L - Cochin University of Science and Technology
L - Cochin University of Science and Technology
L - Cochin University of Science and Technology
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Many workers have suggested that salinity had a strong relation with benthos.<br />
lIarkantra <strong>and</strong> Parulckar (1991), Vizakat et al.,(l99l) <strong>and</strong> Harkantra <strong>and</strong> Parulckar<br />
(1994) reported decreased population <strong>of</strong> benthos during monsoon months <strong>and</strong> its<br />
recolonisation after the monsoon indicated the role <strong>of</strong> salinity in benthic production.<br />
Ingole <strong>and</strong> Parulekar (1998) stated that salinity could act as a community regulator<br />
determining the physiological activity <strong>of</strong> marine organisms. They observed two<br />
maxima in faunal abundance first in December <strong>and</strong> second in March. This agrees<br />
with the present study as high benthic biomass was observed during pre-monsoon<br />
<strong>and</strong> it might be due to the second recolonisation after the post-monsoon season with<br />
increasing salinity as observed by the above authors along with other ecological<br />
parameters. Temperature <strong>and</strong> salinity <strong>of</strong> the sea water were regarded as important<br />
regulators <strong>of</strong> the reproductive cycle <strong>of</strong> marine invertebrates (Kinne, 1977; lngole <strong>and</strong><br />
Parulekar, 1998) <strong>and</strong> those marine species inhabiting the tropical region generally<br />
have very narrow range <strong>of</strong> temperature tolerance since they normally live in a<br />
temperature regime that is closer to their upper tolerance limit. Therefore important<br />
variables controlling the distribution <strong>and</strong> abundance <strong>of</strong> benthic organisms in the<br />
tropical regime were salinity (Parulekar <strong>and</strong> Dwivedi, 1974; Alongi, 1990;) <strong>and</strong><br />
sediment stability (Wildish <strong>and</strong> Kristmanson, 1979; Warwick <strong>and</strong> Uncles, 1980).<br />
7.2.3. Dissolved oxygen (DO)<br />
During both seasons DO decreased towards deeper depths <strong>and</strong> showed anoxic<br />
condition especially in the northern transect. In shallow depth zones, DO was low in<br />
southern transect <strong>and</strong> comparatively high in the northern transect. Increasing trend <strong>of</strong><br />
biomass towards north showed positive correlation with high DO in the north. But in<br />
the deeper depths (beyond 100 m) DO drastically reduced <strong>and</strong> northern latitude<br />
stations recorded very low values. The lowest biomass was also observed in the<br />
deeper depths (beyond 100 m) during both seasons. This could be due to the<br />
anaerobic or suboxic condition prevailing in that region which could not be tolerated<br />
201
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