Meeting Abstract
The giant acorn barnacle, Balanus nubilus, is a low-intertidal organism that has achieved scientific notoriety owing to its extraordinary muscle fiber dimensions (diameters can exceed 3mm in adults!). At these sizes, metabolically active muscle cells are at risk for insufficient oxygen delivery owing to low SA:V ratios. In addition to the fiber size limitations, B. nubilus likely experience periodic hypoxia during low-tide emersion and lack an oxygen binding pigment (e.g., hemocyanin). This combination of oxygen-depriving features poses a triple-threat to muscle function. As such, we are interested in the unique metabolic and structural adaptations of giant B. nubilus muscle fibers that allow them to maintain function in spite of the internal oxygen environment. The first step in this investigation is to describe the changes in hemolymph gas and electrolyte levels that occur during bouts of aerial emersion. To this end, we measured hemolymph pO2, pCO2, pH and [K+] at 0, 3, 6 and 9h following exposure to air emersion, anoxic immersion, and normoxic immersion. We found that hemolymph pO2 was significantly decreased in the anoxic barnacles by 3h, though both anoxic and air emersion were significantly lower than normoxic barnacles by 9h. We also revealed a significant increase in pCO2 by 6h in the anoxic group, and by 9h in both anoxia and emersion. Thus, tidal emersion only mildly decreases hemolymph pO2 and increases pCO2 compared to the more extreme stress of submerged anoxia. Given the unusually high capacity for aerial oxygen uptake seen in other barnacles, these data were not altogether surprising. What was unexpected, however, was a significant increase in [K+] that occurred by 6h in both the emersion and anoxic groups. The reason for this change is yet to be determined.
