Understanding the mechanisms by which climate variability affects multiple trophic levels in food webs is essential for determining ecosystem responses to climate change. Here we use over two decades ...of data collected by the Palmer Long Term Ecological Research program (PAL-LTER) to determine how large-scale climate and local physical forcing affect phytoplankton, zooplankton and an apex predator along the West Antarctic Peninsula (WAP). We show that positive anomalies in chlorophyll-a (chl-a) at Palmer Station, occurring every 4-6 years, are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode (SAM). Favorable conditions for phytoplankton included increased winter ice extent and duration, reduced spring/summer winds, and increased water column stability via enhanced salinity-driven density gradients. Years of positive chl-a anomalies are associated with the initiation of a robust krill cohort the following summer, which is evident in Adélie penguin diets, thus demonstrating tight trophic coupling. Projected climate change in this region may have a significant, negative impact on phytoplankton biomass, krill recruitment and upper trophic level predators in this coastal Antarctic ecosystem.
Comprehensive approaches are needed to understand accumulation patterns and the relative importance of pathways of entry for microplastics in the marine environment. Here, a highly urbanized ...estuarine environment was sampled along a salinity gradient from the mouth of the Raritan River, (New Jersey, USA) and into the Raritan Bay and the coastal ocean which are further influenced by discharge from the larger Hudson River. Polymers were characterized in two size classes by FTIR and/or Raman spectroscopy. The highest concentration of 500–2000 μm microplastic particles were observed in the mouth of the Raritan during summer low flow conditions, whereas the 250–500 μm microplastic particles were more prevalent in the bay and coastal ocean samples. These results were interpreted using fragmentation and mixing models to provide insight into the sources and fate of microplastics in this estuarine/coastal region. To investigate the potential pathways of entry into the system, samples were collected from various hydraulically connected storm water outfalls and the influent and effluent of wastewater treatment plants and polymer concentrations and types were compared to the estuarine samples. The concentrations of microplastics (500–2000 μm) ranged from 400 to 600 microplastics/m3 in storm water compared to <1–2.75 microplastics/m3 across the estuary. Of interest for analysis is the observed linear correlation between the total concentration of particles in a sample following oxidation and density separation and its microplastic concentration. Overall, the results presented reveal potentially important sources of microplastics in the estuarine environment and have implications for understanding the behavior, transport, and fate of microplastics under varying flow conditions and from estuaries with variable flushing times.
•Estuarine microplastic spatial distribution varied by size indicating different sources/fate.•Polymer identity similar between size classes, some variation by pathway.•Low and high flow microplastic concentrations are compared.•Microplastic concentration in wastewater influent > storm water > wastewater effluent.•Correlation observed between total post-oxidation particles and microplastics.
Ocean acidification has a wide-ranging potential for impacting the physiology and metabolism of zooplankton. Sufficiently elevated CO(2) concentrations can alter internal acid-base balance, ...compromising homeostatic regulation and disrupting internal systems ranging from oxygen transport to ion balance. We assessed feeding and nutrient excretion rates in natural populations of the keystone species Euphausia superba (Antarctic krill) by conducting a CO(2) perturbation experiment at ambient and elevated atmospheric CO(2) levels in January 2011 along the West Antarctic Peninsula (WAP). Under elevated CO(2) conditions (∼672 ppm), ingestion rates of krill averaged 78 µg C individual(-1) d(-1) and were 3.5 times higher than krill ingestion rates at ambient, present day CO(2) concentrations. Additionally, rates of ammonium, phosphate, and dissolved organic carbon (DOC) excretion by krill were 1.5, 1.5, and 3.0 times higher, respectively, in the high CO(2) treatment than at ambient CO(2) concentrations. Excretion of urea, however, was ∼17% lower in the high CO(2) treatment, suggesting differences in catabolic processes of krill between treatments. Activities of key metabolic enzymes, malate dehydrogenase (MDH) and lactate dehydrogenase (LDH), were consistently higher in the high CO(2) treatment. The observed shifts in metabolism are consistent with increased physiological costs associated with regulating internal acid-base equilibria. This represents an additional stress that may hamper growth and reproduction, which would negatively impact an already declining krill population along the WAP.
