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The demand for jellyfish is growing worldwide, especially due to their high nutraceutical value. In this study, the extraction and characterization of crude gelatin from the brown cannonball jellyfish (Stomolophus meleagris), which is periodically found in large volumes on the American Pacific coasts, were carried out. The crude gelatin obtained by alkaline treatment, with subsequent heat and dialysis treatment, showed an ability to quench free radicals (via ABTS and ORAC methods), and protect human cells against oxidative damage (through inhibition of hemolysis by AAPH), and they protected against mutations caused by aflatoxin B1 in the Salmonella enterica Typhimurium TA100 strain. Furthermore, it was established that these extracts were innocuous for eukaryotic cells (genotoxicity assay). The amino acid profiles indicate a high concentration of glycine and proline, as well as charged amino acids. Electrophoretic, FT-IR, and 1H-NMR studies indicated that one of the main proteins present in this crude gelatin is collagen. The presence of collagen and other proteins was identified by proteomic studies. Alkaline crude gelatin from brown jellyfish could be considered as potential candidates to be evaluated as antioxidant agents in foods in future research.

This study focused on a jellyfish monitoring and sampling programme along the eastern Qatar seawaters and reports the first jellyfish records for the Qatar pelagic ecosystem and the occurrence of three scyphozoans: the semaeostome Chrysaora cf. caliparea and the rhizostomes Marivagia stellata and Catostylus perezi, considered as first records of Scyphomedusae for Qatar. Jellyfish monitoring, underwater photography and sample collection were carried out along an inshore-offshore transect composed of five stations along the eastern coast of Qatar. Jellyfish material examined, systematic description, general distribution and sting risk of the three species are provided. The discussion section highlights the blooming capabilities of Chrysaora cf. caliparea and Catostylus perezi, while Marivagia stellata seems scarcer, being spotted for the first time since we started our jellyfish investigation programme in August 2018.

Pelagic cnidarians have been observed stranding annually in the Tetouanise Sea, a site of intense human recreation in northwest Morocco. The abundance and size of jellyfish stranded, between January 2018 and December 2020, on the beaches of the Moroccan Mediterranean were investigated. We present data on the temporal and spatial distribution of the species in relation to environmental variables (e.g., sea surface temperature, salinity, chlorophyll and wind direction). We also examined the negative impacts of jellyfish on human activities in the Moroccan Mediterranean. Five species that represented three scyphozoans and two hydrozoans were frequently observed: Pelagia noctiluca, Velella velella, Physalia physalis, Rhizostoma pulmo and Chrysaora hysoscella. Three different models of seasonal occurrence of jellyfish were identified in this study: (1) P. noctiluca appears throughout the year but with a higher frequency during the summer, (2) P. physalis and V. velella appear in March–May and (3) the late appearing R. pulmo and C. hysoscella from July to August. The abundance of jellyfish varied from season to season, but did not differ between sampling sites. Interannual variations in the abundance of jellyfish were not significantly correlated with the environmental factors examined. However, the east wind played an important role in the stranding and formation of hotspots for jellyfish in the Moroccan coast. Continuous monitoring is needed for a more profound knowledge on the jellyfish bloom dynamics and their potential impacts on ecosystem functioning and socioeconomic activities in the Moroccan Mediterranean.

The scyphozoans are considered as one of the potential bio-indicator species of the coastal marine ecosystems. The genus Crambionella, belonging to the family Catostylidae, represents a total of four species globally. The jellyfish Crambionella orsini (Vanhoffen in Bibliotheca Zool 1:1–52, 1888) is mostly distributed to the western Indian Ocean. In this present study, this species is reported from Lakshadweep for the first time though it was reported from other parts of the Arabian Sea previously. This present paper deals with the morphological characteristics of C. orsini along with its global zoogeographical ranges.

