Gelatinous Zooplankton Research Articles

In-situ observations of gelatinous zooplankton aggregations in inshore and offshore Arctic waters

AbstractGelatinous 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.

The contribution of fish to the diet of loggerhead sea turtles in the western Mediterranean revisited

Early juvenile loggerhead turtles (Caretta caretta) rely on gelatinous zooplankton, whereas individuals larger than 40 cm curved carapace length are adapted to crush hard-shelled invertebrates. Nevertheless, fish were reported to be the staple food of loggerhead turtles in the western Mediterranean 30 years ago. Here, the temporal consistency of such a fish-based diet of loggerhead turtles is assessed through gut content analysis and stable isotope analysis of samples from the Mediterranean coast of Spain spanning three decades. The gut contents of 134 juvenile loggerhead turtles (curved carapace length range: 27–71 cm) from three different periods (1991, 1999–2008 and 2010–2017) were analyzed, as well as a subsample of the same turtles (n = 10 in each period) for both bulk and compound-specific stable isotope ratios (CSIA-AA). Gut content analysis revealed a decline in the frequency of occurrence and numerical abundance of fish and an increasing contribution of gastropods and bivalves throughout time, although pelagic tunicates were always the most frequently observed prey. The δ15Nbulk of turtle bone also dropped throughout the study period, but the values of the stable isotope ratio of N in phenylalanine (δ15NPhe) indicated that 52.5% of that variability was due to a baseline shift over time. Accordingly, the trophic position estimated from CSIA-AA did not follow the decreasing pattern of δ15Nbulk, but fluctuated throughout time. The overall evidence indicates that fish consumption by loggerhead turtles in the study region declined through time, but the trophic position of loggerhead turtles did not change simultaneously. This is probably because low trophic prey such pelagic tunicates and filter-feeding bivalves and suspension-feeding gastropods were the bulk of the diet during the whole study period and fish played a minor role, even when their frequency of occurrence peaked. Past levels of high fish consumption might be due to high levels of fishery discards, currently declining because of the recent reduction of the fishing fleet.

The association of argonauts with gelatinous plankton and other substrates.

The association of argonauts with gelatinous plankton and other substrates.

Management of jellyfish outbreaks to achieve good environmental status

Jellyfish and gelatinous zooplankton (GZ) in general, fulfill important ecological roles with significant impacts, although they are often oversimplified or misunderstood. This paper reviews the impacts, pressures, monitoring methods and current management strategies for various GZ groups. It also introduces potentially applicable indicators for their assessment in ecosystem-based management approaches, such as the European Marine Strategy Framework Directive (MSFD). This multi-faceted review is primarily envisioned to serve as a state-of-the-art document for scientists and policymakers to foster a holistic assessment and management of GZ across European regional seas. The systematic review on global impacts of GZ shows a notable increase in the number of studies since the early 2000s. Stings were the main cause of human health impacts. Mechanisms that impact biodiversity included direct predation, modification of trophic flows or competition for resources. Several GZ taxa may be beneficial to biodiversity acting as biological regulators and provide societal ecosystem services such as food provision or medical applications. The systematic review on monitoring techniques outlined a variety of methods, such as nets (the most common technique), continuous plankton recorder (CPR), polyp and jelly-fall monitoring, acoustic methods, remote aerial and underwater imaging, molecular methods, and citizen science. Furthermore, several currently employed management strategies were enumerated, including the use of anti-jelly nets, bubble curtains, chemical compounds, or the introduction of GZ predators. This study highlights the pressing need for enhanced GZ-dedicated monitoring, assessment, and anticipatory management of GZ populations to address future GZ crises more effectively and cost-efficiently. Moreover, exploring GZ ecosystem services unveils opportunities to harness marine resources while mitigating adverse effects, thereby supporting sustainable blue economies.

