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were located in the nearshore waters. However they noticed an increase in the diversity of benthos in deeper waters as observed by Parulekar et al., (1992). High production reported by Devassy et al., (1987) in the near shore areas (5m depth) was also attributed to the variation in sediment texture. High biomass and numerical abundance in shallow depth zones can be due to high primary productivity (Radhakrishna et al., 1978). Parulekar and Wagh (1975) stated that Arabian Sea is charecterised by rich bottom fauna which is attributed to the inflow of equatorial waters of low salinity causing stratification in the water column. Low benthic biomass at higher depths is probably because of an inflow of subsurface water with low oxygen content. In the present study there was no obvious latitudinal variation in benthic biomass but comparatively high biomass values were observed in north in both seasons. This is in agreement with earlier reports of Neyman (1969), Humphrey (1972), Parulekar and wagh (1975), Parulekar et al., (1982a) and Ansari et al., (1996). As per the differential production in the south and north latitudes, Parulekar and Wagh (1975) demarcated the Arabian Sea shelf into two zones, one north of 20° N upto 23° and south of 20° N upto 17° Nand biomass in the Arabian Sea decreases gradually southward. Humphrey (1972) has attributed high phosphate content and higher primary production to the di fference in biomass production in the northern region as compared to the southern region. The rich bottom life in the Arabian Sea is attributed to rich plankton in the region enhanced by upwelling and intrusion of subsurface water during monsoon (Qasim, 1977). Neyman (1969) suggested that 15° N is the boundary between high and low productive zones. During pre-monsoon, off Ratnagiri showed an exceptional high biomass and density at 75 m depth. This variation observed may be due to the impact of localized biotic or abiotic factors or both. But Elizarov (1968) reported abundance of bottom life in the southern part of Arabian Sea and correlated the abundance to an inflow of equatorial waters of low salinity causing a strongly expressed stratification of water masses. Harkantra et al., 105
(1980) also reported high values in shallow region with more diverse fauna in southern region of west coast and the difference may probably due to the influence of equatorial waters and upwelling. In the areas where ridges and sills develop low oxygen and high H 2S condition, the benthic biomass is either very impoverished or absent (Parulekar, 1986), However study of Joydas (2002) could not found any north-south variation in biomass in the west coast of India. Distribution of benthos showed a different pattern with higher population density in the southern latitude for both seasons as compared to the northern latitude. The change in trend could be due to variations in the size of the organisms. Usually population density and biomass are directly related but if the size variation among individuals is too large, the direct relation is lost. Parulekar and Ansari (1981) studied the macrobenthos of Andaman Sea and reported an inverse relationship between biomass and popUlation density. Ansari et aI., (1994) also reported that biomass did not follow the same trend as that of density due to the presence or absence of large sized organisms whilst Harkantra et al., (1980) observed a direct relation between benthic density and biomass except at few stations having large sized organisms in the west coast of India. The decrease of fauna towards deeper depths was influenced by environmental parameters like temperature, salinity and DO (Ingole et al., 2002; Parulekar and Ansari, 1981). Variation in temperature during pre-monsoon may influence the benthic popUlation. Ingole et al., (2002) reported temperature and salinity were regarded as regulators of the reproductive cycle of the marine invertebrates. Marine species inhabiting the tropical region generally have a narrow range of temperature tolerance since they normally live in a temperature regime that is close to their upper tolerance limit. The important variables controlling the distribution and abundance of benthic organisms in the tropical regime are salinity (Alongi, 1990; Parulekar and Dwivedi, 1974), and sediment stability (Wildish and Kristmanson, 1979; Warwick and Uncle, 1980). Seasonal variations observed in benthic production could be due to 106
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Certificate I hereby certify that t
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Contents Page No. Chapter 1. Introd
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the bottom. Ekman (1935) described
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wonns are the most abundant group a
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leadership of Sir James Clark Ross,
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Ansari et al., (1977b) carried out
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Gopalakrishnan and Nair (1998) cond
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Major objectives:- 1. To understand
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CMFRI (Central Marine Fisheries Res
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Joydas, T.V., Damodaran, R., 2001.