Cnidarian jellyfish can be dominant players in the food webs of highly productive Eastern Boundary Currents (EBC). However, the trophic role of inconspicuous hydromedusae in EBCs has traditionally been overlooked. We collected mesozooplankton from five stations along two cross-shelf transects in the Northern California Current (NCC) during winter and summer of 2018–2019. We analyzed gut contents of 11 hydromedusan species and the prey community to (i) determine prey resource use by hydromedusae and (ii) determine temporal shifts in the trophic niche of hydromedusae, focusing on the two most collected species (Clytia gregaria and Eutonina indicans). Hydromedusae in the NCC fed mostly on copepods, appendicularians and invertebrate larvae. Nonmetric multidimensional scaling of hydromedusan diets showed seasonal shifts in prey resource driven by the abundant C. gregaria, which fed mostly on copepod eggs during winter and fed mostly on appendicularians and copepods during summer. Prey selectivity for copepod eggs increased during winter for C. gregaria and E. indicans. Intriguingly, theoretical ingestion rates show that both species acquire similar amounts of carbon during upwelling and nonupwelling conditions. Hydromedusae’s consistent presence and predation impact across seasons may lead to significant effects in carbon and energy transfer through the NCC food web.

Ephyrae are produced through the strobilation of polyps in the general life cycle of Aurelia coerulea. However, it has been reported that planulae can also metamorphose directly into ephyrae, without passing through the polyp stage. There is a mixture of ephyrae developed from planulae (planula-strobilated ephyrae) and ephyrae developed from polyps (polyp-strobilated ephyrae) in the ephyra population. However, the effect of the planula-strobilated ephyrae on the ephyra population is yet to be determined, since their morphological characteristics have not yet been elucidated. This study aimed to determine the morphological characteristics to distinguish between planula-strobilated and polyp-strobilated ephyrae. The differences in body dimensions, such as total body diameter (TBD), central disc diameter (CDD), lappet stem length (LStL), rhopalial lappet length (RLL), and total marginal lappet length (TMLL) were compared between the two types of ephyra. Thus, we show that body proportions can be used to identify planula- and polyp-strobilated ephyrae. The ranges for identifying planula-strobilated ephyra were 35.0–38.3% for CDD/TBD, 56.7–64.9% for LStL/CDD, 84.7–99.5% for TMLL/CDD, and 31.0–37.5% for RLL/TMLL. This method could be an important basis for devising countermeasures for jellyfish blooms in areas where ephyrae deriving from planula strobilation occur.

Understanding processes occurring in the different life stages of jellyfish is key to advance knowledge on their trophic interactions and population dynamics. We describe four developmental stages of Pelagia noctiluca ephyrae and metaephyrae based on the progress of feeding structures and morphometric measurements on the central disc diameter and total body diameter. Size differs significantly among stages, but it can overlap substantially, suggesting that it is not always coupled with development progress due to different somatic growth. Morphological distinction of stages is biologically important because it implies different levels of food specialization and capture efficiency. We further report a 25% (±13 SD) shrinkage of ephyrae and metaephyrae after storage in 4% formaldehyde solution. This metric can be used in ecological studies focusing on size-related traits of field observed individuals., European Union’s Horizon 2020 Research and Innovation Program (PANDORA project) (grant agreement No. 773713); Spanish Institute of Oceanography (TUNIBAL project) and its joined research initiative with the Balearic Islands Coastal Observing and Forecasting System (SOCIB) (BLUEFIN project); FPI Fellowship from Vicepresidència i Conselleria d’Innovació, Recerca i Turisme of the regional Government of the Balearic Islands co-financed by the 2014–2020 European Social Fund Program (to D.O.); Juan de la Cierva postdoctoral contract from the Spanish Ministry of Science, Innovation and Universities (to I.A.).

In October 2019, during Tropical Storm Lorenzo, an unusual bloom of Physalia physalis (commonly known as the Portuguese man o' war) appeared on the west coast of Ireland. The jellyfish were observed aggregating in high numbers surrounding salmon pens on two Atlantic salmon farms with tentacles extending underwater through the nets into the pens. Acute skin lesions and mortality were reported as a consequence of exposure to P. physalis on both sites. The impact of noxious zooplankton species such as P. physalis may pose a significant and more frequent threat in future if increased adverse weather events continue to transport these and other jellyfish outside their normal range. This is the first published record of Physalia physalis causing mortality in cultured fish.

