Pelagic Organisms Research Articles

Inflation-induced motility for long-distance vertical migration.

The vertical migrations of pelagic organisms play a crucial role in shaping marine ecosystems and influencing global biogeochemical cycles. They also form the foundation of what might be the largest daily biomass movement on Earth. Surprisingly, among this diverse group of organisms, some single-cell protists can transit depths exceeding 50m without employing flagella or cilia. How these non-motile cells perform large migrations remains unknown. It has been previously proposed that this capability might rely on the cell's ability to regulate its internal density relative to seawater. Here, using the dinoflagellate algae Pyrocystis noctiluca as a model system, we discover a rapid cell inflation event post cell division, during which a single plankton cell expands its volume 6-fold in less than 10min. We demonstrate this rapid cellular inflation is the primary mechanism of density control. This self-regulated cellular inflation selectively imports fluid less dense than surrounding seawater and can thus effectively sling-shot a cell and reverse sedimentation within minutes. To accommodate its dramatic cellular expansion, Pyrocystis noctiluca possesses a unique reticulated cytoplasmic architecture that enables a rapid increase in overall cell volume without diluting its cytoplasmic content. We further present a generalized mathematical framework that unifies cell-cycle-driven density regulation, stratified ecology, and associated cell behavior in the open ocean. Our study unveils an ingenious strategy employed by a non-motile plankton to evade the gravitational sedimentation trap, highlighting how precise control of cell size and cell density can enable long-distance migration in the open ocean.

Metazoan Parasites of Antimora rostrata (Günther, 1878) (Gadiformes: Moridae) from the Deep Sea in the Southeastern Pacific Ocean

A total of 127 specimens of the “Blue Antimora” Antimora rostrata (Günther, 1878) were obtained from 2015 to 2019 as bycatch from the artisanal fishery of the Patagonian toothfish (Dissostichus eleginoides (Smitt, 1898)) at depths between 1000 and 2200 m in Northern Chile (app. 22° S 70° W). All individuals were examined for parasites. A total of seventeen parasite taxa, two Copepoda, two Monogenea, seven Digenea, three Nematoda, and three Cestoda, were found, and twelve taxa were found as adults while five taxa were found at the larval stage. Anisakis sp. (Nematoda) and Trypanorhyncha gen. sp. (Cestoda) were the predominant species with a prevalence of 53.5% and 11.8%, respectively. The high prevalence of Anisakis sp. (>50%) suggests that A. rostrata may play a significant role in the life cycle of Anisakis sp. in the southeastern Pacific Ocean. The detected parasite community, consisting predominantly of parasites from pelagic environments rather than benthopelagic, suggests that A. rostrata may fulfill a crucial role as a predator of pelagic organism communities. Additionally, it may undertake vertical migrations in the southeastern Pacific Ocean.

A baseline assessment of contamination in the Sacramento deep water ship channel

The Sacramento Deep Water Ship Channel (SDWSC) in the San Francisco Estuary, which is an active commercial port, is critical habitat for pelagic fish species including delta smelt (Hypomesus transpacificus), longfin smelt (Spirinchus thaleichthys), and Sacramento perch (Archoplites interruptus). Pelagic organism decline has been attributed to covarying factors such as manipulation of habitat, introduction of invasive species, decrease in food production, and contaminant exposure. Quantification of bioavailable toxicant loads in the SDWSC is limited despite previous surveys that have detected elevated contaminant concentrations in the sediments. Therefore, the focus of the present study was to characterize the bioavailability of the contaminants in the SDWSC from six sites along the channel. At each site, organochlorine pesticides (OCPs), pyrethroid insecticides, polyaromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) were quantified in sediment, zooplankton, and suspended solids. In addition, Tenax extraction was used to measure the bioaccessible fraction of sediment-associated contaminants freely dissolved in the water. Bioaccessible contaminants in the sediment provided an uptake route for these stressors into invertebrates and fish with bioaccessible OCPs being found at all sites, particularly 4,4′-dichlorodiphenyldichloroethylene (DDE). Bifenthrin was the only pyrethroid detected in the chosen matrices and it was found at concentrations below levels of concern. Bioaccessible PAHs were found at all sites, with highest detections for phenanthrene and pyrene. No PCBs were detected in sediments, but were detected in both suspended solids and zooplankton. Contaminant concentrations overall were significantly higher in suspended solids, followed by zooplankton and sediments. The highest sediment concentrations of DDE, fluoranthene, pyrene, and dibenzo[a,h]anthracene exceeded sediment quality benchmarks indicating potential risk to sediment-dwelling species. Finally, elevated contaminant levels were found in both suspended solids and zooplankton, suggesting additional risk to pelagic species in the SDWSC.

