Pelagic Food Web Research Articles

Methane fueled lake pelagic food webs in a Cretaceous greenhouse world

Methane (CH4) is a potent greenhouse gas but also an important carbon and energy substrate for some lake food webs. Understanding how CH4 incorporates into food webs is, therefore, crucial for unraveling CH4 cycling and its impacts on climate and ecosystems. However, CH4-fueled lake food webs from pre-Holocene intervals, particularly during greenhouse climates in Earth history, have received relatively little attention. Here, we present a long-term record of CH4-fueled pelagic food webs across the Cretaceous Oceanic Anoxic Event 1a (~120 Mya) that serves as a geological analog to future warming. We show an exceptionally strong expansion of both methanogens and CH4-oxidizing bacteria (up to 87% of hopanoid-producing bacteria) during this Event. Grazing on CH4-oxidizing bacteria by zooplankton (up to 47% of ciliate diets) within the chemocline transferred substantial CH4-derived carbon to the higher trophic levels, representing an important CH4 sink in the water column. Our findings suggest that as Earth warms, microbial CH4 cycling could restructure food webs and fundamentally alter carbon and energy flows and trophic pathways in lake ecosystems.

Spatial distribution projections of suitable environmental conditions for key Baltic Sea zooplankton species

AbstractEnvironmental changes reshape biological communities, inducing cascading effects throughout the food webs. These changes pressure species either to adapt or to track favorable habitats. Estuaries represent an interesting case study to investigate such responses as species will rapidly reach physical boundaries if they cannot adapt fast enough and need to track suitable conditions. One such estuary is the Baltic Sea, characterized by a salinity and temperature gradient that shapes species distribution and imposes physiological stress on organisms. The Baltic Sea is projected to be affected by substantial modifications in environmental conditions by the end of the 21st century, which could have major consequences for species distribution and community composition. However, despite the impending changes and their potential impact, there is a gap in understanding the potential consequences on pelagic species of the Baltic Sea. This study employs long‐term observations of primary zooplankton species in the pelagic food web to model changes in their distribution under future climate projections. We found that the parameters having the largest influence on habitat suitability varied across species, although maximal temperature was the most important for six out of seven species. In addition, there was a shrinkage of suitable area for several key species driven by a decrease in salinity and a rise in water temperature. We discuss the complex interplay between environmental changes and the spatial distribution of pelagic species in the Baltic Sea, highlighting the need for proactive management strategies to mitigate potential ecological impacts in the face of future climate scenarios.

Extreme mismatch between phytoplankton and grazers during Arctic spring blooms and consequences for the pelagic food-web

Food-web structure determines the cycling pathways and fate of new production in marine ecosystems. Herbivorous zooplankton populations are usually seasonally coupled with pelagic primary producers. Synchrony of phytoplankton blooms with reproduction, recruitment and seasonal ascent of their main grazers ensures efficient transfer of organic carbon to higher trophic levels, including commercially harvested species, especially in high-latitude systems. Changes in light, nutrient, and sea-ice dynamics due to accelerating climate change in the Arctic, however, create large uncertainties in how these systems will function in the future. To address such knowledge gaps, we surveyed the pelagic ecosystem of the Barents Sea Polar Front in May of two consecutive years (2021 and 2022) to investigate the pelagic food-web from primary producers to planktivorous fish. In both years we observed unprecedentedly high phytoplankton chlorophyll a values in open as well as ice-covered waters, much of which was invisible to satellite remote sensing. We also measured very low densities of grazing zooplankton across a wide area and extending for at least one month. This extreme mismatch resulted in low feeding by capelin, and further suggests a high potential for vertical export of carbon to the benthos rather than efficient assimilation into the pelagic food web. As the Arctic continues to warm and is characterized by thinner and more mobile sea ice, we may expect higher variability in phytoplankton bloom phenology and more frequent mismatches with grazer life-histories. This could have significant impacts on ecosystem functioning by re-directing the flow of energy through the system towards seafloor rather than to the production of commercially valuable pelagic marine resources.