ACKNOWLEDGEMENTS : This work was financially supported by FCT (Portuguese Foundation for Science and Technology) through project ‘Jellyfisheries—Towards an integrated approach to enhance predictive accuracy of the jellyfish impact on coastal marine ecosystems’ (POCI-01-0145-FEDER-016772) and the Integrated Programme of SR&TD ‘SmartBioR—Smart Valorization of Endogenous Marine Biological Resources Under a Changing Climate’ (Centro-01-0145-FEDER-000018), co-funded by Centro 2020 program, Portugal 2020, European Union, through the European Regional Development Fund. Inês Duarte acknowledges FCT by financially supporting her PhD grant (SFRH/BD/146449/2019). Thanks for financial support are also due to CESAM (UIDB/50017/2020 + UIDP/50017/2020) and MARE (UIDB/04292/2020 + UIDP/04292/2020), to FCT/MEC through national funds, and the cofounding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. We also thank Carlos Estevão Simonka for his prized help and guidance on microscope photography of living organisms and for the professional edition of the photos depicted in Figure 2. Interest on jellyfish research has significantly increased over the last two decades, mostly driven by the potential benefits of their high-end uses. Recent efforts have been put forward towards the commercial use of scyphozoan jellyfish, although the pipeline leading to their full exploitation is still at an early stage of development. Indeed, further research and several technical advances are still required to expand the use of these bioresources to a larger and more sustainable scale. Here, we describe the state of the art of culture systems already available to farm these organisms throughout the different stages of their life cycle and provide an overview of the potential applications of jellyfish aquaculture for food, feed, as source of bioactive compounds for pharmaceutical and other biotechnological applications, as well as to supply the marine aquarium trade. Overall, this work aims to raise awareness on the relevance that jellyfish will likely play on the development of sustainable blue bioeconomy frameworks fostering a sustainable valorisation of marine living resources. info:eu-repo/semantics/publishedVersion

The term bioluminescence refers to a conspicuous light emission displayed by numerous aquatic and terrestrial organisms. This phenomenon has so far not been observed in several taxonomic groups like archaea, protista, platyhelminthes, chelicerata, cephalochordata, amphibians, reptiles, birds, plants, and mammals. However, some luminescent bacteria, fungi and microalgae like dinoflagellates are known. Bioluminescence has become a powerful biological tool and revolutionized several medical, physiological and biotechnological approaches, such as, for example, the study of metabolic pathways of bacteria to mammals. In 2008 O. Shimomura, M. Chalfie and R. Tsien were awarded the Chemistry Nobel prize for their discovery of the protein GFP, which is co-expressed with aequorin, the calcium-activated photoprotein involved in the bioluminescence reaction of the jellyfish Aequorea victoria. Some organisms are known to display bioluminescence only under certain kinds of stimulation and stress conditions; others appear to produce their light without prior stimulation either continuously or intermittently. Despite the discovery of more than 700 genera of bioluminescent organisms from marine, terrestrial, and freshwater environments, there is often still insufficient knowledge about their bioluminescence emission patterns under natural and stress conditions. Furthermore, there are no detailed reviews on stimulation techniques that can be used to test whether organisms previously not having been recognized to be luminescent are luminescent or not. This paper reviews various stimulants, such as chemical, mechanical, photic, thermal, magnetic and electrical ones, used in tests to elicit the emission of light in known bioluminescent organisms. This account should help researchers to extend their investigations to identify organisms hitherto not deemed to be luminescent.

