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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.

Gelatinous zooplankton (GZ), play a crucial role in marine food webs, nutrient cycling, and carbon sequestration, however, quantifying their abundances remains challenging due to their delicate body structure, complex life cycles and variable population dynamics. Their tendency to form sporadic, large-scale aggregations further complicate the differentiation between true ecosystem alterations and stochastic variations in their abundance. In the Arctic Ocean, our understanding of GZ aggregations remains generally incomplete. Using in-situ observations from a towed pelagic camera system, we assessed the diversity and vertical distributions of GZ in fjord and offshore environments in northern Norway and the Svalbard archipelago. We found that Atlantic water masses harbored the highest GZ abundance, while intermediate waters showed the highest diversity. We documented dense aggregations of Beroe spp. in Van Mijenfjorden in Svalbard (observed during ascent of the camera system, not quantified in ind. m−3) and Bolinopsis infundibulum in the open Barents Sea (> 2.67 ind. m−3 at 100 m). Other observed taxa included the hydrozoans Aglantha digitale, Melicertum octocostatum, Solmundella bitentaculata, Pandeidae sp. and Physonectae spp., the scyphozoan Cyanea capillata and the ctenophores Mertensia ovum and Euplokamis sp. By linking the vertical distribution and observations of local aggregations with physical and biotic factors, we described the potential drivers of the distributional patterns observed. Towed camera surveys contribute to accurate in-situ observations, thereby improving our understanding of GZ aggregations and distributions in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

The feeding upon large animals—even larger than the predator—by benthic cnidarians has been reported from many ecosystems but never exhaustively studied to date. By reviewing 38 papers on this topic, this review aims to recap the observations on the predatory behaviour of polyps, to establish feeding plasticity boundaries and to understand the contribute of this trophic strategy to the benthic–pelagic coupling. The reviewed documents published increasingly during the last two decades mostly reported observations on heterotrophic Anthozoa in shallow ecosystems collected through photo/video records. The main prey items are represented by gelatinous zooplankton and echinoderms. The lexical discordance in the considered papers highlights the need to standardize the terminology to describe the feeding behaviour of benthic Cnidaria, opportunistic and characterized by a strong plasticity. Given the importance of large prey in cnidarian trophism, we proposed an unambiguous terminology that will help the online search of literature and address future studies. We suggest identifying micro-predation (predator/prey size ratio ≥ 5:1) and macro-predation (predator/prey size ratio is ≤ 1:1) as distinct feeding modalities, because the capture of large prey involves peculiar movements of polyps, such as stretching and retracting of column and tentacles to pull the prey towards the mouth. [ABSTRACT FROM AUTHOR]

We investigated long-term changes in the abundance and species composition of hyperiid amphipods in the Southern California Bight and nearby waters from twelve springime CalCOFI cruises spanning the period 1951-1997. Sixty-two hyperiid species were detected in the study region. We found dimunition in species diversity and in total hyperiid abundance during the studied period. Despite high interannual variability, there was higher species richness, evenness of species numbers, and abundances of hyperiids in an earlier time period (1951 to 1972) and generally lower species richness, evenness, and abundances in a more recent time period (1979 to 1997). Variations in abundance of total hyperiids were significantly correlated with variations in abundance of presumed gelatinous zooplankton hosts, especially salps, physonect siphonophores, and pyrosomes. Species-specific correlations showed significant associations between ten species of hyperiids and different species of salps, siphonphores, and medusae. Some amphipods were correlated with more than one host. Hyperiid amphipod assemblages appear to be sensitive to large-scale climate changes in the NE Pacific, through either direct responses or indirectly through their association as parasitoids on gelatinous hosts.

Gelatinous zooplankton (GZ), and pelagic tunicates specifically, plays key roles in marine ecosystems, contributing to diets of various predators and oceanic carbon cycling. Nevertheless, biological inventories are often lacking, but are essential in establishing marine biodiversity baselines that, in turn, are critical in detecting broad-scale changes. The use of social media in combination with scientific records provides a powerful tool to broaden the scope of biodiversity studies. This study assesses the diversity of pelagic tunicates (appendicularians and thaliaceans) in the Cuban Exclusive Economic Zone (EEZ) and whether the EEZ acts as an ecotone between the Gulf of Mexico (GoM) and the Caribbean Sea (CS). By reviewing the scientific literature and using citizen science data, a total of 28 species were identified. The most diverse family among the appendicularians was Oikopleuridae (9 species) and among the thaliaceans Salpidae (6 species). Cuba’s northern EEZ was more speciose compared to the southern EEZ, 18 versus 14 species. No endemic species were found in Cuba’s waters and tunicate assemblages were most similar to the GoM. Our data do not support that Cuban waters act as an ecotone (for pelagic tunicates) between the GoM and CS faunas. The study highlights the importance of these GZ in marine food webs and their scarce knowledge in the region. Further long-term studies are required to understand spatiotemporal patterns and ecological roles of tunicates in Cuban ecosystems. [ABSTRACT FROM AUTHOR]

Periodic blooms of salps (pelagic tunicates) can result in high export of organic matter, leading to an outsized role in the oceans biological carbon pump (BCP). However, due to their episodic and patchy nature, salp blooms often go undetected and are rarely included in measurements or models of the BCP. We quantified salp-mediated export processes in the northeast subarctic Pacific Ocean in summer of 2018 during a bloom of Salpa aspera. Salps migrated from 300 to 750 m during the day into the upper 100 m at night. Salp fecal pellet production comprised up to 82% of the particulate organic carbon (POC) produced as fecal pellets by the entire epipelagic zooplankton community. Rapid sinking velocities of salp pellets (400-1,200 m d-1) and low microbial respiration rates on pellets (

This study characterizes the distribution of salp and doliolid species in the northeastern East China Sea during spring and autumn and identifies the factors that regulate their abundance. The data were collected over four years (2019–2023, except 2020). During the survey period, the Tsushima Warm Current Surface and Bottom (TWCS and TWCB, respectively) and Yellow Sea Cold Bottom Water were influential in spring, while the Changjiang Diluted Water, Coastal Water, TWCS, and TWCB were dominant in autumn. The mean sea surface temperature (SST) and sea surface salinity (SSS) in spring and the mean SST in autumn statistically decreased (p < 0.05), while the mean SSS in autumn statistically increased (p < 0.05). The spatial distribution of salp and doliolid species remained consistent in spring and autumn, although the dominant assemblage shifted seasonally. Spring was predominantly characterized by an abundance of salp species, whereas doliolid species were dominant in autumn, with their distribution and abundance influenced by different environmental factors such as temperature and salinity in spring and food availability in autumn. Our results provide valuable data on the factors affecting the presence of salp and doliolid species in the northeastern East China Sea. [ABSTRACT FROM AUTHOR]

