Species-specific effects of two bioturbating polychaetes on sediment chemoautotrophic bacteria

D Vasquez-Cardenas,Fjr Meysman,Hts Boschker,Co Quintana,E Kristensen

doi:10.3354/meps11679

Abstract

Bioturbation has major impacts on sediment biogeochemistry, which can be linked tothe functional traits of the macrofauna involved. Nereis (Hediste) diversicolor and Marenzelleriaviridis are 2 functionally different bioturbating polychaetes that strongly affect the ecology andbiogeochemistry of coastal sediments. However, the different effects of these polychaetes on theactivity and composition of microbial communities and on chemoautotrophic bacteria have notbeen extensively studied. We performed experiments with sediment aquaria that contained eachspecies separately as well as a non-bioturbated control. Bacterial communities in different sedimentzones (surface, burrow, subsurface) were characterized by phospholipid-derived fatty acidanalysis combined with stable isotope labeling ( 13 C bicarbonate) to quantify the dark CO 2 fixationby chemoautotrophic bacteria. Pore water chemistry (SH 2 S and dissolved inorganic carbon) wasadditionally assessed in each treatment. The strong ventilation but low bioirrigation capacity inthe open-ended burrows of N. diversicolor resulted in enhanced aerobic chemoautotrophic activity,potentially by sulfur oxidizing and nitrifying bacteria along the burrow. In contrast, slowerventilation and higher irrigation by M. viridis induced an advective mode of pore water transport.This promotes anaerobic chemoautotrophy around the blind-ended burrow and within the subsurfacesediment. Sulfate-reducing bacteria were the dominant anaerobic chemoautotrophs thatprobably disproportionate sulfur. In conclusion, our analysis shows that bioturbating fauna influencethe microbial community and chemoautotrophic activity in sediments, but that the effectstrongly depends on the structure of the burrow and on species-specific ventilation behavior andirrigation capacity.

Highlights

Marine sediments are characterized by a predictable vertical zonation of electron donors and acceptors, but in the presence of benthic fauna this typical 1-dimensional redox zonation is disturbed through particle reworking and solute transport induced by burrow formation and ventilation, a process known as bioturbation
The surface sediment in Nereis (Hediste) diversicolor (Nd) aquaria was loose and fluffy and detritus accumulations were present around burrow openings, whereas surface sediment in Marenzelleria viridis (Mv) aquaria appeared more compact (Fig. 1)
PLFA patterns in burrow and surface sediment were alike for Nd, whereas in the Mv treatment, the biomarker fingerprint of the burrow resembled that of the subsurface sediment

Summary

Introduction

Marine sediments are characterized by a predictable vertical zonation of electron donors and acceptors, but in the presence of benthic fauna this typical 1-dimensional redox zonation is disturbed through particle reworking and solute transport induced by burrow formation and ventilation, a process known as bioturbation (Aller 1988, Meysman et al.2006, Kristensen et al 2012). Nereis (Hediste) diversicolor and Marenzelleria viridis are 2 burrow-dwelling polychaetes that have contrasting effects on the ecosystem functioning of coastal areas in the Baltic Sea (Kristensen et al 2014). N. diversicolor inhabits a mucus-lined open-ended burrow (typically U- or Y-shaped, up to 20 cm deep) that is regularly flushed by undulatory body movements (Kristensen & Kostka 2005). This intense burrow ventilation results in diffusion-based radial solute transport into the surrounding sediment pore water, but creates only limited advective pore water movement in the surrounding sediment (Pischedda et al 2012, Kristensen et al 2014). M. viridis activity simultaneously maintains reduced conditions in the deeper sediment that stimulate sulfate reduction, while potentially enhancing sulfide oxidation in surface sediments, given the upward flow of solutes (Quintana et al 2007, Kristensen et al 2011, 2014)

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Conclusion