Benthic Primary Production Research Articles

Vulnerability of kelp, Ecklonia radiata, to persistent nitrogen pollution and coastal darkening

Coastal darkening is expected to have pervasive impacts on benthic primary producers. However, the effects of nitrogen enrichment, an often-co-occurring stressor, on benthic primary producers and their functions is less clear. This study investigates the interactive effects of coastal darkening and nitrogenous eutrophication, including nitrogen source (NH4+ vs. NO3−), on the function of the kelp Ecklonia radiata. First, an in-situ experiment was used to assess the differential impacts of NH4+ and NO3− pulse enrichment on the photosynthetic performance and pH modulation capacity of E. radiata. Second, a laboratory experiment was used to assess the longer-term impacts of nitrogen enrichment under low-light conditions mimicking coastal darkening on service provisioning, including photosynthetic performance, pH modulation, nutrient uptake and growth. While pulse nitrogen enrichment had no impacts on the photosynthetic performance of E. radiata in-situ, persistent exposure to either NH4+ or NO3− acted as a stressor to sporophytes as indicated by elevated rates of dark respiration and lamina erosion and reduced photosynthetic efficiency and growth rates. Furthermore, low-light conditions elicited reduced photosynthetic capacity at saturating irradiance, which extended to a reduction in the extent of pH modulation, and significantly increased lamina erosion. While the two stressors appeared to act on distinct parameters, ultimately, both darkening and eutrophication directly reduced net primary production, especially when in combination. These results demonstrate the negative interactive effects of coastal darkening and eutrophication on E. radiata function, while suggesting a vulnerability of E. radiata to even moderate levels of persistent nitrogen enrichment. This vulnerability highlights the need to consider environmental conditions during kelp conservation and restoration, and when attempting to valorise kelp ecophysiology for nature-based solutions.

Spatiotemporal distribution of sedimentary chloropigments and organic carbon in a shelf sea ecosystem, with a focus on the cold water mass

The Yellow Sea is one of the most thoroughly studied shelf seas in the northwestern Pacific. However, many aspects of the northern Yellow Sea sediments remain poorly understood. Sedimentary chloropigments and total organic carbon (TOC) are crucial components that indicate benthic primary productivity and ecosystem functioning in the marginal sea system. The present study investigated the temporal and spatial variations of sediment chloroplastic pigments (Chl-a and Pha-a) and TOC contents in relation to seasons and the northern Yellow Sea Cold Water Mass (NYSCWM). Decadal trends were also examined using linear regression on time-series data from 12 cruises conducted over a nine-year period (2006–2014). The correlations between sedimentary Chorophy-a (Chl-a), Pheophorbide-a (Pha-a), TOC, and their ratios with other abiotic and biotic factors were analyzed to detect any effects of the NYSCWM on the spatiotemporal distribution of sediment Chl-a, Pha-a, TOC contents, as well as the ecological relevance of their ratios as indicators of food quality (freshness) in the benthic system. The NYSCWM substantially influences the spatial and seasonal distribution of sedimentary Chl-a, Pha-a, and TOC contents. High values of Pha-a, TOC, and the ratios of Pha-a/(Chl-a + Pha-a) and TOC/Chl-a were often observed in the central region of the NYSCWM, where Chl-a showed clear seasonal fluctuations while Pha-a and TOC remained relatively constant. While sedimentary TOC appears to negatively mirror the spatial pattern of primary productivity in the water column, the spatial pattern of sedimentary Chl-a in relation to NYSCWM is less evident. However, the contents of Pha-a and TOC in the central NYSCWM sediments were higher than those at surrounding NYSCWM stations. Surface sediment Pha-a/(Chl-a + Pha-a) ratio was negatively correlated with meiofauna abundance and biomass and positively correlated with nematode/copepod ratio. This finding indicates that the quality of sediment organic matter is important to meiofauna. Conversely, the lower organic degradation rate at the lower bottom temperature of the NYSCWM may explain the observed higher Pha-a and TOC contents in its central area. Time-series data collected over nine years at the NYSCWM stations showed a decreasing trend for Chl-a, while TOC and the ratio of Pha-a/(Chl-a + Pha-a) exhibited increasing tendencies. This trend may imply a reduced quality of food supply to the benthic food web in the shelf sea system, along with degraded ecosystem functioning and service under the impacts of global change and anthropogenic disturbances.