Gelatinous zooplankton (GZ) biomass is an important, yet often overlooked, vector of the particulate organic matter downward export and a nutritional prey source for the mesopelagic and benthic communities. To better quantify the potential impact of their blooms on biogeochemistry and food webs, we performed decomposition and sinking experiments under two different temperature regimes, 6 and 12 °C using 260 Salpa aspera, sampled in the Northeast Pacific (48.39°–50.40°N, 126.40°–145.00°W) during May 2021. Salps sank 1312 and 1424 m day−1 on average in 6 and 12 °C, respectively. The fast sinking is common among other salp species. Salp decay was exponential and occurred ~ 1.5 times faster under warmer conditions. Comparison of the published GZ decay rates supported their strong temperature dependence (Q10 = 3.46) and revealed that S. aspera decayed slower than most GZ taxa. Carcass sinking rates were higher than previously reported for this species and slowed after a prolonged decay. Biochemical (proteins, carbohydrates, lipids) and elemental (C: carbon, N: nitrogen) compositions were determined for salps at various decomposition stages. The high water content (~ 97%) and low organic content (27.8 ± 7.1% dry weight) were typical of other thaliaceans. The high C:N ratio (6.61 ± 1.14) of S. aspera, compared to many thaliaceans, suggested that their carcasses are valuable sources of carbon beyond the euphotic zone. [ABSTRACT FROM AUTHOR]

ABSTRACT Salmonid aquaculture, a major component of the Northern European, North American, and Chilean coastal economies, is under threat from challenges to gill health, many of which originate from plankton communities. A first step toward mitigating losses is to characterize the biological drivers of poor gill health. Numerous planktonic taxa have been implicated, including toxic and siliceous microalgae, hydrozoans, and scyphozoans; however, rigorous longitudinal surveys of plankton diversity and gill health have been lacking. In the current study, we present and assess an exhaustive identification approach combining both morphological and molecular methods together with robust statistical models to identify the planktonic drivers of proliferative gill disease (PGD) and fish mortality. We undertook longitudinal evaluation at two marine aquaculture facilities on the west coast of Scotland using daily data collected during the 2021 growing season (March–October). Examining these two different sites, one sheltered and one exposed to the open sea, we identified potentially new, important, and unexpected planktonic drivers of PGD and mortality (e.g., doliolids and appendicularians) and confirmed the significance of some established threats (e.g., hydrozoans and diatoms). We also explored delayed or “lagged” effects of plankton abundances on gill health and undertook a comparison of environmental DNA (eDNA) metabarcoding and microscopy in their ability to identify and quantify planktonic species. Our data highlight the diversity of planktonic threats to salmonid aquaculture as well as the importance of using both molecular and morphological approaches to detect these. There is now an urgent need to expand systematic longitudinal molecular and morphological approaches across multiple sites and over multiple years. The resultant catalogue of main biological drivers will enable early warning systems, new treatments, and, ultimately, a sustainable platform for future salmonid aquaculture in the marine environment.

The waters of Greenland harbour a high species richness and biomass of gelatinous zooplankton (GZP); however, their role in the diet of the many fish species, including commercially exploited species, has not yet been verified. Traditionally, GZP was considered to be a trophic dead end, i.e. with a limited contribution as prey for higher trophic levels. We applied DNA metabarcoding of two gene fragments (COI, 18S V1–V2) to the stomach contents of seven pelagic and demersal fish species in Greenland waters, to identify their prey composition as well as the occurrence of GZP predation. We detected GZP DNA reads in the stomachs of all investigated fish species, with frequency of occurrences ranging from 12.5% (for Melanogrammus aeglefinus) to 50% (for Argentina silus). GZP predation had not yet been reported for several of these species. GZP were found to majorly contribute to the diet of A. silus and Anarhichas denticulatus, particularly, the siphonophore Nanomia cara and the scyphozoan Atolla were of a high importance as prey, respectively. The use of multiple genetic markers enabled us to detect a total of 59 GZP taxa in the fish stomachs with several GZP species being detected only by one of the markers.

The article explores the presence of yellow tails in Iasis cylindrica colonies, suggesting the existence of specialized zooid types within salp colonies. This phenomenon, known as colonial polymorphism, has been observed in other marine invertebrates but not in salps. The article describes the anatomy and characteristics of the yellow zooids, called lepidozooids, and proposes that they may function as a decoy to distract predators. The study emphasizes the importance of direct observation and in situ fieldwork in uncovering new aspects of salp natural history, including the discovery of a pigmented defense mechanism called a lepidosome in I. cylindrica. The text also mentions the widespread presence of pigmentation in salps and its potential role in interactions with predators and symbionts. [Extracted from the article]

Introduction: Currently, Arctic marine ecosystems are witnessing the most rapid physical changes worldwide, leading to shifts in pelagic and benthic communities and food web structure, concomitant with the introduction of boreal species. Gelatinous zooplankton or jellyfish represent one particular group of which several boreal species are prone to undergo significant poleward range expansions and population increases in the Arctic in the course of the ongoing changes. Historically, jellyfish were considered a trophic dead-end, but an increasing number of studies using modern tools have highlighted their role as major prey items in marine food webs. In this study, we aimed to verify the role of jellyfish and other metazoans as food sources in the Arctic polar night food web, when pelagic resources are limited. Methods: We identified the diet of different bentho-pelagic amphipod species in the Atlantifying Kongsfjorden (West Svalbard) during the polar night. We regularly sampled lysianassoid and gammarid amphipods using baited traps and hand nets over a period of one month during the polar night and identified their diet spectrum by applying DNA metabarcoding (COI) to their stomach contents. Results: We demonstrate that all investigated species are omnivorous. Fish species including polar cod and snailfish, likely in the shape of carrion, played an important role in the diet of the scavengers Orchomenella minuta and Anonyx sarsi. Predation and potential scavenging on jellyfish contributed to the diet of all four investigated species, particularly for the species Gammarus setosus and G. oceanicus, as evidenced by high read abundances and high frequencies of occurrence. Besides jellyfish, crustaceans and macroalgae were important components of the diet of the two Gammarus species. Discussion: The diverse jellyfish community present in Kongsfjorden in the polar night is clearly being utilized as a food source, either through pelagic feeding or feeding on jelly-falls, albeit to a different extent in the local amphipod community. These findings provide novel insights into the Arctic food web during the polar night and represent the first evidence of feeding on natural (non-experimental) jelly-falls. [ABSTRACT FROM AUTHOR]

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 COBALTThe fast‐sinking detritus increased carbon sequestration and transfer efficiency to depth, but decreased surface productivity and exportFast‐sinking detritus decreased the size of oxygen minimum zones (OMZs) and water column denitrification, a common model bias [ABSTRACT FROM AUTHOR]

