Assessment of the impacts of shallow gas on taxonomic structure of benthic communities in Bahia Blanca estuary (Argentina)

Shallow biogenic gas deposits located in the surface of the seabed may affect abundance, diversity, biomass and structure of benthic communities. Nevertheless, the magnitude and responsible variables of this effect still not clear. For this, the current study applies sedimentological metrics to the different community patterns associated with gas presence detected by acoustic methods across two seasons (spring and winter). Gas-bearing sediments showed higher organic matter content, lower shear strength and greater textural homogeneity across the column. Gas trapped in sediments was found associated with changes in the structure of benthic community, in species composition as well as in relative abundance and biomass of each taxa. Also, lower total abundance, species richness and diversity and higher total biomass was found in gas site. Higher organic matter content of sediments in gas site explained benthic community patterns across seasons. Gas bubbles trapped in surface of seabed sediments changed physical and chemical properties of sediments affecting benthic communities in ways that seems comparable with shallow water gas seeps and reducing environment. Unlike the latter, gas bubbles trapped have the advantage of having been widely mapped in coastal systems by geophysicists and marine geologists, with high resolution seismic (3.5 kHz) which according to our results seems to affect benthic communities.