Can diving-induced tissue nitrogen supersaturation increase the chance of acoustically driven bubble growth in marine mammals?

The potential for acoustically mediated causes of stranding in cetaceans (w hales and dolphins) is of increasing concern given recent stranding events associated with anthropogenic acoustic activity. We examine a potentially d ebilitating non-auditory mechanism called rectified diffusion. Rectified di ffusion causes gas bubble growth, which in an insonified animal may produce emboli, tissue separation and high, localized pressure in nervous tissue. Using the results of a dolphin dive study and a model of rectified diffusio n for low-frequency exposure, we demonstrate that the diving behavior of ce taceans prior to an intense acoustic exposure may increase the chance of re ctified diffusion. Specifically, deep diving and slow ascent/descent speed contributes to increased gas-tissue saturation, a condition that amplifies the likelihood of rectified diffusion. The depth of lung collapse limits ni trogen uptake per dive and the surface interval duration influences the amo unt of nitrogen washout from tissues between dives. Model results suggest t hat low-frequency rectified diffusion models need to be advanced, that the diving behavior of marine mammals of concern needs to be investigated to id entify at-risk animals, and that more intensive studies of gas dynamics wit hin diving marine mammals should be undertaken. (C) 2001 Academic Press.