Limnology and Oceanography最新文献

Consumer-mediated nutrient dynamics (CND), through which animals' metabolic waste products fertilize primary producers, drive variability in nutrient availability in tropical waters. This variability influences primary productivity and community functioning. Yet, examinations of CND as a driver of nutrient variability in temperate marine ecosystems are limited. Therefore, we assessed the existence and drivers of variation in CND in temperate waters at meso, small, and fine spatial scales. We quantified the occurrence of 48 fish and 92 macroinvertebrate taxa and measured in situ ammonium at 27 northeast Pacific rocky reefs for 3 yr and 16 kelp forests of varying density for 1 yr. Ammonium concentrations ranged from 0.01 to 2.5 μM across rocky reefs separated by tens of kilometers. The relationship between animal abundance and ammonium among sites was mediated by water flow, where flood tides seemed to “wash away” the effect of nutrient regeneration by animals, although enrichment was possible on ebb tides. Ammonium concentration was significantly greater within than outside of kelp forests, a difference that increased with kelp biomass, tidal exchange, and, to a lesser degree, animal biomass. Caging experiments revealed that fine-scale (~ 2 m) ammonium variability and nutrient enrichment were only possible under low-flow conditions. Our results suggest that CND drives nutrient variability at scales ranging from two meters to over 20 km, acting on a finer scale than allochthonous nitrogen sources such as upwelling. Therefore, CND are implicated as a previously overlooked driver of spatial variation in primary productivity in temperate marine systems.

Trace elements are essential micronutrients for primary producers in the ocean, supporting vital metabolic functions. However, their behavior in the northwestern Pacific remains unknown. This study investigated the behavior and benthic fluxes of Mn, Fe, Co, Ni, Cu, Zn, and Cd in the East/Japan Sea and the Yellow Sea. Rare earth element fractionations ([Nd/Er]_PAAS and Ce/Ce* ratios) were used to trace scavenging and water mass inputs. In the East/Japan Sea, trace element distributions were categorized into three categories. Mn, Fe, and Co were influenced by atmospheric deposition in surface waters and benthic input, with fluxes of 742, 96, and 0.8 μmol m⁻² yr⁻¹, respectively. Ni and Cu were depleted from surface waters and had a limited influence from benthic inputs. Zn and Cd were regulated by biological activity. Zn concentrations ranged from 0.6 to 1.5 nmol kg⁻¹ at the surface, peaked at 6.8–11.8 nmol kg⁻¹ at a depth of 500 m, and decreased to 3.5–7.9 nmol kg⁻¹ at the bottom. Zn correlated positively with $��{\mathrm{SiO}}_4^{�4�-�}�$ in the upper 500 m but negatively at greater depths, likely owing to shelf inputs. In the Yellow Sea, all trace elements exhibited a vertically conserved distribution owing to rapid water mixing. These results contribute to the current biogeochemical understanding of the region by providing higher-resolution cross-transect investigations and report the decoupling of Zn–$��{\mathrm{SiO}}_4^{�4�-�}�$ in the East/Japan Sea for the first time.

Carbonate coral sands are an integral part of the carbon and nutrient cycles in subtropical and tropical coastal environments. Recent studies indicate that nearshore carbonate sands may be hotspots for organic matter production and respiration, but the processes and their controls are poorly understood due to a lack of noninvasive in situ measurements. We deployed a new triple-sensor aquatic eddy covariance instrument to quantify seasonal O₂-fluxes over a coral sand platform at ~ 10 m water depth in the Florida Keys. The noninvasive measurements revealed the strong influences of light and bottom currents on magnitude and dynamics of the benthic metabolism. Light penetration through the clear water column facilitated substantial microphytobenthos production, making the seafloor a source of oxygen during daylight hours. Daytime benthic O₂ release to the water column ranged between 0.6 mmol O₂ m⁻² h⁻¹ (winter) and 4.8 mmol O₂ m⁻² h⁻¹ (summer), while nighttime sediment O₂ respiration varied between −1.2 mmol O₂ m⁻² h⁻¹ (winter) and −3.3 mmol O₂ m⁻² h⁻¹ (summer). Bottom currents modulated the fluxes, emphasizing the role of advective pore water exchange for biogeochemical reactions in the highly permeable sediment. Similar magnitudes and dynamics of daytime sediment O₂ release and nighttime O₂ uptake revealed a tight coupling between production and degradation of highly labile photosynthetic products. We use the results to explain why O₂ respiration rates in permeable carbonate sands of oligotrophic subtropical/tropical environments can reach similar magnitudes as those reported from permeable silicate sand beds of nutrient-rich temperate inner shelves.