Coral high molecular weight carbohydrates support opportunistic microbes in bacterioplankton from an algae-dominated reef.

Dissolved organic matter (DOM) released by benthic primary producers fuels coral reef food webs. Anthropogenic stressors cause shifts from coral to algae dominance on many reefs, and resulting alterations in the DOM pool can promote opportunistic microbes and potential coral pathogens in reef water. To better understand these DOM-induced effects on bacterioplankton communities, we compared the carbohydrate composition of coral- and macroalgae-DOM and analyzed the response of bacterioplankton from an algae-dominated reef to these DOM types. In line with the proposed microbialization of reefs, coral-DOM was efficiently utilized, promoting energy transfer to higher trophic levels, whereas macroalgae-DOM likely stimulated microbial respiration over biomass production. Contrary to earlier findings, coral- and not algal-DOM selected for opportunistic microbial taxa, indicating that a change in the prevalent DOM composition, and not DOM type, may promote the rise of opportunistic microbes. Presented results may also apply to other coastal marine ecosystems undergoing benthic community shifts.

Progressive enrichment of benthic primary producer and dreissenid δ15N with depth in Lakes Erie and Ontario

Progressive enrichment of benthic primary producer and dreissenid δ15N with depth in Lakes Erie and Ontario

Food web collapse and regime shift following goldfish introduction in permanent ponds.

In a global context of invasive alien species (IAS), native predators are often eradicated by functionally different IAS, which may induce complex cascading consequences on ecosystem functioning because of the key role predators play in structuring communities and stabilizing food webs. In permanent ponds, the most abundant freshwater systems on Earth, global human-mediated introductions of alien omnivores such as the pet trade goldfish are driving broad-scale patterns of native predators' exclusion, but cascading consequences on food web structure and functioning are critically understudied. We compared food webs of naturally fishless ponds versus ponds where dominant native predators (newts) had been extirpated by invasive goldfish within the last decade. Integrating community-wide isotopic, taxonomic and functional traits approaches, our study reveals that pond food webs collapsed in both vertical and horizontal dimensions following goldfish introduction and the associated exclusion of native predators. Consumer taxonomic diversity was drastically reduced, essentially deprived of amphibians as well as predatory and mobile macroinvertebrates to the profit of burrowing, lower trophic level consumers (detritivores). Changes in community structure and function underlined a regime shift from a macrophyte-dominated system mainly characterized by benthic primary production (periphyton), to a macrophyte-depleted state of ponds hosting communities mainly associated with phytoplankton primary production and detritus accumulation, with higher tolerance to eutrophication and low dissolved oxygen concentration. Results underline major impacts of widely introduced omnivores such as the goldfish on the functioning of pond ecosystems with potentially dramatic consequences on the key ecosystem services they deliver, such as global biodiversity support or water quality improvement. They also shed light on the key role of submerged aquatic vegetation in supporting diverse communities and complex food webs in shallow lentic systems and call for urgent consideration of threats posed by IAS on ponds' ecosystems by managers and policymakers.

Changing phenology of benthic primary producers in inland waters: Current knowledge and future directions

AbstractBenthic primary producers (BPP) in inland waters, including aquatic macrophytes and periphyton, are foundational habitats that are highly sensitive to multiple human drivers of environmental change. However, long‐term seasonal monitoring of BPP is limited, leaving us with little information on the cause, directionality, and consequences of the potential shifts in timing of BPP life cycle events. Here, we review the literature on the phenological changes of BPP and show that BPP respond primarily to temperature, but also to other interactive drivers related to climate change and eutrophication. In addition, we present four rare case studies where BPP display strong and earlier shifts in event timing associated with increasing temperature and discuss potential impacts of these changes on ecosystem functioning. Given the responsive nature of BPP to multiple human drivers, we provide suggestions on how to improve basic monitoring to better understand the future impact of phenological changes of this critical habitat.