A long-headed Cambrian soft-bodied vertebrate from the American Great Basin region.

The fossil record suggests that chordates might have been minor components of marine ecosystems during the first major diversification of animal life in the Cambrian. Vertebrates are represented by a handful of rare soft-bodied stem-lineage taxa known from Konservat-Lagerstätten, including Myllokunmingia and Yunnanozoon from the Stage 3 of South China, and Emmonsaspis and Metaspriggina from Stage 4-Drumian deposits of northeast USA and British Columbia. Here, we describe the first soft-bodied vertebrate from the American Great Basin, a region home to a dozen Cambrian Konservat-Lagerstätten. Found in the Drumian Marjum Formation of Utah, Nuucichthys rhynchocephalus gen. et sp. nov. is characterized by a finless torpedo-shaped body that includes a snout-like anterior head bearing anterolateral eyes, approximately 25 thick myomeres, a large branchial chamber with a keel and approximately seven putative dorsal bars and a spiniform caudal process. Using Bayesian inference, our analysis recovers Nuucichthys within the vertebrate stem, closer to the crown than Pikaia, Yunnanozoon and Myllokunmingia, where it forms a polytomy with its Laurentian relatives, Emmonsaspis and Metaspriggina, and a scion consisting of conodonts and crown-group vertebrates. Based on the eye orientation and absence of fins, we tentatively reconstruct Nuucichthys as a pelagic organism with limited swimming abilities (planktonektic).

Microcystins in the benthic food-web of the Sacramento-San Joaquin Delta, California

Harmful cyanobacteria blooms are a growing threat in estuarine waters as upstream blooms are exported into coastal environments. Cyanobacteria can produce potent toxins, one of which—hepatotoxic microcystins (MCs)—can persist and accumulate within the food web. Filter-feeding invertebrates may biomagnify toxins up to 100× ambient concentrations. As such, bivalves can be used as an environmentally relevant and highly sensitive sentinel for MC monitoring. To date there has been little research on cyanotoxin bioaccumulation in estuaries. The Sacramento-San Joaquin Delta (Delta) aquatic food web has undergone a profound change in response to widespread colonization of aquatic invasive species such as Asian clams (Corbicula fluminea) in the freshwater portion of the Delta. These clams are prolific—blanketing areas of the Delta at densities up to 1000 clams/m2 and are directly implicated in the pelagic organism decline of threatened and endangered fishes. We hypothesized that Asian clams accumulate MCs which may act as an additional stressor to the food web and MCs would seasonally be in exceedance of public health advisory levels. MCs accumulation in Delta Asian clams and signal crayfish (Pacifastacus leniusculus) were studied over a two-year period. ELISA and LC-MS analytical methods were used to measure free and protein-bound MCs in clam and crayfish tissues. We describe an improved MC extraction method for use when analyzing these taxa by LC-MS. MCs were found to accumulate in Asian clams across all months and at all study sites, with seasonal maxima occurring during the summer. Although MC concentrations rarely exceeded public health advisory levels, the persistence of MCs year-round still poses a chronic risk to consumers. Crayfish at times also accumulated high concentrations of MCs. Our results highlight the utility of shellfish as sentinel organisms for monitoring in estuarine areas.

Characterization of deep-sea sponge ground (Asconema setubalense) using structure from motion methodology.

