Nutrient constraints on establishment from seed and on vegetative expansion of the Mediterranean seagrass Cymodocea nodosa

Nutritional constraints were examined on establishment from seed and vegetative development of patches of the seagrass Cymodocea nodosa Ucria (Aschers.) growing in phosphorus-deficient sandy sediments in the shallow Alfacs Bay of the Spanish Mediterranean coast. Seedlings were extremely P-deficient, this P-deficiency increasing with seedling age, which may be a major reason for the failure of most seedlings (90%) to initiate patches, and the arrest of their vegetative proliferation for up to 3 years. Shoots located at the colonising apices of horizontal rhizomes had, in contrast, three-fold higher P and two-fold higher N concentrations, which could facilitate the rapid horizontal expansion of existing patches, Apical shoots may receive nutrients from older shoots connected along the rhizome chains, as suggested by exponentially increasing gradients of N and P concentrations towards the rhizome apex. These results indicate that resource limitation probably plays a more important role in constraining the initiation of patches from seedlings in nutrient-poor areas than the expansion of existing patches.