Glacial melt impacts carbon flows in an Antarctic benthic food web

Most coastal glaciers on the West Antarctic Peninsula are in retreat. Glacial ice scouring and lithogenic particle runoff increase turbidity and shape soft sediment benthic communities. This, in turn, has the potential to induce a shift in these systems from an autotrophic to a heterotrophic state. In this study, we investigated the influence of glacial runoff on carbon flows in the soft-sediment food web of Potter Cove, a well-studied shallow fjord located in the northern region of the West Antarctic Peninsula. We constructed linear inverse food web models using a dataset that includes benthic carbon stocks as well as carbon production and respiration rates. The dataset offers detailed spatial information across three locations and seasonal variations spanning three seasons, reflecting different degrees of disturbance from glacial melt runoff. In these highly resolved food web models, we quantified the carbon flows from various resource compartments (phytoplankton detritus, macroalgae, microphytobenthos, sediment detritus) to consumers (ranging from prokaryotes to various functional groups in meio- and macrofauna). Locations and seasons characterized by high glacial melt runoff exhibited distinct patterns of carbon flow compared to those with low glacial melt runoff. This difference was primarily driven by a less pronounced benthic primary production pathway, an impaired microbial loop and a lower secondary production of the dominant bivalve Aequiyoldia eightsii and other infauna in the location close to the glacier. In contrast, the bivalve Laternula elliptica and meiofauna had the highest secondary production close to the glacier, where they are exposed to high glacial melt runoff. This study shows how the effects of glacial melt propagate from lower to higher trophic levels, thereby affecting the transfer of energy in the ecosystem.

Food webs in isolation: The food-web structure of a freshwater reservoir with armoured shores in a former coastal bay area

Many shallow coastal bays have been closed off from the sea to mitigate the risk of flooding, resulting in coastal reservoir lakes with artificial armoured shorelines. Often these enclosed ecosystems show a persistent decline in biodiversity and ecosystem services, which is likely reflected in their food-web structure. We therefore hypothesize that the food webs of coastal reservoir lakes with armoured shorelines (1) consist of relatively few species with a low food-web connectance and short food chains, and (2) are mainly fuelled by autochthonous organic matter produced in the pelagic zone. To investigate these two hypotheses, we used stable-isotope analysis to determine the food-web structure of lake Markermeer (The Netherlands), a large reservoir lake with armoured shorelines in a former coastal bay area. Contrary to expectation, connectance of the food web in lake Markermeer was comparable to other lakes, while food-chain length was in the higher range. However, the trophic links revealed that numerous macroinvertebrates and fish species in this constructed lake exhibited omnivorous feeding behaviour. Furthermore, in line with our second hypothesis, primary consumers heavily relied on pelagically derived organic matter, while benthic primary production exerted only a minor and seasonal influence on higher trophic levels. Stable-isotope values and the C:N ratio of sediment organic matter in the lake also aligned more closely with phytoplankton than with benthic primary producers. Moreover, terrestrial subsidies of organic matter were virtually absent in lake Markermeer. These findings support the notion that isolation of the lake through shore armouring and the lack of littoral habitats in combination with persistent resuspension of sediments have affected the food web. We argue that restoration initiatives should prioritize the establishment of land-water transition zones, thereby enhancing habitat diversity, benthic primary production, and the inflow of external organic matter while preserving pelagic primary production.

Seafloor primary production in a changing Arctic Ocean

Phytoplankton and sea ice algae are traditionally considered to be the main primary producers in the Arctic Ocean. In this Perspective, we explore the importance of benthic primary producers (BPPs) encompassing microalgae, macroalgae, and seagrasses, which represent a poorly quantified source of Arctic marine primary production. Despite scarce observations, models predict that BPPs are widespread, colonizing ~3 million km2 of the extensive Arctic coastal and shelf seas. Using a synthesis of published data and a novel model, we estimate that BPPs currently contribute ~77 Tg C y−1 of primary production to the Arctic, equivalent to ~20 to 35% of annual phytoplankton production. Macroalgae contribute ~43 Tg C y−1, seagrasses contribute ~23 Tg C y−1, and microalgae-dominated shelf habitats contribute ~11 to 16 Tg C y−1. Since 2003, the Arctic seafloor area exposed to sunlight has increased by ~47,000 km2 y−1, expanding the realm of BPPs in a warming Arctic. Increased macrophyte abundance and productivity is expected along Arctic coastlines with continued ocean warming and sea ice loss. However, microalgal benthic primary production has increased in only a few shelf regions despite substantial sea ice loss over the past 20 y, as higher solar irradiance in the ice-free ocean is counterbalanced by reduced water transparency. This suggests complex impacts of climate change on Arctic light availability and marine primary production. Despite significant knowledge gaps on Arctic BPPs, their widespread presence and obvious contribution to coastal and shelf ecosystem production call for further investigation and for their inclusion in Arctic ecosystem models and carbon budgets.