The hexactinellid sponge Asconema setubalenseKent, 1870 is a deep-sea species characterized by its expansive cup-shaped morphology, which contributes significantly to the three-dimensional complexity of the marine ecosystems. This sponge forms grounds that offer protection to pelagic organisms and juvenile stages. Despite its ecological relevance, there is a lack of information on the ecology, behavior and population structure of this species. The research aimed to conduct a multitemporal analysis of this sponge in the Aviles Canyon System over a ten-year period, focusing on spatial distribution and abundance. Changes in fishing pressure were estimated using the presence of fishing gears as a proxy. Additionally, the study sought to provide a detailed morphometric description through 3D photogrammetric reconstructions based on the latest data. The multi-temporal analysis revealed a subtle increase in sponge density, particularly at depths ranging from 320 to 390 m, exhibiting an irregular spatial distribution in 2022, with maximal values of 0.08 individuals/m2. Despite a small decrease on the loss of fishing gears in the overlapping area between samplings in 2012 and 2022, there was not a clear indication of a decline in fishing pressure over the years. Notably, more sightings of fishing gears were found in transect IC222TV_16 (0.07 gears/m2) than in IC222_TV02 (0.04 gears/m2) in 2022, suggesting potential spatial preferences for fishing activities. Visual analysis of temporal populations revealed an increase of 7% in specimen perturbations over ten years, with the population in IC222_TV16 being healthier (9% of the individuals presenting severe deformations) than in IC222_TV02 (40%). High-density fishing gear locations coincided with areas inhabited by sponges displaying the highest perturbation levels in both transects. Morphometric analysis using data from 2022 indicated a prevalence of individuals with heights concentrated between 0.18 and 0.38 m, osculum and flounce diameters reaching 0.4 and 0.56 m and osculum and flounce surfaces of 0.02–0.04 and 0.06–0.19 m2 respectively. Over 80% of measured specimens exhibited a high degree of asymmetry. Strong correlations were observed between heights and osculum and flounce surfaces, but external factors may be included for explaining wall deformities. These findings contribute valuable insights into the characterization of A. setubalense, serving as a foundation for future research in the area. Moreover, this work highlights the promising potential of photogrammetry as an efficient tool for monitoring of vulnerable marine ecosystems (VME) and marine protected areas.

Navigating uncertainty in maximum body size in marine metazoans.

Body size is a fundamental biological trait shaping ecological interactions, evolutionary processes, and our understanding of the structure and dynamics of marine communities on a global scale. Accurately defining a species' body size, despite the ease of measurement, poses significant challenges due to varied methodologies, tool usage, and subjectivity among researchers, resulting in multiple, often discrepant size estimates. These discrepancies, stemming from diverse measurement approaches and inherent variability, could substantially impact the reliability and precision of ecological and evolutionary studies reliant on body size data across extensive species datasets. This study examines the variation in reported maximum body sizes across 69,570 individual measurements of maximum size, ranging from <0.2 μm to >45 m, for 27,271 species of marine metazoans. The research aims to investigate how reported maximum size variations within species relate to organism size, taxonomy, habitat, and the presence of skeletal structures. The investigation particularly focuses on understanding why discrepancies in maximum size estimates arise and their potential implications for broader ecological and evolutionary studies relying on body size data. Variation in reported maximum sizes is zero for 38% of species, and low for most species, although it exceeds two orders of magnitude for some species. The likelihood of zero variation in maximum size decreased with more measurements and increased in larger species, though this varied across phyla and habitats. Pelagic organisms consistently had low maximum size range values, while small species with unspecified habitats had the highest variation. Variations in maximum size within a species were notably smaller than interspecific variation at higher taxonomic levels. Significant variation in maximum size estimates exists within marine species, and partially explained by organism size, taxonomic group, and habitat. Variation in maximum size could be reduced by standardized measurement protocols and improved meta-data. Despite the variation, egregious errors in published maximum size measurements are rare, and their impact on comparative macroecological and macroevolutionary research is likely minimal.

Informing the Exposure Landscape: The Fate of Microplastics in a Large Pelagic In-Lake Mesocosm Experiment.

