112 reads in the past 30 days
Climate change–induced terrestrial matter runoff may decrease food web production in coastal ecosystemsJanuary 2025
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116 Reads
Published by Wiley and Association for the Sciences of Limnology and Oceanography
Online ISSN: 1939-5590
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Print ISSN: 0024-3590
Disciplines: Environmental studies
112 reads in the past 30 days
Climate change–induced terrestrial matter runoff may decrease food web production in coastal ecosystemsJanuary 2025
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116 Reads
110 reads in the past 30 days
Climate oscillations drive nutrient availability and seagrass abundance at a regional scaleJanuary 2025
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110 Reads
99 reads in the past 30 days
Snow avalanche‐induced disturbances can resurrect extinct zooplankton and alter paleolimnological recordsJanuary 2025
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102 Reads
96 reads in the past 30 days
Cross‐ecosystem trophic structure and benthic–pelagic coupling: Effects of depth, body size, and feeding guildJanuary 2025
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96 Reads
92 reads in the past 30 days
Nutrient pulse scenarios drive contrasting patterns in the functional stability of freshwater phytoplanktonJanuary 2025
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92 Reads
Limnology and Oceanography (L&O) publishes research on all aspects of the sciences of limnology and oceanography. Submissions are judged on their originality and intellectual contribution to the journal’s unifying theme—understanding of aquatic systems.
We welcome articles, reviews, and comments that are physical, chemical, or biological in nature, empirical or theoretical in method, and from elemental to geological, ecological to evolutionary, species to ecosystem, or system to global in scale.
February 2025
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8 Reads
Salt marshes are vital but vulnerable ecosystems. However, our understanding of disturbance‐induced dieback and recovery processes in multi‐specific marshes remains limited. This study utilized remote sensing data (2001–2021) to analyze a dieback event and subsequent recovery in the multi‐specific San Felice marsh within the Venice lagoon, Italy. A significant dieback of Spartina maritima (Spartina) was identified in 2003, likely triggered by a drought event and heat stress. This resulted in a conversion of 4.6 ha of marsh predominantly colonized by Spartina (fractional cover of Spartina > 50%) in 2001 to bare soil in 2003. These bare areas were then gradually encroached by vegetation, indicating the occurrence of the recovery. Despite gradually gaining ground, Spartina only dominated 6.4 ha marshes in 2021, significantly lower than its pre‐dieback area (21.3 ha). However, other species also encroached on the dieback area, such that the aboveground biomass returned to pre‐dieback levels, indicating that the shift in marsh species composition that occurred as a consequence of the event compensated for this ecosystem service. Vegetation recovery, spanning from 1 yr to more than 18 yr, was found to be slowest in areas of lowest elevation. This study provides evidence that dieback and recovery can modify the species composition of multi‐specific marshes over decades. These insights contribute to a better understanding of marsh resilience to drought and elevated temperature, both of which are likely to increase in the future.
February 2025
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12 Reads
Benedict V. A. Mittelbach
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Alexander S. Brunmayr
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Margot E. White
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Timothy I. Eglinton
Organic carbon (OC) burial in lake sediments is comparable to that in marine sediments globally. However, climatic and carbon cycle implications depend on the origin of buried OC. This study utilizes high‐resolution radiocarbon (¹⁴C) measurements in combination with stable carbon isotopes (¹³C) and total organic carbon/total nitrogen ratios to constrain sources and ages of OC deposited since the early 20th century in Lake Constance, the second‐largest lake in central Europe. We differentiate between aquatic, pre‐aged soil, and fossil rock‐derived (petrogenic) OC. The shape and magnitude of the ¹⁴C bomb spike recorded in the sediment profile indicate the sequestration of recently synthesized biospheric OC with a complex overlay from different OC sources. We find that soil‐derived OC is the dominant component of sedimentary OC, with a mean transit time in the catchment of around 110 yr. Additionally, we quantified the ¹⁴C dynamics of dissolved inorganic carbon in the lake, which can be modeled with a mean transit time of around 10 yr. An ordinary kriging spatial analysis revealed that the Alpine Rhine delta and the profundal areas are the primary loci for allochthonous OC deposition. Lake‐wide surface sediment OC fluxes were spatially heterogeneous but averaged 52.0 gC m⁻² yr⁻¹, where 26.7 gC m⁻² yr⁻¹ of mostly stable, allochthonous OC are buried long term. This study highlights the necessity of accounting for both pre‐aged and fossil OC sources, as well as spatial heterogeneity, when assessing the response of lakes and, more broadly, source‐to‐sink systems to ongoing climate and ecosystem change.