Gelatinous zooplankton are increasingly recognized to play a key role in the ocean's biological carbon pump. Appendicularians, a class of pelagic tunicates, are among the most abundant gelatinous plankton in the ocean, but it is an open question how their contribution to carbon export might change in the future. Here, we conducted an experiment with large volume in situ mesocosms (~55–60 m3 and 21 m depth) to investigate how ocean acidification (OA) extreme events affect food web structure and carbon export in a natural plankton community, particularly focusing on the keystone species Oikopleura dioica, a globally abundant appendicularian. We found a profound influence of O. dioica on vertical carbon fluxes, particularly during a short but intense bloom period in the high CO2 treatment, during which carbon export was 42%–64% higher than under ambient conditions. This elevated flux was mostly driven by an almost twofold increase in O. dioica biomass under high CO2. This rapid population increase was linked to enhanced fecundity (+20%) that likely resulted from physiological benefits of low pH conditions. The resulting competitive advantage of O. dioica resulted in enhanced grazing on phytoplankton and transfer of this consumed biomass into sinking particles. Using a simple carbon flux model for O. dioica, we estimate that high CO2 doubled the carbon flux of discarded mucous houses and fecal pellets, accounting for up to 39% of total carbon export from the ecosystem during the bloom. Considering the wide geographic distribution of O. dioica, our findings suggest that appendicularians may become an increasingly important vector of carbon export with ongoing OA. [ABSTRACT FROM AUTHOR]

Abstract Gelatinous zooplankton (GZP), i.e., ctenophores, cnidarian medusae, chaetognaths, appendicularians and salps, are considered climate change winners. This becomes particularly obvious in the Southern Ocean, which has undergone a significant shift from a krill‐based to a salp‐based ecosystem over the last decades. A better knowledge on the role of gelatinous invertebrates as prey is needed to predict the impact of such a gelatinous shift. Until recently, GZP was considered as a “trophic dead end”. However, their true importance in diets has remained unresolved due to the rapid digestion of their watery and soft tissues in predators' stomachs. In this study, we want to validate the paradigm shift from GZP being considered as “survival food” to be considered a “regular” prey item for two demersal fish species (Notothenia rossii and N. coriiceps) of Potter Cove, South Shetland Islands, using a multimarker (COI and 18S) metabarcoding approach. We found that GZP taxa commonly occurred in the diets of both species, represented by pelagic tunicates (appendicularians, salps), cnidarians, chaetognaths and ctenophores. Salps were the most abundant prey group, preyed upon by each individual of both species, reaching 98.7% relative read abundance for 18S. We recovered a wide range of different taxa in their diets, from primary producers to highly abundant invertebrates, thus the two nototheniid species can be regarded as “natural samplers” of the ecosystem in study. Finally, we want to point out the importance of multimarker metabarcoding approaches for broad ecological assessments, given the differential amplification and sequencing success of different markers for specific groups and the unequal taxonomic coverage of the reference databases. The output of each marker was highly complementary, since an important prey item such as salps, was only detected with 18S, while other taxa (e.g., Arthropoda) were represented with a higher taxonomic resolution with COI.

Ctenophores are quick responders to coastal environmental changes and play a crucial role in marine food web dynamics. We report the environmental drivers of a ctenophore swarm (Pleurobrachia spp.) and associated ecological changes in estuarine and coastal waters of the Sundarbans mangrove–estuarine complex in the northern Bay of Bengal (BoB). Plankton and fish samples were collected from estuarine and coastal waters at the peak of estuarine outflow in the northeast monsoon (NEM). Sampling locations at the estuarine mouth witnessed ctenophores (Pleurobrachia pileus and Pleurobrachia globosa) in swarming proportions. Multivariate statistical analysis revealed significant differences in hydrographical and biological properties between the swarm and non-swarm areas. The sea surface salinity, ammonium, and mesozooplankton (MSP) density were positively correlated while microzooplankton (MCZ) density was negatively correlated with the ctenophore swarm. Fish caught from swarm locations, dominated by microbial food web consisted of species of less market value, while those from the non-swarm locations, dominated by conventional plankton food web consisted mainly of commercially important species. Thus, in the first-ever record from a commercially important fishing ground in the BoB, this study provides evidence of how a ‘dead end’ plankton predator affects the plankton food web organization and fisheries in tropical coastal waters. HIGHLIGHTS Occurrence of a ctenophore swarm and its hydrobiological links investigated in the BoB.; The ctenophore swarm and non-swarm locations favoured different plankton trophic pathways.; Active ctenophore predation on copepods favoured the microbial loop in swarm locations.; Predation on swarm-forming ctenophore favoured the conventional food chain.; Ctenophore swarm negatively affected fish community composition.;

Abstract 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.

Simple Summary: Between 2019 and 2022, scientific pelagic trawl surveys in the Western Black Sea monitored the biomass of sprat and moon jellyfish and their spatial variability in the summer. Investigations into the correlation patterns between the two plankton-feeding species revealed that gelatinous plankton can have a weak-to-moderate effect on the spatial distribution of sprat assemblages in coastal areas. Over the past few decades, various causal connections between commercial small pelagic fish species and gelatinous zooplankton have been reported in the Black Sea, which affect the pelagic ecosystem. Recently, moon jellyfish regained dominance among gelatinous plankton; however, biomass fluctuations and interactions with small pelagic fish remain poorly understood. During the summers of 2019–2022, scientific pelagic trawl surveys in the Western Black Sea enabled simultaneous monitoring of small pelagic fish biomass, with sprat as the key species and moon jellyfish as an incidental catch. In total, 153 trawl hauls were conducted across four depth strata from 15 to 100 m, and a "swept area" method was used for biomass estimation. The sprat stock biomass ranged from 10,698 to 29,177 t, with an average value of 19,432 ± 4834 t. The total biomass of moon jellyfish was 2002 ± 868.73 t, and dense aggregations were observed in the coastal waters during certain years. Two scenarios of spatial interactions between planktivorous species were identified and linked to the formation of A. aurita aggregations. We found that changes in jellyfish density were associated with weak-to-moderate effects on the spatial distribution of sprat assemblages in coastal areas. [ABSTRACT FROM AUTHOR]

Scyphozoan jellyfish in Icelandic waters have received limited attention, despite apparent recent increases in blooms and changes in the regional oceanographic setting. The objectives of this study were to describe the species composition, abundance, phenology, and growth of scyphomedusae around Iceland and explore changes by comparing our findings with reports from the 1930s. Specimens were collected with a Bongo net in five regions around Iceland in the spring, summer, and autumn of 2008. Three jellyfish species were collected in the study, Aurelia aurita, followed by Cyanea capillata, and C. lamarckii. In the western and northwestern parts of Iceland, A. aurita abundance was highest in spring and summer, whereas in the North and East, abundances were highest in autumn. Cyanea capillata was not encountered in the Southwest, but in the west, Northwest, and North. There, numbers were highest in spring, whereas in the East, abundance was highest in autumn. Clockwise coastal current dispersal and regional interconnectivity are indicated. Weight-specific growth rates varied between 7.0 and 8.5% d−1 for A. aurita and 11.1 and 15.7% d−1 for C. capillata and are comparable to rates from often food-limited ecosystems at temperate latitudes. Presented evidence suggests that ephyrae and small medusae appear earlier in the season and in previously (in the 1930s) not occupied regions, while some regions (Southwest for C. capillata) were not populated anymore. [ABSTRACT FROM AUTHOR]