Understanding microplastic exposure and effects is critical to understanding risk. Here, we used large, in-lake closed-bottom mesocosms to investigate exposure and effects on pelagic freshwater ecosystems. This article provides details about the experimental design and results on the transport of microplastics and exposure to pelagic organisms. Our experiment included three polymers of microplastics (PE, PS, and PET) ranging in density and size. Nominal concentrations ranged from 0 to 29,240 microplastics per liter on a log scale. Mesocosms enclosed natural microbial, phytoplankton, and zooplankton communities and yellow perch (Perca flavescens). We quantified and characterized microplastics in the water column and in components of the food web (biofilm on the walls, zooplankton, and fish). The microplastics in the water stratified vertically according to size and density. After 10 weeks, about 1% of the microplastics added were in the water column, 0.4% attached to biofilm on the walls, 0.01% within zooplankton, and 0.0001% in fish. Visual observations suggest the remaining >98% were in a surface slick and on the bottom. Our study suggests organisms that feed at the surface and in the benthos are likely most at risk, and demonstrates the value of measuring exposure and transport to inform experimental designs and achieve target concentrations in different matrices within toxicity tests.

Diel Vertical Migrators Respond to Short‐Term Upwelling Events

AbstractPelagic organisms inhabiting coastal upwelling regions face a high risk of advection away from the nearshore productive habitat, potentially leading to mortality. We explored how animals remain in a productive yet highly advective environment in the Northern California Current System using the cabled observatory system located off the Oregon coast. Acoustic scatterers consistent with swimbladder‐bearing fish were only present during the downwelling season as these animals avoided the cold waters associated with strong upwelling conditions in summer and fall. Fish responded to short‐term upwelling events by increasing the frequency of diel vertical migration. Throughout the study, their vertical positions corresponded to the depth of minimum cross‐shelf transport, providing a mechanism for retention. The observed behavioral response highlights the importance of studying ecological processes at short timescales and the abilities of pelagic organisms to control their horizontal distributions through fine‐tuned diel vertical migration in response to upwelling.

PAHs in high Arctic copepods Calanus hyperboreus following exposure of residues from in situ burning of oil spill

In situ burning of marine oil spills reduces the total amount of oil in the environment, but a negative side effect may be the generation of environmentally hazardous polycyclic aromatic hydrocarbons (PAHs) that may pose a risk for bioaccumulation, particularly in organisms having a high lipid content. In this study uptake of PAHs from oil and burn residue were examined in the high arctic copepod Calanus hyperboreus. A major part of the low ring number petrogenic PAHs in the oil was removed during burning and relative higher concentrations of pyrogenic high ring number PAHs was found in the burn residue. This suggests that burning markedly reduces the general PAH exposure load. Furthermore, the pyrogenic PAHs generated during the burn were not bioconcentrated to quantifiable levels in the copepods. We conclude that in situ burning can mitigate the potential risk of PAH uptake for copepods and other pelagic organisms in the marine environment as the pyrogenic PAHs only pose low risk for uptake from the water by the copepods and other pelagic organisms.

Development of a Marine Radioactivity Expert System based on the Extended Marine Food Web: Experiments with Initial Bottom Contamination

An extended version of an expert system was developed as an effort to provide technical support to decision makers for the initial prompt assessment of environmental impacts of marine radioactivity, considering both pelagic and benthic marine food webs. The preliminary version of this system was firstly developed to determine the transfer of radionuclides through a pelagic marine food web (Kim et al, 2020). This system's approach was similar to the Cornell Mixing Zone Expert System (CORMIX) developed by Jirka (1995), as it used idealized settings for the physical/hydrodynamic coastal conditions. Existing or extended systems were executed by taking into account different kinds of radioactivity sources. The initial contamination of bottom sediment is considered in the present study, while the direct discharge to the coastal ocean from the nuclear power plant was considered in the early study. Assuming initial contamination, sensitivity experiments of temporal &lt;sup&gt;137&lt;/sup&gt;Cs variations without/with horizontal advection and diffusion (EXP-WOHAD and EXP-WHAD, respectively) were conducted. In EXP-WOHAD, a total of six test cases were constructed, considering a range of vertical diffusion coefficients and sediment fluxes at the water-sea bed interface. The EXP-WHAD experiments were classified into two categories with six cases each, considering the horizontal diffusion and advection processes. The EXP-WOHAD results show that the vertical diffusion processes in the bottom sediment result in the exponential decay of the &lt;sup&gt;137&lt;/sup&gt;Cs concentrations in the top sediment layer through upward and downward diffusive fluxes, producing pulse-like time variations in &lt;sup&gt;137&lt;/sup&gt;Cs in the water column and the middle sediment layer. These sediment fluxes affect the peak height and its occurrence time in the water column and the middle sediment layer. From EXP-WHAD, it has been confirmed that part of &lt;sup&gt;137&lt;/sup&gt;Cs diffused into the water column experiences horizontal dispersion and thereafter deposition to the bottom sediment. It is noted that due to the limited diffusion to the water column, the &lt;sup&gt;137&lt;/sup&gt;Cs concentrations in benthic organisms are larger than those in pelagic organisms.

