Limnology and Oceanography最新文献

CO₂-induced seawater acidification has been shown to modify predator–prey interactions in many marine taxa. Scyphozoans play an important role in the trophic dynamics of marine ecosystems during their blooms in coastal waters; however, the impacts of seawater acidification on the predation behavior of these animals are poorly understood. Here, we aimed to examine the impact of a decrease in seawater pH on the feeding behavior and growth of ephyrae (juvenile medusae) of the scyphozoan Aurelia coerulea. Combining bulk and single-cell RNA sequencing approaches, we assessed transcriptomic changes of ephyrae under a laboratory-based pH 7.6 condition. We found that the feeding rates and growth of ephyrae were significantly inhibited by a decrease in seawater pH. Furthermore, transcriptome analysis showed that a decline in pH significantly reduced the expression of genes related to toxins and nematocyst structure in ephyrae. These findings were further confirmed by single-cell transcriptomic analyses and revealed that low pH impaired the toxin activity and energy metabolism of stinging cells. The pH recovery experiment indicated that moving ephyrae from seawater with pH 7.6 into seawater with pH 8.1 greatly restored their feeding, growth, and toxin-related and nematocyst structure–related gene expression. However, exposure to pH 7.6 for 23 d could not recover the decrease in the feeding and growth of ephyrae. Together, these findings indicate that CO₂-induced acidification compromised the stinging cells of A. coerulea ephyrae, with concomitant negative consequences on predation and growth that are likely to alter predator–prey interactions, with consequent effects on community structure and ecosystem.

There is growing evidence that the composition of river microbial communities gradually transitions from terrestrial taxa in headwaters to unique planktonic and biofilm taxa downstream. Yet, little is known about fundamental controls on this community transition across scales in river networks. We hypothesized that community composition is controlled by flow-weighted travel time of water, in combination with temperature and dissolved organic matter (DOM), via similar mechanisms postulated in the Pulse-Shunt Concept for DOM. Bacterioplankton and biofilm samples were collected at least quarterly for 2 yr at 30 sites throughout the Connecticut River watershed. Among hydrologic variables, travel time was a better predictor of both bacterioplankton and biofilm community structure than watershed area, dendritic distance, or discharge. Among all variables, both bacterioplankton and biofilm composition correlated with travel time, temperature, and DOM composition. Bacterioplankton beta-diversity was highest at shorter travel times (< 1 d) and decreased with increasing travel time, showing progressive homogenization as water flows downstream. Bacterioplankton and biofilm communities were similar at short travel times, but diverged as travel time increased. Bacterioplankton composition at downstream sites more closely resembled headwater communities when temperatures were cooler and travel times shorter. These findings suggest that the pace and trajectory of riverine bacterioplankton community succession may be controlled by temperature-regulated growth rate and time for communities to grow and change. Moreover, bacterioplankton, and to a lesser extent biofilm, may experience the same hydrologic forcing hypothesized in the Pulse-Shunt Concept for DOM, suggesting that hydrology controls the dispersal of microbial communities in river networks.

Net global losses of seagrasses have accelerated efforts to understand recovery from disturbances. Stressors causing disturbances (e.g., storms, heatwaves, boating) vary temporally and spatially within meadows potentially affecting recovery. To test differential recovery, we conducted a removal experiment at sites that differed in thermal stress for a temperate seagrass (Zostera marina). We also synthesized prior studies of seagrass recovery to assess general patterns. Seagrass shoots were removed from 28.3 m² plots at edge and central sites of a meadow in South Bay, Virginia, USA. We hypothesized faster recovery for edge plots where greater oceanic exchange reduces thermal stress. Contrary to our hypothesis recovery was most rapid in the central meadow matching control site shoot density in 24 months. Recovery was incomplete at the meadow edge and estimated to require 158 months. Differences in recovery were likely due to storm-driven sediment erosion at the edge sites. Based on data from prior recovery studies, which were primarily on monospecific meadows of Zostera, seagrasses recover across a broad range of conditions with a positive, nonlinear relationship between disturbance area and recovery time. Our experiment indicates position within a seagrass meadow affects disturbance susceptibility and length of recovery. Linking this finding to our literature synthesis suggests increased attention to spatial context will contribute to better understanding variation in recovery rates.

