ALGAL NUTRIENT LIMITATION AND THE NUTRITION OF AQUATIC HERBIVORES

Organisms differ in the proportions of major elements that they contain, including N and P, which are known to be highly dynamic and potentially limiting to production of aquatic ecosystems. Such contrasting elemental composition between, for example, algae and herbivores, or between different herbivores, generates a suite of ecological predictions and opens up new dynamical possibilities. Here we review studies relating to the nutritional physiology of aquatic herbivores, especially freshwater pelagic species, and we relate element content to secondary production and nutrient recycling. A variety of evidence from many types of studies-physiological modelling, whole-ecosystem surveys, laboratory growth studies, etc-is assembled into an internally consistent picture of mineral limitation of aquatic herbivores. Herbivores with high nutrient demands (the best example is probably Daphnia and phosphorus) appear frequently to be limited not by the food quantity or energy available to them but by the quantity of mineral elements in their food.