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monitoring committee (Atlantic Mari
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Vizakat Lathika, I-Iarkantra, S. N.
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analysed after acidification by tit
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used as stain prior to sorting and
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space. Therefore, it is very essent
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Fig. I - Station locations 32
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affected at high temperature. Most
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layers exhibit different oceanograp
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Transect wise variation in temperat
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3.2.2.3. Dissolved oxygen (DO) Dist
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monsoon temperature initially incre
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opined that limited mixing. high or
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Naqvi, S. W. A., Noronha, R. J., Re
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orr Mormugao orr Vernal 35.36 35.32
Page 62 and 63: The continental shelf and its adjoi
Page 64: sediments (4 stations). Silty sand
Page 68 and 69: fine sediments with comparatively h
Page 70 and 71: Narayana, 1991 ). Limited input of
Page 73 and 74: In general. two ditlerent patterns
Page 75 and 76: et al., (1980) reported values in t
Page 77 and 78: organisms living in the water and t
Page 79 and 80: Hashimi, N. H., Kidwai, R. M., Nair
Page 81 and 82: Postma, H., 1967. In Estuaries, Lau
Page 85: Depths Sand Silt Clay Organic matte
Page 90: • PRE'MONSOON SOUTHERN'TRANSECTS
Page 96 and 97: as the best indicators of the envir
Page 99 and 100: showed that northern transects have
Page 101 and 102: decreased from shallow to deeper de
Page 103: different depth zones showed that a
Page 106 and 107: cm 2 with a dominance of nematodes.
Page 108 and 109: and 6.08 g/m 2 were recorded during
Page 112 and 113: changes in the hydrographical and t
Page 114 and 115: factor for such a large difference
Page 116 and 117: Belegvad, H., 1932. Investigations
Page 118 and 119: Parulekar, A. H., Harkantra, S. N.,
Page 120: Savich, M. S., 1972. Quantitative d
Page 123 and 124: Traosects Polychaetes Crustaceans M
Page 125: Miscellaneous Transects Nematodes C
Page 128 and 129: Depths Nematodes Cope pods Foramini
Page 136 and 137: Wagh, 1975; Parulekar et ai, 1976;
Page 138 and 139: ones and 17 were included in the 'r
Page 140 and 141: Nephtydae (2%). Among the 20 sedent
Page 143 and 144: At 75 m zone, 31 groups/species wer
Page 145 and 146: Porbandar. At 50 m depth zone, fluc
Page 148 and 149: otTMumbai and Ratnagiri and low eve
Page 150 and 151: species richness at each depth zone
Page 153 and 154: E2.2.2.!. Richness (Margalef's inde
Page 155: I ):.2.2.2.4. Dominance (Pie/ou's i
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Tablc 17. Contd .. - Sternaspidae 0
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Table 20. contd .. G. alba 20 25 20
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150 Taxa 30m 50m 75m lOOm 150 m m D
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9% 1% o poIychaete • crustacea o
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a) c) e) g) Plate 5 a) Prinospio sp
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a) c) e) Plate 7 a) Cardium sp. d)
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7/. /ntroduct ion 7.2. Hydrography
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also showed a similar pattern with
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y most of the organisms. It was als
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with sand of which total density (r
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muddy bottom of the west coast of I
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crustaceans and miscellaneous group
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the organic rich environment with h
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Icvci (p
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mcioHmna serve primarily as rapid m
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surface chlorophyll a was 0.36mg I
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Devassy, V. P., Achuthankutty, C. T
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Longhrust, A. R., Pauly, D., 1987.
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Sikora, W. B., 1977. The ecology of
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Faunal groups Silty Clayey Mixed Sa
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Mannagoa to Porbandar located betwe
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against gastropods during pre- mons
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