Pelagic tunicates (salps, pyrosomes) and fishes generate jelly falls and/or fecal pellets that sink roughly 10 times faster than bulk oceanic detritus, but their impacts on biogeochemical cycles in ...the ocean interior are poorly understood. Using a coupled physical‐biogeochemical model, we find that fast‐sinking detritus decreased global net primary production and surface export, but increased deep sequestration and transfer efficiency in much of the extratropics and upwelling zones. Fast‐sinking detritus generally decreased total suboxic and hypoxic volumes, reducing a “large oxygen minimum zone (OMZ)” bias common in global biogeochemical models. Newly aerobic regions at OMZ edges exhibited reduced transfer efficiencies in contrast with global tendencies. Reductions in water column denitrification resulting from improved OMZs improved simulated nitrate deficits relative to phosphate. The carbon flux to the benthos increased by 11% with fast‐sinking detritus from fishes and pelagic tunicates, yet simulated benthic fluxes remained on the lower end of observation‐based estimates.
Plain Language Summary
Marine ecosystems play a critical role in the global carbon cycle through the food web regulation of air‐sea carbon fluxes and the transfer of particulate matter from the upper oceans to depth. Recent evidence has suggested that the detritus from fishes and gelatinous zooplankton (GZ), specifically the pelagic tunicates such as salps and pyrosomes, may have a disproportionate impact on the ocean's biological pump due to them sinking approximately 10 times faster than bulk detritus. These fluxes result in increased sequestration of particulate carbon and nutrients into the deep oceans, but their impact on biogeochemical cycles at depth is poorly understood. Here, we investigated the sensitivity of deep ocean carbon, oxygen, and nutrient cycles to fast‐sinking detritus from tunicates and fishes. We found that the fast‐sinking detritus decreased surface productivity and export, as well as the size of ocean oxygen minimum zones (OMZs). Also, we examined whether observational evidence of seafloor oxygen consumption could support the increased detrital fluxes (and respiration) at depth, and found that even with the increased oxygen consumption, the modeled values were still below the observations. This suggests that these processes could be realistically incorporated into future generations of Earth System Models.
Key Points
We incorporated fast‐sinking detritus from pelagic tunicates and fishes into a modified version of the ocean biogeochemical model COBALT
The fast‐sinking detritus increased carbon sequestration and transfer efficiency to depth, but decreased surface productivity and export
Fast‐sinking detritus decreased the size of oxygen minimum zones (OMZs) and water column denitrification, a common model bias
Over the last decade, ocean temperature on the U.S. Northeast Continental Shelf (U.S. NES) has warmed faster than the global average and is associated with observed distribution changes of the ...northern stock of black sea bass (Centropristis striata). Mechanistic models based on physiological responses to environmental conditions can improve future habitat suitability projections. We measured maximum, standard metabolic rate, and hypoxia tolerance (Scrit) of the northern adult black sea bass stock to assess performance across the known temperature range of the species. Two methods, chase and swim-flume, were employed to obtain maximum metabolic rate to examine whether the methods varied, and if so, the impact on absolute aerobic scope. A subset of individuals was held at 30°C for one month (30chronic°C) prior to experiments to test acclimation potential. Absolute aerobic scope (maximum-standard metabolic rate) reached a maximum of 367.21 mgO2 kg-1 hr-1 at 24.4°C while Scrit continued to increase in proportion to standard metabolic rate up to 30°C. The 30chronic°C group exhibited a significantly lower maximum metabolic rate and absolute aerobic scope in relation to the short-term acclimated group, but standard metabolic rate or Scrit were not affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, calculated from Scrit as an estimate of potential aerobic scope, closely matched the measured factorial aerobic scope (maximum / standard metabolic rate) and declined with increasing temperature to a minimum below 3. This may represent a critical threshold value for the species. With temperatures on the U.S. NES projected to increase above 24°C in the next 80-years in the southern portion of the northern stock's range, it is likely black sea bass range will continue to shift poleward as the ocean continues to warm.