CLADOCERA COMMUNITIES OF LAKE ARCTO-PIMBERTO (NENETS AUTONOMOUS DISTRICT) IN THE MIDDLE AND LATE HOLOCENE&lt;a href="#FN1"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/a&gt;

The analysis of the subfossil Cladocera community in the bottom sediments from Lake Arcto-Pimberto located in the Pechora River delta (Nenets Autonomous District) was carried out. A 95-cm-long continuous core of bottom sediments was collected in the deepest part of the lake and covers approximately 6400 years of sediment accumulation during Middle and Late Holocene. 17 cladoceran taxa were identified in the studied core. Species with Holarctic and Palearctic distributions prevailed in the lake. Most of the identified subfossil remains belong to pelagic species living in the open part of the lake. Found fragments of chitinized remains of Rhynchotalona falcata and Alonopsis elongata indicate the presence of sandy soils in the water body. The samples were dominated by Bosmina (Eubosmina) longispina and Chydorus cf. sphaericus, which are evenly distributed along the continuous sediment core. We have studied the history of the development and evolution of the lake based on changing of the taxonomic composition of microcrustaceans in the bottom sediment core. The structure of the subfossil Cladocera community stayed relatively constant. The ratio of pelagic and littoral-phytophilic taxa changed slightly. Depending on the changes in the species composition of the cladoceran assemblage, the sediment core was divided into 4 ecological zones. In the early history of sedimentation in the lake, there is a small peak in the abundance of crustaceans, followed by decrease and further gradual increase towards the upper horizons of the column. Between from 5700 cal. years BP to 2100 cal. years BP there is an increase in abundance of pelagic organisms, with a decrease in abundance of littoral taxa. This marks the presence of a well-developed pelagic part of the reservoir at that time. In the upper zones, we observe the taxonomic diversity of littoral organisms and an increase in abundance of their remains. The Shannon-Weaver species diversity Index showed a simple organization of the community of subfossil Cladocera. The Pantle and Buck saprobity Index characterized the lake as oligosaprobic, this status is maintained throughout its evolution of the lake.

Long-Term Trends in Seasonality and Abundance of Three Key Zooplankters in the Upper San Francisco Estuary

Zooplankton provide critical food for threatened and endangered fish species in the San Francisco Estuary (estuary). Reduced food supply has been implicated in the Pelagic Organism Decline of the early 2000s, and further changes in zooplankton abundance, seasonality, and distribution may continue to threaten declining fishes. While we have a wealth of monitoring data, we know little about the abundance trends of many estuary zooplankton species. To fill these gaps, we reviewed past research and then examined trends in seasonality and abundance from 1972 to the present of three key but understudied zooplankton species (Bosmina longirostris, Acanthocyclops spp., and Acartiella sinensis) that play important roles in the estuary food web. We fit Bayesian generalized additive mixed models of each taxon’s relationship with salinity, seasonality, year, and geography on an integrated database of zooplankton monitoring in the upper estuary. We found marked changes in the seasonality and overall abundance of each study species. Bosmina longirostris no longer peaks in abundance in the fall months, Acanthocyclops spp. precipitously declined in all months and lost its strong relationship with salinity, and A. sinensis adult abundance has become more strongly related to salinity while juveniles have developed wider seasonal abundance peaks. Through these analyses, we have documented the relationship of each species with salinity and seasonality since the beginning of monitoring or their introduction, thus increasing our understanding of their ecology and importance in the estuary. These results can inform food-web models, be paired with fish data to model the contributions of these species toward fish abundance trends and be mirrored to elucidate other species’ trends in future studies.

