Meeting Abstract
The isopod Pentidotea resecata can be found living on the eelgrass Zostera marina and Macrocystis spp along the western coast of the United States. Two separate color morphs can be found, a brown morph which lives on Macrocystis and a green color morph on Zostera marina. Diet consists mainly of their primary substrate along with epiphytes such as diatoms which often grow on the substrate surface. In this study respirometry was done on individuals of the green color morph to determine whether chloroplasts consumed in their diet maintained functionality. Light and dark respirometry was conducted on living specimens with as many diatoms and other epiphytes removed from their body surface as possible. Each isopod was then sacrificed and its gut removed before repeating both light and dark respirometry to determine the contribution to photosynthesis from the epiphytes. Most individuals used for respirometry were between 4.5 and 5 cm to eliminate variation in metabolic rate due to body mass. These sizes are all greater than the size range reported in the literature. Little size-dependent variation in metabolic rate was seen within the range used. All respirometry was conducted with partial pressures of oxygen above 100 mm Hg and no oxyconformity was observed. During live respirometry the mean respiration rate was consistently higher during the dark than during the light, indicating photosynthesis. Comparison of whole-animal respiration with that of animals with their guts removed showed that although epiphytes do contribute to both respiration and photosynthesis, the material within the gut is likely contributing as well. Over a three week experimental period the level of respiration increased in the dark, possibly due to increased diatom load. Trends in metabolism over time as measured during the light were not as clear.