Fluorescent nectar in non-flying mammal-pollinated plants – observations and considerations in some Asparagaceae

Background and aims – Fluorescence is the emission of light by a fluorophore that has absorbed light of shorter wavelengths. While the role of fluorescence in visual communication has been documented in some animals (budgerigars, gelatinous zooplankton), it is controversially discussed in plants. Floral nectar fluorescence has been mainly found in flowers pollinated by bees. It has been suggested as direct visual cue by which bees can evaluate the available quantity of nectar, thus being important for pollination and foraging efficiency. However, this function has been questioned, since fluorescence is said to be obscured by floral reflections due to low quantum efficiency. The aim of this study was to examine the nectar of plants pollinated by non-flying mammals, namely Eucomis regia, Massonia grandiflora, M. echinata, and M. pustulata (Asparagaceae) from South Africa. Material and methods – To detect possible fluorescence in flowers, the plants were illuminated in a darkened room under UV light and photographed with a camera equipped with a UV/IR cut filter (transmitting at 400–700 nm). Key results – Within the inflorescences, the nectar of all species showed blue to bluish fluorescence and UV absorption. Separated nectar also fluoresced. Conclusion – As fluorescence in flowers occurs not only in bee-pollinated plants but also in plants pollinated by wind, and by nocturnal or crepuscular pollinators (non-flying mammals, bats, moths) for which floral scent is an important attractant, floral fluorescence seems to have no adaptive value for the attraction of flower visitors. We discuss the potential role of fluorescence in flowers as just a by-product of compounds that might have other functions such as visual attraction by reflection (or UV absorbance), protection of genetic material in pollen from UV induced damage, or as a floral filter causing nectar to be bitter, repelling ineffective pollinators but not effective ones.

Chemical composition and egg production capacity throughout bloom development of ctenophore Mnemiopsis leidyi in the northern Adriatic Sea.

High abundances of gelatinous zooplankton (GZ) can significantly impact marine ecosystem by acting as both sink and source of organic matter (OM) and nutrients. The decay of GZ bloom can introduce significant amount of OM to the ocean interior, with its variability influenced by GZ life traits and environmental factors, impacting microbial communities vital to marine biogeochemical cycles. The invasive ctenophores Mnemiopsis leidyi has formed massive blooms in the northern Adriatic Sea since 2016. However, the variability in the chemical composition and egg production of blooming populations, as well as the role of environmental factors in governing this variability, remains largely unknown. Our analysis of biometry, chemical composition, and fecundity of M. leidyi sampled in the Gulf of Trieste in 2021 revealed stable carbon and nitrogen content throughout bloom development, with no significant correlation with seawater temperature, salinity, oxygen, and chlorophyll a concentration. Although the studied population exhibited homogeneity in terms of biometry and chemical composition, the number of produced eggs varied substantially, showing no clear correlation with environmental variables and being somewhat lower than previously reported for the study area and other Mediterranean areas. We observed a positive correlation between the wet weight of individuals and the percentage of hatched eggs, as well as a significant positive correlation between the percentage of hatched eggs and ambient seawater temperature. Additionally, we noted that the speed of hatching decreased with decreasing seawater temperature in autumn, corresponding to the end of M. leidyi bloom.

A belly full of jelly? DNA metabarcoding shows evidence for gelatinous zooplankton predation by several fish species in Greenland waters.

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.

Dynamic population modeling of bacterioplankton community response to gelatinous marine zooplankton bloom collapse and its impact on marine nutrient balance

The diverse microbial community in the ocean, encompassing various metabolic types, interacts with the wide array of compounds in the dissolved organic matter (DOM) pool, thereby influencing the ocean’s biogeochemical state and, consequently, the global climate. Our understanding of the interactions between specific DOM constituents and microbial consortia remains limited, necessitating further refinement to achieve a mechanistic comprehension of the relationship between the DOM field and the microbial metabolic network. Attaining this level of understanding is crucial for accurately predicting the marine ecosystem’s response to natural and anthropogenic perturbations. To address this gap, we developed a bacterial population model based on the von Foerster equation. This model aims to describe the complex microbial-mediated degradation of gelatinous zooplankton (hereinafter ‘jellyfish’) detritus, as an important, but largely overlooked source of DOM in the ocean. By considering microbial growth and decay, as well as DOM uptake, and nutrient release, the model is able to describe the microbial community’s life cycle, and the biochemical transformations of the jellyfish-derived organic matter. We fitted the model to results of laboratory microcosm experiments conducted to simulate scenarios experienced by ambient microbiomes during decay of two different jellyfish species in the northern Adriatic Sea. By interpreting the fitted parameters, we highlight the differences in the microbial response to different jellyfish species, namely how these affect the microbial community composition and the release of nutrients. This model has been specifically designed for integration with ocean circulation models to create a comprehensive physical-biogeochemical ocean model. Such an extended model can be utilized for multi-scale simulations to assess the system’s response to jellyfish and jellyfish-derived organic matter. Given that jellyfish blooms may become more prevalent under future ocean scenarios, this modeling approach is essential for understanding their potential impact on marine ecosystems.