February 2025
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13 Reads
Cell surface properties can strongly mediate microbial interactions with predators in soil and host‐pathogen systems. Yet, the role of microbial surface properties in avoiding or enhancing predation in the ocean is less well known. Appendicularians are globally abundant marine suspension feeders that capture marine microorganisms in a complex mucous filtration system. We used artificial microspheres to test whether the surface properties of prey particles influenced selection by the appendicularian, Oikopleura dioica. We used a range of microsphere sizes (0.5, 1, 2, and 3 μm), concentrations (~ 10³–10⁶ particles mL⁻¹), and two charges (amine‐modified, more positive vs. carboxylate‐modified, more negative) to represent open‐ocean microbial communities. We found that appendicularians selected between the particles of different charge. More negatively charged particles were enriched in the gut by up to 3.8‐fold, while more positive particles were enriched in the mucous filters by up to 4.7‐fold, leading to different particle fates. These results expand understanding of the mechanisms by which filter‐feeders select between prey and reveal a mechanism by which marine bacteria could rapidly alter their susceptibility to predation, either through adaption or acclimation.
February 2025
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34 Reads
Off‐coast phytoplankton blooms occur frequently in the frontal region of the eutrophic Taiwan Strait during the northeasterly monsoon relaxation period, as consistently revealed by extensive cruise and satellite observations. Realistic model simulations have shown that restratification by frontal baroclinic instability (BCI) plays a crucial role in triggering blooms under nutrient‐rich conditions. This study deciphered the distinct contributions of submesoscale and mesoscale BCIs to bloom development using sensitivity tests of an idealized model of the Taiwan Strait featuring an intense alongshore front with ample nutrients. In three‐dimensional fine simulations with both submesoscale and mesoscale BCIs present, blooms were triggered by the cessation of a down‐front wind. Chlorophyll a was higher in submesoscale front regions than in mesoscale regions, primarily because of the higher upper‐ocean stability resulting from more effective restratification by submesoscale BCI. In three‐dimensional coarse simulations, mesoscale BCI led to relatively lower upper‐ocean stability and weaker blooms following wind relaxation, consistent with those in mesoscale regions in corresponding three‐dimensional fine simulations. In two‐dimensional simulations without submesoscale and mesoscale BCIs, blooms could not be triggered despite the cessation of a down‐front wind, primarily because of the absence of significant near‐surface restratification by BCIs. Furthermore, although symmetric instability was present in two‐dimensional fine simulations, its contribution to blooms was limited because of its minimal restratification effect. These results show that BCIs play the predominant role in triggering off‐coast blooms in eutrophic coastal front regions such as the Taiwan Strait.
February 2025
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12 Reads
Local and regional‐scaled studies point to the important role of lake type (natural lakes vs. reservoirs), surface water connectivity, and ecological context (multi‐scaled natural settings and human factors) in mediating lake responses to disturbances like drought. However, we lack an understanding at the macroscale that incorporates multiple scales (lake, watershed, region) and a variety of ecological contexts. Therefore, we used data from the LAGOS‐US research platform and applied a local water year timeframe to 62,927 US natural lakes and reservoirs across 17 ecoregions to examine how chlorophyll a responds to drought across various ecological contexts. We evaluated chlorophyll a changes relative to each lake's baseline and drought year. Drought led to lower and higher chlorophyll a in 18% and 20%, respectively, of lakes (both natural lakes and reservoirs included). Natural lakes had higher magnitudes of change and probabilities of increasing chlorophyll a during droughts than reservoirs, and these differences were particularly pronounced in isolated and highly‐connected lakes. Drought responses were also related to long‐term average lake chlorophyll a in complex ways, with a positive correlation in less productive lakes and a negative correlation in more productive lakes, and more pronounced drought responses in higher‐productivity lakes than lower‐productivity lakes. Thus, lake chlorophyll responses to drought are related to interactions between lake type and surface connectivity, long‐term average chlorophyll a, and many other multi‐scaled ecological factors (e.g., soil erodibility, minimum air temperature). These results reinforce the importance of integrating multi‐scaled ecological context to determine and predict the impacts of global changes on lakes.
February 2025
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16 Reads
Ocean buoyancy gliders provide a comprehensive view of the water column, offering more than simply a snapshot of a single moment in time or space. In this study, we applied the established machine learning method, k‐means clustering, to a glider dataset collected in the summer of 2015 in the northern Gulf of Mexico. Clustering analysis of chromophoric dissolved organic matter and salinity revealed the physical structure of water masses, both vertically within the water column and horizontally along the shelf. Supplementary statistical analyses, including principal component analysis and ANOVA, of individual clusters confirmed the clusters were statistically distinct from one another and provided insights into the factors contributing to their differentiation. The clusters identified in the glider dataset represent water masses variously distinguished by river plumes, wind‐induced upwelling effects, shifts in currents, density‐induced stratification, and biological processes. This study demonstrates that applying machine learning clustering methods to subsurface glider data is a novel technique that enhances the analytical capabilities of both glider and other oceanographic datasets.