Global emergent responses of stream microbial metabolism to glacier shrinkage

Most cryospheric ecosystems are energy limited. How their energetics will respond to climate change remains largely unknown. This is particularly true for glacier-fed streams, which interface with the cryosphere and initiate some of Earth’s largest river systems. Here, by studying resource stoichiometry and microbial energetics in 154 glacier-fed streams sampled by the Vanishing Glaciers project across Earth’s major mountain ranges, we show that these ecosystems and their benthic microbiome are overall carbon and phosphorus limited. Threshold elemental ratios and low carbon use efficiencies (median: 0.15) modelled from extracellular enzymatic activities corroborate resource limitation in agreement with maintenance metabolism of benthic microorganisms. Space-for-time substitution analyses suggest that glacier shrinkage will stimulate benthic primary production in glacier-fed streams, thereby relieving microbial metabolism from carbon limitation. Concomitantly, we find that increasing streamwater temperature will probably stimulate microbial growth (temperature sensitivity: 0.62 eV). Consequently, elevated microbial demands for phosphorus, but diminishing inputs from subglacial sources, may intensify phosphorus limitation as glaciers shrink. Our study thus unveils a ‘green transition’ towards autotrophy in the world’s glacier-fed streams, entailing shifts in the energetics of their microorganisms.

Dominance of net autotrophy in arid landscape low relief polar lakes, Nunavut, Canada.

The Arctic is the fastest warming biome on the planet, and environmental changes are having striking effects on freshwater ecosystems that may impact the regional carbon cycle. The metabolic state of Arctic lakes is often considered net heterotrophic, due to an assumed supply of allochthonous organic matter that supports ecosystem respiration and carbon mineralization in excess of rates of primary production. However, lake metabolic patterns vary according to regional climatic characteristics, hydrological connectivity, organic matter sources and intrinsic lake properties, and the metabolism of most Arctic lakes is unknown. We sampled 35 waterbodies along a connectivity gradient from headwater to downstream lakes, on southern Victoria Island, Nunavut, in an area characterized by low precipitation, organic-poor soils, and high evaporation rates. We evaluated whether lakes were net autotrophic or heterotrophic during the open water period using an oxygen isotopic mass balance approach. Most of the waterbodies were autotrophic and sites of net organic matter production or close to metabolic equilibrium. Autotrophy was associated with higher benthic primary production, as compared to its pelagic counterpart, due to the high irradiance reaching the bottom and efficient internal carbon and nutrient cycling. Highly connected midstream and downstream lakes showed efficient organic matter cycling, as evidenced by the strong coupling between gross primary production (GPP) and ecosystem respiration, while decoupling was observed in some headwater lakes with significantly higher GPP. The shallow nature of lakes in the flat, arid region of southern Victoria Island supports net autotrophy in most lakes during the open water season. Ongoing climate changes that lengthen the ice-free irradiance period and increase rates of nutrient evapoconcentration may further promote net autotrophy, with uncertain long-term effects for lake functioning.

Benthic primary production in Young Sound, Northeast Greenland

The extreme and variable light climate of polar marine environments imposes a substantial limitation on benthic primary production and demands efficient adaptive capacities of the primary producers. This chapter reviews the composition, abundance, primary production and adaptive strategies of benthic primary producers in Young Sound. Benthic primary producers occurred in the 0-50 m depth range and the relative importance of microalgae, crustose coralline macroalgae and foliose macroalgae varied systematically with depth. On a summer day with optimal light conditions benthic primary production showed a maximum of c.
 70 mmol O2 m-2 d-1 in shallow water. Production rates declined gradually to c. 20 mmol O2 m-2 d-1at 10–20 m depth and to 2.5 mmol O2 m-2 d-1 at 30 m depth.
 Foliose macroalgae contributed markedly to primary production in shallow water but became insignificant at water depths >15 m, while benthic diatoms contributed most to primary production at intermediate water depths (5-30 m). At water depths greater than 30 m only coralline algae occurred, but their production was low because of their low abundance, low Pmax and the low ambient irradiance at those depths. All algal groups were well adapted to the ambient irradiance and could, within minutes, acclimate their photosynthetic performance to changing light conditions. The benthic primary production in Young Sound markedly surpassed the pelagic primary production down to water depths of 20 m and the results thereby underline the potential importance of benthic primary production in shallow-water Arctic ecosystems.

