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Schematic overview of the experimental setup. Sediment cores were placed inside a plastic tray. Water bath, permanently cooled by a flow-through thermostat (arrows indicate flow direction) (1) and light source (daylight white LEDs) darkened with shading foil to induce different photon fluence rates (2). Light came only from the top. Three sediment cores with mounted measuring module (A-C) equipped with magnetic stirrer and fluorescent sensor spot (3) are connected to a control unit (4) via optical fiber. A fourth dummy core filled with in situ surface water (D) is used for temperature measurement and compensation during the experiment. MPB: Microphytobenthic biofilm on top of the sediment.
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The shallow coastal water zone of the tide-less southern Baltic Sea is dominated by exposed sandy sediments which are typically inhabited by microphytobenthic communities, but their primary production is poorly studied, and hence four stations between 3.0 and 6.2 m depth were investigated. Sediment cores were carefully taken to keep the natural lay...
Citations
... The patches of O 2 production directly correlated to areas colonized by auto-fluorescent phototrophic O 2producing microorganisms, while the O 2 -consuming areas were non-fluorescent, most likely representing colonies of non-photosynthetic O 2 respiring microorganisms (Fig. 2E). Both these functional groups of microorganisms are known to colonize sand grains [48][49][50][51] , however their ability to noticeably affect O 2 gradients over such small scales has not been reported before. The chlorophyll-a containing photosynthetic patches had median O 2 production rates of 19 µmol O 2 L −1 h −1 (Fig. 2E, red). ...
... We confirmed that the development of anoxic microenvironments is a persistent feature in a total of 1764 model runs where O 2 consumption rates in the microbial colonies, diffusion coefficients, flow velocity and microbial distributions were varied. It is likely that this mechanism of anoxic microsite formation is active throughout the oxic silicate sands of the continental shelves, as they are all exposed to similar physical forcing and flow conditions 2 and furthermore, exhibit similar microbial communities 9,51,58-60 and microbial colonization patterns 32,34,48 . ...
The permeable silicate sediments which cover more than 50% of the continental shelves are a major, but poorly constrained sink for the vast amount of anthropogenic nitrogen (N) that enters the ocean. Surface-attached microbial communities on sand grains remove fixed-N via denitrification, a process generally restricted to anoxic or low oxygen (O2) environments. Yet, in sands, denitrification also occurs in the centimeters thick well-oxygenated surface layer, which leads to additional and substantial N-loss. So far however, the underlying mechanisms that drive denitrification in oxic sands are poorly resolved. In this study, we applied a non-invasive microfluidic technique to visualize and quantify how sediment-attached microorganisms shape O2 availability on the surface of silicate sand grains. This revealed a remarkable heterogeneity in rates; with colonies of O2 consuming and producing microorganisms situated within micrometers of each other. Using a mechanistic approach to model respiration on the surface of a single silicate sand grain we showed that the high rates of O2 consumption within the microbial colonies on the sand-grain surface outpace O2 supply from the surrounding pore water. As a result anoxic microenvironments develop on the sand grain surface, which so far have been invisible to conventional techniques. The model results indicate that anaerobic denitrification occurring in these anoxic microenvironments can account for up to 74% of denitrification in oxygenated sands, with the remainder occurring in the presence of oxygen. In a preliminary upscaling approach, using a global dataset we estimated that anoxic microenvironments in oxygenated surface layers could be responsible for up to a third of the total N-loss that occurs in silicate shelf sands. Consequently, denitrification in anoxic microenvironments drives substantial anthropogenic-N removal from continental silicate shelf sands.
... Improved underwater light conditions will facilitate the wider distribution of benthic diatoms, and they may contribute a significant fraction of the total system primary production at DZBC. For the Gulf of Gdańsk, which is the nearest data set to the DZBC, Kuriyama et al. (2021) calculated a share of 23% of the total primary production originating from benthic diatoms based on published data (Renk & Ochocki 1998;Urban-Malinga & Wiktor 2003). A recent study on the Bothnian Bay (Northern Baltic Sea) reported similar values with a share of 31% of the total annual primary production by microphytobenthic communities (Ask et al. 2016), and these authors also pointed to the lack of data regarding benthic primary production in the Baltic Sea. ...