Paleoclimatic conditions during the accumulation of the Upper Jurassic and Lower Cretaceous organic carbon-rich deposits of the Ulyanovsk-Saratov trough (eastern Russian platform)

Relevance of the work. Black shale horizons may reflect abrupt paleoclimate changes. In the northeast of the Ulyanovsk-Saratov Trough (UST), two black shale horizons widely occur, the Middle Volgian Promzino Formation and the Lower Aptian Ulyanovsk Formation. Despite years of research, the role of paleoclimate in their accumulation is still under discussion. The aim of the research was to assess the climate as a factor of the accumulation of the Middle Volgian and Lower Aptian organic carbon-rich deposits in the northeastern UST. Methods. To reconstruct paleoclimate and to evaluate its impact on the black shale deposition, a comprehensive isotope study of calcitic and aragonitic shells of several groups of benthic and pelagic organisms was performed. Besides, the lithological and geochemical features of organic carbon-rich and host deposits were studied using optical microscopy, XRD, and pyrolysis. Results. Isotope study allowed to construct benthic and pelagic palaeotemperature curves and to reconstruct paleoclimate in the UST during the formation of black shales. Based on these data and data on lithological and geochemical features of sediments, the depositional mechanisms of the Promzino and Ulyanovsk Formations were clarified. Conclusions. No causal link has been revealed between climate changes and the deposition of the Middle Volgian black shales. At the end of the Middle Volgian, a short-term cooling has been recorded, probably related to the volcanic activity of the northern Tethyan margin. The Lower Aptian black shales were formed during the hyperthermal. This hyperthermal controlled the accumulation of organic carbon-rich sediments by increasing the input of nutrients and/or providing conditions for its stratification and stagnation.

Multizone Aquatic Ecological Exposures to Landfill Contaminants from a Groundwater Plume Discharging to a Pond.

While it is recognized that groundwater contaminant plumes can impact surface waters, there remains little information on the magnitude, spatial extent, and especially temporal variability of the resulting exposure to the variety of aquatic organisms, particularly for stagnant surface waters (e.g., ponds). The present study of a historic landfill plume discharging to a pond investigated contaminant exposure to multiple aquatic zones (endobenthic, epibenthic, pelagic) over approximately 1 year within a temperate climate. Landfill tracers included the artificial sweetener saccharin, ammonium, chloride, and specific conductance. Sampling of pond sediment porewater (upwelling groundwater) and continuous geophysical imaging of the subsurface showed a relatively stable plume footprint covering approximately 26% of the pond, although with spatially varying leachate composition, revealing year-round exposure to endobenthic (within sediments) organisms. Substantial and variable contaminant exposure to epibenthic organisms within the plume footprint was shown by elevated specific conductance measured directly above the sediment interface. Exposure varied daily at times and increased through winter to values representing undiluted plume groundwater. Exposure to pelagic organisms (overlying water) covered a larger area (~50%) due to in-pond circulation. The stream outlet concentrations were stable at approximately 10 times dilution for chloride and saccharin, but were substantially less in summer for ammonium due to in-pond processes. Whereas groundwater contaminants are typically assumed elevated at base flows, the outlet stream contaminant mass discharges to downstream receptors were notably higher in winter than summer, following stream flow patterns. Insights from the present study into the timings and locations of contaminant plume exposure to multiple ecological zones of a pond can provide guidance to contaminated site and aquatic ecosystem managers on improved monitoring, assessment, and remediation protocols. Environ Toxicol Chem 2023;42:1667-1684. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Water and sediment toxicity and hazard assessment of DCOIT towards neotropical marine organisms

