Limnology and Oceanography最新文献

The global proliferation of nonindigenous species remains a critical stressor driving both biodiversity loss and socioeconomic costs. These impacts frequently depend on environmental contexts, but few studies have investigated how seasonal variations coupled with climate changes, like warming, could modulate nonindigenous species ecological impacts. The Japanese brush-clawed shore crab Hemigrapsus takanoi is a successful nonindigenous species in northern European waters and is currently spreading in the Baltic Sea. In this study, we used generalized linear models and the comparative functional response approach to examine the predatory impact of H. takanoi toward blue mussels Mytilus sp. across four seasons under current and future temperature scenarios (i.e., ambient and + 6°C warming). We further integrated H. takanoi Q₁₀ values and field abundances across seasons to examine population-level feeding impacts toward blue mussels. The nonindigenous species exhibited a consistent type II functional response (i.e., inversely prey density-dependent response) across all seasons, temperatures and sexes, with males consistently consuming more mussels than females across all seasons. Warming generally decreased handling times and increased attack rates, but these effects varied by season and sex, with the most pronounced temperature responses observed in autumn and spring. Population-level impact calculations integrating field abundance data of H. takanoi indicated that under ambient conditions, feeding impacts toward blue mussels currently peak in the summer months, but as temperature increases, this feeding impact is anticipated to shift later in the year into autumn. These findings underline the critical need for multifaceted research approaches to better understand and predict the context-dependent ecological impacts of nonindigenous species, particularly in the face of ongoing climate change and shifting population characteristics.

Coccolithophores are pivotal players in ocean biogeochemistry, yet the impact of changing pH on the physiology of different species remains unclear as there has been a dominant focus on Gephyrocapsa huxleyi. Meta-analyses of existing experimental data are challenging due to the differences in multidimensional culture conditions. This study investigated the response of three species—Gephyrocapsa huxleyi, Coccolithus braarudii, and Chrysotila carterae—under varying CO₂ conditions (via pH). The sensitivity to pH differed between species, but all species showed reduced growth rates under the highest CO₂ (lowest pH) treatment possibly due to high [H⁺]-related inhibition. Low pH impacted cellular physiology and elemental stoichiometry, while the impact of high pH was less adverse. The changes in elemental production induced by low pH could exert a negative influence on the contribution of coccolithophores to nutrient and carbon export, especially for biogeochemically relevant open-ocean species. pH also affected coccolith formation, especially in C. braarudii, through CO₂ limitation at high pH and low calcite saturation state at low pH. Contrasting species-specific pH sensitivities highlighted the potential for species like G. huxleyi to further outperform others like C. braarudii in an acidic ocean. Literature synthesis showed that coccolithophores show a broad CO₂ optimum, although growth rates and particulate inorganic carbon to particulate organic carbon ratios consistently declined with increasing CO₂. Strain-specific CO₂ optima partly contributed to the variability within responses of individual species, giving the misleading perception of a broad species-level CO₂ optimum. Strain-specific optima exist possibly due to their adaptation to carbonate chemistry conditions at the place of origin.

The North Pacific subtropical gyre is a globally important contributor to carbon uptake despite being a persistently oligotrophic ecosystem. Supply of the micronutrient iron to the upper ocean varies seasonally to episodically, and when coupled with rapid biological consumption, results in low iron concentrations. In this study, we examined changes in iron uptake rates, along with siderophore concentrations and biosynthesis potential at Station ALOHA across time (2013–2016) and depth (surface to 500 m) to observe changes in iron acquisition and internal cycling by the microbial community. The genetic potential for siderophore biosynthesis was widespread throughout the upper water column, and biosynthetic gene clusters peaked in spring and summer along with siderophore concentrations, suggesting changes in nutrient delivery, primary production, and carbon export seasonally impact iron acquisition. Dissolved iron turnover times, calculated from iron-amended experiments in surface (15 m) and mesopelagic (300 m) waters, ranged from 9 to 252 d. The shortest average turnover times at both depths were associated with inorganic iron additions (14 $��\pm �$ 9 d) and the longest with iron bound to strong siderophores (148 $��\pm �$ 225 d). Uptake rates of siderophore-bound iron were faster in mesopelagic waters than in the surface, leading to high Fe : C uptake ratios of heterotrophic bacteria in the upper mesopelagic. The rapid cycling and high demand for iron at 300 m suggest differences in microbial metabolism and iron acquisition in the mesopelagic compared to surface waters. Together, changes in siderophore production and consumption over the seasonal cycle suggest organic carbon availability impacts iron cycling at Station ALOHA.

