23/08/2026
Thousands of clams on Chengmara Khal's pipes!
Is this just biofouling, or a warning sign of increasing salinity in coastal Bangladesh?
FIELD DATA SHEET
Malacological & Environmental Observation
1. GENERAL INFORMATION
Item Details
Observer Name-Jasmin Nahar
Affiliation- Satkhira, Khulna, Bangladesh
Date of Observation- 22 August 2026
Time-11:00 AM BST
Weather Condition-Sunny with Light Clouds
2. SITE INFORMATION
Item Details
Site Name-Changmara Canal
Location- Moukhali, Parulia, Debhata Upazila, Satkhira District
Water Body Type-Tidal Canal / Brackish Water Channel
Tidal Influence -Yes
Water Depth -3 feet/4 feet
Water Clarity- Turbid
Dominant Substrate -Concrete + Iron Pipe, Submerged Wooden Post
3. BIOLOGICAL DATA
Item Details
Species Name- Corbicula fluminea
Common Name -Asian Clam / কালো নদী ঝিনুক
Family- Cyrenidae
Feeding Habit-Filter Feeder
Attachment Type - Epifaunal - Attached to hard substrate
Average Shell Length-1 inch / ~2.5 cm
Shell Color- Black
Population Density -60-70 individuals per square inch
Distribution Pattern- Dense clusters in 2-3 layers
Presence in Soft Mud- Absent
4. ECOLOGICAL NOTES
Habitat: Brackish, shallow, tidal canal
Bioindicator Potential: Possible indicator of increasing salinity
Impact:Biofouling on irrigation structures
Seasonality: Observed year-round presence
5. DOCUMENTATION
Item Status
Photograph Taken-Yes
Sample Collected-No
Remarks:
High density of _C. fluminea_ observed on both concrete and wooden structures. This suggests wide substrate tolerance in brackish tidal conditions.
Signature:
Jesmin Nahar
RESEARCH NOTE / FIELD REPORT
Title:
Colonization of _Corbicula fluminea_ on Hard Substrates in a Tidal Canal of Coastal Bangladesh: A Field Observation from Changmara Canal Satkhira
Author:
Jasmin Nahar, Satkhira, Khulna,Bangladesh
Abstract
Dense colonization of the Asian clam _Corbicula fluminea_ was observed on artificial hard substrates in Changmara Khal, Debhata Upazila, Satkhira District, Bangladesh on 22 August 2026. The species was found attached to concrete-iron culvert pipes and submerged wooden structures in brackish, turbid, and shallow tidal waters. The average shell length was 1 inch with an estimated density of 60-70 individuals per square inch. The observation suggests that _C. fluminea_ exhibits year-round presence and utilizes any stable hard substrate for attachment and reproduction in coastal canals influenced by tidal activity. This colonization may contribute to biofouling and serves as a potential bioindicator of salinity intrusion.
Keywords:Corbicula fluminea, Biofouling, Brackish water, Tidal canal, Salinity intrusion, Satkhira
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1. Introduction
In coastal regions of Bangladesh, tidal canals are experiencing increased salinity due to sea level rise and reduced freshwater flow. Hard substrates such as culverts, pipes, and wooden structures provide ideal attachment sites for sessile bivalves. _Corbicula fluminea_, commonly known as the Asian clam, is a freshwater to brackish water tolerant species known for rapid colonization. This report documents a field observation of dense _C. fluminea_ colonization in Changmara Khal.
2. Materials and Methods
Study Site:Changmara Khal, Moukhali, Parulia, Debhata, Satkhira, Bangladesh.
Date & Time:22 August 2026, 11:00 AM
Weather:Sunny with light clouds
Observation Method:* Direct visual survey of culvert structures. Water type, depth, and substrate were recorded. Density was estimated per square inch on the pipe surface.
3. Results
The canal water was observed to be brackish, turbid, and shallow with active tidal influence. Dense clusters of _Corbicula fluminea_ were recorded on two types of hard substrates:
1. Concrete-Iron Culvert Pipe: 2-3 layer thick colonization. Shell color black, average length 1 inch.
2. Submerged Wooden Structure: Similar colonization pattern observed on wooden posts.
The estimated density was 60-70 individuals per square inch. No live specimens were observed in soft muddy substrate.
4. Discussion
The presence of _C. fluminea_ on both concrete and wood indicates its ability to colonize any stable hard substrate in brackish environments. The species is a filter feeder and thrives in 2-8 ppt salinity, which is common in tidal canals of Satkhira. Year-round presence is expected due to its high reproductive rate.
Ecological Implications:
Negative: Biofouling can reduce water flow in irrigation structures.
Positive: The species acts as a bioindicator for salinity intrusion and contributes to water filtration.
This observation highlights the need for regular monitoring of canal infrastructure in coastal areas.
5. Conclusion
Corbicula fluminea_ shows successful colonization on concrete and wooden substrates in Changmara Khal. Its density correlates with brackish and tidal conditions. Further long-term monitoring is recommended to assess its impact on water management in coastal agriculture.
Acknowledgement
Field observation conducted by Jasmin Nahar.
Figure 1. Dense colonization of Corbicula fluminea on a concrete culvert pipe in Changmara Khal, Debhata, Satkhira. Date: 22.08.2026.`
© All Reserved ---Jesmin Naha
