AbstractThe marine environment covers more than 70% of the earth surface and is one of the richest biospheres of the world. Biological and chemical investigations of marine ecosystems have provided insights into a fascinating and complex world underwater. The biological and chemical diversity is very high due to the array of natural conditions. It encompasses a high thermal range from −1.5°C to 350°C and a pressure range of 1–1,000 atm. The food conditions vary between nutrient rich and nutritionally sparse regions and photic and non-photic zones. Marine organisms have to adapt to these wide variety of living conditions. The adaptation capabilities are different from those of land-based organisms (Lindequist and Schweder 2001). Marine organisms live in close associations and therefore in nutrition and substrate competition (Ianora et al. 2006). In order to ensure survival and fitness it is necessary to produce secondary metabolites. The variety of secondary metabolites provides a biochemical reflection of the biotic interactions. The function of secondary metabolites is manifold. Allelochemicals are used for intra- and interspecies signaling and communication, for the deterrence of predators and herbivores or the suppression of competing neighbors. Bacterial and fungal invasion can be inhibited. Secondary metabolites can also be used for protection against UV radiation.