Strains from the picocyanobacteria genus Synechococcus are currently found across a wide range of photoperiods and photosynthetically active radiation. Future scenarios now forecast range expansions of marine Synechococcus into new photic regimes. We found that strains of temperate, coastal phycocyanin-rich and phycoerythrin-rich Synechococcus grew fastest under moderate photosynthetically active radiation, and a 24-h photoperiod, despite a cumulative diel photon dose equivalent to conditions where growth was slower, under higher light and shorter photoperiods. Under optimal conditions, a phycoerythrin-rich Synechococcus strain achieved a highest recorded cyanobacterial chlorophyll-specific exponential growth rate (μ) of 4.5 d⁻¹. Two phycoerythrin-rich strains demonstrated wider ability to modulate light capture capacity, whereas two phycocyanin-rich strains showed less change in light capture across increasing cumulative diel photon dose. All four coastal strains showed a decrease of effective absorption cross-section for photosystem II photochemistry, vs. increasing cumulative diel photosynthetically active radiation doses. Within each strain, μ showed consistent, saturating responses to increasing cumulative diel photosystem II electron flux, with more variations in responses of μ to cumulative photosynthetically usable radiation. As photoperiod opportunists, coastal picocyanobacteria show potential to expand into longer photic regimes as higher latitudes warm.

Small phytoplankton, consisting of pico and nano size fractions, are diverse in size and taxonomy. Yet, the differences in their productivity and taxonomic diversity are poorly described. Here, we measured the cell-specific carbon fixation rates of picocyanobacteria Synechococcus, picoeukaryote, and nanoeukaryote populations, while unveiling their taxonomic composition in oligotrophic subtropical and high-nutrient low-chlorophyll subantarctic waters. We coupled 24 h in situ radiolabeled ¹⁴C incubations to flow cytometry sorting and DNA metabarcoding from the same incubated samples, offering a direct account of the community associated with the carbon fixation rates measured. In both water masses, nanoeukaryotes had the highest cell-specific carbon fixation rate, followed by picoeukaryotes and Synechococcus (2.24 ± 29.99, 2.18 ± 2.08, and 0.78 ± 0.55 fgC cell⁻¹ h⁻¹, respectively). The cell-specific carbon fixation rates and growth rates of Synechococcus were threefold higher in subtropical compared to subantarctic waters, while the rates of picoeukaryotes and nanoeukaryotes had no significant difference between the biogeochemically-contrasting water masses. Sorted picoeukaryote populations were dominated by Mamiellophyceae, Pelagophyceae, Prymnesiophyceae, and Chrysophyceae, while nanoeukaryote populations were dominated by Dinophyceae and Prymnesiophyceae. Despite significant differences in their taxonomic composition, the sorted picoeukaryote populations in subantarctic waters and nanoeukaryote populations in subtropical and subantarctic waters were dominated by taxa reported in the literature as able to engage in phago-mixotrophic strategies (Prymnesiophyceae, Chrysophyceae, and Dinophyceae), suggesting that such trophic strategy might be applied by discrete small photosynthetic eukaryote populations to alleviate macronutrient and iron stress.

Anthropogenic stressors are omnipresent in marine environments and interfere with organisms of all sizes, from large whales to small organisms. We investigated potential interactive multistressor effects of increased temperature with chronic low-frequency sound on the development and movement patterns of the calanoid copepod Acartia tonsa, a model species for small marine zooplankton. Copepods were reared while exposed to chronic low-frequency sound around 15 and 22 dB re 1 μPa² Hz⁻¹ above control sound pressure levels at frequencies between 110 and 120 Hz, at 21°C (increased temperature) and 18°C (control temperature). For each sound and temperature scenario, we assessed after-incubation development rate, stage distribution, and movement patterns. We found that fewer copepods reached the developmental stages copepodites IV to VI in low-frequency sound conditions, even though warmer conditions increased developmental rate. By using high-speed videography in both control and low-frequency sound conditions, we observed that copepods showed more escape behaviors (drops) and fewer feeding-associated behaviors (helical swimming) when exposed to low-frequency sound (~ 42 dB higher than normal at 142 Hz). Copepods reared with added low-frequency sound showed fewer feeding-associated behaviors and did not reverse these trends despite the absence of added sound in their feeding environment. These significant behavioral changes suggest detrimental negative, life-long, consequences for copepods exposed to low-frequency sound.