Phytoplankton community composition as a driver of annual autochthonous organic carbon dynamics in the northern coastal Baltic Sea

Phytoplankton are the major primary producers in the pelagic system. They greatly influence biogeochemical cycles but little is known about the importance of shifting phytoplankton community composition for carbon dynamics. This study investigates the impact of seasonal changes in coastal phytoplankton communities on pelagic carbon fluxes. A field sampling campaign, covering an annual cycle in primary production, was conducted to assess the seasonal changes of phytoplankton communities and relevant organic carbon parameters in the coastal Baltic Sea. The monitoring frequency ranged from 1 to 3 wk, adapted to match the seasonal phytoplankton blooms. In addition, sediment traps were deployed to determine the particulate carbon and nutrient export to the seafloor in every season. We found that the phytoplankton biomass during the spring bloom was as high as 550 µg C l-1 and was dominated by diatom species (88% of total phytoplankton biomass). In comparison, the more species-rich summer bloom reached a combined maximum biomass of 236 µg C l-1. However, the highest export flux of particulate organic carbon was found in the middle of August (561 mmol C m-2 d-1) and, not as expected, around the spring bloom in May (226 mmol C m-2 d-1), suggesting a high potential for carbon recycling within the pelagic food web rather than being exported to the seafloor or advected laterally. Our study emphasizes the importance of keystone species and diversity for carbon transport processes in marine coastal ecosystems and highlights complex relationships between phytoplankton biomass production, community composition and carbon dynamics.

Trophic flows to mesozooplankton support the conventional paradigm of pelagic food web structure in ocean ecosystems

Abstract The current conventional paradigm of ocean food web structure inserts one full level or more of microzooplankton heterotrophic consumption, a substantial energy drop, between phytoplankton and mesozooplankton. Using a dataset with contemporaneous measurements of primary production (PP), size-fractioned mesozooplankton biomass, and micro- and mesozooplankton grazing rates from 10 tropical to temperate ocean ecosystems, we examined whether the structural inefficiencies in this paradigm allow sufficient energy transfer to support active metabolism and growth of observed zooplankton standing stocks. Zooplankton carbon requirements (ZCR) were determined from allometric equations that account for ecosystem differences in temperature and size structure. ZCRs were relatively low (∼30% of PP or less) for both oligotrophic systems and bloom biomass accumulation in eutrophic coastal waters. Higher relative ZCRs (>30% PP) were associated with elevated mesozooplankton grazing scenarios (bloom declines, abundant salps), advective subsidies, and open-ocean upwelling systems. Microzooplankton generally dominated as grazers of PP but were equal or secondary to direct herbivory as nutritional support for mesozooplankton in five of eight regional studies. All systems were able to satisfy ZCR within the conventional food-web interpretation, but balanced open-ocean upwelling systems required the most efficient alignments of contributions from microzooplankton grazing, direct herbivory, and carnivory to do so.

Multi-disciplinary approach identifies pelagic nutrient linkage by sawsharks

Quantifying the trophic role of a species is key to understanding its ecology and ecological role. Their trophic role can influence community composition, ecosystem stability, and nutrient transport and cycling between habitats through ingestion, egestion, and excretion, which requires an understanding of species diet and habitat use. Despite the regular occurrence of sawsharks in Australian temperate fisheries, there remains limited information on their trophic ecology or habitat use, but they are assumed to be benthic consumers. We used fatty acid and stable isotope profiles along with stomach content analysis to investigate the trophic ecology of two sympatric species of sawsharks, the common sawshark (Pristiophorus cirratus) and southern sawshark (Pristiophorus nudipinnis) in south-eastern Australia. Stable isotope analysis of δ13C, δ15N, and δ34S in sawshark muscle revealed that P. nudipinnis fed at a higher trophic level than P. cirratus, and mixing models and stomach contents indicated P. nudipinnis was surprisingly reliant on pelagic and benthopelagic prey sources. In contrast, P. cirratus preyed on more benthic invertebrate species, not found in P. nudipinnis. This bentho-pelagic partitioning between species was supported by P. nudipinnis fatty acid profiles having higher levels of tracers associated with dinoflagellate basal sources (16:1/16:0, 22:6ω3) than P. cirratus, indicating a reliance on pelagic food webs. These data demonstrate that sawsharks are mesopredators that play a substantial role linking pelagic and benthic food webs and highlights the value of incorporating multiple biochemical tracers to provide a comprehensive representation of an animal’s trophic ecology and role in and between ecosystems.

