MONITORING OF NUTRIENT AVAILABILITY AND LIMITATION USING THE MARINE MACROALGA CERAMIUM-RUBRUM (HUDS) C AG

The macroalga, Ceramium rubrum (Huds.) C. Ag., was transplanted at eight stations in the Limfjord. At approximately monthly intervals, samples were collected and analysed for nitrogen and phosphorus content to evaluate the significance of nitrogen and phosphorus as limiting factors for algae growth. The highest concentration of dissolved nutrients was found in the inner parts of the fjord and the lowest concentration occurred in the western part. A similar pattern was shown by the tissue concentrations of nitrogen and phosphorus in the macroalgae, indicating that tissue concentrations are suitable for monitoring nutrient availability in coastal areas. The lowest tissue concentrations of nitrogen were recorded during the summer period. At several occasions, the internal concentrations were below the critical concentration level showing that nitrogen limited the growth. Internal phosphorus concentrations were below the critical concentration level in May. For both nutrients, high storage capacities were recorded, being factors of eight and 18 times higher than the minimum concentrations of nitrogen and phosphorus, respectively. It was concluded that in the Limfjord, nitrogen was the main limiting factor for macroalgae growth during summer, whereas phosphorus controlled the growth in May. The applicability of tissue concentrations for monitoring purposes is discussed and it is considered that tissue concentrations in macroalgae, when evaluated against established critical concentrations, provide a valuable tool for determining nutrient limitation in coastal areas. © 1990.