Diet and trophic structure of fishes in the Barents Sea: Effects of size within (ontogenetic) and between species

A large data set on stomach content (over 27,000 individual fish) – collected in the Barents Sea in 2015 – was used to examine ontogenetic and interspecific changes in diet with size for 35 fish species. The analysis combined the use of hierarchical clustering and random forest. Two different diet metrics were used (% weight of prey types per weight of stomach content or per weight of fish, the latter reflecting also feeding intensity), and data were analysed based on average diet of predator groups (species and size groups) across the entire sample series (from the whole Barents Sea in different seasons), or for data broken down by geographical areas and seasons. Similar trophic groups (clusters) were identified for the various data sets suggesting that the results on trophic structure were robust. The trophic groups including size information were broadly similar to groups found earlier with data averaged at species level. Hierarchical clustering produces a hierarchy of trophic groups (or trophic guilds) at various levels of diet dissimilarity. With 12 clusters identified, one cluster had fish as dominant prey, and 5–6 others had either plankton or benthos as dominant prey. The clusters tended to be distinct and homogenous with one dominant prey category in average diet (often > 60 %). This was especially the case for the plankton clusters, with copepods, euphausiids, hyperiid amphipods, or gelatinous zooplankton as dominant prey in each of 4 trophic groups. The benthos clusters tended to be less dissimilar with more overlap in diet composition, with predominance of either hard-shelled forms (echinoderms and molluscs) or softer prey (polychaetes and crustaceans) for groups of clusters. There were clear patterns of ontogenetic shifts in fish diet. Fish that clustered as piscivores at larger size tended to grow from being planktivores when smaller. Smaller species of planktivores or benthivores shifted position among trophic groups but remained within the categories of planktivores or benthivores, respectively. Taxonomy (species) tended to be more important than size for explaining the diet composition of the different clusters of fish predators.

Once Is Not Enough: Seasonal Patterns in Abundance of Hydromedusae Are Not Consistent in the Coastal Waters of the Bay of Panama.

Hydromedusae and other gelatinous zooplankton are poorly understood but important consumers in the plankton. Blooms of large-bodied medusae which may have detrimental ecological impacts have captured significant attention, yet the seasonal patterns of local abundance and diversity, and the factors that control them, are not well documented for the much more diverse tiny hydromedusae. There is virtually no published information on their phenology or ecology in tropical coastal systems. It has previously been suggested that increased productivity stimulated by upwelling promotes production of tiny hydromedusa and blooms as their abundance can be much higher during upwelling than during non-upwelling periods in the tropics. However, this conclusion was based on a single year of sampling in the Bay of Panama. To determine if a single year of sampling is sufficient to understand seasonal patterns in abundance and occurrence of blooms, we repeated this study 20 years later. Sampling 153 times between April 2022 and April 2023, we found similar genus-level diversity and overall counts of animals compared to the previous study, with medusae of Bougainvillia, Campalecium, Obelia, and Turritopsis accounting for 79% of the animals collected. However, we found that relative abundance was much higher during the non-upwelling season compared to the upwelling season, the opposite result compared to the previous study. These results highlight how strong baseline understanding of phenologies and the ecological conclusions drawn from them must be based on multiple years of data, even in regions with very strong seasonal changes in environmental conditions. In the case of the upwelling regions of the Tropical Eastern Pacific, further research is necessary to understand the generalizability of these patterns, and to determine if contrasting results are due to inter-annual differences in oceanographic drivers or changing environmental baselines.