Penaeid trawls often have poor ecological efficiencies measured as unwanted bycatches (with high discard mortality) and

Gelatinous and soft-bodied zooplankton (GZ) have long been considered to have low energetic value (‘trophic dead end hypothesis’) and be insufficient to sustain higher trophic levels. However, the nutritional composition and energy content of GZ are often poorly known for entire groups, ignoring species-, size-, and stage-specific differences. In this study, organic matter and elemental composition (carbon and nitrogen) were measured for >1000 specimens from 34 GZ species collected from neritic and oceanic waters of the Northeast Pacific between 2014 and 2020. Species included 3 gastropods, 16 hydrozoans, 2 nude ctenophores, 6 scyphozoans, 3 tentaculate ctenophores, and 4 thaliaceans. Organic content and elemental composition were used to estimate energy content using published conversion factors and differed between and within taxonomic classes. Size-dependent variability was shown for several species. Differences in organic content and elemental composition by development stage were observed in a salp and scyphomedusa species, highlighting the need to consider life cycle stages separately. The relative energy values of GZ were generally low and highly variable, although some taxa were comparable to crustaceans. The findings of the present study emphasise the need for a more detailed consideration of GZ in marine food web models and time series analyses, to take into account their inter- and intraspecific variability.

Matrix metalloproteinase (MMP)-9 belongs to the zinc-dependent endopeptidase family, which is associated with important inflammatory processes and plays an important role in cell metabolism, embryonic development, and wound repair. The present study was performed using Pampus argenteus individuals fed with different feeds. The full-length cDNA of the MMP-9 gene was 2783 bp and encoded 681 amino acids. The amino acid sequence analysis of Pampus argenteus MMP-9 showed that it contained a highly conserved fibronectin type II domain and heme domain, and it was evolutionarily closely related to the MMP-9 of Seriola dumerili. Real-time PCR, western blotting, and enzyme activity assay were used to analyze the expression of MMP-9 in P. argenteus under different feeding conditions, in various tissues, and on different feeding days. The results showed that the expression of MMP-9 in group A (fed with jellyfish for the first 20 days) and B’ group (fed with jellyfish for subsequent 15 days) was significantly higher than that in other groups (P < 0.05) and the expression in the kidney was significantly higher than that in other tissues (P < 0.05). The expression increased gradually with the increase in feeding time. The results suggest that MMP-9 expression is induced in P. argenteus fed with jellyfish and plays a very important role in the immune response of the body.

Gelatinous plankton present a challenge to marine fish aquaculture that remains to be addressed. Shifting plankton distributions, suggested by some to be a result of factors such as climate change and overfishing, appear to be exacerbated by anthropogenic factors linked directly to aquaculture. Fish health can be negatively influenced by exposure to the cnidarian hydrozoan and scyphozoan life stages commonly referred to as “jellyfish”. Impact is particularly pronounced in gill tissue, where three key outcomes of exposure are described; direct traumatic damage, impaired function, and initiation of secondary disease. Cnidarian jellyfish demonstrated to negatively impact fish include Cyanea capillata, Aurelia aurita, and Pelagia noctiluca. Further coelenterates have also been associated with harm to fish, including sessile polyps of species such as Ectopleura larynx. An accurate picture of inshore planktic exposure densities within the coastal environments of aquaculture would aid in understanding cnidarian species of concern, and their impact upon fish health, particularly in gill disease. This information is however presently lacking. This review summarises the available literature regarding the impact of gelatinous plankton on finfish aquaculture, with a focus on cnidarian impact on fish health. Present strategies in monitoring and mitigation are presented, alongside identified critical knowledge gaps.

Velella velella is a pleustonic cnidarian noted worldwide for mass stranding of the colonial phase. Utilizing a 20 yr dataset (2000-2019; 23265 surveys) collected by the COASST citizen science program, we examined the spatio-temporal occurrence of mass strandings of V. velella along the Pacific Northwest coast from Washington to northern California, USA. V. velella mass strandings were documented in 14 years, with expansive events in 2003-2006 and 2014-2019. Events predominantly occurred in spring and were synchronous (April) among years, concurrent with shifts to prevailing onshore winds. Autumn mass stranding events occurred infrequently, with no consistent phenology (2005: November; 2014: August). In stranding years, reports of V. velella were mostly synchronous throughout the surveyed area, and events consistently spanned >400 km of coastline, with highest reporting rates in the vicinity of the Columbia River plume, collectively suggesting extensive V. velella blooms throughout the northern California Current system in some years. Annual metrics of spring V. velella reporting rate (proportion of beaches; January-June) were modeled as a function of indices representing sea surface temperature anomaly (SSTa), easterly (onshore) wind speed, and regional upwelling. The best models (based on Akaike’s information criterion corrected for small sample size) indicated that SSTa averaged over the preceding winter (December-February) was positively correlated with spring reporting rate, suggesting that mass strandings of V. velella may be more prevalent in warmer years. As planetary warming continues, and V. velella strandings are easily recorded by citizen science programs globally, we suggest that stranding prevalence may be one relatively easy measure providing evidence for epipelagic ecosystem response.

