Dept. of Marine Bioresource Science

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    Variation in the Gut Plankton Composition of Clam Meretrix meretrix Collected from the South-east Coast of Bangladesh
    (Faculty of Veterinary Medicine, Chattogram Veterinary and Animal Sciences University, Khulshi, Chattogram-4225, Bangladesh, 2025-08) Siddika, Ayesha
    Meretrix meretrix, commonly known as the Asian hard clam, is a key species in coastal ecosystems due to its role in water filtration and nutrient cycling, and it holds significant commercial value for fisheries and aquaculture across South and Southeast Asia. It has great potential for coastal aquaculture and export contributing to the blue economy of Bangladesh. For the sustainable development of clam aquaculture the knowledge on feeding biology and environmental parameter is crucial. The study was conducted to assess the seasonal and spatial variation in water and gut plankton composition across five sites-Chowfaldandi, Khutakhali, Moheshkhali, Monkhali, and Rejukhal along the southeast coast of Bangladesh, over four seasons (pre-monsoon, monsoon, post-monsoon, and winter) considering environmental parameters including temperature, pH, turbidity, salinity, and dissolved oxygen (DO). For gut plankton study, gut contents of live Meretrix meretrix were preserved in 20% formalin and examined microscopically using a digital camera for enhanced visualization. To better understand the feeding ecology of M. meretrix, environmental conditions and planktonic assemblages were systematically recorded throughout the study. Water temperature, pH, salinity, turbidity and dissolved oxygen ranged from 23.4±0℃ to 34.6 ±0℃, 6.3±0.7 to 8.1±0.26, 0±0 ppt to 33.5±1.32 ppt, 4.37±0.34NTU to 43.1±2.76 NTU and 4.77±0.03 ppm to 18.07±2.23 ppm, respectively. In this study a total of 56 water plankton genera under 10 classes and 69 gut plankton genera under 12 classes were recorded. Bacillariophyceae emerged as the dominant phytoplankton group, with a high percentage of Coscinodiscus and Cyclotella found in both the water column and the gut of clams across all seasons and locations. Single-species blooms of Skeletonema were observed during the monsoon at Monkhali (92.1%), Moheshkhali (76.6%), and Rejukhal (41.8%). The gut plankton composition varied by site and season. In Chowfaldandi, Cyclotella consistently dominated across all seasons, peaking in the monsoon (33.0%) and winter (31.0%). Khutakhali exhibited seasonal dominance of Cyclotella and Coscinodiscus, with the highest abundance of Coscinodiscus (44.8%) in winter. In Moheshkhali, Coscinodiscus was dominant during the monsoon (27.7%), post-monsoon (21.1%), and winter (28.3%). At Monkhali, Cyclotella peaked during the post-monsoon (47.0%), while Achanthidinium (20.01%) and Coscinodiscus were prominent during the pre-monsoon and monsoon, respectively. In Rejukhal, Coscinodiscus was dominant in the post-monsoon (33.3%), while Cyclotella prevailed xvii during the pre-monsoon, monsoon, and winter. Ivlev’s Electivity Index indicated a consistent preference for Bacillariophyceae and Fragilariophyceae in clams from Monkhali, with active rejection of other plankton classes, including Zooplankton and Zygnematophyceae. Principal Component Analysis (PCA) demonstrated strong correlations between environmental variables (temperature, salinity, dissolved oxygen, turbidity) and plankton assemblages in both the water column and clam gut, highlighting the influence of seasonal hydrodynamics and nutrient availability on feeding behavior. The study further identifies local environmental factors driving spatial differences in gut plankton, with implications for optimizing clam culture and managing coastal bivalve resources under changing ecological conditions. These findings contribute to the understanding of the trophic ecology of Meretrix meretrix in tropical estuarine systems and support sustainable fisheries management in Bangladesh’s coastal zones. Importantly, the insights into selective feeding preferences of clams may aid in formulating effective clam aquaculture strategies and contribute to the development of Bangladesh's blue economy.