Mediterranean Marine Mammals: Possible Future Trends and Threats Due to Mercury Contamination and Interaction with Other Environmental Stressors.

Despite decreasing anthropogenic mercury (Hg) emissions in Europe and the banning and restriction of many persistent organic pollutants (POPs) under the Stockholm Convention, Mediterranean marine mammals still have one of the highest body burdens of persistent pollutants in the world. Moreover, the Mediterranean basin is one of the most sensitive to climate change, with likely changes in the biogeochemical cycle and bioavailability of Hg, primary productivity, and the length and composition of pelagic food webs. The availability of food resources for marine mammals is also affected by widespread overfishing and the increasing number of alien species colonizing the basin. After reporting the most recent findings on the biogeochemical cycle of Hg in the Mediterranean Sea and the physico-chemical and bio-ecological factors determining its exceptional bioaccumulation in odontocetes, this review discusses possible future changes in the bioavailability of the metal. Recent ocean-atmosphere-land models predict that in mid-latitude seas, water warming (which in the Mediterranean is 20% faster than the global average) is likely to decrease the solubility of Hg and favor the escape of the metal to the atmosphere. However, the basin has been affected for thousands of years by natural and anthropogenic inputs of metals and climate change with sea level rise (3.6 ± 0.3 mm year-1 in the last two decades), and the frequency of extreme weather events will likely remobilize a large amount of legacy Hg from soils, riverine, and coastal sediments. Moreover, possible changes in pelagic food webs and food availability could determine dietary shifts and lower growth rates in Mediterranean cetaceans, increasing their Hg body burden. Although, in adulthood, many marine mammals have evolved the ability to detoxify monomethylmercury (MMHg) and store the metal in the liver and other organs as insoluble HgSe crystals, in Mediterranean populations more exposed to the metal, this process can deplete the biological pool of Se, increasing their susceptibility to infectious diseases and autoimmune disorders. Mediterranean mammals are also among the most exposed in the world to legacy POPs, micro- and nanoplastics, and contaminants of emerging interest. Concomitant exposure to these synthetic chemicals may pose a much more serious threat than the Se depletion. Unfortunately, as shown by the literature data summarized in this review, the most exposed populations are those living in the NW basin, the main feeding and reproductive area for most Mediterranean cetaceans, declared a sanctuary for their protection since 2002. Thus, while emphasizing the adoption of all available approaches to mitigate anthropogenic pressure with fishing and maritime traffic, it is recommended to direct future research efforts towards the assessment of possible biological effects, at the individual and population levels, of chronic and simultaneous exposure to Hg, legacy POPs, contaminants of emerging interest, and microplastics.

Effect of alternative natural diet on microplastic ingestion, functional responses and trophic transfer in a tri-trophic coastal pelagic food web