February 2025
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61 Reads
Many studies have reported the paradoxical observation of high concentrations of low‐density microplastics (plastic particles < 5 mm) in deep‐sea sediments despite their buoyancy. The incorporation of buoyant microplastics into marine snow has been observed to enhance microplastic settling. Previous studies on the vertical movement of buoyant microplastics have been unable to theoretically account for these ocean observations and no study has comprehensively elucidated microplastic transport pathways in the ocean from the surface to seafloor. Here, we establish a one‐dimensional theoretical model, that embraces key elements of the flocculation process, to explain how marine snow acts as a vector to transport buoyant microplastics to deep water and the ocean bottom. Microplastics reach the ocean floor through multiple cycles of aggregation, settling, and disaggregation between marine snow and microplastics. Each settling cycle results in a net settling of 200–400 m. We demonstrate that microplastics with different sizes show distinct vertical settling behaviors and only microplastics less than 100 μm in diameter can reach the ocean bottom. This theoretical model refines our ability to predict and understand the global and long‐term fate, transport, and inventory of microplastics in the ocean interior, the influence of microplastics on the biological carbon pump and the efficacy of plastic management policies.
February 2025
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22 Reads
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Anoxic waters in the ocean's oxygen deficient zones (ODZs) limit the vertical migrations of zooplankton and mesopelagic fish impacting their ecology and influence on biogeochemical processes. Using an oxypleth‐tracking, nighttime‐only sampling protocol, this research reconstructed the trophic interactions of fish larvae and adults, and zooplankton, across the Eastern Tropical North Pacific ODZ. Bulk zooplankton δ¹⁵N increased latitudinally by ~ 3.3‰ from Costa Rica to Baja California due to anoxia‐derived denitrification and consequent enrichment of nitrogen sources for producers. Zooplankton δ¹⁵N also increased with depth, with an abrupt 3.4‰ increase below the anoxic core (~ 900 m depth), indicating a distinct trophic structure in the resident zooplankton community. Above the anoxic core, δ¹⁵N was similar for fish larvae (10.1‰) and zooplankton (10.5‰), reflecting a shared food source. An exception was the hypoxia‐tolerant myctophid Diogenichthys laternatus (δ¹⁵N = 7.5‰) that possibly feeds on chemoautotrophy‐derived material at the oxic‐anoxic interface. The δ¹⁵N of fish adults residing below the anoxic core, like the meso‐bathypelagic Notolychnus valdiviae (17.11‰) and Cyclothone spp. (15.89‰), was, on average, 4.8‰ higher than larval stages sampled at shallower depths, and 1.2‰ higher than zooplankton below the anoxic core. This stark increase in fish and zooplankton δ¹⁵N directly below the anoxic core suggests that anoxic waters act as a barrier for the downward trophic transfer by vertical migrants into the deep sea. Considering the current trends of ocean deoxygenation, this anoxia‐derived disruption of the migrant pump could limit the carbon sequestration potential of ODZs.
February 2025
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57 Reads
Hydrothermal transformations of dissolved organic matter (DOM) are governed by temperature and sedimentary organic carbon content, resulting in the release of hydrothermal DOM containing bioavailable compounds fueling benthic microbes. However, the temperature‐dependent molecular changes in porewater DOM from organic‐rich hydrothermal sediments, and the extent to which these changes contribute to the marine recalcitrant DOM, remain largely unexplored. Here we investigated the DOM composition of hydrothermal porewater and bottom water samples from the Guaymas Basin, Gulf of California, where basaltic sill intrusions generate hydrothermal petroleum in organic‐rich sediments. Samples containing hydrothermal petroleum with in situ temperatures from 4°C to > 106°C were analyzed using Fourier‐transform ion cyclotron resonance mass spectrometry and parallel factor analysis of excitation‐emission matrices from fluorescent DOM (FDOM). We found that the porewater DOM composition was strongly influenced by temperature and petroleum dissolution, evidenced by the enrichment of hydrothermal DOM with highly unsaturated, oxygen‐depleted aromatic, sulfur‐containing molecular formulae and petroleum‐associated FDOM compared to a cold reference site. In bottom waters, hydrothermal DOM accounted for ~ 26% of the DOM molecular formulae, with 82% exhibiting hydrogen‐to‐carbon ratios < 1.5, indicating their recalcitrance. The remaining ~ 18% of the hydrothermal molecular formulae were aliphatic and saturated, representing the release of bioavailable DOM to the ocean. Our results show that hydrothermal sediments are a source of both bioavailable and recalcitrant DOM, releasing water‐soluble petroleum‐derived compounds to the deep ocean. Our study highlights the need for more quantitative research on the contribution of hydrothermal sediments to deep‐sea DOM cycling.