DCOIT is an effective antifouling biocide, which presence in the environment and toxicity towards non-target species has been generating great concern. This study evaluated the waterborne toxicity of DCOIT on marine invertebrates (i.e., survival of brine shrimp Artemia sp., larval development of the sea urchin Echinometra lucunter and the mussel Perna perna), as well as DCOIT-spiked-sediment toxicity on the fecundity rate of the copepod Nitrocra sp. And the mortality of the amphipod Tiburonella viscana. The data outcomes were used to calculate environmental hazards and risks, which were compared to their corresponding values obtained from temperate regions. Waterborne toxicity can be summarized as follows: Artemia sp. (LC50–48h = 163 (135–169) μg/L), E. lucunter (EC50–36h = 33.9 (17–65) μg/L), and P. perna (EC50–48h = 8.3 (7–9) μg/L). For whole-sediment toxicity, metrics were calculated for T. viscana (LC50-10d = 0.5 (0.1–2.6) μg/g) and Nitrocra sp, (EC50-10d = 200 (10–480) μg/kg). The DCOIT hazard was assessed for both tropical and non-tropical pelagic organisms. The predicted no-effect concentration (PNEC) for tropical species (0.19 μg/L) was 1.7-fold lower than that for non-tropical organisms (0.34 μg/L). In whole-sediment exposures, DCOIT presented a PNEC of 0.97 μg/kg, and the risk quotients (RQs) were >1 for areas with constant input of DCOIT such as ports ship/boatyards, marinas, and maritime traffic zones of Korea, Japan, Spain, Malaysia, Indonesia, Vietnam, and Brazil. The presented data are important for supporting the establishment of policies and regulations for booster biocides worldwide.

Vertical, spatial, size, and taxonomic variations in stable isotopes (δ13C and δ15N) of zooplankton and other pelagic organisms in the western North Pacific

Stable isotopes (δ13C and δ15N) of zooplankton and other marine organisms are useful for evaluating trophic levels and the food web structure of marine ecosystems. Further, taxonomic variations and regressions between δ15N and δ13C can provide details of regional differences in the food web structure. Despite their ecological importance, information on the taxonomic differences in the stable isotopes of various pelagic biota and vertical, latitudinal, and size variations in the stable isotopes of the mesozooplankton are scarce in the western North Pacific. In this study, we compared regional differences in the taxonomic variations of the stable isotopes of the all pelagic organisms collected by gillnets and various plankton nets in the subarctic and transitional domains (37–44°N) of the western North Pacific during spring. Additionally, we evaluated the vertical, size, and latitudinal variations in the stable isotopes of mesozooplankton in the western North Pacific. Regressions between δ15N and δ13C were highly significant for the subarctic and transitional domains, while they varied significantly between the two regions (P < 0.0001, ANCOVA). These regional differences in the stable isotopes were characterised by the high δ15N and low δ13C values in the subarctic region, whereas the opposites trend was observed in the transitional domains. Vertical observations from the sea surface to a depth of 3000 m at five stations (29°, 31°, 33°, 37°, and 41°N) showed that there were no significant changes in the δ13C stable isotope of mesozooplankton with depth across the stations. However, for δ15N, the significance of regressions increased with increasing depths at the subtropical stations (29°, 31°, and 33°N), while no significant trends with depth were observed for the subarctic and transitional domain stations (37°, 41°N). The dominance of interzonal copepods (e.g., Neocalanus spp.) in the mesozooplankton biomass in the subarctic and transitional region may mask the vertical changes in δ15N values in that region. Further, δ13C varied neither with size nor latitude. In contrast, δ15N showed clear size and latitudinal patterns. Thus, δ15N values increased with increasing zooplankton size (112 μm < 407 μm < 925 μm), and significant regressions increased with increasing latitude for all three size classes (P < 0.001). Subsequent ANCOVA revealed that the regression did not vary with organism size. Thus, the changing latitudinal patterns in δ15N values (higher for high latitude) had much greater effects than the size differences for mesozooplankton.