The patchy distribution of microplastics (MP) and their size range similar to planktonic organisms, are likely to have major ecological consequences, through MP ingestion, food dilution, and transfer across trophic levels. Our study applied a community module using tritrophic food chain with zooplankton as prey, and a planktivorous seabass fry as predator. We conducted a series of feeding experiments and recorded the direct uptake of MP under six different concentrations ranging from 25 to 800 particles L−1. We also estimated the indirect transfer of MP via trophic link. The ingestion rates for Brachionus plicatilis, Mesocyclops isabellae, and Lates calcarifer, were 3.7 ± 0.3 MP ind−1 min−1, 1.69 ± 0.1 MP ind−1 min−1, and 3.51 ± 0.52 MP ind−1 h−1, respectively. In the presence of a natural diet, rotifers and copepods ingested significantly lower number, whereas, fish fry ingested a higher number of MP, suggesting further vulnerability to the consumers of MP-contaminated fish and potential biomagnification at higher trophic levels. Overall, the MP uptake rate increased with increasing concentration, and finally leveled off, indicating a type II functional response to MP concentration. The presence of natural diet led to a lower Km value. In the indirect transfer experiment, 74 % of B. plicatilis and 78 % of M. isabellae individuals were contaminated with MP, when offered as prey. Brachionid mastax and MP particles were observed in the gut of copepods. The fish fry gut content also recorded brachionid mastax, MP-contaminated copepods, and MP particles, showing direct evidence of trophic transfer pointing to a cascading effect on higher trophic levels including humans via piscivory.

Rhizaria in the oligotrophic ocean exhibit clear temporal and vertical variability

Recently studies have shown that Rhizaria, a super-group of marine protists, have a large role in pelagic ecosystems. They are unique in that they construct mineral tests out of silica, calcium carbonate, or strontium sulfate. As a consequence, Rhizaria can have large impacts on the ocean’s cycling of carbon and other elements. However, less is known about Rhizaria ecology or their role in the pelagic food-web. Some taxa, like certain Radiolarians, are mixotrophic, hosting algal symbionts. While other taxa are flux-feeders or even predatory carnivores. Some prior research has suggested that Rhizaria will partition vertically in the water column, likely due to different trophic strategies. However, very few studies have investigated their populations over extended periods of time. In this study, we present data investigating Rhizaria abundance and vertical distribution from over a year of monthly cruises in the Sargasso Sea. This study represents the first quantification of Rhizaria throughout the mesopelagic zone in an oligotrophic system for an extended period of time. We use this data to investigate the hypothesis that Rhizaria taxonomic groups will partition due to trophic mode. We also investigate how their abundance varies in accordance with environmental parameters. Rhizaria abundance was quantified using an Underwater Vision Profiler (UVP5), an in-situ imaging device. Ultimately, we show that different Rhizaria taxa will have unique vertical distribution patterns. Models relating their abundance to environmental parameters have mixed results, yet particle concentration is a common predictive variable, supporting the importance of heterotrophy amongst many taxa.

The Cambrian Odaraia alata and the colonization of nektonic suspension-feeding niches by early mandibulates.

The diversity of cephalic morphologies in mandibulates (myriapods and pancrustaceans) was key to their evolutionary success. A group of Cambrian bivalved arthropods called hymenocarines exhibit diagnostic mandibulate traits that illustrate this diversity, but many forms are still poorly known. These include the odaraiids, typified by Odaraia alata from the Burgess Shale (Wuliuan), characterized by its unique tubular carapace and rudder-like tail fan, and one of the largest Cambrian euarthropods at nearly 20 cm in length. Unfortunately, odaraiid cephalic anatomy has been largely unknown, limiting evolutionary scenarios and putting their mandibulate affinities into question. Here, we reinvestigate Odaraia based on new specimens from the Burgess Shale and describe exquisitely preserved mandibles with teeth and adjacent structures: a hypostome, maxillae and potential paragnaths. These structures can be homologized with those of Cambrian fuxianhuiids and extant mandibulates, and suggest that the ancestral mandibulate head could have had a limbless segment but retained its plasticity, allowing for limb re-expression within Pancrustacea. Furthermore, we show the presence of limbs with spinose endites which created a suspension-feeding structure. This discovery provides morphological evidence for suspension feeding among large Cambrian euarthropods and evinces the increasing exploitation of planktonic resources in Cambrian pelagic food webs.

