Impact of bioturbation by Arenicola marina on microbiological parameters in intertidal sediments

Abstract

The impact of bioturbation by the lugworm Arenicola manna on sediment microflora and biochemical activities was investigated in intertidal sediments of the North Sea. Burrow walls and fecal casts were compared with surface and subsurface sediment surrounding the burrows. At the main study site burrow walls contained twice as much organic matter as the sediment surface. Viable counts of aerobic proteolytic and chitinolytic bacteria peaked at external and internal boundary layers (sediment surface and burrow walls). Burrow walls showed maximal bacterial production (incorporation of tritiated thymidine into DNA), maximal microheterotrophic activity (incorporation and mineralization of glucose and acetate) and highest levels of certain hydrolytic enzymes (alkaline phosphatase and sulfatase). Rates of chemoautotrophic COz fixation in both burrow walls and surrounding subsurface sedment were 3 to 4 times higher than at the sediment surface, suggesting a short-cucuited CO2 turnover driven by an elevated catabolism. In a second, more polluted study area, burrow walls were again the main site of microheterotrophic activity, but only minor differences were noted for CO2 fixation. Biogeochemical consequences of bioturbation by A, marina could be understood essentially as a shifting of catabolic and anabolic microbial activity peaks from the top to subsurface layers, where burrow walls showed the most conspicuous effects. Nevertheless, protease peaks in the fecal casts indicated also that this shifting pattern can be reversed for certain parameters.