International Journal of Marine Science, 2017, Vol.7, No.12, 102-113
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temperature whereas subsurface water temperature remained similar or up to 2°C less than that of surface water
temperature (Table 1; Table 2). Aken (2008) mentioned that water temperature is an important parameter
which influences the dissolution-precipitation, adsorption–desorption, oxidation–reduction and physiology
of biotic community in an aquatic environment.
Salinity plays a great role in the occurrence and distribution of macrobenthos (Pearson, 1970; Pearson and
Rosenberg, 1978; Rosenberg, 2001; Ysebaert et al., 2003). In this study it was observed that the surface and
subsurface water salinity were almost similar. During monsoon, only (1‰) water salinity was recorded at
Sandwip, while at all other sites salinity were almost zero. During post-monsoon water salinity was 15‰ at
Sandwip and 8‰ at Hatiya (Table 1; Table 2) and other sites it was zero. The abundance pattern of Amphipods
(F=1.575E4 & p=0.000) showed strong relation to salinity during post-monsoon. Kumar and Khan (2013)
reported that there was a significant positive correlation between salinity and benthic faunal diversity (r=0.381;
p<0.05). Jones (1987) described that Polychaetes, Crustaceans and mollusks mostly interact with salinity. Hodda
and Nicholas (1985) investigated the meiofauna around the Hunter river-estuary, New South Wales, Australia
and described salinity as the key factor influencing the relative abundance of species distribution.
In the present study
in situ
subsurface water pH and soil extracted water pH changes were almost similar. It was
observed that the subsurface water pH and soil extracted water pH remained slightly acidic at all sites and seasons
except for Barisal in monsoon. Hossain and Marshall (2014) reported that pore-water of Sungai Brunei Estuary,
Borneo was slightly acidic. The distribution and abundance of Polychaetes (F=193.78 & p=0.49) was greatly
affected by soil pH in both monsoon. Gaskill (2014) reported that benthic macro-invertebrate richness is
significantly correlated with pH (p = 0.034) and species richness decreased because of lower pH.
In the study it was observed that both the OC and OM percentage were more during post-monsoon than monsoon
season at all sites. The maximum amount of soil Organic Matter (OM) 1.43% was found at Sandwip and the
lowest 0.11% was recorded at Chandpur in monsoon. During post-monsoon the highest OM (1.04%) was at Bhola
and the minimum (0.36%) was at Barisal (Table 3).
The total organic carbon and grain size affect habitat selection, feeding behavior and survival of benthic
organisms (Jegadeesan and Ayyakkannu, 1992; US Army Corps of Engineers, 1996). Murugan and Ayyakkannu
(1991) found a high significant correlation between benthic fauna and organic carbon in the South East coast of
India. The Organic matter and sediment characteristics have massive influence in the occurrence of benthic fauna
(Pearson, 1970; Pearson and Rosenberg, 1978; Rosenberg, 2001; Ysebaert et al., 2003). According to Levin and
Talley (2000) soil organic matter and soil grain size have an effect on benthic communities.
Investigating soil composition it was observed that sand percentage was highest and at five sites in both season.
The soil texture remained unchanged at Hatiya, Barisal and Chandpur sites; whereas at Sandwip and Bhola it
changes slightly Figure 2 (A and B). Greater benthos species occurred more at Chandpur and Barisal and the soil
texture of these two sites were sandy loam and loam respectively. Harakanta and Parulekar (1985) reported
benthic fauna are relatively rich in finer soft bottom which have similarity with the present investigation. In case
of Sandwip and Hatiya soil texture were clay loam and sandy clay loam which are comparatively compact for
benthos to penetrate at Sandwip, Hatiya and Bhola. During post-monsoon percentage of sand was highest among
all sites and the abundance was lowest. Changes in soil texture composition have a significant effect on the
abundance and distributions of some invertebrates; particularly deposit feeders (Whitlatch, 1980). Jones (1987)
reported that fine sediment generally contained more organic carbon and carbonate than coarse sediment.
4 Conclusion
In the present study, a total of 17 major taxa were identified of which 10 and 15 major taxa were recorded during
monsoon and post-monsoon season respectively. Macrobenthos abundance was greater during post-monsoon than
monsoon in the study sites. In the lower Meghna water was slightly acidic. Salinity, soil pH and water temperature
were found responsible for the variations in benthos community assemblage (p<0.05). Canonical Corresponding