Spatiotemporal changes of pelagic food webs investigated by environmental DNA metabarcoding and connectivity analysis.

Environmental DNA metabarcoding (eDNA metaB) is fundamental for monitoring marine biodiversity and its spread in coastal ecosystems. We applied eDNA metaB to seawater samples to investigate the spatiotemporal variability of plankton and small pelagic fish, comparing sites with different environmental conditions across a coast-to-offshore gradient at river mouths along the Campania coast (Italy) over 2 years (2020-2021). We found a marked seasonality in the planktonic community at the regional scale, likely owing to the hydrodynamic connection among sampling sites, which was derived from numerical simulations. Nonetheless, spatial variability among plankton communities was detected during summer. Overall, slight changes in plankton and fish composition resulted in the potential reorganization of the pelagic food web at the local scale. This work supports the utility of eDNA metaB in combination with hydrodynamic modelling to study marine biodiversity in the water column of coastal systems. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Current status and trends for commercial stock of japanese anchovy <i>Engraulis japonicus</i> (Engraulidae) in Russian waters of the Japan Sea

Japanese anchovy Engraulis japonicus of the Tsushima Current stock migrate to the northwestern Japan Sea in warm season and play there an important role in the pelagic food web. According to survey and fishery data, the commercial stock of this species declines recently that determines decreasing of intensity of its migrations into the Russian waters, though its level is still appropriate for fishery. The anchovy releases ashore occur sometimes on the Far-Eastern coast, likely in cases of unstable environments that have become more frequent under climate change. More intense research of the pelagic ecosystem in the northwestern Japan Sea is necessary to clarify the status of fishery resources formed by southern migrants, including anchovy, sardine and mackerel.

Bridging the spawner-recruit disconnect II: Revealing basin-scale correlations between zooplankton and lobster settlement dynamics in the Gulf of Maine

In recent decades, recruitment of young-of-year lobsters to benthic nursery habitats in the Gulf of Maine was regionally synchronized and exhibited correlative links with changes in the abundance of the copepod Calanus finmarchicus, a foundational zooplankton species of the pelagic food web. The spatial scale at which recruitment dynamics were correlated indicated that recruitment processes were not as strongly coupled to trends in spawner abundance as might be expected, but, rather, were influenced by common, ecosystem-scale processes. Here we explored how local- and basin-scale zooplankton dynamics and oceanographic indicators in the Gulf of Maine correlated with lobster settlement indices and each other since the late 1980s. Our analysis indicates that lobster settlement trends in southwestern Gulf of Maine study areas, from Midcoast Maine to Cape Cod Bay, tend to be significantly correlated with basin-wide C. finmarchicus dynamics and the composition of waters entering the Gulf of Maine through the Northeast Channel. In contrast, lobster settlement in the northeastern Gulf, from Penobscot Bay to the Bay of Fundy, tended to correlate more strongly to C. finmarchicus variability in the Bay of Fundy region, which was distinct in earlier years but converged with the broader basin-scale processes in the latter years. Our results are consistent with the hypothesis that the combined effect of climate-related declines in abundance and phenological shifts of C. finmarchicus have contributed to declines in lobster settlement over the past decade, and justify further research into the mechanisms of this interaction. These changes also align with the weakening influence of cold Labrador Slope Water and strengthening effects of warm Gulf Stream waters that precipitated an ecosystem-wide regime shift in the Gulf of Maine over the past decade and may have greater implications for lobster recruitment than previously suspected.

Zooplankton fecal pellet flux drives the biological carbon pump during the winter–spring transition in a high‐Arctic system

AbstractRecent 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.

