Effect of siltation on coral reef health in Mabini Protected Landscape and Seascape, Davao de Oro, Philippines

Abstract

Coral reefs are vital marine ecosystems characterized by high biodiversity and significant ecological roles; however, increasing siltation threatens their stability. In Mabini Protected Landscape and Seascape (MPLS), Mabini, Davao de Oro, Philippines, recent monitoring recorded declining coral cover, with siltation identified as a major stressor. This study assessed the seasonal effects of siltation on coral reef health by comparing indicators between low- and high-siltation sites. Coral reefs were surveyed using photo-transect method, fish visual census for indicator reef fish, and frequency of occurrence for coral disease. Siltation was measured using sediment traps and multiparameter water-quality device. Results showed higher mean live hard coral cover in low-siltation site (58.65% HCC) compared to high-siltation site (36.07% HCC). Coral genera diversity and butterflyfish abundance were also higher in low-siltation site (34 TAUs; 41.2 ind. 100m-2) than in high-siltation site (21 TAUs; 12.8 ind. 100m-2). Higher frequency of disease-affected coral colonies in high-siltation site (56 colonies) compared to low-siltation site (33 colonies). Whereas mean coral mortality did not differ significantly between low-siltation (0.25 CMI) and high-siltation (0.18 CMI) sites. Mean turbidity and sediment deposition rates were markedly higher in high-siltation site during both the dry (31.97 NTU; 150.95 g m⁻² day⁻¹) and wet (76.66 NTU; 278.52 g m⁻² day⁻¹) seasons, compared to low-siltation site during the dry (4.04 NTU; 16.29 g m⁻² day⁻¹) and wet (15.17 NTU; 73.66 g m⁻² day⁻¹) seasons. These findings indicate that siltation is a primary driver of reef degradation in MPLS and support ridge-to-reef management strategies for coral reef conservation.

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