It is often suggested that gelatinous zooplankton may benefit from anthropogenic pressures of all kinds and in particular from climate change. Large pelagic tunicates, for example, are likely to be favored over other types of macrozooplankton due to their filter‐feeding mode, which gives them access to small preys thought to be less affected by climate change than larger preys. In this study, we provide model‐based estimate of potential community changes in macrozooplankton composition and estimate for the first time their effects on benthic food supply and on the ocean carbon cycle under two 21st‐century climate‐change scenarios. Forced with output from an Earth System Model climate projections, our ocean biogeochemical model simulates a large reduction in macrozooplankton biomass in response to anthropogenic climate change, but shows that gelatinous macrozooplankton are less affected than nongelatinous macrozooplankton, with global biomass declines estimated at −2.8% and −3.5%, respectively, for every 1°C of warming. The inclusion of gelatinous macrozooplankon in our ocean biogeochemical model has a limited effect on anthropogenic carbon uptake in the 21st century, but impacts the projected decline in particulate organic matter fluxes in the deep ocean. In subtropical oligotrophic gyres, where gelatinous zooplankton dominate macrozooplankton, the decline in the amount of organic matter reaching the seafloor is reduced by a factor of 2 when gelatinous macrozooplankton are considered (−17.5% vs. −29.7% when gelatinous macrozooplankton are not considered, all for 2100 under RCP8.5). The shift to gelatinous macrozooplankton in the future ocean therefore buffers the decline in deep carbon fluxes and should be taken into account when assessing potential changes in deep carbon storage and the risks that deep ecosystems may face when confronted with a decline in their food source. [ABSTRACT FROM AUTHOR]

H.G. Moser was not particularly well known regarding the Elopomorpha, but he began his seminal 1981 fish larvae morphology review by describing the mysteries of European eels and their leptocephali, and he eventually described some California Current leptocephali. Descriptions of all types of leptocephali and then microscope photographs have revealed complex pigmentation patterns and diverse body shapes that parallel the features of the other teleost fish larvae that his review showed so clearly, some of which appear to mimic gelatinous zooplankton (GZ). Most recently, underwater photographs and video of leptocephali indicate that predator avoidance through transparency, shape-change-mediated mimicry, or morphological features have evolved in response to natural selection from predation in ways generally similar to other fish larvae. Several families of leptocephali perform remarkable curling into round or flattened shapes or use expandable chromatophores when threatened, which appears to mimic GZ for predation reduction. Like a number of other teleost fish larvae, some leptocephali have body extensions or telescopic eyes, and at least one has a long caudal filament with pigmented swellings that is similar to the remarkable GZ mimicry appendages of some fish larvae. The morphology and use of mimicry of leptocephali in comparison to other fish larvae is reviewed as a tribute to H.G. Moser's remarkable career. [ABSTRACT FROM AUTHOR]

We investigated long-term changes in the abundance and species composition of hyperiid amphipods in the Southern California Bight and nearby waters from twelve springime CalCOFI cruises spanning the period 1951-1997. Sixty-two hyperiid species were detected in the study region. We found dimunition in species diversity and in total hyperiid abundance during the studied period. Despite high interannual variability, there was higher species richness, evenness of species numbers, and abundances of hyperiids in an earlier time period (1951 to 1972) and generally lower species richness, evenness, and abundances in a more recent time period (1979 to 1997). Variations in abundance of total hyperiids were significantly correlated with variations in abundance of presumed gelatinous zooplankton hosts, especially salps, physonect siphonophores, and pyrosomes. Species-specific correlations showed significant associations between ten species of hyperiids and different species of salps, siphonphores, and medusae. Some amphipods were correlated with more than one host. Hyperiid amphipod assemblages appear to be sensitive to large-scale climate changes in the NE Pacific, through either direct responses or indirectly through their association as parasitoids on gelatinous hosts.

This study characterizes the distribution of salp and doliolid species in the northeastern East China Sea during spring and autumn and identifies the factors that regulate their abundance. The data were collected over four years (2019–2023, except 2020). During the survey period, the Tsushima Warm Current Surface and Bottom (TWCS and TWCB, respectively) and Yellow Sea Cold Bottom Water were influential in spring, while the Changjiang Diluted Water, Coastal Water, TWCS, and TWCB were dominant in autumn. The mean sea surface temperature (SST) and sea surface salinity (SSS) in spring and the mean SST in autumn statistically decreased (p < 0.05), while the mean SSS in autumn statistically increased (p < 0.05). The spatial distribution of salp and doliolid species remained consistent in spring and autumn, although the dominant assemblage shifted seasonally. Spring was predominantly characterized by an abundance of salp species, whereas doliolid species were dominant in autumn, with their distribution and abundance influenced by different environmental factors such as temperature and salinity in spring and food availability in autumn. Our results provide valuable data on the factors affecting the presence of salp and doliolid species in the northeastern East China Sea.

A four-decade data of jellyfish aggregation from 1980 to 2020 were taken to discern whether there has been an actual rise in jellyfish swarm in Indian coastal and estuarine waters. Despite frequent jellyfish aggregations and beach strandings in Indian waters, jellyfish aggregations have been poorly investigated and there is a dearth of information on the swarm-forming jellyfish, their preferred season, and the location of swarming. Therefore, our review aims to account for the frequency of swarming phenomenon annually and the appearance of new swarm-forming jellyfish species. The term ‘jellyfish’ refers to the medusae stage of phylum Cnidaria (Cubozoa, Hydrozoa, and Scyphozoa) only in this review. The present work postulates a geospatial spread and swarm-forming jellyfish species to increase in recent times. More than 23 coastal locations of India have witnessed jellyfish aggregations and beach stranding in the last four decades. Seasonal oceanographic conditions prevailing during the summer monsoon, fall, and early winter promoted jellyfish aggregations and swarming. Only two jellyfish species were known to form aggregates during 1981–1990, but the diversity of jellyfish species increased to nine by 2011–2020. The development of predictive models from remote sensing data can be useful to warn humans and coastal industries of the approaching swarm. HIGHLIGHTS Geospatial spread, frequency of jellyfish swarms, and the number of swarm-forming species increased in the coastal and estuarine waters of India.; More than 23 locations along the coast of India have witnessed jellyfish aggregations, swarms, and beach stranding in the last four decades.; Seasonal oceanographic conditions during the summer monsoon, fall, and early winter promote jellyfish aggregations.;

Salp grazing is important in shaping planktonic food-web structure. However, little is known about the size ranges of their prey in the field or how grazing impacts size structure. This study investigated the feeding habits of seven different species of salps, representing a variety of sizes and life stages across subtropical and subantarctic waters east of New Zealand. Scanning electron microscopy was used to examine the gut contents of 58 salps, which were then compared to water column plankton communities characterized via epifluorescence microscopy, FlowCam, and flow cytometry. While most of the gut contents resembled ambient waters, substantial differences were found amongst some co-occurring species, such as increased retention of submicron bacteria amongst smaller salps like Thalia democratica. We found that even for those salps capable of feeding on bacteria efficiently, nanoplankton and small microplankton still made up the majority of gut biomass. Larger microplankton were rarer in the guts than in the water column, potentially suggesting an upper size-threshold in addition to the lower size-threshold that has been the focus of most previous work. Salp carbon-weighted predator to prey size ratios were variable, with the majority falling between 1000:1 and 10,000:1 depending largely on the size of the salp. Taken together our results indicate that despite being able to feed on submicron particles, picoplankton make up at most 26.4% (mean = 6.4%) of salp gut carbon and are relatively unimportant to the energetics of most salps in this region compared to nanoplankton such as small dinoflagellates and diatoms. [ABSTRACT FROM AUTHOR]