Broadly distributed species need to perform well in a range of environmental conditions, but knowledge of how wide-ranging marine larvae perform along latitudinal gradients remains limited. The fatty acid composition of larvae is important for their physiological responses to changing conditions. Here, we investigated the fatty acid composition of the last, non-feeding stage of barnacle larvae (cyprids) using an integrative (larvae–environment) and comparative (latitudinal) approach. We measured fatty acids in the pelagic particulate matter and cyprids from Chthamalus bisinuatus, Chthamalus proteus, and Semibalanus balanoides from tropical to polar (Arctic) latitudes to identify potential food sources during the feeding larval stages (nauplius) that precede the cyprids and to ascertain larval capacity to integrate neutral (energetic) and polar (structural) fatty acids. We demonstrate that particulate matter in tropical waters mainly consisted of low-quality saturated fatty acids derived from detrital pathways, while particulate matter from polar waters was rich in polyunsaturated fatty acids originating from living microalgae. Across the studied regions, neutral fatty acids were assimilated from various food sources including diatoms, dinoflagellates, detritus, and microeukaryotes. Cyprids consistently retained higher essential fatty acid levels than the relative share in the particulate matter. Particularly, the essential docosahexaenoic acid (22:6ω3), which was scarce in the particulate matter, was highly retained across all species but highest for the tropical cyprids. We argue that this latitudinal pattern in fatty acid retention is related to periods of reduced nutrient intake, increased energetic and/or synthetic requirements, and responses to physical large-scale differences in environmental conditions.

Blooms of the coccolithophore Gephyrocapsa huxleyi (formerly Emiliania huxleyi) are routinely infected by a specific lytic virus (EhV) that kills host cells and drives bloom termination. However, the impact of EhV on nutrient retention and stoichiometric ratios of particulate organic matter remains unknown, limiting our current understanding of the biogeochemical significance of the G. huxleyi–EhV interaction. To tackle this knowledge gap, we surveyed both nitrate, phosphate, and alkalinity consumption by the cells, as well as the elemental composition (C : N : P) of particulate organic matter during infections in culture. We found that within 24 h of infection, alkalinity concentration in the solution stabilized, and nutrient uptake declined to low levels. In parallel, the molar ratio of carbon to nitrogen in particulate organic matter increased by 10–17% and the nitrogen to phosphorus ratio declined by 5–12% relative to the noninfected algal cultures. These variations likely resulted from intracellular lipid accumulation as part of viral infection as well as the differential retention of phosphorus-rich macromolecular pools in decaying cells, respectively. After infection, as most host cells lysed, we detected a progressive enrichment in phosphorus and nitrogen relative to carbon in the remaining particulate organic matter, which could be attributed to the accumulation of colonizing heterotrophic bacteria with a distinct elemental composition. This study indicate that marine viruses influence the elemental stoichiometry and fate of phytoplankton-born organic materials in the oceans.

Akimova, A., M. A. Peck, G. Börner, C. Damme, and M. Moyano. 2023. Combining modeling with novel field observations yields new insights into wintertime food limitation of larval fish. Limnol. Oceanogr. 68: 1865–1879. doi: 10.1002/lno.12391.

The authors apologize for those errors and ensure the readership that all calculations were performed with the correct equation shown above. Therefore, these corrections have no consequences for any of the figures, results, discussions, or conclusions of the article.

High-latitude oceans experience strong seasonality where low light limits photosynthetic activity most of the year. This limitation is pronounced for algae within and underlying sea ice, and these algae are uniquely acclimated to low light levels. During spring melt, however, light intensity and daylength increase drastically, triggering blooms of ice algae that play important roles in carbon cycling and ecosystem productivity. How the algae acclimate to this dynamic and heterogeneous environment is poorly understood. Here, we measured ¹⁴C-carbon fixation rates, photophysiology, and ribulose 1,5-bisphosphate carboxylase oxygenase (Rubisco) content of sea-ice algae in coastal waters near the western Antarctic Peninsula during spring, ranging from a low-light-acclimated, bottom community to a light-saturated bloom. Carbon fixation rates by sea-ice algae were similar to other Antarctic sea-ice measurements (2–49 mg C m⁻² d⁻¹), and there was little phytoplankton biomass in the underlying water at the time of sampling. Net-to-gross ratios of carbon fixation were generally high and showed no relationship with ice type. We found algal photophysiology and Rubisco concentrations varied in relation to the different types of ice, altering the balance between the photochemical and biochemical processes that constrain carbon fixation rates. For algae inhabiting the bottom layers of sea ice, rates of carbon fixation were largely constrained by light availability whereas in surface seawater, interior and rotten/brash ice, carbon fixation rates could be calculated with reasonable accuracy from measurements of Rubisco concentrations. This work provides additional insight and means to evaluate carbon fixation rates as sea ice continues to change in future.

