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N. and Stewart, J. W. B., Soil Biol. Biochem., 1988, 20, 459–464. 28. Salih, H. M., Yahya, A. I., Abdul-Rahem, A. M. and Munam, B. H., Plant. Soil., 1989, 120, 181–185. ACKNOWLEDGEMENT. R.M. thanks Dr Johanna Dobereiner, EMBRAPA, Brazil for providing type strains. Received 23 March 2000; revised accepted 5 July 2000 S. SESHADRI *,‡ R. MUTHUKUMARASAMY # C. LAKSHMINARASIMHAN † S. IGNACIMUTHU * *Entomology Research Institute, Loyola College, Chennai 600 034, India # Main Bio-control Research Laboratory, Tamil Nadu Co-operative Sugar Federation, Chengalpattu 603 001, India ‡ Department of Botany, AVVM Sri Pushpam College, Poondi 613 503, India Jellyfish ingress: A threat to the smooth operation of coastal power plants Coastal areas are often preferred for set- ting up power stations due to the easy availability of sea water for condenser cooling. In such coastal power stations, there are instances of plant shutdown due to excessive accumulation of fouling debris inside the cooling circuits. In one of the power stations in UK, the quantity of fouling debris removed was about 40 tonnes per year and this was at times as high as 130 tonnes 1 . Recently, there have been a few instances, when jellyfish in large numbers entered the sea water cooling system of the Madras Atomic Power Station (MAPS) at Kalpakkam, causing plant shutdown 2 . While moderate ingress of jellyfish leads to a reduction in the plant efficiency, large arrivals may even lead to forced shut down of a power plant 2–4 . The present study deals with the ingress of jellyfish in MAPS cooling water system and its impact on the power plant operation. MAPS consisting of two units, each of 235 MW(e) capacity is located at Kal- pakkam (12°33′N and 80°11′E), 65 km south of Chennai (Figure 1) on the east coast of India. The power plant uses sea water as its condenser coolant. The sea water intake is located 420 m away from the shore and is connected through an approach jetty (Figure 1). Sea water enters the cooling water system through 16 win- dows (3.2 m height and 2 m width) located radially in the intake structure. From the intake point, water flows into the forebay by gravity. The sea water travels through the Travelling Water Screens (TWS) at the forebay before 12 pumps (6 for each unit) draw the sea water for condenser cooling as well as for cooling the process water heat exchan- gers. The TWS is made up of stainless steel mesh (20 mm pore size) with a plat- form to collect debris attached at an angle of 90° (Figure 1). The TWS moves vertically and takes about 12 min to complete a rotation. Jellyfish arriving at the TWS were collected in the forebay during the period from January 1995 to December 1996. During collection, individuals arriving for a period of one hour, every alternate day were pooled. They were separated into different species and weighed using a common balance. From these data jelly- fish landing was calculated and expressed as tonne/month. Jellyfish-induced water blockage in the conduit was assessed by determining the water level difference between the fore- bay and the intake (head loss). The meas- urement was done from the platform at the respective places using a lead and line. Three species of jellyfish were obser- ved during the study period, namely Crambionella stuhlmanni, C. buitendijki and Dactylometra quinquicirrha. Among these three species, D. quinquicirrha was the dominant one. In 1995 and 1996, the percentages of each species of the jelly- fish to the total jellyfish collected were: D. quinquicirrha 45 and 40%, C. buit- endijki 34 and 36%, C. stuhlmanni 21