Although gelatinous zooplankton are key members of marine ecosystems and food webs, their trophic ecology is poorly described across the deep pelagic. We used stable carbon (bulk tissue) and nitrogen (bulk tissue and amino acid) isotope analysis to estimate the trophic positions (TPs) of abundant gelatinous zooplankton (chaetognaths, cnidarians, ctenophores, mollusks, pelagic tunicates) across depth habitats. We collected gelatinous zooplankton from a range of feeding guilds, sampling animals from 0 to 3000 m on four cruises across the years 2020 to 2023 within the southern California Current Ecosystem. Within taxonomic groups, bulk carbon (δ¹³C) and nitrogen isotope (δ¹⁵N) values were similar, regardless of animal size. Gelatinous zooplankton spanned 2.4 trophic levels. Trophic positions were highest for animals that consume other gelatinous zooplankton (e.g., Aegina spp., TP = 3.8) and lowest for grazers (e.g., Pyrosoma atlanticum, TP = 1.9). Trophic positions based on δ¹⁵N values of amino acids often agreed with diets reported from the literature, where available, while TPs calculated using bulk tissue δ¹⁵N values were often lower. Animal δ¹⁵N (bulk and source amino acid) values increased with increasing depth, suggesting that shallow and deep-pelagic taxa rely on distinct basal food resources. Medusae residing from 600 to 1000 m had less variable bulk tissue δ¹³C and δ¹⁵N values across locations and seasons than ctenophores, medusae, and pelagic tunicates collected from 0 to 600 m, suggesting that deep-pelagic taxa rely on stable food resources at depth. Animal δ¹⁵N and δ¹³C values were relatively consistent between seasons, potentially suggesting stability in the trophic structure of the jelly web.

Salinity is a well-known environmental factor that profoundly influences vegetation growth and ecological functions of coastal salt marshes. This study conducted an in-situ control experiment to assess the effects of salinity on the morphological and physiological traits of coastal Phragmites australis, as well as its carbon sequestration capacity (including CO₂ uptake, CH₄ emissions, and vegetation and soil organic carbon densities). Field investigations and microbial abundance analyses were integrated to provide a comprehensive assessment. The results showed that the growth characteristics and photosynthetic activity of P. australis increased initially but declined as salinity rose, peaking at a moderate level (5‰). Despite concurrent peaks in CO₂ uptake and CH₄ emissions at 5‰ salinity, the net negative daytime CO₂-eq flux indicated that this salinity level provided the strongest net cooling effect, driven by stronger CO₂ uptake relative to CH₄-induced warming. Under higher salinity levels (> 10‰), P. australis exhibited an adaptive strategy of reduced carbon allocation to roots, leading to a significant decrease in soil organic carbon density. Through the identification of salinity thresholds that optimize growth and carbon sequestration of P. australis, this study delivers a mechanistic understanding for advancing adaptive management and restoration efforts of coastal salt marsh ecosystems to enhance their blue carbon sequestration, particularly in the context of sea-level rise.

Yang, G., A. Atkinson, E. A. Pakhomov, S. L. Hill, and M. F. Racault. 2022. “Massive Circumpolar Biomass of Southern Ocean Zooplankton: Implications for Food Web Structure, Carbon Export, and Marine Spatial Planning.” Limnology and Oceanography 67: 2516–2530. https://doi.org/10.1002/lno.12219.

In-text citations of “Johnson et al. 2022” should have been stated as “Johnston et al. 2022.”

In the reference list, the entry “Johnson, N. M., and others. 2022” should have been stated as “Johnston, N. M., and others. 2022.”

The authors apologize for this error.

Particles are a key component of aquatic light climate due to their attenuation of light. Near the water surface, waves and sheared currents can induce a preferential orientation of nonspherical particles that alters their inherent optical properties and the associated light attenuation. This modeling study focuses on how particle shape, and the corresponding preferential orientation, impacts the light climate in an aquatic environment. We assume aquatic particles, such as bacteria, algae, and microplastic pollutants, are optically homogeneous spheroids that move with the flow. The model computes their preferential orientations within the upper water column in flow driven by linear water waves and sheared currents. This is combined with the anomalous diffraction optical approximation to examine the effect of particle orientation on the beam attenuation coefficient. We find that the preferential orientation by waves and shear tends to increase the projected area of the spheroid compared to random (isotropic) orientation. This has particle size-dependent effects on light attenuation: for particles comparable in size and shape to algae or microplastics, the preferential orientation corresponds to an increase of 10–25% in the beam attenuation coefficient, whereas there is a decrease of 10–20% in the beam attenuation coefficient for smaller particles comparable in size to bacteria. Overall, our results reveal how preferential orientation of nonspherical particles by waves and currents can impact light climate in the upper water column.