Benthic primary production decreases internal phosphorus loading from lake sediments under light supplement

In aquatic ecosystems, light penetrating the sediment surface in shallow lakes may regulate the internal phosphorus (P) release through benthic primary production, which subsequently affects oxidation, pH levels, and alkaline phosphatase activity in the upper sediment. To study the effects of light exposure on the P dynamics at the sediment-water interface under eutrophic conditions, a two-month mesocosm experiment was conducted in twelve cement tanks (1000 L each). The tanks were equipped with Light-Emitting Diode (LED) lights, and surface sediments collected from eutrophic Lake Nanhu (China) were exposed to four different light intensities (0, 50, 100, 200 μmol m−2 s−1). The results revealed that: 1) Both the total phosphorus concentration and the phosphorus release flux from the sediment were lower in the light treatments (mean value, 0.59–0.71 mg L−1 and 0.00–0.01 mg m−2 d−1, respectively) than in the control treatment (0.77 mg L−1 and 0.01 mg m−2 d−1, respectively), indicating that light supplement could decrease the internal P release. 2) Benthic primary production promoted by light directly absorbed soluble reactive phosphorus and decreased the internal P release. The resulting improved production could also increase dissolved oxygen concentrations at the sediment-water interface, thus indirectly inhibiting internal P release. 3) The relative contributions of direct absorption and indirect inhibition on the internal P release ranged between 23% to 69% and 31% to 77% depending on the light intensity.

Changes in sea floor productivity are crucial to understanding the impact of climate change in temperate coastal ecosystems according to a new size-based model

The multifaceted effects of climate change on physical and biogeochemical processes are rapidly altering marine ecosystems but often are considered in isolation, leaving our understanding of interactions between these drivers of ecosystem change relatively poor. This is particularly true for shallow coastal ecosystems, which are fuelled by a combination of distinct pelagic and benthic energy pathways that may respond to climate change in fundamentally distinct ways. The fish production supported by these systems is likely to be impacted by climate change differently to those of offshore and shelf ecosystems, which have relatively simpler food webs and mostly lack benthic primary production sources. We developed a novel, multispecies size spectrum model for shallow coastal reefs, specifically designed to simulate potential interactive outcomes of changing benthic and pelagic energy inputs and temperatures and calculate the relative importance of these variables for the fish community. Our model, calibrated using field data from an extensive temperate reef monitoring program, predicts that changes in resource levels will have much stronger impacts on fish biomass and yields than changes driven by physiological responses to temperature. Under increased plankton abundance, species in all fish trophic groups were predicted to increase in biomass, average size, and yields. By contrast, changes in benthic resources produced variable responses across fish trophic groups. Increased benthic resources led to increasing benthivorous and piscivorous fish biomasses, yields, and mean body sizes, but biomass decreases among herbivore and planktivore species. When resource changes were combined with warming seas, physiological responses generally decreased species’ biomass and yields. Our results suggest that understanding changes in benthic production and its implications for coastal fisheries should be a priority research area. Our modified size spectrum model provides a framework for further study of benthic and pelagic energy pathways that can be easily adapted to other ecosystems.

Unveiling the ecological significance of algal mats and meadows: Insights into phosphorus cycling and primary production of benthic algae in post-mining lakes

