This symposium presents different ecological and physiological strategies used by invertebrates to successfully adapt to aquatic environments. Adaptation has been studied mainly in adult animals, but the papers comprising the symposium emphasize ontogenetic strategies, starting from the principle that natural selection acts on all stages of development. Adaptive strategies may thus differ strikingly between developmental stages of the same organism. Invertebrates offer a wide array of ecophysiological models for study, and these are exemplified by the contributions to the symposium, which are briefly summarized. Future research in the field will 1, expand the number of models for comparative purposes; 2, examine the strategies, not only of larvae and juveniles, but also of embryos, eggs and reproductive cells; and 3, investigate the genetic basis of ontogenetic strategies.