Characteristics of the mediterranean seagrass Posidonia oceanica contributing to high-frequency acoustic scattering

Abstract

Posidonia oceanica meadows are the most important ecosystem for the life cycle of coastal Mediterranean benthos with a fundamental role in the primary production of the neritic system and a decisive influence on other vegetation and animal communities. Posidonia oceanica meadows are undergoing a slow but progressive regression, the most common cause of which is enhanced turbidity and the consequent reduction of water transparency. The first step towards the preservation of coastal environments is to define their extent and condition. Echographic surveys allow general maps to be obtained, but accurate seafloor characterization requires knowledge of the characteristics of seabed vegetation which affect acoustics propagation. A preliminary study quantified the gas within the leaves of Posidonia oceanica as a function of the plant life cycle. An order of magnitude of the volume of the different elements considered and their relative importance expressed as percentages is given. The values obtained were considered with reference to the seasonal changes of the phenological variables from which they depend and also to the main structural variable: the density of leaves. A future step based on the present work will be the development of a model of acoustic scattering by Posidonia oceanica derived from a model developed for gassy sediments. The final result would enhance the capability of rapidly acquire information on the extention of meadows, plant density and height. From an operational point of view it could improve the performance of minehunting sonars.