103 / 2023-07-30 16:15:40

Assessment of Water Characteristics in Relation to Phytoplankton Assemblages in Cockle Culture Mudflat Area of Selangor, Malaysia.

Blood cockle, Physical Water Parameter, Nutrient, Phytoplankton, Primary production

Blood cockles, Tegillarca granosa, an important economic species in Malaysia have been experiencing profound decline in the production rate since 2010. Mass mortality of blood cockles had been cited as among the factors which can be attributed due to external factors such as elevation of ammonia, sedimentation and fluctuation in natural algal food supply. Cockle culture areas are usually located in near-fringe mudflats adjacent to estuaries along coastal zones that receives high input of land-based pollutants, posing high risk for the well-being of the cultured blood cockles. Phytoplankton is an important component in the aquatic ecosystem, forming the basal food source that supports marine food webs including the filter feeding blood cockles. The assemblages of phytoplankton community are affected by the availability of nutrients and other physical water parameters. Despite the numerous ecological studies on blood cockles, the simultaneous assessments on both water characteristics and phytoplankton assemblages in cockle culture areas are scarce. This study aims to determine the changes in water characteristics (physical water parameters and nutrients) on the community composition, abundance and diversity of phytoplankton associated with the cockle culture activity. Field samplings were performed during neap/flood condition at three locations namely; Bagan Sungai Buloh (SB), Assam Jawa (AJ), and Kuala Selangor (KS) from May 2022 to January 2023. Samples were analyzed for nutrient (nitrate, nitrite, ammonia, phosphate) concentrations, particulate organic matter (POM) content and assemblages (density, diversity and species composition) of phytoplankton community were enumerated. Phytoplankton proliferation favors low N/P ratio showing increase in phytoplankton density at phosphate-repleted conditions during southwest and northeast monsoon. Spatially, the culture site in SB and KS had higher phytoplankton density compared to AJ. This could be attributed due to the presence of two major rivers that contributed to higher nutrient levels in KS and SB which enhanced phytoplankton proliferation. Higher phytoplankton density was recorded in culture sites in comparison to non-culture site due to the proximity of culture site to the river mouths. Overall, six (6) phytoplankton phyla were identified namely Bacillariophyta (68 taxa), Myzozoa (13), Chlorophyta (2), Ciliophora (6), Cyanobacteria (1) and Foraminifera (1), Ochrophyta (1), alongside 14 other unidentified taxa. The phytoplankton community was dominated by Bacillariophyta cells in all the sampled sites (at least 96% mean composition). Several genera identified have been associated with harmful algae bloom (HAB), however it was found in low concentration suggesting low risk of HAB. No signs of hypoxic condition or eutrophication was observed throughout the study. The outcome of this study seeks to contribute baseline information that can be useful for comparative study to assess or evaluate risk when selecting areas for blood cockle culture.