Canal

Biotic Communities

The assemblage of biotic community indicates the productivity of water body. Phytoplankton population, the biological wealth of an aquatic ecosystem (Boyd, 1972), responsible for wide assemblage of biotic community and regulate the food web (Falkowaski et al., 2008).  Zooplankton, being the primary consumer in food chain, plays an important role in transfer of energy to the higher trophic level. Zooplankton is also fed upon by many juvenile and adult zooplanktivorous fish species (Sommer et al., 2003) and hence it can be termed a key factor in the control of fish stock sizes (Payne and Rippingale, 2001). The occurrence of these organisms largely depends on the seasonal variations of physico-chemical parameters, physiographic factors and flow characteristics of the water body.

Phytoplankton and zooplankton populations in the selected canals exhibited significant variations in abundance in seasons. Cyanophyceae excelled as a major microfloral component (>35%) followed by Bacillariophyceae (>28%) and Chlorophyceae (>17%). Other algal groups (Coscinodiscophyceae, Euglenophyceaea, Trebouxiophyceae, Mediophyceae, Xanthophyceae, Conjugatophyceae, Synurophyceae) contributed partially and fluctuated much in seasons. Dinophyceae contributed least (<1%) contribution to the algal community. Diatoms were the most diverse group across the seasons in these canals. Compositions of zooplankton represented; Crustacean nauplius>Rotifera>Copepoda>Copepod eggs >Cladocera>Ostracoda in the stated order. Richness (Margalef, 1958) and Shannon-Weiner diversity index (Shannon, 1949) with a calculated value >2.95 in the studied canals indicated moderately rich phytoplankton diversity in the systems. Similarly, Pielou’s evenness index (Pielou, 1977) also calculated with a mean value 0.88 showed the evenly spatial distributions of phytoplankton in the studied canals.

Periphyton is the heterogeneous group of community assemblage that attached in plants, woods, stones and various other substrates.  It has great importance as primary producers together with phytoplankton and macrophytes (Sing et al., 2002) which provides foods to many aquatic organisms. The periphytic associations in the selected canals of Sundarbans showed the dominance of six groups which represented as Bacillariophyceae > Cyanophyceae > Coscinodiscophyceae > Chlorophyceae > Conjugatophyceae > Nematoda. Diatoms invariably constituted the bulk of the population (> 66%) of the total periphytic community attached in the natural substrates.  Macrobenthos; Pila virens, Bellamya bengalensis, Pila globossa, Meiniplotica scabra, Tarebia granifera, Thiara lineata were very common irrespective of seasons in the canals.

Small indigenous fishes (SIFs) are the major catch in these canals contributing >75% (showed percentage on the basis of studied canals) of the total catch. Amblypharyngodon mola, Puntius sophore, Pethia ticto, Parambassis ranga, Chanda nama, Trichogaster spp., Anabas testudineus, Macrognathus pancalus, Glossogobius giuris, Channa punctata, C. marulius, Salmophasia bacaila, Notopterus notopterus, Mystus gulio, Mystus spp. Chelon parsia, C. tade were the major catch. Penaied and non-penaied prawns also contributed a good amount of share (<10.0%) to the total fish catch.

A typical view of a canal in Sundarbans