There is increasing focus on the frequency of jellyfish blooms in the Northeast Atlantic because of negative interactions with humans. However, uncertainty exists as to whether perceptions of increasing bloom frequencies reflect reality due to limitations within long-term population trend data. This study, therefore, developed and applied a semi-quantitative mapping approach to visualise bloom suitability based on the physiological tolerances of seven jellyfish to ocean temperature, salinity and a prey index across the Northeast Atlantic. A 10% increase and a 10% decrease in the environmental parameters was then applied to the maps to assess model sensitivity and the potential influence of environmental change on bloom suitability. The study found that optimal physiological temperatures and salinities combined with peaks in prey abundance drove higher bloom suitability and determined distribution. Several locations predicted to be at high risk of bloom occurrence off British and Irish coasts were found to coincide with areas of high anthropogenic activity that could be impacted by blooms. In the absence of long-term datasets on jellyfish population dynamics, the results and methods developed in this study allow an understanding of historic bloom events and predictions of future populations that will be useful in informing monitoring and management.

This study correlated the abundance of five jellyfish species in the south-west coast of India, South-eastern Arabian Sea, Crambionella orsini, Lychnorhiza malayensis, Chrysaora caliparea, Netrosto...

Historically, gelatinous zooplankton have been considered important consumers or predators in marine food webs, but more recently they have also been recognized as important prey for many marine species. Here, we summarized data obtained from >100 Northeast Pacific fish predators based on extensive gut content analysis (~450000 stomachs examined) from broad-scale demersal trawl surveys ranging from the Bering Sea to Southern California. In the Bering Sea, we identified 27 predators on jellyfish and 23 on urochordates. In the Aleutian Islands, 14 and 18 predators were identified, respectively, and for the Gulf of Alaska, a total of 23 and 32 such predators were documented. Off the West Coast of the contiguous USA, we identified 16 coelenterate predators and 7 urochordate predators. Many of these predators were not previously known to prey on gelatinous zooplankton. Dominant consumers of coelenterates include prowfish, rockfishes, walleye pollock, sablefish, and grenadiers, and primary consumers of urochordates included rockfishes, Atka mackerel, and sablefish. Pronounced seasonal and interannual variability in gelatinous taxa occurrence was observed in several dominant fish predators. The occurrence of jellyfish prey was generally much higher in diets of fishes examined fresh at sea when compared with diets of the same species examined in the laboratory following preservation. Differences in occurrence were less pronounced with the more durable urochordate prey. We suggest that many existing estimates of predation on easily dissolved gelatinous prey may underestimate the true predation rate and the importance of these organisms in marine food webs.

Large and small specimens of two species of metagenic Scyphozoa (true jellyfishes) can be found in nearshore waters off central Namibia throughout the year. Whereas populations of Chrysaora africana are largely restricted to inshore waters, C. fulgida occurs across the shelf, with small individuals found inshore and large individuals primarily found offshore. We examined stable isotopes δ15N and δ13C of both species in Walvis Bay and found that large-sized C. fulgida have lower δ15N values than small individuals and C. africana throughout the year. These differences are interpreted to reflect cross-shelf changes in δ15N baseline levels, with greater nitrogen recycling (and hence lower δ15N values) occurring offshore. The occasional/seasonal nearshore appearance of large C. fulgida with low δ15N values therefore implies routine, onshore advection. The values of δ13C did not show cross-shelf differences, which suggests that jellyfish populations across the shelf are supported by phytoplankton-based food chains. This study emphasises the value of using stable isotopes to examine the mesoscale structuring of jellyfish populations. Keywords: Chrysaora africana, coastal upwelling, eastern boundary currents, energy flow, jellyfish, metagenesis, molecular markers

