Impact of sewage on the distribution, abundance and community structure of rocky intertidal macroalgae of the Colaba coast, Mumbai, India

摘要

Three transects T_1, T_2, T_3 in the intertidal area of Colaba were sampled for macroalgal distribution, abundance, species composition, diversity and standing stock estimation during 1997-98. Transect T_2 was in the vicinity of the sewage discharge point and T_1 and T_3 were on either side of T_2 at a distance of about 800m. Comparatively, less number of species and different pattern of macroalgal assemblages were recorded at the discharge point, while transects distance from discharge point showed more number of species, luxuriant growth and well developed macroalgae. The opportunistic species such as Ulva fasciata, Enteromorpha spp., Cladophora vagabunda., etc. were abundant at the vicinity of the discharge point T_2. Highly branched, coarse and calcareous species like Laurentia papillosa, Solieria robusta, Gracilaria corticata, Caulerpa spp, Cheilosporum spectabile, Amphiroa fragilissima etc. were found abundantly at T_1 and T_3. These species, although contribute substantially to the biomass, their composition differs at all the three transects and also at the littoral level. Highest biomass of 1.43 kg m~(-2) was recorded at T_1 while lowest of 0.76kg m~(-2) was at T_2. There was a shift in the composition of macroalgal species from bioticallycompetent to stress tolerant and opportunistic at T_2. The factors responsible for structuring macroalgal communities at Colaba were distance from the sewage discharge point, degree of tidal flushing and tolerance capacity of the macroalge to sewage.