Investigating Factors Contributing to Phytoplankton Biomass Declines in the Lower Sacramento River

Phytoplankton subsidies from river inputs and wetland habitats can be important food sources for pelagic organisms in the Sacramento–San Joaquin Delta (Delta). However, while the Sacramento River is a key contributor of water to the Delta, providing 80% of the mean annual inflow, the river is only a minor source of phytoplankton to the system. The reason for low phytoplankton biomass in the Sacramento River is not well understood but appears to be associated with a 65- km stretch of the lower river where chlorophyll-a (Chl-a) concentrations can decline by as much as 90%. We conducted two surveys along the lower Sacramento River, in spring and fall of 2016, to investigate the relative contributions of different factors potentially driving this Chl-a decline. Our study evaluated the change in Chl-a concentrations as a result of dilution from tributaries, light availability, nutrient concentrations, nutrient uptake, phytoplankton productivity, zooplankton grazing, and clam grazing. Chl-a concentration decreased from 14 µg L–1 to 1.8 µg L–1 in the spring and from 4.0 µg L–1 to 1.2 µg L–1 in the fall. Dilutions from the Feather River and American River contributed to 39% and 11% of Chl-a decline, respectively, during the spring. Average water depths roughly doubled downstream of the American River confluence, reducing water column light availability and lowering productivity. Zooplankton and clam grazing rates were generally low. Using a mass balance analysis, the measured variables explained 76% of the observed decline in Chl-a in the spring, suggesting additional losses from unidentified factors. We found that phytoplankton biomass is regulated by multiple potential factors in the lower Sacramento River, emphasizing the need for practitioners of restoration and management programs to evaluate multiple potential factors when attempting to enhance phytoplankton production in the Delta, or other large river systems.

Investigation of the ultrastructures and retinal arrangements of larval stomatopod eyes

Though the transparent apposition eyes of larval stomatopod crustaceans lack most of the unique retinal specializations known from their adult counterparts, increasing evidence suggests that these tiny pelagic organisms possess their own version of retinal complexity. In this paper, we examined the structural organization of larval eyes in six species of stomatopod crustaceans across three stomatopod superfamilies using transmission electron microscopy. The primary focus was to examine retinular cell arrangement of the larval eyes and characterize the presence of an eighth retinular cell (R8), which is typically responsible for UV vision in crustaceans. For all species investigated, we identified R8 photoreceptor cells positioned distal to the main rhabdom of R1-7 cells. This is the first evidence that R8 photoreceptor cells exist in larval stomatopod retinas, and among the first identified in any larval crustacean. Considering recent studies that identified UV sensitivity in larval stomatopods, we propose that this sensitivity is driven by this putative R8 photoreceptor cell. Additionally, we identified a potentially unique crystalline cone structure in each of the species examined, the function of which is still not understood.

Warming Affects Bioconcentration and Bioaccumulation of Per- and Polyfluoroalkyl Substances by Pelagic and Benthic Organisms in a Water-Sediment System.

Warming and exposure to emerging global pollutants, such as per- and polyfluoroalkyl substances (PFAS), are significant stressors in the aquatic ecosystem. However, little is known about the warming effect on the bioaccumulation of PFAS in aquatic organisms. In this study, the pelagic organisms Daphnia magna and zebrafish, and the benthic organism Chironomus plumosus were exposed to 13 PFAS in a sediment-water system with a known amount of each PFAS at different temperatures (16, 20, and 24 °C). The results showed that the steady-state body burden (Cb-ss) of PFAS in pelagic organisms increased with increasing temperatures, mainly attributed to increased water concentrations. The uptake rate constant (ku) and elimination rate constant (ke) in pelagic organisms increased with increasing temperature. In contrast, warming did not significantly change or even mitigate Cb-ss of PFAS in the benthic organism Chironomus plumosus, except for PFPeA and PFHpA, which was consistent with declined sediment concentrations. The mitigation could be explained by the decreased bioaccumulation factor due to a more significant percent increase in ke than ku, especially for long-chain PFAS. This study suggests that the warming effect on the PFAS concentration varies among different media, which should be considered for their ecological risk assessment under climate change.