Functioning of Philippine seagrass species under deteriorating light conditions; Proefschrift Technische Universiteit Delft.

Industrialization, urbanization and agricultural intensification result in increased sediment loading and eutrophication of S.E.Asian coastal waters and associated deterioration of light availability to seagrasses inhabiting coastal waters. In the present study, different (internal and external) factors affecting the capacity of seagrasses to persist under longer-term light reduction were studied in a series of field and laboratory experiments in Southern Philippines. Two species were investigated in this study: Halodule uninervis and Thalassia hemprichii, a 'pioneering' and 'climax' species, respectively. Shading led to pronounced shoot mortality in both species, but the longer-lived Thalassia hemprichii survived better and also recovered more rapidly than the other species, probably due to a larger store of reserve carbohydrates In the rhizomes and a dghter clonal integration, as was confirmed by stable Isotope (13C and 15N) re-allocation patterns. Anoxic sediment conditions worsened the effect of shading. Responses to shading were observed in chlorophyll content and shoot morphology, but not in photosynthetic capacity