Linking Environmental Factors to Phenolic Concentrations in Seagrasses of Silliman Beach and Olympia Island, Negros Oriental

Seagrass meadows are essential in sustaining marine biodiversity, supporting fisheries, and protecting shorelines. Despite their importance, seagrasses are increasingly exposed to multiple stressors, including sedimentation, nutrient enrichment, pollution, and coastal development. These pressures can trigger biochemical responses such as the accumulation of phenolic compounds. In this study, phenolic concentrations in seagrasses were quantified, and the environmental factors influencing their concentration were identified. Seagrass samples were collected from Silliman Beach (Dumaguete City) and Olympia Island (Bais City), Philippines. Phenolic content was measured using the Folin–Ciocalteu method.  Water quality parameters were monitored twice monthly from July 2024 to April 2025, and sediment nutrient analyses were conducted monthly. Results revealed lower phenolic concentrations in the seagrasses at Olympia Island (5.24 to 26.50 mg TAE/g) than at Silliman Beach (6.82 to 50.5 mg TAE/g). Syringodium isoetifolium exhibited the highest phenolic concentration at Silliman Beach, followed by Thalassia hemprichii, Cymodocea rotundata, and Halodule pinifolia. Enhalus acoroides showed the lowest concentrations in both Silliman Beach and Olympia Island. Canonical correspondence analysis showed that phosphorus primarily influenced phenolic accumulation in Syringodium isoetifolium. In other seagrass species, total suspended solids, total dissolved solids, and nutrients correlated with the phenolic concentrations. Increased phenolic production in seagrasses reflects adaptive stress responses and resource allocation toward defense. Therefore, phenolic levels should be incorporated as a biomarker to monitor ecosystem health and guide conservation strategies in Philippine seagrass habitats.