Diet of non-breeding leach’s storm-petrels (Hydrobates leucorhous) in the sub-polar frontal zone of the North Atlantic

In order to understand the drivers of the distribution and abundance of pelagic seabirds it is necessary to know what they eat, yet there remains little detailed, geo-referenced information on the diets of pelagic seabird. In particular, due to sampling difficulties, information is lacking for non-breeding stages, smaller species, such as storm-petrels, and remote oceanic areas, which may include important diversity hotspots. In this study, we aimed to characterize the trophic ecology of Leach’s storm-petrels foraging in the vicinity of the North Atlantic Current and Evlanov Seamount Marine Protected Area using a combination of survey methods. On a cruise undertaken in June 2017 to characterize the distribution and ecology of seabirds in the region, nineteen Leach’s storm-petrels were caught, sampled and released unharmed. Regurgitations and faecal samples were collected, as well as blood and feather tissues for stable isotope analyses. Of the 12 males, 6 females and 1 unsexed bird, 84% were in active flight feather moult, suggesting they were non-breeders. Prey species, assayed via molecular metabarcoding, were dominated by mesopelagic fish, principally lanternfishes (Myctophidae) and hatchetfishes (Sternoptychidae), but also included cephalopods and crustaceans. Additionally, almost half of the birds had microplastics in their regurgitates. Stable isotopic ratios did not differ significantly between sexes. Our results, combined with those of previous studies, suggest that within the oceanic North Atlantic, Leach’s storm-petrels feed at a similar trophic level to much larger seabirds, targeting mesopelagic fishes that are a key component of the North Atlantic pelagic food web.

The Spatial Distribution of Copepod Functional Traits in a Highly Anthropized Mediterranean Coastal Marine Region

Copepods dominate marine zooplankton in abundance and play key roles in pelagic food webs. These small crustaceans show high taxonomic and functional diversity. Although there has been considerable research on their taxonomy, only a few studies have focused on their functional traits. In this study, we analyzed the functional traits of 95 copepod species, considering their body size, trophic regime, feeding behavior, and spawning strategy. Based on samples collected during two surveys (autumn 2020 and summer 2021) located in the coastal waters of three gulfs (Gaeta, Naples, and Salerno) in the highly populated Campania region (the central Tyrrhenian Sea, NW Mediterranean), we identified nine functional groups of copepods with different characteristics. The group that comprised herbivorous copepods with feeding currents and a broadcast strategy was the most abundant in both seasons and all gulfs. This group was dominated by Acartia clausi, Centropages typicus, Temora stylifera, and the Paracalanus parvus complex. The other functional groups showed differences in their temporal and spatial distribution. Our study reports the functional diversity of copepods along the Campania coast, thus contributing to advancing our knowledge of the planktonic trophic structure in a region of considerable importance due to its marine resources and services.

Ecotoxicological Assessment of Microplastics and Cellulose Particles in the Galápagos Islands and Galápagos Penguin Food Web.

Microplastic pollution threatens some of the world's most iconic locations for marine biodiversity, including the remote Galápagos Islands, Ecuador. Using the Galápagos penguin (Spheniscus mendiculus) as a sentinel species, the present study assessed microplastics and suspected anthropogenic cellulose concentrations in surface seawater and zooplankton near Santa Cruz and Galápagos penguin colonies (Floreana, Isabela, Santiago), as well as in penguin potential prey (anchovies, mullets, milkfish) and penguin scat. On average, 0.40 ± 0.32 microplastics L-1 were found in surface seawater (<10 μm; n = 63 L), while 0.003, 0.27, and 5.12 microplastics individual-1 were found in zooplankton (n = 3372), anchovies (n = 11), and mullets (n = 6), respectively. The highest concentration (27 microplastics individual-1) was observed in a single milkfish. Calculations based on microplastics per gram of prey, in a potential diet composition scenario, suggest that the Galápagos penguin may consume 2881 to 9602 microplastics daily from prey. Despite this, no microplastics or cellulose were identified in 3.40 g of guano collected from two penguins. Our study confirms microplastic exposure in the pelagic food web and endangered penguin species within the UNESCO World Heritage site Galápagos Islands, which can be used to inform regional and international policies to mitigate plastic pollution and conserve biodiversity in the global ocean. Environ Toxicol Chem 2024;43:1442-1457. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Diverging phenology of American lobster (Homarus americanus) larvae and their zooplankton prey in a warming ocean