The production of plastics has exponentially increased over time such that the observation of microplastics in the oceans has become a major concern given how frequently these particles and marine biota may interact. Microplastics can be ingested by diverse species, including invertebrates, which can lead to physical damage due to their small size and potentially chemical damage related to the ingestion of monomers, polymeric additives, or adsorbed chemicals. This study reports on the first evidence of microplastics in Mnemiopsis leidyi. Microplastics were described by type, quantified, and had their chemical composition identified. In total, 328 samples of microplastic (MP) candidates were observed: blue fibers were the most abundant, followed by black, red, and green fibers as well as blue fragments. Three types of microplastics were chemically identified as polyurethane, unplasticized polyvinylchloride, and polyethylene polylauryllactam. Overall, this study demonstrated that Mnemiopsis leidyi have the capacity to incorporate microplastics. Although more studies are needed, Mnemiopsis leidyi is relatively abundant on the Atlantic coast and should be recommended for use as a bioindicator for microplastics. [ABSTRACT FROM AUTHOR]

Despite their abundance in marine ecosystems, studies on siphonophores are limited. In this study, 26 species of siphonophores in the Northwest Pacific Ocean were identified during multiple cruises of the R/V ISABU from 2018–2020, and various factors that may affect the occurrence of siphonophores, including water temperature, salinity, zooplankton biomass, and trophic niche were investigated. Statistical analysis revealed that the distribution of siphonophores and their biomass could be divided into two water mass groups, affected by the Kuroshio and Oyashio Currents. The species with high contributions to distinguishing the water mass groups (including Chelophyes contorta, Dimophyes arctica, Bassia bassensis, and Eudoxoides spiralis—mainly belonging to the Diphyidae) showed species-specific correlations with water temperature and salinity. This suggests that diphyids can be used as indicator species for currents and hydrological factors that influence water mass. The biomass of siphonophores exhibited a trend opposite to that of non-gelatinous zooplankton and showed no association with other gelatinous zooplankton. These results can be interpreted from an ecological niche perspective. Through nitrogen and carbon stable isotope analyses, the dietary sources of siphonophores could potentially overlap with those of chaetognaths or non-gelatinous zooplankton. Because the trophic position of siphonophores (2.4–3.2) also falls in the range of those of chaetognaths (2.8–3.4) and non-gelatinous zooplankton including copepods, euphausiids, and amphipods (2.4–3.5), diet competition with carnivorous mesozooplankton could be predicted. Considering that the diversity and biomass of most siphonophores are strongly positively correlated with water temperature and salinity, expansion of the Kuroshio Current is expected to lead to an increase in siphonophores in the Northwest Pacific in the future. The findings of this study are anticipated to provide novel insights into climate change prediction and response and enhance our understanding of siphonophore communities.

Global warming causes profound environmental shifts in the Arctic Ocean, altering the composition and structure of communities. In the Fram Strait, a transitional zone between the North-Atlantic and Arctic Ocean, climate change effects are particularly pronounced and accelerated due to an increased inflow of warm Atlantic water. Gelatinous zooplankton are known as key predators, consuming a great variety of prey and playing an important role in marine ecosystems. Insufficient knowledge of how gelatinous zooplankton are affected by environmental change has resulted in a notable gap in the understanding of the future state of Arctic ecosystems. We analyzed the diversity and abundance of gelatinous zooplankton down to 2600 m depth and established the first regional baseline dataset using optical observations obtained by the towed underwater camera system PELAGIOS (Pelagic In situ Observation System). Our data estimate the abundance of 20 taxa of gelatinous zooplankton. The most abundant taxa belong to the family of Rhopalonematidae, mainly consisting of Aglantha digitale and Sminthea arctica, and the suborder Physonectae. Using the observational data, we employed a joint species distribution modelling approach to better understand their distributional patterns. Variance partitioning over the explanatory variables showed that depth and temperature explained a substantial amount of variation for most of the taxa, suggesting that these parameters drive diversity and distribution. Spatial distribution modelling revealed that the highest abundance and diversity of jellyfish are expected in the marginal sea-ice zones. By coupling the model with climate scenarios of environmental changes, we were able to project potential changes in the spatial distribution and composition of gelatinous communities from 2020 to 2050 (during the summer season). The near-future projections confirmed that with further temperature increases, gelatinous zooplankton communities in the Fram Strait would become less diverse but more abundant. Among taxa of the Rhopalonematidae family, the abundance of Aglantha digitale in the entire water column would increase by 2%, while a loss of up to 60% is to be expected for Sminthea arctica by 2050. The combination of in situ observations and species distribution modelling shows promise as a tool for predicting gelatinous zooplankton community shifts in a changing ocean.

The production of plastics has exponentially increased over time such that the observation of microplastics in the oceans has become a major concern given how frequently these particles and marine biota may interact. Microplastics can be ingested by diverse species, including invertebrates, which can lead to physical damage due to their small size and potentially chemical damage related to the ingestion of monomers, polymeric additives, or adsorbed chemicals. This study reports on the first evidence of microplastics in Mnemiopsis leidyi. Microplastics were described by type, quantified, and had their chemical composition identified. In total, 328 samples of microplastic (MP) candidates were observed: blue fibers were the most abundant, followed by black, red, and green fibers as well as blue fragments. Three types of microplastics were chemically identified as polyurethane, unplasticized polyvinylchloride, and polyethylene polylauryllactam. Overall, this study demonstrated that Mnemiopsis leidyi have the capacity to incorporate microplastics. Although more studies are needed, Mnemiopsis leidyi is relatively abundant on the Atlantic coast and should be recommended for use as a bioindicator for microplastics.

The freshwater hydrozoan Craspedacusta sowerbii was introduced to habitats around the world and they spread into the surrounding water bodies thereafter. Despite an increase in reported observations, little is known about its genetics, physiology and ecology. The present study examined the organic content, elemental composition and energy content of jellyfish collected in Canada and the USA and compared these metrics with their marine counterparts and other co-occurring zooplankton. Specimens from the sampled lakes were sexed and molecularly characterized. Molecular, stoichiometric and energetic information is critical in determining distribution pathways and trophic connections. Molecular analyses showed two closely related sequences in North America, one shared by the Canadian and Japanese specimens, while another one is widely present across the Americas. Organic and all elemental contents were higher compared to marine jellyfish species. Estimated energy content of C. sowerbii was 20–27 kJ g DW−1, which is 2-fold higher than for marine hydrozoans and compared well with cladocerans, copepods and rotifers. Estimated C/P values indicated that cladocerans and copepods are suitable prey for C. sowerbii and that jellyfish may compete with juvenile fish to fulfill similar nutrient demands. Freshwater jellyfish were stoichiometrically and energetically different from marine hydrozoans, indicating higher importance in freshwater food webs than previously thought. [ABSTRACT FROM AUTHOR]