Fish reproduction is energetically costly, leading to a suite of energy allocation strategies for maximizing lifetime reproductive potential. Assessing energetic allocation for species that inhabit a ...wide distributional range can provide insight into different strategies found across individuals and populations. The Northern stock of black sea bass (Centropristis striata) inhabits the U.S. Northeast continental shelf from Cape Hatteras, NC, to the Gulf of Maine, and spawns inshore throughout this distribution from April to October. To assess energy allocation towards spawning, C. striata were collected in four regions across this distribution and throughout their spawning season. By assessing energetic allocation (lipid, energy density and total energy) in muscle, liver and gonad tissues, C. striata were identified as mixed breeders because while they mobilized somatic energy stores towards reproductive development, they also used energy acquired from their diet to sustain reproductive output throughout the spawning season. Unlike male fish, female fish both invested more energy into liver and gonad tissues and exhibited regional differences in energetic values. For both sexes, C. striata in the northern portion of the distribution had lower energetic values both in the somatic stores and towards gonadal development than the fish in the southern portion of the distribution, possibly because of longer migration distance. Overall, the authors found significant spatial variation in energetic constraints that may affect reproductive output and success (recruitment), a relevant result as C. striata are a popular recreational and commercial species throughout this distribution.
Microplastic (MP) pollution has been widely reported across water matrices including in estuaries, which are important for the understanding of oceanic MPs. Estuaries can greatly alter the fate, ...transport, size distribution, and abundance of plastic pollution. The aim of this study was to quantify and characterize MP pollution in the Delaware Bay estuary USA, including the size distribution. Samples (N = 31) were collected from the mouth of the Delaware River to the coastal ocean including multiple frontal zones across two sampling campaigns (2019 and 2022). MP were extracted from the collected particles using wet peroxide oxidation and density separation with saturated sodium chloride. Particles collected on 500 μm mesh sieves were analyzed via Fourier transform infrared (FTIR) spectroscopy. Across all samples, 324 of the 1015 particles analyzed were MP, and 11 macroplastics were observed. MP concentrations ranged from below detection to 4.12 MP/m3 (mean 0.34 ± 0.80 MP/m3). No significant differences were observed between sampling sites; nonetheless, the two highest MP concentrations were observed when sampling along frontal zones with visible debris including macroplastics. Polyethylene (53%) and polypropylene (43%) were the most abundant polymers observed. The majority of the non-plastic particles were classified as particulate natural organic matter (82% of non-plastics). Particles from samples collected during 2022 (N = 864) also had color, morphology, and two size dimensions recorded. MP particle size was significantly associated with sampling site, with the coastal ocean sampling site generally having the smallest MPs. A correlation between total post-extraction particles and total plastic particles was observed. Aspect ratios for the plastics ranged from one to 40.7, with larger ratios for fibers, with a mean (±standard deviation) of 3.39 ± 4.72 (unitless). These aspect ratios can be used to select shape factors used to estimate the total volume of MP in the studied size range. Overall, these results can help inform fate, transport, and risk assessments related to estuarine plastic pollution.
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•Polyethylene and polypropylene were most prevalent MP in the Delaware Bay estuary.•Peak plastic concentrations were observed in frontal zones.•Microplastic particle size varied by sampling site, sometimes by polymer type.