Pan‐Arctic distribution modeling reveals climate‐change‐driven poleward shifts of major gelatinous zooplankton species

AbstractAnthropogenic activities, including climate change, are hypothesized to cause increases in gelatinous zooplankton population sizes and blooms. In the most rapidly changing ecosystem, the Arctic Ocean, this hypothesis has not yet been verified, and gelatinous zooplankton is commonly excluded from large‐scale modeling studies. Our modeling study is based on an extensive biogeographic dataset, aggregating from four open‐source databases (Ocean Biodiversity Information System, Global Biodiversity Information Facility, Jellyfish Database Initiative, and PANGAEA). It includes data on eight of the most reported gelatinous zooplankton taxa of the pan‐Arctic region (Aglantha digitale, Sminthea arctica, Periphylla periphylla, Cyanea capillata, Oikopleura vanhoeffeni, Fritillaria borealis, Mertensia ovum, and Beroe spp.). By coupling three‐dimensional species distribution models with oceanographic components from the Max Planck Institute Earth System Model (MPI‐ESM1.2), run for historical (1950–2014) and future (2050–2099) periods under the shared socioeconomic pathway SSP370 scenario forcing, we identified species with expanding or contracting habitat ranges in response to climate change. Our projections indicated a general tendency for gelatinous zooplankton distributions to shift, with varying degrees of suitable habitat expansion (largest for the scyphozoan C. capillata ~ +180%) or contraction (largest for the hydrozoan Sm. arctica ~ −15%). Seven of the eight species modeled, which—similar to the majority of gelatinous taxa occurring in the Arctic Ocean—predominantly represented arcto‐boreal and boreal taxa, are projected to shift to northern latitudes. Hence, profound impacts on the Arctic marine environment and associated ecosystem services can be expected.

Investigating pelagic biodiversity and gelatinous zooplankton communities in the rapidly changing European Arctic: An eDNA metabarcoding survey

AbstractFram Strait, the gateway between the Arctic and Atlantic Oceans, is undergoing major climate change‐induced physical and biological transformations. In particular, rapid warming and ongoing “Atlantification” are driving species range shifts and altering food web structures in the Arctic. Understanding and predicting the consequences of these processes on future ecosystems requires detailed assessments of local and pelagic biodiversity. Gelatinous zooplankton (GZP) is an important component of pelagic communities, and recent evidence indicates that such communities are undergoing major changes in the Fram Strait. However, as sampling GZP is challenging, they are regularly underestimated in biodiversity, distribution, and abundance. To overcome this and address existing ecological knowledge gaps, we investigated patterns of pelagic metazoan diversity in Fram Strait using environmental DNA (eDNA) metabarcoding of the cytochrome c oxidase I (COI) gene. We successfully detected a broad range of taxa from the marine metazoan and GZP communities across sampling locations and ocean depth zones. We demonstrate the vertical structuring of diversity and elucidate relationships between taxa and water mass indicators, such as salinity and temperature. Furthermore, when comparing eDNA data with net and video transect data for GZP at the same period and location, we found that eDNA uncovered a higher number of taxa, including several that were not detected by the other methods. This study is a contribution to the formation of baseline Arctic GZP biodiversity datasets, as well as future research on changing marine metazoan biodiversity and community composition.

Biased dry weight: The matter of residual water in seven pelagic tunicate species