The complex distribution of gelatinous zooplankton at the shelf and open ocean of the Southwestern Atlantic Ocean (31°-38°S) was closely linked to the prevailing water masses. Species composition differed significantly between subtropical and subantarctic assemblages in both neritic and oceanic environments. Diversity was lower in neritic and Malvinas assemblages but higher to the north of the Brazil-Malvinas Confluence. The influence of the Brazil Current was evident through the dominance of warm-water species such as Flaccisagitta enflata, Fl. hexaptera, Pterosagitta draco, Pseudosagitta lyra , and Salpa fusiformis , which displayed the highest abundances and different maturity stages north of the Confluence. The cold-waters originating from subantarctic regions were indicated by the presence of Ps. gazellae, Eukrhonia hamata, and Serratosagitta tasmanica , which showed higher abundances and the co-occurrence of different maturity stages south of the Confluence. The spread of low-salinity water into oceanic stations was indicated by the presence of species such as Parasagitta friderici and Pa. tenuis , which are typically found in neritic waters with low salinity. The coexistence of typical species from both warm- and cold-waters at oceanic stations in the Confluence section reflects the complex oceanographic structure of one of the most intense open-ocean fronts in the world ocean. [Display omitted] • Species groups differed in subtropical, subantarctic, neritic and oceanic domains. • Population dynamics of salps and chaetognaths species is linked to cold- or warm-water. • Low-salinity tolerant species beyond shelf break indicate presence of freshwaters. • Warm- and cold-water species coexistence reflects a complex hydrographic structure. [ABSTRACT FROM AUTHOR]

Over the past few decades, various causal connections between commercial small pelagic fish species and gelatinous zooplankton have been reported in the Black Sea, which affect the pelagic ecosystem. Recently, moon jellyfish regained dominance among gelatinous plankton; however, biomass fluctuations and interactions with small pelagic fish remain poorly understood. During the summers of 2019–2022, scientific pelagic trawl surveys in the Western Black Sea enabled simultaneous monitoring of small pelagic fish biomass, with sprat as the key species and moon jellyfish as an incidental catch. In total, 153 trawl hauls were conducted across four depth strata from 15 to 100 m, and a “swept area” method was used for biomass estimation. The sprat stock biomass ranged from 10,698 to 29,177 t, with an average value of 19,432 ± 4834 t. The total biomass of moon jellyfish was 2002 ± 868.73 t, and dense aggregations were observed in the coastal waters during certain years. Two scenarios of spatial interactions between planktivorous species were identified and linked to the formation of A. aurita aggregations. We found that changes in jellyfish density were associated with weak-to-moderate effects on the spatial distribution of sprat assemblages in coastal areas.

Porpita porpita occurs in the tropical and sub-tropical waters of the Pacific, Atlantic, and Indian Oceans, and the mass numbers of stranded colonies seem to be increasing. Although its presence in Indian waters is minimal, this is the first record ever made of P. porpita in Visakhapatnam coastal waters. The present study provided a detailed description of the species and its global distribution. Further, the perceived increase in gelatinous zooplankton blooms in the observed area indicates that jellyfish can negatively affect fisheries because they compete with zooplanktivorous fish, prey upon fish eggs and larvae, and indirectly compete with higher trophic levels by reducing the plankton available to planktivores. Conversely, jellyfishes also play a vital role in regulating global marine plankton food webs, spatio-temporal dynamics, and biomass, which is a role that has been generally neglected so far.

In western boundary current systems, strong currents transport oligotrophic oceanic waters towards the coast. Thaliaceans may have an advantage in these systems due their ability to filter small particles such as the bacterioplankton, typically responsible for the primary production in oligotrophic waters. Here, we evaluated the structure of the thaliacean community present in the tropical South Atlantic Ocean western boundary current system to test the hypothesis that species distribution and abundance are structured by the circulation and thermohaline features. For that purpose, we used data collected though 40 mm mesopelagic trawls above the slope and around oceanic seamounts and islands. Results reveal distinct patterns in the thaliacean community structure. Over the continental slope, under the influence of the strong North Brazilian Undercurrent, Pyrosoma atlanticum was highly abundant. Soestia zonaria was also present but in a lesser amount. Offshore, around oceanic islands and Seamounts under the influence of the central branch of South Equatorial Current, Doliolida spp. were the dominant thaliacean, co-occurring with P. atlanticum in lower abundance. Mesh selectivity is a potential drawback in these results since the coarse aperture may have lost smaller species and early life stages. [ABSTRACT FROM AUTHOR]

The two congeneric hyperiids Themisto libellula and T. abyssorum provide an important trophic link between lower and higher trophic levels in the rapidly changing Arctic marine ecosystem. These amphipods are characterized by distinct hydrographic affinities and are hence anticipated to be impacted differently by environmental changes, with major consequences for the Arctic food web. In this study, we applied DNA metabarcoding to the stomach contents of these Themisto species, to comprehensively reveal their prey spectra at an unprecedented-high-taxonomic-resolution and assess the regional variation in their diet across the Fram Strait. Both species feed on a wide variety of prey but their diet strongly differed in the investigated summer season, showing overlap for only a few prey taxa, such as calanoid copepods. The spatially structured prey field of T. libellula clearly differentiated it from T. abyssorum, of which the diet was mainly dominated by chaetognaths. Our approach also allowed the detection of previously overlooked prey in the diet of T. libellula, such as fish species and gelatinous zooplankton. We discuss the reasons for the differences in prey spectra and which consequences these may have in the light of ongoing environmental changes. [ABSTRACT FROM AUTHOR]

This study investigates the role of winter oceanographic conditions on the horizontal and vertical spatial structure of Pyrosoma atlanticum at different ontogenetic stages. Data were obtained on two oceanographic cruises (February 2017 and 2018) in the NW Mediterranean. Small colonies were exceptionally abundant in 2017, linked to an earlier development of spring conditions and the subsequent seasonal phytoplankton bloom. The mesoscale distribution of P. atlanticum differed depending on the colony size. Large colonies (≥7 mm) were found on the slope all along the density front, whereas small (<4 mm) and medium colonies (4–6.9 mm) extended their distribution over the shelf because of instabilities of the front, and were mostly absent in the cold, low-salinity coastal waters. The analysis of their vertical distribution showed that at night colonies of all sizes remained close to the surface, where chlorophyll- a levels were high, whereas during the day they migrated to deeper layers, reaching greater depths as the colony size increased. The migratory behaviour started when colonies were 4–6.9 mm long. The relative importance of the species in the downward carbon transport is discussed. Our results highlight the need to further study the ecology of this efficient filter feeder in the Mediterranean. [ABSTRACT FROM AUTHOR]