Post-mining lakes are anthropogenic water bodies increasing globally due to mining suppression and recultivation. These lakes have ecological and socioeconomic significance, providing freshwater sources, wildlife habitats, and recreation potential. However, research on primary producers in these lakes is limited, with most studies focusing on phytoplankton while neglecting algal mats and meadows. If developed in high biomass, algal mats and macroalgal meadows play a crucial role in aquatic ecosystems. They contribute to the trophic structure, nutrient fluxes, primary production and to the purification of entire waterbodies. Yet, there is a lack of knowledge regarding the nutrient acquisition and the contribution of algal mats and meadows to total primary production and phosphorus (P) cycling, especially in oligotrophic lakes, including post-mining lakes. Our team investigates the benthic algal primary producers - algal mats and meadows in the littoral zone of tree newly established post-mining lakes located in the Czech Republic (Europe). Our main objectives are to describe the quality and quantity of primary producers, quantify the contribution of algal mats and meadows to the primary production and phosphorus cycling in the oligotrophic post-mining lakes. We have studied them throughout all seasons with a special focus on the generally neglected winter/spring season. Our sampling strategy encompasses three gradients of variability along which the composition and ecological role of benthic algae change: spatial variability along the depth gradient within each lake, itemporal variability throughout the seasons within each lake and successional variability between the lakes of different age. spatial variability along the depth gradient within each lake, itemporal variability throughout the seasons within each lake and successional variability between the lakes of different age. The methodological approach consists of measuring the limnological and chemical parameters of lakes, taxonomic determination, biomass estimation and C:N:P stoichiometry of algal biomass along the whole gradient of the euphotic zone (0-15m). The in situ measurement of primary production of benthic algae from various depths using the oxygen meter Fibox 3 (PreSens, Germany) with a combination of laboratory experiments was employed too (Čapková 2022). We measure the kinetic parameters of P uptake of algal mats and meadows using 33P-labelled orthophosphates under controlled conditions similar to the nature (Konopáčová 2021). According to our survey, algal mats and meadows exhibited high productivity in the entire littoral zone. Algal mats dominate the depth up to 3m Fig. 1 and are highly diverse, with more than 400 identified taxa (Bešta 2022). Macroalgal meadows formed by the genus Chara together with the genus Vaucheria, are key taxa occupying the deeper zone (3-15m) Fig. 2. The distribution of benthic algae in lakes is influenced by depth gradients, substrate quality, seasonality and age of lakes foundation, resulting in complex spatio-temporal patterns. Specific emphasis is placed on the fate of P, which is the limiting nutrient in investigated lakes. High C:P molar ratios in microalgal mats indicate strong P deficiency in studied lakes. Over the vegetation season, microalgal biomass doubled, while the P content in biomass dropped to 60% of the values from the start of the vegetation season. The maximum uptake velocity and specific P uptake affinity decreased by an order of magnitude from April to October, and P uptake affinity was measured for comparison in plankton too. Based on our results, we proposed a possible mechanism underlying a stable coexistence of planktonic and benthic primary producers, with plankton prospering primarily in summer and autumn and algal mats and meadows in winter and spring seasons. By integrating data collected during five years of investigation, our study aims to provide a comprehensive understanding of the ecological roles of primary producers in post-mining lakes.

Scaling up benthic primary productivity estimates in a large intertidal estuary using remote sensing

As two main primary producers in temperate intertidal regions, seagrass and microphytobenthos (MPB) support estuarine ecosystem functions in multiple ways including stabilizing food webs and regulating sediment resuspension among others. Monitoring estuary productivity at large scales can inform ecosystem scale responses to environmental stressors (climate change, pollution and habitat degradation). Here we use a case study to show how Sentinel-2 data can be used to estimate estuary-wide emerged and submerged gross primary productivity (GPP) on intertidal flats by coupling a new machine learning model to map seagrass and unvegetated habitats with literature-derived photosynthesis-irradiance (P – I) relationships. The model consisted of (1) supervised classification with random forest to delineate seagrass and unvegetated areas and (2) artificial neural network (ANN) regression to predict % seagrass coverage. Our seagrass delineation by supervised classification had an overall accuracy of 0.96, while the ANN regression on seagrass coverage provided high predictive accuracy (R2 = 0.71 and RMSE = 0.11). The estimated GPP showed seagrass contributed slightly more to intertidal benthic productivity than MPB in the case-study estuary over the 3-year study period. This model can be used to predict the response of seagrass and MPB GPP to sea level rise, which shows that the future state may be very sensitive to increased turbidity. For example, by the year 2100, the model shows a sharp decline in productivity with sea level rise, assuming current turbidity trends, (loss of up to 52–53 % for seagrass and 23–45 % for MPB, a function of whether shoreward migration of seagrass is incorporated). However, GPP under conditions of unchanging turbidity (and no seagrass migration), exhibits minimal negative impact of sea level rise (loss of 3 % for seagrass and increase of 29 % for MPB). Therefore, controlling water turbidity might be an efficient solution to maintaining the current GPP as sea level rises.

Isotopic-based evidence for reduced benthic contributions to fish after a whole-lake addition of nanosilver.