The Darß-Zingst Bodden Chain is a tide-less shallow lagoon at the Southern Baltic coast. It was and is studied in almost all hydrological, biogeochemical as well as floristic and faunistic aspects. Benthic diatoms were studied using light and scanning electron microscopy (SEM) in the early 1970s and one sampling site was now revisited. A total of 103 diatom taxa were recorded in sediment and on macrophyte samples collected between 2015 and 2019. In the sediment samples, epipsammic diatoms accounted for almost 90% of the total valve counts. In the 1970s, only three epipsammic species were observed, while we recorded a total of 27 epipsammic taxa, most of which were very small (<12 µm). Since those earlier studies, many of these species have been newly described or transferred from other genera. Moreover, small diatoms may have been misidentified, overlooked or counted as important. This study emphasizes, in addition, the need to combine light microscopy with electron microscopy to allow the unambiguous identification also of small entities, and to reach a comprehensive overview over the diatom flora present in different benthic habitats. ARTICLE HISTORY
... Above the taxonomic threshold point along the salinity gradient of the medium spatial scale, benthic biomass correlated positively with the functional diversity of communities. Although marine diatoms are highly important for the global primary production of carbon (Nelson et al., 1995), and benthic diatoms strongly contribute to benthic productivity and biomass Kuriyama et al., 2021), studies on the diversity-biomass relationship on marine or brackish benthic diatoms are rare. Thus, generalizing or comparing our result of the positive relationship between functional diversity and benthic biomass or the productivity of benthic ecosystems to other regions is difficult, but this finding agrees with our previous study where we showed a positive relationship between functional diversity of soft bottom benthic diatoms and benthic biomass in a brackish archipelago (Virta et al., 2019). ...
The responses of biotic communities and ecosystems to climate change may be abrupt and non-linear. Thus, resolving ecological threshold mechanisms is crucial for understanding the consequences of climate change and for improving environmental management. Here, we present a study on the threshold responses of benthic diatom communities that are an important component of all aquatic environments and strongly contribute to global primary production. We reach beyond the taxonomic perspective by focusing on the diversity and functions of diatom communities and benthic biomass along gradients of salinity and wind disturbance, whose climate-change-induced changes have been predicted to strongly affect biotic communities in the marine and brackish systems in the future. To improve the generality of our results, we examine three self-collected datasets from different spatial scales (6–830 km) and ecosystem types. We collected samples from rock pools or from littoral stones and studied taxonomic thresholds using Threshold Indicator Taxa Analysis (TITAN2). We investigated threshold responses of community diversity, community functions, and benthic biomass using t-tests and regression analysis. Our results indicated that decreasing salinity may result in increasing diversity but decreasing biomass of brackish communities, while the effects of increasing wind disturbance were contradictory among spatial scales. Benthic biomass correlated with the taxonomic and functional diversity, as well as with the body size distribution of communities, highlighting the importance of considering community functions and organismal size when predicting ecosystem functions. The most pronounced effects of decreasing salinity and increasing wind disturbance on community functions were changes in the abundance of low-profile diatom species, which, due to the high resilience of low-profile diatoms, may lead to changes in ecosystem functioning and resilience. To conclude, decreasing salinity and increasing wind disturbance may lead to threshold responses of biotic communities, and these changes may have profound effects on ecosystem functioning along marine coastal areas.
... Microphytobenthic communities typically consist of various phototrophic algal groups, such as Bacillariophyceae, Chlorophyceae, Dinophyceae, and Cyanobacteria, but benthic diatoms often dominate in terms of biodiversity and biomass [13][14][15]. These taxa live either in the interspaces and porewater between soft bottom particles (=epipelic) or directly attached to soft bottom particles (=epipsammic) in the top millimeters of such coastal sedimentary structures [16]. ...
... These taxa live either in the interspaces and porewater between soft bottom particles (=epipelic) or directly attached to soft bottom particles (=epipsammic) in the top millimeters of such coastal sedimentary structures [16]. The sediment type and the degree of exposition (disturbance) control the diatom activity, since small-sized epipsammic taxa typically occur on exposed sandy sediments ( [15] and the references therein), whereas larger epipelic species are limited by sand-scouring processes [17]. The distribution of the soft bottom grain-size along with their hydrodynamically influenced dynamics can affect the benthic diatom biomass and productivity [18]. ...
... The distribution of the soft bottom grain-size along with their hydrodynamically influenced dynamics can affect the benthic diatom biomass and productivity [18]. Therefore, the wind conditions are a key factor for the strength of currents and waves that physically shape and even disturb exposed sediments and their inhabitants in the Southern Baltic Sea [15], while, at sheltered, soft bottom sites, these forces are dampened. ...
Benthic diatom communities dominate sheltered shallow inner coastal waters of the atidal Southern Baltic Sea. However, their photosynthetic oxygen production and respiratory oxygen consumption is rarely evaluated. In the Baltic Sea carbon budget benthic diatom communities are often not included, since phytoplankton is regarded as the main primary producer. Therefore, two wind-protected stations (2–49-cm depths) were investigated between July 2010 and April 2012 using undisturbed sediment cores in combination with planar oxygen optodes. We expected strong fluctuations in the biological activity parameters in the incubated cores over the course of the seasons. The sediment particles at both stations were dominated by fine sand with a median grain size of 131–138 µm exhibiting an angular shape with many edges, which were less mobile compared to exposed coastal sites of the Southern Baltic Sea. These sand grains inhabited dense communities of rather small epipsammic diatoms (<10 µm). Chlorophyll a as a biomass parameter for benthic diatoms fluctuated from 64.8 to 277.3-mg Chl. a m⁻² sediment surface. The net primary production and respiration rates exhibited strong variations across the different months at both stations, ranging from 12.9 to 56.9 mg O2 m⁻² h⁻¹ and from −6.4 to −137.6 mg O2 m⁻² h⁻¹, respectively. From these data, a gross primary production of 13.4 to 59.5 mg C m⁻² h⁻¹ was calculated. The results presented confirmed strong seasonal changes (four-fold amplitude) for the activity parameters and, hence, provided important production biological information for sheltered sediments of the Southern Baltic Sea. These data clearly indicate that benthic diatoms, although often ignored until now, represent a key component in the primary production of these coastal habitats when compared to similar studies at other locations of the Baltic Sea and, hence, should be considered in any carbon budget model of this brackish water ecosystem.
