Thalassia testudinumand associated epiphytes from field plots were compared with plants from laboratory microcosms to determine if laboratory observations obtained from plants undergoing seasonal growth patterns were characteristic of plants in natural systems. The measurements selected for characterizing Thalassia health were chlorophyll and protein content of leaves and carbohydrate content of rhizomes. For epiphytes, we measured standing crop and chlorophyll content. Mean values for field and laboratory data were statistically analyzed for two experiments conducted over six-week intervals and for one experiment extended to twelve weeks. Thalassia plants in the laboratory followed similar trends of field plants during the six-week experiments, but the laboratory plants differed significantly from field plants at twelve weeks. Chlorophyll content of epiphyte communities colonizing Thalassia leaves was significantly different in the laboratory compared to field communities, but trends from test initiation to the six-week sampling were consistent between field measurements and laboratory test systems.