February 2025
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52 Reads
Upwelling systems and their associated oxygen deficient zones (ODZs) are hotspots of nitrous oxide (N2O) production in the ocean. The Benguela Upwelling System (BUS) is a highly productive region and an important, yet variable source of N2O to the atmosphere. This study examined underlying processes and microbial key players governing N2O production in the BUS during the austral winter. ¹⁵N‐tracer incubation experiments were conducted to track N2O production from NH4⁺ oxidation and denitrification. N2O production and consumption mechanisms over a longer temporal scale were determined through natural‐abundance isotope analyses. Metagenomics and 16S rRNA gene amplicon sequencing were used to identify potential key prokaryotes driving N2O production. Our results showed that, compared with permanent ODZs, the BUS is characterized by a higher oxidative and a lower reductive N2O production, both of which exhibit substantial spatial variability. N2O production peaked in low‐oxygen (O2) waters, with nearly equal contributions of oxidative and reductive processes, suggesting their co‐occurrence across an O2 concentration range broader than previously thought. However, the observed N2O isotope signatures implied a legacy of recent and extensive N2O reduction to N2. Metagenomic and 16S rRNA gene data identified denitrifiers belonging to Thioglobaceae and the archaeal ammonia‐oxidizers Nitrosopumilaceae among the potential key drivers of N2O production. Our study provides a comprehensive picture of N2O production in the BUS, revealing significant variability in the N‐cycling regime and underlying N2O production mechanisms, and demonstrating the value of combining direct rate measurements with more integrative approaches, such as molecular omics and natural‐abundance stable isotope tracers.
February 2025
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71 Reads
The biogeochemistry of dissolved organic matter (DOM) is poorly understood in tropical coastal waters. Here, we quantified the biological and photochemical lability of dissolved organic carbon, nitrogen, and phosphorus, in the tropical coastal waters of Singapore. We conducted experiments during the inter‐monsoon, the mid‐southwest monsoon, and the late southwest monsoon seasons, which span the greatest range of biogeochemical conditions found in the area. The DOM lability was quantified as concentration changes during 90‐d biodegradation and 7‐d photoreactor incubations. Overall, DOM showed low lability, even though dissolved organic nitrogen and dissolved organic phosphorus accounted for most of the dissolved nitrogen and phosphorus. In the biodegradation experiments, only 5–15% of dissolved organic carbon, 0–7% of dissolved organic nitrogen, and 8–21% of dissolved organic phosphorus were degraded. The addition of labile dissolved organic carbon, intended to test priming effects and to ensure the microbes were not carbon‐limited, had no measurable impact on the results. During our photochemical experiments only 2–10% of the dissolved organic carbon were degraded, while neither dissolved organic nitrogen nor dissolved organic phosphorus showed consistent photochemical losses. The DOM optical properties (absorbance and fluorescence spectra) showed limited or no changes during the biodegradation experiments but larger declines in the photochemical experiments. Overall, the biodegradation of DOM was highest during the inter‐monsoon, when autochthonous DOM was most dominant, while photolability was greater during the terrestrial DOM‐rich southwest monsoon. Our results illustrate that in some tropical coastal environments, DOM can be fairly resistant to biological and photochemical degradation, and thus does not represent a large stock of potentially available nutrients.
February 2025
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83 Reads
The management strategy for the Antarctic krill (Euphausia superba) fishery is being revised. A key aim is to spatially and temporally allocate catches in a manner that minimizes impacts to both the krill stock and dependent predators. This process requires spatial information on the distribution and abundance of krill, yet gaps exist for an important fishing area surrounding the South Orkney Islands in the south Scotia Sea. To fill this need, we create a dynamic distribution model for krill in this region. We used data from a spatially and temporally consistent acoustic survey (2011–2020) and year‐specific environmental covariates within a two‐part hurdle model. The model successfully captured observed spatial and temporal patterns in krill density. The covariates found to be most important included distance from shelf break, distance from summer sea ice extent, and salinity. The northern and eastern shelf edges of the South Orkney Islands were areas of consistently high krill density and displayed strong spatial overlap between intense fishing activity and foraging chinstrap penguins. High mean krill density was also linked to oceanographic features located within the Weddell Sea. Our data suggest that years in which these features were closer to the South Orkney shelf were also years of positive Southern Annular Mode and higher observed krill densities. Our findings highlight existing fishery–predator–prey overlap in the region and support the hypothesis that Weddell Sea oceanography may play a role in transporting krill into this region. These results will feed into the next phase of krill fisheries management assessment.