The coastal waters of the West Antarctic Peninsula (WAP) are associated with large phytoplankton blooms dominated by large (>20µm) diatoms however, nanoplankton (<20µm) are also an important ...component of the food web. The dominant nanoflagellates in the WAP are cryptomonad algae. Using a twenty-year time series collected by the Palmer Long Term Ecological Research program at the United States Palmer Research Station, we assessed long-term patterns and stability in the coastal phytoplankton communities in the WAP. There was significant interannual variability in the integrated water column chlorophyll a (chl-a) concentrations, which varied by a factor of 5 over the 20-year time series. There has been a significant positive increase in the seasonally integrated concentration of chl-a over the time series. The dominant phytoplankton were diatoms, with cryptophytes the second most abundant. Mixed flagellates also constituted a significant fraction of the chl-a but showed less interannual variability than diatoms and cryophytes. Peak phytoplankton biomass was observed in summer months, when monthly averaged wind speed was lower than in the fall and autumn. Cryptophytes were most abundant during the summer months (December-January) after the seasonal retreat of sea ice. While diatoms were observed over the full range of observed salinities 32–34.5) as well as over the full range of in situ temperatures (−1.5 to 2.5°C), the cryptophyte populations were observed in locations with lower salinity 32.5–33.75) and colder water (−1 to 1°C). Environmental factors that favored a shallower seasonal mixed layer resulted in larger diatom blooms compared to the other phytoplankton taxa. During summer with lower phytoplankton biomass, a larger proportion of the chlorophyll a was associated with cryptophytes. These results demonstrate that continued temperature changes along the West Antarctic Peninsula will result in changes in phytoplankton concentration and community composition, which has significant ramifications for the food web.
•Sea ice distributions in Antarctic Peninsula affect phytoplankton biomass/composition.•The dominant phytoplankton groups are diatoms and cryptophytes, at Palmer Station.•Sea ice increases associated with phytoplankton concentrations at Palmer Station.
Microplastics (MP) are considered emerging contaminants in the water environment, and there is an interest in understanding their entry into the food web. As a growing body of literature demonstrates ...the ingestion of MP by zooplankton in controlled laboratory studies, few data are available demonstrating in situ observations of MP in zooplankton. A field survey was performed to collect zooplankton in the highly urbanized Hudson-Raritan estuary. Following washing, sorting by species, and enumeration, three dominant species of copepods (Acartia tonsa, Paracalanus crassirostris and Centropages typicus) were digested. MP were filter concentrated and characterized by size, morphology, and color via microscopy and polymer type by micro-FTIR imaging and/or Raman spectroscopy. MP were observed in all extracts performed on the three copepod species with averages ranging from 0.30 to 0.82 MP individual−1. Polyethylene and polypropylene were the dominant polymer types observed and fragments and beads the most commonly observed morphologies for MP. These data were used to estimate the flux of MP through zooplankton based on gut turnover times, which we compare to estimates of MP entering this environment though the local waterways. The estimated fluxes were sufficiently large, indicating that ingestion by zooplankton is a major sink of MP in the size range subject to zooplankton feeding in surface estuarine waters.
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•Microplastics (MPs) were ubiquitous in copepods sampled from Hudson-Raritan estuary.•Range of MP polymers, morphologies, and sizes were observed from copepod extracts.•Flux estimates indicate zooplankton ingestion is a major contributor to MP fate.
The West Antarctic Peninsula (WAP) has experienced significant change over the last 50 years. Using a 24 year spatial time series collected by the Palmer Long Term Ecological Research programme, we ...assessed long-term patterns in the sea ice, upper mixed layer depth (MLD) and phytoplankton productivity. The number of sea ice days steadily declined from the 1980s until a recent reversal that began in 2008. Results show regional differences between the northern and southern regions sampled during regional ship surveys conducted each austral summer. In the southern WAP, upper ocean MLD has shallowed by a factor of 2. Associated with the shallower mixed layer is enhanced phytoplankton carbon fixation. In the north, significant interannual variability resulted in the mixed layer showing no trended change over time and there was no significant increase in the phytoplankton productivity. Associated with the recent increases in sea ice there has been an increase in the photosynthetic efficiency (chlorophyll a-normalized carbon fixation) in the northern and southern regions of the WAP. We hypothesize the increase in sea ice results in increased micronutrient delivery to the continental shelf which in turn leads to enhanced photosynthetic performance.
This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'.
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