Pelagic tunicates are cosmopolitan and, at times, highly abundant members of open-ocean ecosystems that are important for food web dynamics and biogeochemical cycling. Ecosystem models often use wet weights to parameterize biota. This may be erroneous for gelatinous plankton, such as pelagic tunicates, with high water content, compared to crustaceans. Furthermore, poorly quantified residual water should also be corrected when using dry weights for parameterization. This study aims to estimate the residual water content (as well as elemental and organic contents) for seven tunicate species. Tunicates (one pyrosome and six salps, N = 107), were collected during several research expeditions and analyzed for inter- and intraspecific variability. The H-surplus method was applied for the residual water content calculation. The residual water ranged from 1.5 to 20.6% (average ± SD: 8.9 ± 4.2%) of dry weight across species and did not differ significantly between taxonomic orders. Furthermore, the life cycle stage (blastozooid versus oozooid) and tissue type (tunic versus whole organism) were found to be insignificant in explaining residual water content patterns. Elemental and organic contents, however, were lower in tunics than in whole organisms, and in the salp Thetys vagina, stomachs had significantly higher elemental and organic contents compared to whole organisms. Effects of size and drying method (oven versus freeze-drying) significantly impacted the residual water content of pelagic tunicates. Accounting for residual water content in zooplankton is discussed from an ecological perspective and is strongly advised for future modeling studies.

Are winter conditions impacting annual organic production in the northern Adriatic? Verifications and future projections

Primary production in the northern Adriatic (NAd) reaches its yearly peak in the winter with high-intensity variations from year to year. According to the hypothesis, the intensity of local winter primary production, controlled by the degree of the spreading of Po River waters across the NAd, reflects on the annual secondary production of the ongoing year. The hypothesis is evaluated here based on the new data set and extends from 2018 to 2020, referring additionally to 2017 data which are already published. Data collected in 2017 and 2020 support the hypothesis, pointing to the large organic outputs after highly productive winters. Despite the lack of seasonal data for 2018 and 2019, large annual production was deducted by large abundances of the allochthonous gelatinous zooplankton species – Mnemiopsis leidyi. Numerical models show that in 2018–2020 the NAd was mostly “separated” from the rest of the Adriatic Sea by a northern branch of a large cyclonic gyre with high salinity water (from central Adriatic and/or Kvarner Bay) entering the NAd along the eastern (Istrian) coast. Such a circulation system could favour the spreading of the Po River waters across the NAd, inducing high primary production in winter, at the beginning of the yearly pelagic cycle, with a subsequent retention/accumulation of organic matter produced in the following months in the area. Using climate projections of temperature and salinity and the associated circulation and following the observed biological relations, a prediction of the organic matter production in the NAd can be obtained. With increased horizontal density gradients in future winters, an intensification of transversal motions across the NAd is expected. Thus, the retention of the Po waters with higher winter production in the NAd may be predicted. Following the hypothesis, a higher annual organic production and a probable higher occurrence of gelatinous plankton in the east of the NAd are expected.

Lepocreadiidae (Trematoda) associated with gelatinous zooplankton (Cnidaria and Ctenophora) and fishes in Australian and Japanese waters

We examined gelatinous zooplankton from off eastern Australia for lepocreadiid trematode metacercariae. From 221 specimens of 17 species of cnidarian medusae and 218 specimens of four species of ctenophores, infections were found in seven cnidarian and two ctenophore species. Metacercariae were distinguished using cox1 mtDNA, ITS2 rDNA and morphology. We identified three species of Prodistomum Linton, 1910 [P. keyam Bray & Cribb, 1996, P. orientale (Layman, 1930), and Prodistomum Type 3], two species of Opechona Looss, 1907 [O. kahawai Bray & Cribb, 2003 and O. cf. olssoni], and Cephalolepidapedon saba Yamaguti, 1970. Two species were found in cnidarians and ctenophores, three only in cnidarians, and one only in a ctenophore. Three Australian fishes were identified as definitive hosts; four species were collected from Scomber australasicus and one each from Arripis trutta and Monodactylus argenteus. Transmission of trematodes to these fishes by ingestion of gelatinous zooplankton is plausible given their mid-water feeding habits, although such predation is rarely reported. Combined morphological and molecular analyses of adult trematodes identified two cox1 types for C. saba, three cox1 types and species of Opechona, and six cox1 types and five species of Prodistomum of which only two are identified to species. All three genera are widely distributed geographically and have unresolved taxonomic issues. Levels of distinction between the recognised species varied dramatically for morphology, the three molecular markers, and host distribution. Phylogenetic analysis of 28S rDNA data extends previous findings that species of Opechona and Prodistomum do not form monophyletic clades.

