Can Diving-induced Tissue Nitrogen Supersaturation Increase the Chance of Acoustically Driven Bubble Growth in Marine Mammals?

Abstract

The potential for acoustically mediated causes of stranding in cetaceans (whales and dolphins) is of increasing concern given recent stranding events associated with anthropogenic acoustic activity. We examine a potentially debilitating non-auditory mechanism called rectified diffusion. Rectified diffusion 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 diffusion for low-frequency exposure, we demonstrate that the diving behavior of cetaceans prior to an intense acoustic exposure may increase the chance of rectified 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 nitrogen uptake per dive and the surface interval duration influences the amount of nitrogen washout from tissues between dives. Model results suggest that low-frequency rectified diffusion models need to be advanced, that the diving behavior of marine mammals of concern needs to be investigated to identify at-risk animals, and that more intensive studies of gas dynamics within diving marine mammals should be undertaken.

Could beaked whales get the bends?

“…Modelling efforts on diving mammals, on the other hand, have reported divergent results when investigating the effect that changes in ascent rate has on tissue and blood P N 2 (Houser et al, 2001;Fahlman et al, 2006Fahlman et al, , 2007Zimmer and Tyack, 2007). Fahlman et al (2006) suggested that a reduction in the ascent coupled with an increase in tot Q  close to the surface could reduce Pv N 2 by as much as 45%.…”

“…Houser et al (2001) used the results published by Ridgway and Howard (1979) in a theoretical model based on gas diffusion to show that beaked whale diving patterns (based on simulated dive data) could lead to chronic tissue accumulation of N 2 gas. Their simulations illustrated the potential increase in N 2 caused by relatively shallow (100 m, 9 min) dives with short (1 min) surface intervals.…”

Cuvier's beaked whale (Ziphius cavirostris) head tissues:physical properties and CT imaging

“…Recently, the use of high-intensity anthropogenic sounds, particularly midfrequency (2-4·kHz) sonar, has been associated with mass strandings of Cuvier's beaked whales (Evans and England, 2001;Frantzis, 1998;Simmonds and Lopez-Jurado, 1991). Physiological mechanisms including rectified diffusion of gas bubbles in tissues (Crum and Mao, 1996;Houser et al, 2001), gas emboli formation in body fats (Jepson et al, 2003;Fernandez et al, 2004) or bubble or lung resonance (Finneran, 2003) may explain the observed hemorrhaging in the lungs, acoustic pathways, brain, spinal cord, kidneys and eyes, congestion and bubbles in the brain, and embolisms in body fats in stranded animals (Evans and England, 2001;Fernandez et al, 2004). The role that sound exposure played in these strandings and subsequent deaths remains controversial.…”

Mitigation provisions to be implemented for marine seismic surveying in Latin America: a review based on fish and cetaceans

“…Whales typically balance dives to manage nitrogen bubble formation; a sound stimulus may disrupt the animals' normal dive regime (Houser et al 2001). A sudden change in air pressure allows the formation of in vivo nitrogen bubbles that can migrate into the circulatory system, causing tissue damage (Southall et al 2007).…”