Effect of the microphytobenthos photosynthesis on seabed backscattering properties

Abstract

The development of hydroacoustic techniques for benthic habitat classification requires understanding of biological effects on seabed geoacoustic properties. The study addresses only one biological process that could potentially change the properties—photosynthesis of benthic microalgae. The previous investigations demonstrated that the impact could be important in warm southern marine waters of relatively high salinity. This motivated us to study the effect of the microphytobenthos photosynthesis on the backscattering properties of the sandy sediments of the southern Baltic Sea, an area of lower temperature and salinity. The five multiday laboratory experiments, different in hydrophysical or biological conditions, were conducted. The backscatter data were acquired in the small tank with sandy bottom under controlled constant temperature and salinity with simulated “day” and “night” conditions (light/dark (L/D) photocycles). Oxygen content in the water column as well as biological and biooptical parameters were additionally monitored. The diel variations of the backscattered signal energy were analyzed. The study demonstrated the impact of microphytobenthos photosynthesis on the backscattering properties of the marine sediment and its sensitivity to the abiotic (illumination level) and biotic (benthic microalgal biomass and macrozoobenthos bioturbation) factors.