Modeling seagrass bed dynamics under environmental impacts of intensive mariculture activities in Bolinao and Anda, the Philippines

Abstract

This study assessed the estuarine-scale dynamics of mixed seagrass beds in Bolinao and Anda coastal areas in the Philippines, where seagrass beds have declined primarily due to eutrophication-induced degradation of light environment caused by unregulated mariculture activities in the adjacent areas. A seagrass model, driven by a coupled hydrodynamic-biogeochemical model, was developed and applied to the two-dominant species in the area – Thalassia hemprichii and Enhalus acoroides, and validated using observed spatial seagrass shoot density. The results showed the degradation of light environment in the seagrass beds, especially near mariculture areas, due to advective fluxes of water with high phytoplankton biomass and high nutrients from fish farms. The seagrass model driven by the reproduced water quality showed high reproducibility of seagrass above-ground biomass distribution of the two co-existing species, with R2 values of 0.78 and 0.60 for T. hemprichii and E. acoroides, respectively. Scenario analysis was conducted to examine the effectiveness of individual- and inter-municipality mariculture management (e.g., regulating fish feed input) in improving the light environment and facilitating the recovery of seagrasses. Results showed that the light environment could be significantly enhanced by an inter-municipality scheme compared to individual efforts of Bolinao and Anda municipalities, since their waters are interconnected through hydrodynamics. In conjunction with the improvement of light conditions, the recovery in seagrass abundance is most significant under the cooperative management scheme, thus highlighting its effectiveness.