Vertical trophic structure and niche partitioning of gelatinous predators in a pelagic food web: Insights from stable isotopes of siphonophores

AbstractGelatinous zooplankton are increasingly recognized as key components of pelagic ecosystems, and there have been many recent insights into their ecology and roles in food webs. To examine the trophic ecology of siphonophores (Cnidaria, Hydrozoa), we used bulk (carbon and nitrogen) and compound‐specific (nitrogen) isotope analysis of individual amino acids (CSIA‐AA). We collected samples of 15 siphonophore genera using blue‐water diving, midwater trawls, and remotely operated vehicles in the California Current Ecosystem, from 0 to 3000 m. We examined the basal resources supporting siphonophore nutrition by comparing their isotope values to those of contemporaneously collected sinking and suspended particles (0–500 m). Stable isotope values provided novel insights into siphonophore trophic ecology, indicating considerable niche overlap between calycophoran and physonect siphonophores. However, there were clear relationships between siphonophore trophic positions and phylogeny, and the highest siphonophore trophic positions were restricted to physonects. Bulk and source amino acid nitrogen isotope (δ15N) values of siphonophores and suspended particles all increased significantly with increasing collection depth. In contrast, siphonophore trophic positions did not increase with increasing collection depth. This suggests that microbially reworked, deep, suspended particles with higher δ15N values than surface particles, likely indirectly support deep‐pelagic siphonophores. Siphonophores feed upon a range of prey, from small crustaceans to fishes, and we show that their measured trophic positions reflect this trophic diversity, spanning 1.5 trophic levels (range 2.4–4.0). Further, we demonstrate that CSIA‐AA can elucidate the feeding ecology of gelatinous zooplankton and distinguish between nutritional resources across vertical habitats. These findings improve our understanding of the functional roles of gelatinous zooplankton and energy flow through pelagic food webs.

The unpredictability of scyphozoan jellyfish blooms

The study of jellyfish blooms has gained attention in the recent decades because of the importance of forecasting and anticipating them and avoiding their interference with human activities. However, after thirty years of scientific effort (monitoring systems, empirical laboratory and field studies, modeling, etc.), the occurrence of blooms remains unpredictable, and their consequences unavoidable. Climate change, eutrophication, overfishing, coastal construction, and species translocation have been suggested as stressors that increase them, but robust evidence to support these claims is limited. The widespread belief that jellyfish blooms are “increasing in number” has been challenged in recent years. Among the gelatinous zooplankton, the bloom forming species are concentrated in the class Scyphozoa, and the number of species with at least one recorded bloom has increased during the last decade. The analyses of long-term time series show seasonality in the dynamic of each blooming jellyfish species population, but the blooms vary in intensity and there are years of an unexplained absence of jellyfish. In this review, we focus on the current state of knowledge, uncertainties and gaps in the critical points that can strongly influence the intensity of the bloom or even lead to the absence of the medusa population. These points include ephyrae, planulae and scyphistoma natural, predatory or fishing mortality, the molecular pathway of strobilation, benthic population dynamics, planula settlement and ephyra to medusa transition success. Some of these points account for certain empirical laboratory evidence under controlled conditions, and are difficult to be studied on the field, but the different sources of non-typically recorded variability need to be addressed to improve our understanding of jellyfish population dynamics.

Bacterial degradation of ctenophore Mnemiopsis leidyi organic matter.

