A Living Laboratory: The Maryland Crayfish Project

Biological engineers differ from other engineers in that they must consider not only the abiotic components of a system but the biotic components as well. While this relationship may appear to be obvious, it is the implications of this relationship that defines the field. Successful biological engineering can only be achieved if the students develop an understanding of their designs as systems. These systems respond significantly differently from the isolated parts. The understanding is achieved through knowledge in three areas, (1) the behavior of the abiotic components, (2) the behavior of the biotic components, and (3) the relationships between the biotic and abiotic components, and the resulting dynamic responses of the system. In our program this is achieved through a combination of laboratory experiences and classroom instruction. In one of these laboratories, the emphasis is on the experimental design and practical implementation of systems with living components. The premise of the exercise is that, if students truly understand the requirements of living creatures, they can keep those animals alive and healthy. Over the last few years, this laboratory has involved the design of an ecosystem to support crayfish in a sealed (airtight, watertight, but light admitting) system. Early in this laboratory, the students are asked to identify critical variables for supporting these animals, and to decide if, when, and how they should be measured. This decision-making process moves from a thought experiment to a physical process and the students are asked to design and make measurements on the crayfish and their environment. Next, the students set up their ecological microcosms and try to stabilize them. During this phase of the laboratory, the students become aware of the complexity of their challenge. As the self-organization proceeds, environmental variables within the microcosm become inextricably linked. Finally, the students seal the tanks for several periods. Requiring that the tanks remain sealed for progressively increasing periods requires the students to examine the microcosm’s response to the perturbation, identify the problems and their respective source(s), and redesign the system. This iterative failure and redesign cycle results in stronger designs and increases the student’s confidence in their design abilities.