dotted with 31 kayals (estuaries) lying roughly parallel to the Lakshadweep sea and separated from it by a narrow strip of land 0.4 to 12 km wide. The abundant availability of coconut husk and the generally shallow nature of the kayals have led to the emergence of the coir industry as a massive cottage industry in the state. Fresh coconut husks, steeped in the shallow regions of kayals are allowed to remain soaked in water for periods ranging from 4–12 months. Retting is brought about by the pectinolytic activity of microorganisms liberating large amounts of organic matter and chemicals into the environment. The retting zones in estuaries are thus exposed to prolonged periods of anoxic condition resulting from a total oxygen depletion and remarkably high concentrations of hydrogen sulphide, thus causing extensive damage to the living, aquatic resources in the region. The paper deals with indicator organisms specific to pollution from retting of coconut husk in the kayals of Kerala.