Silver nanoparticles (AgNPs) are added as antibacterial and anti-odor agents to a wide range of textiles, with high potential for release into aquatic environments via domestic wastewater. Previous work demonstrating the negative impacts of AgNP exposure on periphyton production suggests benthic primary production could be reduced in aquatic ecosystems impacted by AgNP discharge. To evaluate the potential for AgNPs to alter benthic-pelagic coupling in aquatic ecosystems, tissue-stable isotope ratios of carbon and nitrogen from northern pike (Esox lucius) and yellow perch (Perca flavescens) were measured before, during, and after the addition of AgNPs to a whole-lake ecosystem, and compared to those collected from a nearby reference lake. A shift in carbon isotope ratios toward more negative values was observed in both P. flavescens and E. lucius collected from the lake where AgNPs were added, with no shift in similar magnitude observed in E. lucius from the reference lake. Consequently, Bayesian estimates of benthic energy consumed decreased by 32% for P. flavescens and by 40% for E. lucius collected after AgNP additions relative to pre-addition estimates, greater in magnitude or opposite in direction of trends observed in our reference lake. Analyses suggest no changes in fish nitrogen isotope ratios related to AgNP additions. We hypothesize that the observed reduction in littoral energy use of fish reported here is a response to AgNP settling in littoral benthic habitats-the main habitat in lakes supporting periphyton-as AgNP has been shown elsewhere to significantly reduce the rates of periphyton production. Further, our study highlights the need to broaden the scope of risk assessments for AgNPs and other emerging contaminants prone to settling to consider habitat-specific impacts on resource utilization by organisms after their release into aquatic ecosystems.

Microbiomes and metabolomes of dominant coral reef primary producers illustrate a potential role for immunolipids in marine symbioses

The dominant benthic primary producers in coral reef ecosystems are complex holobionts with diverse microbiomes and metabolomes. In this study, we characterize the tissue metabolomes and microbiomes of corals, macroalgae, and crustose coralline algae via an intensive, replicated synoptic survey of a single coral reef system (Waimea Bay, Oʻahu, Hawaii) and use these results to define associations between microbial taxa and metabolites specific to different hosts. Our results quantify and constrain the degree of host specificity of tissue metabolomes and microbiomes at both phylum and genus level. Both microbiome and metabolomes were distinct between calcifiers (corals and CCA) and erect macroalgae. Moreover, our multi-omics investigations highlight common lipid-based immune response pathways across host organisms. In addition, we observed strong covariation among several specific microbial taxa and metabolite classes, suggesting new metabolic roles of symbiosis to further explore.

Microphytobenthic impact on benthic pelagic nutrient exchange in temperate shallow estuaries

Microphytobenthos (MPB) form a light-sensitive “nutrient filter” between sediment and bottom water in shallow coastal systems and the MPB activity is believed to have important implications for nutrient availability in such systems. We quantified this light-driven control on nutrient fluxes by analyzing benthic flux measurements from >3000 sediment cores sampled in five Danish estuaries. Light responses and the seasonality of benthic primary production (BPP), benthic nutrient fluxes and the MPB impact on these fluxes showed that MPB significantly intercepted fluxes of ammonium (NH4+), nitrate (NO3−) and dissolved silica (DSi) both under light and dark conditions. Phosphate (PO43−) fluxes were only significantly intercepted in light. The microphytobenthos had a large relative impact on nutrient fluxes during spring and a weaker impact in the autumn, despite significant photosynthetic activity of the MPB at this time of the year. The proportion of the annual sediment-water flux impacted by MPB reached maximum values of 65%, 73%, 89% and 96% for NH4+, NO3−, PO43− and DSi, respectively. The relative impact depended on the magnitude of the base fluxes and the relative impact increased with light availability at the stations above a threshold of 5% light at the seafloor. This documents that changing light regimes alter the MPB control on nutrient dynamics in shallow systems.

Coastal marine megaripple fields are metabolic hotspots with highly dynamic oxygen exchange

AbstractMegaripples are current‐generated seafloor bedforms of well‐sorted sand or gravel and wavelengths over 1 m. In this aquatic eddy covariance study, we measured large rates of benthic primary production and respiration for a shallow‐water sandy megaripple field exposed to strong tidally driven currents and intense sunlight. Current and light were the main short‐term drivers of a highly dynamic oxygen exchange. Daytime oxygen release as high as 300 mmol m−2 d−1 and nighttime oxygen uptake up to −100 mmol m−2 d−1 were likely sustained by current‐driven transport of oxygen, nutrients, and organic matter (fuel) into and out of the sand and superimposed by rapid internal cycling. Seasonal differences in temperature (45%) and light (69%) between April and September were the main long‐term drivers of substantially greater rates of gross primary production and respiration in September. The megaripples functioned as an intense metabolic hotspot with carbon cycling rates larger than those of most near‐shore sediments.