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Generally, opportunistic and resident macrobenthic invertebrate communities comprise
an ecologically significant and functional component of coastal ecosystems (Simboura
et al., 1995 and 2000). Infaunal organisms in these environments interact profusely with the
substrate and create extensive bioturbational features in the form of burrows, tubes and mounds
on the sediment. The present study deals with the carnivorous macrobenthic
polychaete Diopatra cuprea which is a dominant infaunal inhabitant in the intertidal mudflats
of Gangasagar along the southern fringe of Sagar Island, West Bengal and the sandy
Talsari coast, Orissa of eastern India. The two study locations are about 80 km apart along the
east and west and face the Bay of Bengal in the south (Figure 1). The intertidal flats are
produced in the meso-macrotidal coastal environments having semi-diurnal tides with slight
time-velocity asymmetry. D. cuprea living in these two locations display two texturally distinctive
substrate preference for regions having closely similar climate and
hydrography.
At Gangasagar, situated at the sea face of the Sagar Island, at the mouth of the
Hugli estuary, horizontal to sub-horizontal silt-dominated mudflats occur in shallow,
sheltered runnels between the shore-parallel sandy ridges of the beach profiles. The tunnels are
low-energy areas and are characterized by the deposition of suspensional mud at falling tides.
In contrast, at Talsari, located east of the Subarnarekha
delta, D. cuprea constructs tubes on the sandy megaripple flats occupying the floor in a sinuous tidal creek. The
megaripples refer to high energy, upper part of the lower flow regime structures (Harms and
Fahnestock, 1965). The contrast in the sand, silt and clay percentages in the Gangasagar sand
ranges from 5.6 to 20.4%, silt from 79.0 to 91.2% and clay from 0.69 to 7.7%; whereas, at
Talsari, the sediments are coarser, with sand ranging from 77.9 to 98.8% and silt from 1.1 to 22.0%. |