Background. Gelatinous zooplankton in epipelagic environments often have highly transparent bodies to avoid detection by their visual predators and prey; however, the digestive systems are often exceptionally opaque even in these organisms. In a holoplanktonic gastropod, Pterotrachea coronata, the visceral nucleus is an opaque organ located at the posterior end of its alimentary system, but this organ has a mirrored surface to conceal its internal opaque tissue. Results. Our ultrastructural observation proved that the cortex of the visceral nucleus comprised a stack of thin cellular lamellae forming a Bragg reflector, and the thickness of lamellae (0.16 mm in average) and the spaces between the lamellae (0.1 mm in average) tended to become thinner toward inner lamellae. Based on the measured values, we built virtual models of the multilamellar layer comprising 50 lamellae and spaces, and the light reflection on the models was calculated using rigorous coupled wave analysis to evaluate their properties as reflectors. Our simulation supported the idea that the layer is a reflective tissue, and the thickness of the lamella/space must be chirped to reflect sunlight as white/silver light, mostly independent of the angle of incidence. Conclusions. In P. coronata, the cortex of the visceral nucleus comprised multicellular lamellae that form a chirped Bragg reflector. It is distinct in structure from the intracellular Bragg structures of common iridophores. This novel Bragg reflector demonstrates the diversity and convergent evolution of reflective tissue using reflectinlike proteins in Mollusca. [ABSTRACT FROM AUTHOR]

We surveyed the epipelagic cnidarian fauna from the Western Equatorial Atlantic Ocean. A characteristic feature in this area is the freshwater discharge of the Amazon River, the largest continental inflow in the world’s oceans. We analyzed 87 plankton and 90 neuston samples collected at the neritic and oceanic provinces of the Western Tropical Atlantic under the influence of the Amazon River Plume off the north coast of Brazil. We studied 34,772 organisms corresponding to 7 orders, 31 families, and 93 species. Among them, Forskalia tholoides was a new record to the coast off South America, and 20 taxa were new regional records. Species accumulation curves and diversity estimators did not reach an asymptote and clearly suggested the occurrence of a considerably higher number of species. Sampling in different seasons, with different gears, and including deeper waters certainly will further increase the number of known pelagic cnidarian species in the area. Open ocean had higher diversity than the continental shelf, both for holoplanktonic and some meroplanktonic taxa. This trend can be related to complex circulation and topography. In conclusion, we observed high diversity in the epipelagic cnidarian community. The heterogeneity of habitats in the area is likely the main factor responsible for the high biodiversity, with samples from estuarine, coastal, neritic (with a large reef system), and oceanic waters. The wide salinity range caused by the Amazon River Plume and other oceanographic mesoscale processes such as eddies and opposite currents add further complexity to the environment. [ABSTRACT FROM AUTHOR]

This data article includes a qualitative and quantitative description of the gelatinous macrozooplankton community of the North Sea during January-February 2021. Sampling was conducted during the 1st quarter International Bottom Trawl Survey (IBTS) on board the Danish R/V DANA (DTU Aqua Denmark) and the Swedish R/V Svea (SLU Sweden), as part of the ichthyoplankton investigation during night-time. A total of 147 stations were investigated in the western, central and eastern North Sea as well as the Skagerrak and Kattegat. Sampling was conducted with a 13 m long Midwater Ring Net (MIK net, Ø 2 m, mesh size 1.6 mm, cod end with smaller mesh size of 500 µm), equipped with a flow meter. The MIK net was deployed in double oblique hauls from the surface to c. 5 m above the sea floor [1,2]. Samples were visually analysed unpreserved on a light table and/or with a stereomicroscope or magnifying lamp within 2 hours after catch. A total of 13,510 individuals were counted/sized. Twelve gelatinous macrozooplankton species or genera were encountered, namely the hydrozoan Aequorea vitrina, Aglantha digitale, Clytia spp., Leuckartiara octona, Tima bairdii, Muggiaea atlantica; the scyphozoans Cyanea capillata and Cyanea lamarckii and the ctenophores Beroe spp., Bolinopsis infundibulum, Mnemiopsis leidyi, Pleurobrachia pileus. Abundance data are presented on a volume specific (m−3) and area specific (m−2) basis. Size data have been used to estimate wet weights based on published length-weight regressions (see Table 1). For the groups i) hydrozoan jellyfish, ii) scyphozoan jellyfish, iii) ctenophores, as well as iv) grouped gelatinous macrozooplankton, spatial weight specific distribution patterns are presented. This unpublished dataset contributes baseline information about the gelatinous macrozooplankton diversity and its specific distribution patterns in the extended North Sea area during winter (January-February) 2021. These data can be an important contribution to address global change impacts on marine systems, especially considering gelatinous macrozooplankton abundance changes in relation to anthropogenic stressors.

Southern Ocean ecosystems are currently experiencing increased environmental changes and anthropogenic pressures, urging scientists to report on their biodiversity and biogeography. One major marine taxonomically diverse and trophically important group that has, however, stayed largely understudied until now is the gelatinous zooplankton, including cnidarians, ctenophores and tunicates. This data scarcity is predominantly due to many of these fragile, soft-bodied organisms being easily fragmented and/or destroyed with traditional net sampling methods. Progress in alternative survey methods including, for instance, optics-based methods is slowly starting to overcome these obstacles. As video annotation by human observers is both time-consuming and financially costly, machine learning techniques should be developed for the analysis of in-situ image-based datasets. This requires taxonomically accurate training sets for correct species identification and the present paper is the first to provide such data.In this study, we twice conducted three week-long in situ optics-based surveys of gelatinous zooplankton found under the ice in the McMurdo Sound, Antarctica. Our study constitutes the first optics-based survey of gelatinous zooplankton in the Ross Sea and the first study to use in situ observations to describe taxonomic, trophic, and behavioral characteristics of gelatinous zooplankton from the Southern Ocean. Despite the small geographic and temporal scales of our study, we provided new undescribed morphological traits for all observed gelatinous zooplankton species (eight cnidarian and four ctenophore species). Three ctenophores and one leptomedusa likely represent undescribed species. Furthermore, along with the photography and videography, we prepared a Common Objects in Context (COCO) dataset, so that this study is the first to provide a taxonomist-ratified image training set for future machine learning algorithm development concerning Southern Ocean gelatinous zooplankton species.

The jellyfish Pelagia noctiluca form extensive aggregations in the Mediterranean Sea that can exert top-down control on prey and cause mass-mortalities in fish farms. The description of extensive aggregations of P. noctiluca in the northeast Atlantic in 2007 coupled with a subsequent mortality event of farmed salmon in Northern Ireland prompted further investigation of the species in this region. We collected standardised P. noctiluca biomass from 1938 fisheries trawls over 11 years (2008–2018) covering ∼200,000 km2 of northeast Atlantic shelf seas. While a linear trend in P. noctiluca was not identified, the mean annual biomass exhibited significant fluctuations, with particularly elevated levels in 2009, 2013, 2014 and 2016 (0.05, 0.02, 0.01 and 0.02 kg ha−1, respectively). Mean biomass was higher in the northern (0.028 kg ha−1) and western portions (0.005 kg ha−1) of the study area compared to the southwestern (0.003 kg ha−1) and southeastern portions (0.001 kg ha−1). A binomial generalised linear mixed model of P. noctiluca biomass data indicated that higher P. noctiluca occurrence was driven by a positive Eastern Atlantic Pattern index (strongest effect), south-easterly winds, a negative North Atlantic Oscillation index and lower sea-surface temperatures (weakest effect). The fixed effects accounted for 36.81% of the variance in P. noctiluca occurrence data, while a random year effect further explained an additional 24.06% of the variance. These conditions may destabilise the European Slope Current in autumn-winter which promotes the transport of P. noctiluca from oceanic sources onto the northeast Atlantic shelf. Our findings represent a dramatic shift in our understanding of this species in the northeast Atlantic which may have significant ecological impacts, from predation on fish eggs and larvae to providing food for oceanic sunfish. • Pelagia noctiluca can form extensive aggregations in the northeast Atlantic. • Extensive aggregations covering∼40,000 km2 were found in 8 of 11 years. • P. noctiluca are more common to northeast Atlantic waters than previously thought. • P. noctiluca presence here is driven by hydroclimatic indices and wind patterns. • Ecological impacts include predation on fish eggs and food for ocean sunfish. [ABSTRACT FROM AUTHOR]

