The cardiovascular system is the first to become functional in embryos and is followed by a series of interdependent interactions that result in a functional adult. As a result of the cardiovascular systems' importance in oxygen and carbon dioxide transport, a change in its normal development could have a critical impact on adult function. The physiology of embryonic cardiovascular systems is quite different from those of adults because functions change as the embryo matures. Despite the critical role the cardiovascular system plays in embryonic function, little is know about how the environment can effect its developmental pattern. Crustaceans present a valuable taxonomic group useful for this research because of their diverse array of developmental patterns and morphological plasticity. The objectives of this research by Dr. Reiber are three fold: First, measurements of cardiac functions during development (rates, pressures and flows) in embryonic and larval crayfish and shrimp will be made to establish a foundation on which further work can be initiated. Second, the mechanisms of cardiac regulation during development will be determined. And lastly, once basic developmental patterns of cardiac regulation have been determined, the changes in cardiac physiology associated with environmental stress will be investigated by exposing embryos of defined developmental stages to modified conditions (water oxygen and temperature). This research will make significant contributions toward understanding both the fundamental patterns of cardiac development and the impact of early cardiac function has on developmental outcomes.