Blooms of gelatinous zooplankton, an important source of protein-rich biomass in coastal waters, often collapse rapidly, releasing large amounts of labile detrital organic matter (OM) into the surrounding water. Although these blooms have the potential to cause major perturbations in the marine ecosystem, their effects on the microbial community and hence on the biogeochemical cycles have yet to be elucidated. We conducted microcosm experiments simulating the scenario experienced by coastal bacterial communities after the decay of a ctenophore (Mnemiopsis leidyi) bloom in the northern Adriatic Sea. Within 24 h, a rapid response of bacterial communities to the M. leidyi OM was observed, characterized by elevated bacterial biomass production and respiration rates. However, compared to our previous microcosm study of jellyfish (Aurelia aurita s.l.), M. leidyi OM degradation was characterized by significantly lower bacterial growth efficiency, meaning that the carbon stored in the OM was mostly respired. Combined metagenomic and metaproteomic analysis indicated that the degradation activity was mainly performed by Pseudoalteromonas, producing a large amount of proteolytic extracellular enzymes and exhibiting high metabolic activity. Interestingly, the reconstructed metagenome-assembled genome (MAG) of Pseudoalteromonas phenolica was almost identical (average nucleotide identity >99%) to the MAG previously reconstructed in our A. aurita microcosm study, despite the fundamental genetic and biochemical differences of the two gelatinous zooplankton species. Taken together, our data suggest that blooms of different gelatinous zooplankton are likely triggering a consistent response from natural bacterial communities, with specific bacterial lineages driving the remineralization of the gelatinous OM.IMPORTANCEJellyfish blooms are increasingly becoming a recurring seasonal event in marine ecosystems, characterized by a rapid build-up of gelatinous biomass that collapses rapidly. Although these blooms have the potential to cause major perturbations, their impact on marine microbial communities is largely unknown. We conducted an incubation experiment simulating a bloom of the ctenophore Mnemiopsis leidyi in the Northern Adriatic, where we investigated the bacterial response to the gelatinous biomass. We found that the bacterial communities actively degraded the gelatinous organic matter, and overall showed a striking similarity to the dynamics previously observed after a simulated bloom of the jellyfish Aurelia aurita s.l. In both cases, we found that a single bacterial species, Pseudoalteromonas phenolica, was responsible for most of the degradation activity. This suggests that blooms of different jellyfish are likely to trigger a consistent response from natural bacterial communities, with specific bacterial species driving the remineralization of gelatinous biomass.

An updated end-to-end ecosystem model of the Northern California Current reflecting ecosystem changes due to recent marine heatwaves.

The Northern California Current is a highly productive marine upwelling ecosystem that is economically and ecologically important. It is home to both commercially harvested species and those that are federally listed under the U.S. Endangered Species Act. Recently, there has been a global shift from single-species fisheries management to ecosystem-based fisheries management, which acknowledges that more complex dynamics can reverberate through a food web. Here, we have integrated new research into an end-to-end ecosystem model (i.e., physics to fisheries) using data from long-term ocean surveys, phytoplankton satellite imagery paired with a vertically generalized production model, a recently assembled diet database, fishery catch information, species distribution models, and existing literature. This spatially-explicit model includes 90 living and detrital functional groups ranging from phytoplankton, krill, and forage fish to salmon, seabirds, and marine mammals, and nine fisheries that occur off the coast of Washington, Oregon, and Northern California. This model was updated from previous regional models to account for more recent changes in the Northern California Current (e.g., increases in market squid and some gelatinous zooplankton such as pyrosomes and salps), to expand the previous domain to increase the spatial resolution, to include data from previously unincorporated surveys, and to add improved characterization of endangered species, such as Chinook salmon (Oncorhynchus tshawytscha) and southern resident killer whales (Orcinus orca). Our model is mass-balanced, ecologically plausible, without extinctions, and stable over 150-year simulations. Ammonium and nitrate availability, total primary production rates, and model-derived phytoplankton time series are within realistic ranges. As we move towards holistic ecosystem-based fisheries management, we must continue to openly and collaboratively integrate our disparate datasets and collective knowledge to solve the intricate problems we face. As a tool for future research, we provide the data and code to use our ecosystem model.

An in situ digital synthesis strategy for the discovery and description of ocean life.

Revolutionary advancements in underwater imaging, robotics, and genomic sequencing have reshaped marine exploration. We present and demonstrate an interdisciplinary approach that uses emerging quantitative imaging technologies, an innovative robotic encapsulation system with in situ RNA preservation and next-generation genomic sequencing to gain comprehensive biological, biophysical, and genomic data from deep-sea organisms. The synthesis of these data provides rich morphological and genetic information for species description, surpassing traditional passive observation methods and preserved specimens, particularly for gelatinous zooplankton. Our approach enhances our ability to study delicate mid-water animals, improving research in the world's oceans.