| Summary: | Maintaining the abundance of phytoplankton in mangrove areas concerning water quality is essential to sustain fish productivity. However, water quality degradation decreases fish abundance and impacts the fisher’s economy. Thus, it is necessary to preserve and maintain the phytoplankton abundance concerning the water quality of the mangrove area to sustain the demand for protein food and increase fish productivity. This study aimed to (i) assess the water quality and phytoplankton abundance and (ii) determine the appropriate spatial interpolation method to determine the water quality of Tuba Island, Langkawi. Water quality parameters (pH, salinity, dissolved oxygen (DO), and temperature) and phytoplankton abundance were collected surrounding the Tuba River. Spatial interpolation was applied to interpolate and map the location of water quality parameters. The total abundance of phytoplankton was calculated within 13,718.75–29,822.92 ind/m3 and 17,843.75–27,515.63 ind/m3 in September and December 2020. The regression equation was established to estimate the water quality related to the abundance and pigment based on observed sample data. The results indicate the highest coefficient of determination (R2) of the DO–pH with 94%; for others, the relationship (pH–Temp and DO-Temp) showed less relationship with R2 = 30%. The inverse distance weighted (IDW) showed a better performance with errors of root mean square error (RMSE) (0.060–1.25), mean absolute error (MAE) (0.004–0.128), and mean absolute percentage error (MAPE) (0.429–15.673) (0.176–2.835), MAE (0.031–8.037), and MAPE (3.39–33.5). The map distribution of water quality and phytoplankton abundance could help increase fisheries’ activities by preserving Tuba Island Langkawi’s water quality and phytoplankton abundance. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.
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