... (st. 1) was swept into the peatland during the last saltwater inflow event in January 2019. This is in agreement with a recently submitted study on microphytobenthic primary production at an exposed sandy beach next to the Hütelmoor (Kuriyama et al., 2021), in which the authors report Planothidium delicatulum as most the abundant species (25% of the community) attached to sand grains. Even though salinity of the coastal German Baltic Sea in Mecklenburg-Pomerania rarely exceeds 14 S A (Lippert et al., 2017) and therefore is not considered a marine habitat, growth response of other marine species (Algae Base) found in the Baltic Sea such as Navicula perminuta (Woelfel et al., 2014), indicate that euryhaline marine species are also able to live in brackish environments. ...
The German Baltic Sea coastline is characterized by sea-land transitions zones, specifically coastal peatlands. Such transition zones exhibit highly fluctuating environmental parameters and dynamic gradients that affect physiological processes of inhabiting organisms such as microphytobenthic communities. In the present study four representative and abundant benthic diatom strains [Melosira nummuloides, Nitzschia filiformis, Planothidium sp. (st. 1) and Planothidium sp. (st.2)] were isolated from a Baltic Sea beach and three peatlands that are irregularly affected by Baltic Sea water intrusion. Ecophysiological and cell biological traits of the strains were investigated for the first time as function of light, temperature and salinity. The four strains exhibited euryhaline growth over a range of 1-39 S A , surpassing in situ salinity of the respective brackish habitats. Furthermore, they showed eurythermal growth over a temperature range from 5 to 30 • C with an optimum temperature between 15 and 20 • C. Growth rates did not exhibit any differences between the peatland and Baltic Sea strains. The photosynthetic temperature optimum of the peatland diatom isolates, however, was much higher (20-35 • C) compared to the Baltic Sea one (10 • C). All strains exhibited light saturation points ranging between 29.8 and 72.6 µmol photons m −2 s −1. The lipid content did not change in response to the tested abiotic factors. All data point to wide physiological tolerances in these benthic diatoms along the respective sea-land transitions zones. This study could serve as a baseline for future studies on microphytobenthic communities and their key functions, like primary production, under fluctuating environmental stressors along terrestrial-marine gradients.
In Japan, fishers plant trees in upstream watersheds, known as “fishery forests,” to improve coastal environments and secure fishery production. Based on observation and experience, fishers have traditionally believed that their practices are fit for their intended purpose. Fishers have found it difficult to continue their practices due to budget constraints caused by a recent decline in coastal fisheries. As such, they are currently faced with the dilemma of deciding whether to restore watershed forests to improve the coastal environments or minimize expenses in an effort to secure financial sustainability. This draws attention to further issues: whether or not fishers can obtain a net return on their efforts, and if so—when. To this end, we examine the economic value of the traditional ecological knowledge using data of terrestrial and aquatic ecosystems in Hiroshima, Japan. The results show that, while fishery forests mostly pay their costs in the long run, the costs are higher than the benefits for the first several years because of the initial costs of afforestation. With the aim of contributing to holistic watershed management, we propose policy instruments that could be employed to alleviate front-loaded costs so that fishers can engage in traditional ecological knowledge-based practices.
Multiple methods exist to measure the benthic flux of dissolved oxygen (DO), but many are limited by short deployments and provide only a snapshot of the processes occurring at the sediment–water interface. The gradient flux (GF) method measures near bed gradients of DO and estimates the eddy diffusivity from existing turbulence closure methods to solve for the benthic flux. This study compares measurements at a seagrass, reef, and sand environment with measurements from two other methods, eddy covariance and benthic chambers, to highlight the strengths, weaknesses, and uncertainty of measurements being made. The results show three major areas of primary importance when using the GF method: (1) a sufficient DO gradient is critical to use this method and is limited by the DO sensor precision and gradient variability; (2) it is important to use similar methods when comparing across sites or time, as many of the methods showed good agreement but were often biased larger or smaller based on the method; and (3) in complex bottom types, estimates of the length scale and placement of the DO sensors can lead to large sources of error. Careful consideration of these potential errors is needed when using the GF method, but when properly addressed, this method showed high agreement with the other methods and may prove a useful tool for measuring long‐term benthic fluxes of DO or other chemical sensors or constituents of interest that are incompatible with other methods.