Recent research highlighted significant marine biological activity during the Arctic winter, with poorly known implications for the biological carbon pump. We used moored instruments to (1) track the development of the pelagic food web of a high-Arctic marine ecosystem from winter to spring, and (2) assess the role of zooplankton-mediated processes in the sinking export of particulate organic carbon (POC). Zooplankton collected by a sediment trap at 40 m depth in Kongsfjorden showed a shift in species composition in February coinciding with an inflow of Atlantic water and the return of sunlight. The Atlantic copepod Calanus finmarchicus and the Arctic Calanus glacialis became dominant in the post-inflow assemblage of large mesozooplankton. However, large copepods were never abundant (0.3–4.6 ind m⁻³) in January–April in the upper 40 m. Despite the low chlorophyll fluorescence, POC export increased substantially, from 2–13 mg C m⁻² d⁻¹ in January–February to 13–35 mg C m⁻² d⁻¹ in March–April 2014. By late March, zooplankton fecal pellets contributed largely (23–100%) to this significant POC export before the phytoplankton bloom. The lack of change in copepod and euphausiid population sizes suggests that enhanced feeding activity in the surface layer supported the increasing fecal pellet export. Our results revealed the swift response of active zooplankton in winter, evidenced by increased carbon export, to improved food availability.

In the Eastern Tropical North Pacific Oxygen Minimum Zone (ETNP-OMZ), fish larvae undergo development amidst highly variable dissolved oxygen environments. As OMZs expand, understanding the implications of low-oxygen environments on fish development becomes increasingly relevant for fisheries management and ecosystem modeling. Using horizontal zooplankton tows to track five oxygen levels (oxic [200 μmol/kg], hypoxic [100 μmol/kg] suboxic [10 μmol/kg], anoxic [<1 μmol/kg], and deep [10 μmol/kg at ~ 1000 m depth]), this study analyzed the three-dimensional distribution of fish larvae and adults across the ETNP-OMZ. Results revealed a wide midwater anoxic core, extending from Costa Rica to Baja California, that was almost devoid of fish larvae (< 1 larvae/1000 m³). Early larval stages primarily inhabited the oxic and hypoxic levels above the core, while postflexion and transformation stages occurred across a wider oxygen gradient, including the deep level below the anoxic core. Epipelagic species (e.g., Auxis sp.) were predominantly found in the surface oxic level, whereas coastal-demersal species (e.g., Bregmaceros bathymaster, Ophidion spp.) were prevalent in the hypoxic level above the core. Meso-bathypelagic species (e.g., Diogenichthys laternatus, Cyclothone spp.) were present throughout the study area, including below the anoxic core as transformation larvae and juveniles. These findings indicate that a vertical expansion of anoxic waters in OMZs could further constrain the habitat of epipelagic species, while also affecting the ontogenic vertical movements of meso-bathypelagic species.

The spatial organization of vegetation has been shown to be a strong indicator of ecological state in multiple ecosystems. In this study, we analyze the relationships between spatial complexity metrics in submerged aquatic vegetation (SAV) landscapes, and we explore the potential of satellite remote sensing to quantify these metrics in submerged environments. To do so, we estimated an array of complexity metrics over both simulated and real SAV landscapes of contrasted spatial organization. All these landscapes were artificially manipulated to (i) simulate remote sensing noise associated with the low signal-to-noise ratio (SNR) of aquatic environments and environmental noise generated by wind and waves, and (ii) reduce their spatial resolution from very high (2 m) to medium (30 m). Among these treatments, spatial resolution and low SNR (represented by sensor noise) had the strongest impacts on the perceived spatial complexity of the landscapes, while the impact of environmental noise was highly dependent on resolution. Although single metrics were deemed insufficient to characterize the spatial complexity of a landscape, a combination of informational complexity metrics such as the clumpy index, mean information gain, landscape shape index, and edge density provided a robust explanation of variation in the real and simulated datasets. These findings suggest that remote sensing has a strong potential for the ecological monitoring of SAV by contributing to establishing the link between SAV spatial structure and ecological status.