The present study described the spatial patterns of the medusae assemblages in the southern Gulf of Mexico during the dry season of 2016 (May–June). The assemblages, defined based on Bray–Curtis similarity index, were described in terms of species composition, abundances, diversity, dominance, and the hydro-biological characterization of each of them. A total of 42 species were identified (40 Hydrozoa and 2 Scyphozoa), of which, 21.43% correspond to holoplanktonic specimens and 78.57% were meroplanktonic. The hydromedusae species Aglaura hemistoma (Trachymedusae) and Liriope tetraphylla (Limnomedusae) were the most frequent and abundant, accounting for 63.51% of the total abundances. Three groups of sampling stations with faunal affinity were identified, which showed different hydrological intervals and abundances of zooplankton groups (food availability), suggesting the existence of three communities composed of medusae species with affinity to the environmental parameters of each assemblage. With this regional characterization, A. hemistoma was the dominant species in the Yucatán shelf, L. tetraphylla in southern Campeche Bank, while L. tetraphylla and Nausithoe punctata (Coronatae) were dominant in the Veracruz shelf and the oceanic zone of the study area. The dominance of L. tetraphylla and A. hemistoma can be understood as the result of different adaptive aspects, such as the plasticity of the holoplanktonic condition of these species, the different feeding strategies, and trophic spectrum, which allows them to adapt to environmental variability in each one of these regions (e.g., high temperatures, salinities) and feed of a particular food source without competing among them. [ABSTRACT FROM AUTHOR]

Our perception of deep-sea communities has evolved as various sampling approaches have captured different components of deep-sea habitats. We sampled midwater zooplankton assemblages in Monterey Bay, California to quantify community composition (abundance and biomass) and biodiversity (at the Order level) across three depth ranges, and the effects of sampling methodology on community parameters. We collected zooplankton using two types of opening-closing trawls [Tucker Trawl and Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS)] and video recordings from a remotely operated vehicle (ROV). We quantified the relative contributions of microbes to community biomass using synoptic water-bottle casts and flow cytometry. Overall, the pelagic community was most similar between the Tucker trawl and ROV (dissimilarity = 52.4%) and least similar between the MOCNESS and ROV (dissimilarity = 65.8%). Dissimilarity between sampling methods was driven by the relative abundances of crustaceans and gelatinous taxa, where gelatinous animals (cnidarians, ctenophores, tunicates) were more abundant in ROV surveys (64.2%) and Tucker trawls (46.8%) compared to MOCNESS samples (14.5%). ROV surveys were the only method that sufficiently documented the most physically delicate taxa (e.g., physonect siphonophores, lobate ctenophores, and larvaceans). Biomass was also one order of magnitude lower in MOCNESS trawls compared to Tucker trawls. Due to these large differences, the relative contributions of microbes to total biomass were substantially lower in Tucker trawl samples (mean = 7.5%) compared to MOCNESS samples (mean = 51%). These results illustrate that our view of planktonic composition and community biomass is strongly dependent on sampling methodology.

Jellyfish are the best-known group of gelatinous zooplankton; they refer to organisms from the phylum Cnidaria, including animals with cnidocytes (stinging cells). As part of our research on jellyfish that swarm in the bay of Al Hoceima conducted during the period (2021-2022), a study of the diversity of species of jellyfish in the bay has proved to be of paramount importance because of the risks associated with their proliferation, especially in summer periods. The species composition and frequency of occurrence of the jellyfish community in Al Hoceima Bay (The northern coast of Morocco) were studied during two seasons, summer 2021 and winter 2022. Zooplankton sampling was conducted within the epileptic layer (between 0 and 80 m) at 9 stations. A total of 9 species of Hydromedusae and Scyphomedusae were identified in the study area. The populations of Hydromedusae are represented by Trchymedusae (4 species), Anthomedusae (2 species), and Leptomedusae (one species). The Trachymedusa Aglaura hemistoma was widely distributed in the bay, as it was found in six sampling stations, with a frequency of occurrence Fi>66% during the summer period. The Antomedusae Pantachogon militare was inventoried for the first time in the southwestern Mediterranean Sea.The population of Scyphomedusae is represented by two species, Pelagia noctiluca and Rhizostoma Pulmo, both species showed dense aggregations in the Bay during the summer of 2022.

The waters of Greenland harbour a high species richness and biomass of gelatinous zooplankton (GZP); however, their role in the diet of the many fish species, including commercially exploited species, has not yet been verified. Traditionally, GZP was considered to be a trophic dead end, i.e. with a limited contribution as prey for higher trophic levels. We applied DNA metabarcoding of two gene fragments (COI, 18S V1-V2) to the stomach contents of seven pelagic and demersal fish species in Greenland waters, to identify their prey composition as well as the occurrence of GZP predation. We detected GZP DNA reads in the stomachs of all investigated fish species, with frequency of occurrences ranging from 12.5% (for Melanogrammus aeglefinus ) to 50% (for Argentina silus ). GZP predation had not yet been reported for several of these species. GZP were found to majorly contribute to the diet of A. silus and Anarhichas denticulatus , particularly, the siphonophore Nanomia cara and the scyphozoan Atolla were of a high importance as prey, respectively. The use of multiple genetic markers enabled us to detect a total of 59 GZP taxa in the fish stomachs with several GZP species being detected only by one of the markers., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

Invasion rates have increased in the past 100 y irrespective of international conventions. What characterizes a successful invasion event? And how does genetic diversity translate into invasion success? Employing a whole-genome perspective using one of the most successful marine invasive species world-wide as a model, we resolve temporal invasion dynamics during independent invasion events in Eurasia. We reveal complex regionally independent invasion histories including cases of recurrent translocations, time-limited translocations, and stepping-stone range expansions with severe bottlenecks within the same species. Irrespective of these different invasion dynamics, which lead to contrasting patterns of genetic diversity, all nonindigenous populations are similarly successful. This illustrates that genetic diversity, per se, is not necessarily the driving force behind invasion success. Other factors such as propagule pressure and repeated introductions are an important contribution to facilitate successful invasions. This calls into question the dominant paradigm of the genetic paradox of invasions, i.e., the successful establishment of nonindigenous populations with low levels of genetic diversity. [ABSTRACT FROM AUTHOR]