Ecological community structure, which has traditionally been described in terms of taxonomic units, is driven by dispersal and environmental filters. Traits have recently been recognized as alternative units for quantifying community parameters, but they may have important differences with taxonomic units. For example, as taxon-based community structure is determined by the local species pool, it may be more dispersal-limited, whereas trait-based community structure may be more regulated by environmental conditions because traits are less tied to specific habitat locations. This implies that the relative importance of these two filters may vary depending on the units describing community structure, but no study has yet quantified how the contributions of these filters can differ. In this study, we examined zooplankton assemblages in 87 artificial reservoirs throughout the Japanese archipelago to quantify the relative importance of two filters by examining the effects of spatial configuration (reflecting dispersal filters) and biotic and abiotic variables (reflecting environmental filters) for taxon- and trait-based community structure. Variation in the taxon-based community structure was explained equally well by the spatial and the environmental variables, while variation in the trait-based community structure was explained more by environmental variables. These results support the idea that environmental filters play a more central role in determining trait-based community structures, and show that the relative importance of spatial and environmental filters changes with the way we define community structure.

Salt marshes are important carbon sinks; however, identification of the drivers of carbon burial rates is challenging because estuaries sit at terrestrial and marine interfaces. Here, we address the questions: what are the sources of organic matter sequestered in minerogenic salt marshes, and how do sources change through time? We characterized down-core sediment biogeochemistry (C : N, δ¹³C, δ¹⁵N) for the last century in seven Oregon USA high marshes and used a mixing model to elucidate differences in organic matter sources across estuaries and through time. Autochthonous biomass production consistently accounted for only half of overall organic matter accumulation, and the remainder was allochthonous, originating from a combination of estuarine and terrestrial sources. Salt marshes with high sediment loads buried more terrestrial organic matter, whereas those with low loads and substantial subtidal habitat buried more estuarine-derived organic matter. When assessed through depth/time, stable isotope trends indicated that decomposition is not the primary control. Instead, organic matter became increasingly more terrestrial in recent decades, especially in salt marshes with low fluvial loads. We hypothesize that salt marshes with lower loads took longer to regain lost elevation following coseismic subsidence of the 1700 ce Cascadia earthquake. This result magnifies the role of river floods in sediment and carbon accumulation on the marsh surface. Ultimately, the highest carbon burial rates coincided with highest fractions of terrestrially sourced organic matter, though spatiotemporal complexities obscured any potentially significant trends. While the term “blue” typically excludes terrestrial carbon, minerogenic salt marshes still perform the important ecosystem function of burying organic matter.

Coastal wetlands are important for their ability to regulate global climate through the sequestration and long-term storage of carbon. Accurate quantification of ecosystem-specific carbon dynamics (including sequestration, storage, and fluxes) is needed to develop accurate carbon budgets that inform climate change mitigation. Most work to quantify carbon dynamics either use subsampling in core habitats or benefit transfers to upscale values. While these approaches are valuable, our understanding of carbon dynamics across ecosystem transitions and overall heterogeneity remains a critical gap in coastal ecosystems as boundaries are not always clear. In this study, we established transects across both mangrove and seagrass ecotones into adjacent tidal flats in Singapore to quantifying vegetation cover, soil carbon storage, and CO₂ fluxes. Vegetation cover in all transitions and soil carbon storage in most transitions followed a decreasing sigmoidal pattern from vegetated to unvegetated portions, but differed in rate and width. CO₂ fluxes followed a peak distribution in mangrove–tidal flat transitions with maximum values occurring within the mangroves and were correlated with pneumatophore density, while seagrasses saw a linear increase in CO₂ fluxes from the seagrass to tidal flat. Seascape analysis of soil carbon showed site-specific impacts that resulted in differences in carbon stocks (0%–8%) as well as the width of these transitions. This study highlights the importance of understanding ecotones to better account for edge effects, which can lead to the over or under estimation of carbon, and provides a needed step in increasing the accuracy of blue carbon assessments in these critical ecosystems.

The timing of biological events, known as phenology, plays a key role in shaping ecosystem dynamics, and climate change can significantly alter these timings. The Gulf of Maine on the Northeast U.S. Shelf is vulnerable to warming temperatures and other climate impacts, which could affect the distribution and production of plankton species sensitive to phenological shifts. In this study, we apply a novel data-driven modeling approach to long-term datasets to understand the population variability of Calanus finmarchicus, a lipid-rich copepod that is fundamental to the Gulf of Maine food web. Our results reveal how phenology impacts the complex intermingling of top-down and bottom-up controls. We find that early initiation of the annual phytoplankton bloom prompts an early start to the reproductive season for populations of C. finmarchicus in the inner Gulf of Maine, resulting in high spring abundance. This spring condition appears to be conducive to enhanced predation pressure later in the season, consequently resulting in overall low C. finmarchicus abundance in the fall. These biologically controlled dynamics are less pronounced in the outer Gulf of Maine, where water exchanges near the boundary have a greater influence. Our analysis augments existing hypotheses in fisheries oceanography and classical ecological theory by considering unique plankton life-history characteristics and shelf sea dynamics, offering new insights into the biological factors driving C. finmarchicus variability.