Species composition and plant performance of mixed seagrass beds along a siltation gradient at Cape Bolinao, The Philippines

The response of mixed Southeast Asian seagrass beds to siltation was analyz ed based on field data, a transplantation experiment and experimental manip ulation of light availability in seagrass populations along a silt gradient at Cape Bolinao, The Philippines. Seagrass species diversity, shoot densit y and depth penetration declined with increasing amounts of suspended mater ial and increasing water column light attenuation along the silt gradient. The seagrass species could be ranked according to decreasing tolerance to s iltation as: Enhalus acoroides > Cymodocea serrulata > Halodule uninervis > Thalassia hemprichii > Halophila ovalis > Cymodocea rotundata > Syringodiu m isoetifolium. A gradual decline in shoot density and depth penetration of the different species along the silt gradient suggested that changes in th e vertical Light attenuation coefficient in the water column, primarily cau sed by differences in suspended inorganic solids, was the most important fa ctor affecting seagrass performance. However, inconsistency among the speci es in response to increasing water depth, artificial shading and transplant ation indicated that other factors, such as siltation-derived changes in se diment conditions, contribute to the sequential loss of seagrass species al ong the silt gradient.