January 2025
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30 Reads
Ocean eddies are mesoscale features that can extend > 100 km and maintain cohesiveness for months, impacting planktonic community structure and water column biogeochemical cycles. Standing stocks of protists in the water column and on sinking particles were investigated using microscopy, in situ imagery, and metabarcoding across an anticyclonic to cyclonic eddy dipole in the North Pacific Subtropical Gyre during July 2017. The water column was sampled from the surface to 500 m and particle interceptor traps were deployed at 150 m. Protistan assemblage composition varied substantially between sample type and analytical approach across the eddy dipole. Alveolates represented 63% of sequences from water samples. In contrast to water samples, rhizarian protists represented 79% of trap sequences obtained by metabarcoding of sediment trap material. Microscopy of trap material supported the important contribution of Rhizaria to sinking particles and revealed increased relative abundances of ciliates in the anticyclonic eddy and diatoms in the cyclonic eddy. In situ imagery confirmed the presence of relatively large Rhizaria that were not adequately assessed from water samples but contributed significantly to particle flux. Together, these data demonstrate differing perspectives of planktonic protistan community composition and contributions to sinking particles gained from the application of different sampling and analytic approaches. Our observations and analyses indicate a specific subset of the protistan community contributed disproportionately to organic matter downward export.
January 2025
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42 Reads
Seagrasses are considered foundation species in marine and estuarine ecosystems by contributing biomass, providing habitat, and damping waves and currents. Globally, seagrass health and primary productivity are threatened by factors that affect light availability, such as shading by algae and epiphytes, self‐shading, and increased water column turbidity. This study focuses on how plant motion and reconfiguration lead to shading of an individual plant by itself and its neighbors, and how wave conditions, plant material properties, and shoot density affect light availability along a seagrass blade. We use a simple ray‐optics shading model with the plant motion model of Zhu et al. (2020; Journal of Geophysical Research: Oceans 125:e2019JC015517) for a flexible blade under wavy flow to understand how phase‐resolved plant behavior affects light availability as a function of vertical location in the water column. Results show that that shading of a plant by its neighbors occurs more under wave crests and troughs, and that factors that increase blade tip excursion (large wave height or wave period, or high plant flexibility) reduce light exposure. We develop a simplified theory and parameterization for average light exposure as a function of flow and plant conditions (as captured by the Cauchy number, buoyancy parameter, and ratio of stem spacing to blade length). These results help delineate optimal conditions for maximizing light exposure to seagrass' photosynthetic tissue in restoration projects, and facilitate the inclusion of flow‐vegetation interactions in biological models of seagrass production.
January 2025
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76 Reads
Large‐scale anthropogenic river modifications have caused the loss of critical floodplain nursery habitats for riverine fish, leading to population declines. Restoration efforts have been implemented to recover these habitats, but with varying success. Understanding how larval and juvenile fish use habitats in dynamic river environments is essential for improving restoration strategies. We assessed ontogenetic shifts in habitat use by young‐of‐the‐year fishes in the lower Rhine, analyzing 2167 samples across 18 restored floodplains over three growing seasons (2018–2020). Five distinct nursery habitats were identified: (1) exposed, fast‐flowing habitats with coarse substrate; (2) turbid, nonflowing areas with high turbidity and chlorophyll; (3) shallow, vegetated habitats with macrophytes and shoreline vegetation; (4) deeper, sheltered habitats with structural complexity; and (5) shallow, slow‐flowing areas. Habitat use shifted significantly with ontogeny across species. Larvae generally preferred shallow habitats (< 50‐cm depth), either in slow‐flowing areas (e.g., asp, ide, monkey goby, nase, and whitefin gudgeon) or vegetated zones with macrophytes (e.g., bleak, bitterling, bream, round goby, and zander). Juveniles increasingly used deeper habitats (> 50‐cm depth), favoring fast‐flowing areas (e.g., asp, barbel, ide), or deeper, nonflowing habitats (e.g., bream, zander). Our findings thus highlight the critical importance of habitat heterogeneity and connectivity for riverine fish biodiversity. Restoration strategies should prioritize the creation of a mosaic of shallow, low‐velocity habitats for larvae, alongside deeper, fast‐flowing, or sheltered areas for juveniles. Additionally, the movement of rheophilic species from floodplain habitats to the main river channel emphasizes the need for maintaining continuous connectivity between floodplains and the river.
