NUTRITIONAL INTERACTION IN AN ALGA-BARNACLE ASSOCIATION

Nitrogen is the major growth-limiting nutrient for marine algae. One p otential source of nitrogen for marine algae is ammonium released by i nvertebrates. Many mid-intertidal reefs in northeastern New Zealand ar e dominated by a close association between the honey comb barnacle Cha maesipho columna and an encrusting brown alga Pseudolithoderma sp. Gro wth of Pseudolithoderma was enhanced in the presence of live C. column a, which released ammonium at a greater rate than the maximum rate of ammonium uptake by Pseudolithoderma. Algal tissue on barnacle tests ha d a lower C:N ratio than tissue located more than 2 cm from the neares t barnacle, suggesting the barnacle is an important source of nitrogen for the alga. The role of nutrient exchange in determining ecological patterns of species in marine communities is discussed.