The diazotrophic cyanobacterium Trichodesmium is sensitive to ultraviolet (UV) radiation under phosphate (P)-replete conditions, but little is known about UV impacts on its physiology under P-limitation. Here we show that periodic exposures to low or moderate levels of UV (4–12 W m⁻² UVA, 0.5–1 W m⁻² UVB) under P-limited (0.5 μM) conditions enhanced its growth by approximately 31% and increased its N₂-fixation rates by 75–175%. N₂-fixation efficiency (N₂ fixed per O₂ evolved) increased by 41–245% at low and moderate levels of solar radiation with UV compared to under low photosynthetically active radiation (PAR) alone (150 μmol photons m⁻² s⁻¹). Particulate organic N-normalized N₂-fixation rates were enhanced up to 173%, with increasing inhibition of photosynthetic O₂ evolution and quantum yield in P-limited cells. Exposure to high solar radiation levels with UV (1500 μmol photons m⁻² s⁻¹ PAR, 32 W m⁻² UVA, 2 W m⁻² UVB) decreased N₂-fixation rates of P-replete (5 μM) cells by up to 88% and harmed Trichodesmium in P-limited cultures, leading to rapid death within 2 weeks. Our results imply that UV irradiances during most sunlit periods other than noon are beneficial to Trichodesmium, especially under P-limited conditions, offering an underlying mechanism for the common observation of surface Trichodesmium blooms in tropical oceans.

Exploring the response of phytoplankton composition and diversity to water travel time (WTT) in rivers is crucial for understanding the biogeographic patterns of these organisms and for protecting watershed ecosystems. This study investigated the effects of WTT on phytoplankton biomass, community composition, and diversity by analyzing 182 samples collected over two seasons from the mainstems and tributaries of the Hanjiang and Danjiang River basins, China. Our study found that, in free-flowing river reaches, phytoplankton biomass fluctuated and increased progressively from the headwaters to downstream areas along the river flow. Water travel time was the key factor driving phytoplankton biomass and diversity rather than water quality. As WTT increased, phytoplankton biomass, the proportion of Cyanophyta, and the theoretical maximum number of genera (N) increased, while the critical percentage of taxon extinction (a) and the evenness of the taxon distribution (k) decreased. In comparison, the Shannon index showed no distinct pattern of changes. In cascade dam-controlled river reaches, dams and tributaries disrupted the longitudinal continuity of rivers. Both dam barriers and tributary inflow reduced the contribution rate of upstream phytoplankton communities to downstream reaches. Additionally, dams reduced downstream phytoplankton biomass by altering flow conditions, shifting the dominant control to water quality for phytoplankton community composition and diversity indices. In autumn, increased tributary flow into the mainstem reduced the contribution of upstream phytoplankton communities to downstream areas through a dilution effect. Overall, WTT plays a pivotal role in shaping the biogeography of phytoplankton, while cascade dams and tributaries disrupt the natural riverine longitudinal patterns.

Cyanobacteria blooms are a leading threat to water quality globally. Despite this, the timing and frequency of toxin production associated with harmful blooms are not well understood. Here we explore cyanobacteria bloom dynamics and cyanotoxin production in two heavily instrumented shallow, eutrophic bays of Lake Champlain through the lens of ecological stoichiometry. We use nutrient resource supply ratios (DIN : TP), seston nutrient ratios (C : N : P), and high-frequency buoy data to explore which nutrients limit cyanobacteria growth across the bloom season, how seston nutrient ratios relate to cyanotoxin production, and which environmental conditions trigger bloom development. We identified differences in limiting nutrients across the season, where Missisquoi Bay was mainly phosphorus limited, and St. Albans Bay was nitrogen limited. Despite differences in biomass and severity of the cyanobacteria blooms, microcystin and anatoxin concentrations did not differ between each bay. Additionally, microcystin production only occurred when seston C : N ratios indicated low to moderate nitrogen limitation (C : N < 14.6), supporting experimental findings that toxin synthesis may be tightly coupled with seston C : N : P elemental ratios. Taken together, these results highlight the complex interplay between nutrient cycling and environmental conditions in selecting functional traits of cyanobacteria that determine cyanobacteria bloom evolution and cyanotoxin production. Our study provides a comprehensive exploration of cyanobacteria blooms through the lens of ecological stoichiometry coupled with high-frequency monitoring that explains the divergence in bloom severity between two shallow, eutrophic bays of Lake Champlain.