January 2025
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71 Reads
Submerged macrophytes are key components in many freshwater and marine ecosystems, contributing to ecosystem functions and services. In temperate shallow lakes, spring epiphyton shading can be decisive for submerged macrophyte development, potentially leading to macrophyte collapse and a shift to undesired, turbid conditions. Global change can alter epiphyton phenology; however, the consequences for submerged macrophytes and their stabilizing effects on clear‐water conditions remain to be elucidated. Based on field data, we propose a general epiphyton shading phenology for submerged macrophytes in temperate shallow lake ecosystems. We express the temporal dynamics of epiphyton shading in terms of onset and relative increase (slope) of epiphyton development as well as epiphyton grazing impacts (onset, duration) using a Boltzmann function. This function is added to the ecosystem model PCLake+ as a customizable, macrophyte‐specific shading factor. We then assess how changes in the epiphyton phenology and the presence of grazing on epiphyton affects submerged macrophyte biomass in a generic temperate shallow model lake under control and warm winter scenarios. The results from the model provide a proof‐of‐concept that epiphyton shading can provoke macrophyte loss and shifts between alternative equilibria. Threshold values for critical shifts depend on epiphyton shading phenology. Earlier onset and longer duration of grazing can maintain macrophytes in nutrient or climate conditions under which they would otherwise collapse. Our results show the pivotal importance of epiphyton phenology in determining lake ecosystem‐wide responses stressing the need for better incorporation of epiphyton into both models and monitoring.
January 2025
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17 Reads
Seawater hypoxia is increasing globally and can drive declines in organismal performance across a wide range of marine taxa. However, the effects of hypoxia on early life stages (e.g., larvae and juveniles) are largely unknown, and it is unclear how evolutionary and life histories may influence these outcomes. Here, we addressed this question by comparing hypoxia responses across early life stages of three cnidarian species representing a range of life histories: the reef‐building coral Galaxea fascicularis, a broadcast spawner with horizontal transmission of endosymbiotic algae (family Symbiodiniaceae); the reef‐building coral Porites astreoides, a brooder with vertical endosymbiont transmission; and the estuarine sea anemone Nematostella vectensis, a non‐symbiotic broadcast spawner. Transient exposure of larvae to hypoxia (dissolved oxygen < 2 mg L⁻¹ for 6 h) led to decreased larval swimming and growth for all three species, which resulted in impaired settlement for the corals. Coral‐specific responses also included larval swelling, depressed respiration rates, and decreases in symbiont densities and function. These results indicate both immediate and latent negative effects of hypoxia on cnidarian physiology and coral–algal mutualisms specifically. In addition, G. fascicularis and P. astreoides were sensitized to heat stress following hypoxia exposure, suggesting that the combinatorial nature of climate stressors will lead to declining performance for corals. However, sensitization to heat stress was not observed in N. vectensis exposed to hypoxia, suggesting that this species may be more resilient to combined stressors. Overall, these results emphasize the importance of reducing anthropogenic carbon emissions to limit further ocean deoxygenation and warming.
January 2025
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77 Reads
Understanding the response of microbial communities to different ecological regimes in eutrophic lakes and the underlying assembly mechanisms is of great significance for revealing the biodiversity maintenance mechanisms of lake ecosystems under alternative stable states. However, our current understanding of the response of sediment microbial communities under emergent macrophytes to regime shifts remains limited. Here, we demonstrated, for the first time, the asynchronous variations of littoral sediment bacterial and fungal communities, regarding the microbial diversities, assembly mechanisms, and inter‐kingdom interactions across three lake regional regimes: macrophyte‐dominated, transitional, and phytoplankton‐dominated. We found the alpha diversities of the bacterial and fungal communities showed opposite trends, as the transitional regime had the highest bacterial but lowest fungal diversities. Stochastic processes, dominated by dispersal limitation, determined fungal community assembly, whereas deterministic processes, especially variable selection, shaped the bacterial community. The highest number of species–environment interactions and proportion of intra‐kingdom interactions were observed in the co‐occurrence network of the transitional regime; however, this network had the lowest proportion of inter‐kingdom (bacteria–fungi) interactions among the three lake regional regimes. Furthermore, the macrophyte‐dominated regime was observed to have the most complex network structure and maintain the highest microbial community stability. The rhizosphere of Phragmites australis enhanced the inter‐kingdom interactions of bacterial and fungal communities. These findings provide a preliminary ecological perspective for understanding the hysteresis of regimes in response to environmental stress at the microbial community level and emphasize the importance of distinguishing ecologically distinct microbial taxa in future studies focused on alternative stable states.