Abstract We build on previous research describing correlative links between changes in the abundance of the copepod Calanus finmarchicus, a foundational zooplankton species of the pelagic food web, and diminishing recruitment of young-of-year American lobster (Homarus americanus) to benthic nurseries in the Gulf of Maine. Using parallel 31-year time series of lobster larvae and zooplankton collected on the New Hampshire coast between 1988 and 2018, we investigated how changes in phenology of stage I larval lobster and their putative copepod prey, C. finmarchicus, affect their temporal overlap and potential to interact during the larval season. We found that over the time series both the lobster egg hatch and first appearance of larvae began earlier in the season, a trend significantly correlated with ocean warming. The last appearance of larvae in late summer has been delayed, however, thereby extending the larval season. Even with the longer larval lobster season, the C. finmarchicus season has increasingly been ending before the peak abundance of stage I lobster larvae. The net effect is a widening mismatch in phenology of the two species, an outcome consistent with the hypothesis that changes in abundance and phenology of C. finmarchicus have contributed to recent declines in lobster recruitment.

Mercury dynamics at the base of the pelagic food web of the Gulf of Gdańsk, southern Baltic Sea

Planktonic organisms, which have direct contact with water, serve as the entry point for mercury (Hg), into the marine food web, impacting its levels in higher organisms, including fish, mammals, and humans who consume seafood. This study provides insights into the distribution and behavior of Hg within the Baltic Sea, specifically the Gulf of Gdańsk, focusing on pelagic primary producers and consumers. Phytoplankton Hg levels were primarily influenced by its concentrations in water, while Hg concentrations in zooplankton resulted from dietary exposure through suspended particulate matter and phytoplankton consumption. Hg uptake by planktonic organisms, particularly phytoplankton, was highly efficient, with Hg concentrations four orders of magnitude higher than those in the surrounding water. However, unlike biomagnification of Hg between SPM and zooplankton, biomagnification between zooplankton and phytoplankton was not apparent, likely due to the low trophic position and small size of primary consumers, high Hg elimination rates, and limited absorption.

Amazing Graze: Shifts in Jellyfish and Clam Distributions During Dry Years in the San Francisco Estuary

Aquatic invasive species have drastically changed how the San Francisco Estuary functions. During the past 2 decades, the effects of invasive species in the estuary may have increased in response to frequent and severe drought conditions. The invasive overbite clam (Potamocorbula amurensis), and the Asian Clam (Corbicula fluminea) have well documented consequences on the estuarine food web, but their responses to drought are not well understood. Another invasive species, the jellyfish Maeotias marginata, can further affect the food web, but these effects have not been studied. We investigated the population responses of these invasive species to dry years and their potential effects on the pelagic food web using data from the Interagency Ecological Program’s monitoring surveys. We found M. marginata rapidly moves upstream with changing salinities during dry years, though it sees its highest abundance during high-outflow years in Suisun Bay and Suisun Marsh. Grazing rates of M. marginata in the estuary have not been quantified but are potentially high during localized blooms. The two invasive clams overlap in distribution, but have opposite population responses to drought conditions, with increases in P. amurensis densities and decreases in C. fluminea densities in dry years. With increasing P. amurensis densities, the clams’ combined annual filtration rates increase during drier years in the confluence and Suisun Marsh. Like M. marginata, P. amurensis also shifts upstream during droughts, but because adults cannot move immediately with a change in salinity, the population center of distribution shifts upstream the year after a dry year as a result of juvenile recruitment. If multiple dry years occur in a row, and both P. amurensis and M. marginata move upstream together, their effects on the food web could be compounded, and phytoplankton and zooplankton biomass could steeply decline in the confluence, affecting higher trophic levels in the estuary.