Tidal and Diel Variability in Physico-Environmental Parameters in Calatagan Marine Protected Area

Abstract

Mangrove ecosystems are highly dynamic coastal habitats where physicochemical conditions fluctuate in response to tidal and diel (day–night) drivers, yet most monitoring frameworks rarely integrate both temporal dimensions. This study presents the first high-frequency, 24-hour simultaneous assessment of tidal and diel physicochemical and atmospheric parameters across three ecologically distinct coastal stations — a mangrove stand, a tidal channel, and an open sea area with coral reef and seagrass beds — within the Ang Pulo Mangrove Forest of the Calatagan Marine Protected Area (MPA), Batangas, Philippines. Physico-chemical parameters (salinity, temperature, dissolved oxygen, nitrate, depth) and atmospheric variables (air temperature, wind speed, humidity, light intensity) were measured every three hours over a full 24-hour cycle using calibrated field instruments. Statistical analyses employed Kruskal–Wallis tests, Wilcoxon rank-sum pairwise comparisons, Spearman’s rho correlation, repeated-measures ANOVA, and multivariate MANOVA. Results revealed significant tidal and diel influences on multiple parameters: nitrate peaked at 119.45 mg/L in the mangrove station during morning low tide, while dissolved oxygen and salinity shifted predictably with tidal influx; air temperature and light intensity peaked at midday, and humidity rose consistently at night. Significant three-way interaction effects among tidal phase, time of day, and station (p < 0.05) underscored the spatial and temporal heterogeneity of this coastal system. These findings provide a novel baseline for understanding short-term environmental dynamics in tropical mangrove-coastal systems, introduce a replicable monitoring approach for Marine Protected Areas, and establish an empirical foundation for adaptive, site-specific management strategies in tropical MPAs confronting environmental variability and climate-related pressures.