January 2025
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30 Reads
Owing to the rapid progress of high‐throughput sequencing technologies, microbial assemblages have gained growing interest in environmental impact assessment. However, research on microbial community responses, particularly those of benthic biofilm, to browning (increased concentrations of dissolved organic carbon [DOC]), is scarce. We used data from 55 boreal streams to examine if biofilm bacterial communities exhibit changes in diversity and community composition along a gradient of browning (3.6–27 mg DOC L⁻¹). Species richness increased slightly with increasing DOC, whereas community composition changed markedly across the gradient, especially in the active community. Pseudomonadota and Bacteroidota were overall dominant bacterial phyla. In the active community, Bacteroidota became relatively less abundant and Pseudomonadota more abundant with increasing DOC. Nitrate‐N (NO3‐N) and DOC were the most important predictors of bacterial community turnover. The greatest change in community composition occurred between 75 and 100 μg NO3‐N L⁻¹. For DOC, the first change point was at the low‐end of the gradient, followed by a major change in strongly brownified waters (> 20 mg L⁻¹). Bacterial communities became phylogenetically more similar than expected by chance as DOC increased. Concordance between bacterial and benthic invertebrate communities was very high, indicating that browning exerts a strong control over both taxonomic groups. Our results suggest that microbial communities, particularly the active portion of the community, may provide a sensitive and reliable tool for stream bioassessment. We defined a threshold‐type response in bacterial assemblages to water browning but more research is needed on microbial responses to multiple simultaneous stressors related to global warming and land‐use intensification.
January 2025
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44 Reads
A highly resolved time series of dissolved major element (calcium, strontium, magnesium, and lithium) concentrations in the north Gulf of Aqaba, Red Sea, reveals variability in major cation concentrations beyond analytic uncertainties. This variability is composed of an interannual component that is most important for calcium, and a short‐term daily‐timescale component that is most important for lithium. As evident from covariation in calcium, potential alkalinity, and Sr/Ca, the calcium carbonate cycle of the Gulf of Aqaba is dominated by coral calcification, and there was an increase in calcification rates between 2017 and 2018. Variability in lithium concentrations, and larger changes in magnesium concentrations than expected from magnesium distribution coefficients in carbonate minerals, suggest an active cycle of aluminosilicate mineral dissolution, and precipitation of secondary silicate minerals.
January 2025
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54 Reads
Essential biomolecules, such as physiologically essential fatty acids, can critically influence consumers' performance and the ecosystem's functioning. Eicosapentaenoic (EPA; 20:5ω3) and docosahexaenoic (DHA; 22:6ω3) fatty acids are physiologically crucial for consumers, and they must be either obtained from the diet or bioconverted from precursors. We monitored the synthesis of EPA and DHA by primary producers in the largest man‐made ecosystem (Lake Kariba) and in situ fatty acid production, trophic transfer, and endogenous production of EPA and DHA in the tropical lake food web using ¹³C‐labeling, compound‐specific isotopes, and gene expression of fads2 and elovl5 genes in most abundant fish species. Seston pigment analysis and 23S rRNA sequencing revealed that cyanobacteria dominated primary producers throughout three seasons, and the biosynthesis rate of EPA and DHA was under the detection limit. Moreover, due to the low zooplankton densities and EPA and DHA content in zooplankton, the transfer of EPA and DHA from phytoplankton–zooplankton to upper trophic levels is low. The low production of EPA and DHA by primary producers is mitigated by bioconversion of α‐linolenic acid to EPA and DHA in two tilapia species, especially by Nile tilapia (Oreochromis niloticus) known to feed on cyanobacteria. Compound‐specific isotope analysis revealed that tigerfish (Hydrocynus vittatus), the main predatory fish on the lake, was more closely related to Nile tilapia than to lake planktivorous fish (Limnothrissa miodon). Therefore, trophic interaction between cyanobacteria and algivorous fish has replaced traditional phytoplankton and zooplankton trophic interaction in the synthesis and transfer of EPA and DHA to upper trophic levels.
January 2025
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110 Reads
Seagrasses are increasingly recognized for their ecosystem functions and services. However, both natural and anthropogenic stressors impact seagrass functional traits, for example by altering nutrient regimes. Here, we synthesize 27 yr of data from regional, long‐term seagrass and water quality monitoring programs of south Florida to investigate the impacts of relative nutrient availability on seagrass abundance (as expressed by percent cover) across an oligotrophic seascape. We employ linear mixed‐effect models and generalized additive models to show that seagrass abundance is driven by interannual variations in nutrient concentrations, which are ultimately controlled by climate oscillations (El Niño Southern Oscillation Atlantic Multidecadal Oscillation) via regional rainfall‐runoff relationships. Our study suggests that climate oscillations drive interannual variations in seagrass cover on a regional scale, with high‐rainfall years leading to increased nitrogen availability and higher seagrass abundance in typically nitrogen‐limited backreef meadows. Conversely, these periods are associated with reduced seagrass cover at the more P‐limited inshore sites and in Florida Bay, with yet unknown consequences for the provision of seagrass ecosystem services. We show that nutrient delivery from runoff can have diverging impacts on benthic communities, depending on spatial patterns of relative nutrient limitation, with some N‐limited seagrass meadows showing resilience to periodic nutrient enrichment.
