Ecological Significance of Sterols in Aquatic Food Webs

Sterols are indispensable for a multitude of physiological processes in all eukaryotic organisms. In most eukaryotes, sterols are synthesized de novo from low molecular weight precursors. Some invertebrates (e.g., all arthropods examined to date), however, are incapable of synthesizing sterols de novo, and therefore have to acquire sterols from their diet. Here, we aim to demonstrate that such nutritional requirements not only affect the performance of an individual in its environment but may also have major consequences for the function of aquatic ecosystems. Starting from general patterns of occurrence and biosynthesis of sterols, we next explore the physiological properties and nutritional requirements of sterols. These aspects are then integrated into a more ecological perspective. We emphasize their effects on aquatic food webs in general and on herbivorous zooplankton in particular with the major aim to outline how the interplay of physiological capabilities of individual herbivores and trophic interactions in the food web will determine the effect of low dietary provision of sterols on structure and function of aquatic ecosystems