Respiratory physiology of Aplysia californica (J.E. Morton & C.M. Yonge, 1964) and Aplysia brasiliana (J.E. Morton & C.M. Yonge, 1964) upon aerial exposure

A comparison was made between the effects of aerial exposure on the respiratory physiology of two species of Aplysia; the sluggish Pacific Aplysia californica (J.E. Morton & C.M. Yonge, 1964) and the active Atlantic Aplysia brasiliana (J.E. Morton & C.M. Yonge, 1964). The objectives of the study were three-fold: (1) To compare the effects of aerial exposure on rates of oxygen uptake for both species; (2) To determine if metabolic adjustments are utilized during periodic long-term aerial exposure, particularly the presence (or absence) of an O 2 debt and the accumulation of anaerobic metabolites; (3) To determine Aplysia's ability to tolerate desiccation due to aerial exposure. Both species endured a < 10% loss in body weight within a 10-h period of aerial exposure. However, A. californica lost significantly less weight than A. brasiliana Both species are oxygen conformers in water and exhibited similar rates of oxygen uptake. In air, there was a rapid reduction in rates of aerial oxygen uptake, to 16% of aquatic values. In A. californica, a two-fold increase in aquatic oxygen uptake was found immediately following a 4-h period of aerial exposure, indicating the repayment of an oxygen debt. However, calculations indicate that only 19% of the oxygen debt was repaid within a 4-h recovery period, suggesting that this species depresses its overall metabolic rate upon aerial exposure. The presence of anaerobic energy production was verified by the accumulation of whole-body alanine (seven-fold increase), hemolymph d-lactate (eight-fold increase), and the concomitant degradation of aspartate and glutamine (two-fold decrease). On the other hand glutamate, serine, glycine, and taurine concentrations were unaffected by aerial exposure. It was concluded that Aplysia's physiological adaptations to stranding include a high tolerance to desiccation, depressed rates of aerial oxygen uptake, reliance on anaerobic metabolism, and overall metabolic depression. These features are characteristic of sublittoral species subject to short periods of aerial exposure.