Effects of monsoon weather on seasonal water quality dynamics in Langgun Island Aquaculture Industry Zone, Langkawi, Malaysia

Monsoon-driven climatic variability is a major environmental factor influencing water quality dynamics in open sea aquaculture systems in tropical regions. Monthly water quality monitoring was conducted over a 1-year period at two marine cage sites and a control site within the Langgun Island Aquaculture Industry Zone (ZIA). Significant seasonal differences in water quality were observed across the Southwest monsoon and Northeast monsoon periods. The Southwest monsoon was associated with elevated rainfall (4.36 mm day−¹), lower dissolved oxygen (DO) levels (4.09 ± 0.40 ppm) and higher reported fish mortality than the other monsoon periods (2,619 deaths day−¹). In contrast, the Northeast monsoon exhibited improved hydrographic stability with significantly higher DO levels (4.85 ± 0.51 ppm) and a 27.5% reduction in fish mortality. Principal Component Analysis (PCA) showed that PC1 (21.87%) and PC2 (16.21%) distinguished seasonal water quality patterns, together explaining 38.07% of the observed variation. These findings provide baseline information to support seasonally adaptive water quality monitoring and management strategies that enhance the sustainability of aquaculture operations in this zone.