Acoustics of seagrass photosynthesis

Abstract

The paper reviews experiments in the Mediterranean that have investigated the use of low frequency sound transmission measurements (0.2–20 kHz) to study metabolism of seagrasses in situ in a noninvasive way and to better evaluate primary production at the scale of a meadow, for Posidonia oceanica and Cymodocea nodosa species. As sound interacts with the canopy and rhizosphere, the cumulative effect of multiple scattering from the aerenchymatic tissues of leaf blade, rhizome, and root changes the character of the environment impulse response. Diel variations of received energy and statistical features are due to oxygen movement which modifies the plant scattering function. During periods of high net photosynthesis, pressurization of the lacunal gas modifies the tissue mechanical properties. High internal oxygen partial pressures cause the release of oxygen into the diffusive boundary layer which can result in bubble formation on the tissue surface when local oxygen concentration exceeds solubility. In situ experimental results will be discussed in the light of laboratory acoustic and microscopic investigations of the tissues. [Work supported by ONR, ONR Global.]