Patch Distribution and Within-Patch Dynamics of the Seagrass Zostera noltii Hornem. in Los Toruños Salt-Marsh, Cádiz Bay, Natural Park, Spain

Abstract

Patch distribution and small-scale (i.e., within-patch) temporal variability in plant morphology, biomass, shoot density, tissue nutrient content and growth were studied in the intertidal seagrass Zostera noltii at Los Toruāos salt-marsh (Cádiz, Spain). The area covered by Z. noltii was 7.3%, and decreased exponentially with depth. The lack of recruitment from seedlings largely explained the normal patch size distribution observed. Overall, lower biomass, shoot density, above-ground to below-ground biomass ratios and higher leaf elongation rates were recorded at the patch edge, where biomass dynamics were primarily controlled by recruitment and mortality processes. In contrast, temporal variation in above-ground biomass in the patch centre depended largely on changes in shoot leaf number and size. There was no correlation between total biomass and shoot density in the patch centre suggesting that below-ground biomass may be space-limited. Low aboveground biomass and shoot elongation rates were recorded in May, regardless of position within the patch, and were coincident with the abundance of Ulva sp. mats. Light reduction by Ulva canopies also resulted in a mobilization of carbohydrate reserves. Such resource reallocation may represent an important short-term survival strategy, maintaining leaf and rhizome elongation capacity.