In Search of a Field-Based Relationship Between Benthic Macrofauna and Biogeochemistry in a Modern Brackish Coastal Sea

ORIGINAL RESEARCH published: 19 December 2018 doi: 10.3389/fmars.2018.00489 In Search of a Field-Based Relationship Between Benthic Macrofauna and Biogeochemistry in a Modern Brackish Coastal Sea Edited by: Teresa Radziejewska, University of Szczecin, Poland Reviewed by: Oleg P. Savchuk, Stockholm University, Sweden Brygida Wawrzyniak-Wydrowska, University of Szczecin, Poland *Correspondence: Mayya Gogina † Present Address: Bo Liu, Marine Geochemistry, Alfred-Wegener-Institute for Polar and Marine Research (AWI), Bremerhaven, Germany Claudia Morys, Department of Estuarine and Delta Systems, NIOZ Netherlands Institute for Sea Research, Utrecht University,Yerseke, Netherlands Specialty section: This article was submitted to Coastal Ocean Processes, a section of the journal Frontiers in Marine Science Received: 30 April 2018 Accepted: 04 December 2018 Published: 19 December 2018 Citation: Gogina M, Lipka M, Woelfel J, Liu B, Morys C, Böttcher ME and Zettler ML (2018) In Search of a Field-Based Relationship Between Benthic Macrofauna and Biogeochemistry in a Modern Brackish Coastal Sea. Front. Mar. Sci. 5:489. doi: 10.3389/fmars.2018.00489 Mayya Gogina 1*, Marko Lipka 2 , Jana Woelfel 3 , Bo Liu 2† , Claudia Morys 4† , Michael E. Böttcher 2 and Michael L. Zettler 1 1 Biological Oceanography, Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany, 2 Geochemistry & Isotope Biogeochemistry, Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany, 3 Chemical Oceanography, Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany, 4 Institute for Biosciences - Marine Biology, University of Rostock, Rostock, Germany During several cruises in the southern Baltic Sea conducted in different seasons from 2014 to 2016, sediment cores were collected for the investigation of pore-water biogeochemistry and associated nutrient fluxes across the sediment-water interface. Six stations were positioned along a salinity gradient (ranging from 22 to 8) and covered various sedimentary habitats ranging from mud to sand. Integrated fluxes of nutrients in the supernatant water and sediment oxygen consumption were additionally derived from incubations of intact sediment cores. Subsequently, sediment from the pore-water and incubation cores was sieved for taxonomic identification and estimation of benthic macrofauna density. This combined dataset was used to determine the dominant factors influencing the vertical distribution of geochemical parameters in the pore-waters of the studied habitats and to find similarities and patterns explaining significant variations of solute fluxes across the sediment-water interface. A statistical relationship between the thickness of sulfide-free surface sediments, solute fluxes of sulfide, ammonium, and phosphate as well as oxygen consumption and taxonomic and functional characteristics of macrobenthic communities were tested. Our data and modeling results indicate that bioturbation and bioirrigation alter near-surface pore-water nutrient concentrations toward bottom water values. Besides sediment properties and microbial activity, the biogeochemical fluxes can further be explained by the functional structure of benthic macrofauna. Community bioturbation potential, species richness, and biomass of biodiffusers were the best proxies among the tested set of biotic and abiotic parameters and could explain 63% of multivariate total benthic flux variations. The effects of macrobenthos on ecosystem functioning differ between sediment types, specific locations and seasons. Both, species distribution and nutrient fluxes are temporally dynamic. Those natural patterns, as well as potential anthropogenic and Frontiers in Marine Science | www.frontiersin.org 1 December 2018 | Volume 5 | Article 489 Gogina et al. Macrofauna-Biogeochemistry Field-Based Relationship natural disturbances (e.g., fishery, storm events), may cause impacts on field data in a way beyond our present capability of quantitative prediction, and require more detailed seasonal studies. The data presented here adds to our understanding of the complexity of natural ecosystem functioning under anthropogenic pressure. Keywords: benthic macrofauna, ecosystem functioning, nutrient fluxes, sediment biogeochemistry, pore-water gradients, Baltic Sea INTRODUCTION (2017)]. There is a certain lack of consensus even with regard to the direction of the effects. Increased faunal activity imply more intense redistribution of sediment particles, oxygenation of the sediment, decline of hydrogen sulfide, reduction of phosphate release into the bottom water (as phosphates are accumulated in the sediment bound to iron minerals), general decrease of the ammonium outflux, and an increase in the dinitrogen gas efflux due to coupled nitrification/denitrification in bioturbated sediments (Karlson et al., 2007; Norkko et al., 2012; Janas et al., 2017). Contradicting with the above, other authors (e.g., Pelegri and Blackburn, 1994; Mermillod-Blondin et al., 2004; Jordan et al., 2009; Gilbertson et al., 2012) describe the increased ammonium flux from the sediment to the overlying water column observed in the presence of burrowing invertebrates. In the Gulf of Finland, Maximov et al. (2014) found evidence for an effect of an increased population of invasive polychaete Marenzelleria spp. on binding of phosphate in sediments and reducing eutrophication conditions. This all suggests not only natural variability in nutrient cycling between regions, but also high context-dependency due to the complex interplay of multiple processes even on a very local scale (e.g., within few kilometers or less, Gammal et al., 2017), making basin scale extrapolations difficult. There is a lack of such estimates, especially based on field data (in situ derived), in respect of the German part of the southwestern Baltic Sea. This underlines the importance of further field studies and quantitative estimates, crucial for understanding and parameterization of the biogeochemical processes in order to support scientifically sound ecosystem management, to ensure the health of the Baltic Sea ecosystem and to mitigate unfavorable changes. Overall physical transports between the free water column and sediment interstitial water, low in diffusion-dominated and high in advection-dominated habitats, control microbial activity inside sediments (Aller, 1994). According to Mermillod-Blondin (2011) bioturbation (particle mixing) and biodeposition (settling of feces and pseudofeces) produced by benthic invertebrates may play a bigger role in diffusion-dominated habitats where they can significantly modify water and particle fluxes at the water–sediment interface, whereas only slight influence of ecosystem engineers is expected in advection dominated habitats predominantly controlled by hydrological processes. Here it is important to specify that generally diffusion is the transport of dissolved material along a concentration (...truncated)