NUTRIENT LIMITATION OF PHILIPPINE SEAGRASSES (CAPE BOLINAO, NW PHILIPPINES) - IN-SITU EXPERIMENTAL-EVIDENCE

Nutrient limitation of Enhalus acoroides, Thalassia hemprichii and Cym odocea rotundata in 2 mixed seagrass beds (Silaqui and Lucero) in Cape Bolinao, NW Philippines was investigated through a 4 mo in situ nutri ent addition experiment. Leaf growth of T. hemprichii and E. acoroides significantly increased by 40 to 100% and 160%, respectively, followi ng fertilization. Leaf biomass of the 3 species also increased signifi cantly by 60 to 240% following nutrient additions. The increased growt h and biomass with fertilization was supported by enhanced photosynthe tic activity, consequently by higher chlorophyll and nutrient concentr ations in the photosynthetic tissues. These results demonstrated nutri ent Limitation of seagrass growth and photosynthetic performance at th e 2 sites in Cape Bolinao. The nature and extent of nutrient limitatio n, however, varied between sites and among species. T. hemprichii and E. acoroides appeared to be mainly P deficient and N deficient, respec tively (from significant increases in tissue P and N concentration fol lowing fertilization, respectively). The deficiency was moderate (26% of requirement) for T. hemprichii but substantial for E. acoroides (54 % of requirement). Moreover, N and P deficiency was greater in Lucero than in Silaqui, consistent with the higher ambient nutrient concentra tion in the porewater and sediment nutrient and organic matter content in Silaqui. These results emphasize the importance of local differenc es in the factors controlling nutrient losses and gains in seagrass me adows and, more importantly, the importance of identifying the species -specific traits that generate the interspecific plasticity of nutrien t status.