January 2025
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56 Reads
Upwelling in the South Yellow Sea is a phenomenon that plays an important role in nutrient transport and biological productivity. Based on remote sensing data from 2000 to 2022 and in situ observations from 2012 to 2022, we investigated the interannual variability of cold‐water mass frontal upwelling and its contribution to the transport of nutrients in the South Yellow Sea. The results showed that the upwelling positions during summer were consistent with the fronts of the cold‐water masses. The influence of upwelling on nutrient distribution and transport varied interannually, and the El Niño‐Southern Oscillation during winter might influence the intensity of summer frontal upwelling by modulating summer winds. Nutrient fluxes via upwelling from 2012 to 2022 were estimated: 0.08 × 10⁸–25.9 × 10⁸ mol month⁻¹ of dissolved inorganic nitrogen, 0.003 × 10⁸–0.67 × 10⁸ mol month⁻¹ of dissolved inorganic phosphate, and 0.12 × 10⁸–40.8 × 10⁸ mol month⁻¹ of dissolved silicate. Nutrient fluxes during summer were comparable to the summer inputs from the Changjiang River. The dissolved inorganic nitrogen/dissolved inorganic phosphate ratio in frontal upwelling decreased from 38.6 in 2012 to 20.0 in 2022, and the dissolved silicate/dissolved inorganic nitrogen ratio increased from 0.93 in 2012 to 2.48 in 2022. Nutrient composition and fluxes carried by upwelling can alleviate the limitations of both phosphorus and silicon in the South Yellow Sea. Upwelling nutrients in the frontal zone of the Yellow Sea Cold Water Mass could promote local phytoplankton growth and contribute to the development of Ulva prolifera.
January 2025
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83 Reads
Iron (Fe) and phosphorus (P) availability constrain the growth and N2 fixation of diazotrophic cyanobacteria in the global ocean. However, how Fe and P limitation may modulate the effects of ocean acidification on the unicellular diazotrophic cyanobacterium Crocosphaera remains largely unknown. Here, we examined the physiological responses of Crocosphaera watsonii WH8501 to CO2 enrichment under both nutrient‐replete and steadily Fe‐ or P‐limited conditions. Increased CO2 (750 μatm vs. 400 μatm) reduced the growth and N2 fixation rates of Crocosphaera, with Fe limitation intensifying the negative effect, whereas CO2 enrichment had a minimal impact under P limitation. Mechanistically, the high CO2 treatment may have led to a reallocation of limited Fe to nitrogenase synthesis to compensate for the reduction in nitrogenase efficiency caused by low pH; consequently, other Fe‐requiring metabolic pathways, such as respiration and photosynthesis, were impaired, which in turn amplified the negative effects of acidification. Conversely, under P limitation, CO2 enrichment had little or no effect on cellular P allocation among major P‐containing molecules (polyphosphate, phospholipids, DNA, and RNA). Cell volumes were significantly reduced in P‐limited and high CO2 cultures, which increased the surface : volume ratio and could facilitate nutrient uptake, thereby alleviating some of the negative effect of acidification on N2 fixation. These findings highlight the distinct responses of Crocosphaera to high CO2 under different nutrient conditions, improving a predictive understanding of global N2 fixation in future acidified oceans.
January 2025
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102 Reads
We present a detailed observational study of the effects of the impulse wave caused by a snow‐avalanche on an alpine lake (Lake Peñalara, Sierra de Guadarrama, Spain). The avalanche broke the lake's ice cover (> 50 cm thick) and caused the lake to overflow. The impulse wave altered the lake water column stratification and physicochemical properties (dissolved oxygen, conductivity) in the short (hours) and mid‐term (days and weeks). It also caused the mobilization of hundreds of cubic meters of sediment, changing the lake morphometry. The sediment reconfiguration is likely the cause of the observed increased sedimentation rate and changes in the zooplankton density and composition in the following 4 yr after the avalanche, including the resurrection of a cladoceran species (Daphnia pulicaria) that had disappeared from the lake decades ago. Events such as the one we present can have significant paleolimnological implications: in this case, 75 cm of the sediment sequence were lost. Given these results, we propose that past avalanches could be the explanation to the almost complete removal of sediment from the deepest part of the lake around 260 yr cal BCE.
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The University of Oklahoma, United States