Scyphozoan jellyfish blooms display high interannual variability in terms of timing of appearance and size of the bloom. To understand the causes of this variability, the conditions experienced by the polyps prior to the production of ephyrae in the spring were examined. Polyps reared from planula larvae of Aurelia aurita medusae collected from southern England (50°49′58.8; − 1°05′36.9) were incubated under orthogonal combinations of temperature (4, 7, 10 °C) and duration (2, 4, 6, 8 weeks), representing the range of winter conditions in that region, before experiencing an increase to 13 °C. Timing and success of strobilation were recorded. No significant production of ephyrae was observed in any of the 2- and 4-week incubations, or in any 10 °C incubation. Time to first ephyra release decreased with longer winter incubations, and more ephyrae were produced following longer and colder winter simulations. This experiment indicates that A. aurita requires a minimum period of cooler temperatures to strobilate, and contradicts claims that jellyfish populations will be more prevalent in warming oceans, specifically in the context of warmer winter conditions. Such investigations on population-specific ontogeny highlights the need to examine each life stage separately as well as in the context of its environment.

Climate change events and anthropogenic activities (e.g. translocation of non-indigenous species) have been proposed to account for the rise of jellyfish blooms in coastal environments. Bloom-forming scyphozoan jellyfish of the genus Aurelia have successfully invaded new habitats and have caused damaging blooms. In attempting to understand the underlying reasons for their success, researchers have investigated immediate effects of changing environmental conditions (e.g. temperature) on scyphistomae of single/unknown generations, with a particular focus on asexual reproduction. However, it remains unclear how scyphistomae respond to changing conditions over longer time-scales or across generations, and how those responses influence bloom occurrence. Here, we examined the role of transgenerational acclimation in asexual reproduction of A. aurita scyphistomae in a 72 d orthogonal experiment, combining 3 parental with 3 offspring temperatures of 8, 12 and 16°C. The null hypothesis was that the thermal history of the parental (F0) generation will not affect asexual reproduction in the offspring (F1) generation. Our results indicated that, provided with a transgenerational temperature change, parent scyphistomae do modify the reproductive output and timing of offspring. Scyphistomae from ‘cold’ (8°C) parents displayed the greatest reproductive output (2.86 buds per scyphistoma) and earliest budding commencement (23.86 d) at warm temperature (16°C). Scyphistomae from ‘warm’ (16°C) parents displayed the greatest reproductive potential (2.63 buds) at medium temperature (12°C). Cold temperature (8°C) caused considerable inhibition of asexual reproduction in offspring scyphistomae, independent of the parental thermal history. Transgenerational acclimation may benefit potentially invasive jellyfish species facing climate-related and/or human-induced changes in the global marine environment, by facilitating asexual reproduction and subsequent bloom events.

Seasonal dynamics of the scyphomedusa Pelagia noctiluca were studied along with their relation to certain environmental factors between the study period that extends from January 2018 to December 2019. During 2018, stranded individuals of P. noctiluca appeared throughout this year, but their high frequency was reported in the summer. While in contrast, P. noctiluca in 2019 was reported in a very low number only during the winter season and had not been detected in the other seasons of this year. The overall results revealed that the inter-annual variations in the abundance of jellyfish were not significantly (P

Post-collapse of seasonal blooms of gelatinous zooplankton (Cnidaria, Ctenophora, and Thaliacea) sinking carcasses transports labile carbon (jelly-C) to benthic continental margins and the deep sea. In recent decades, bloom frequency and intensity have increased globally; however, how sinking jelly-C affects benthic communities is poorly known. Further, as climate change and other anthropogenic impacts may increase gelatinous blooms in the future, understanding the contributions and impacts of jelly-C upon benthic communities is of pivotal importance. Thus, in this study, we assessed jelly-C deposits post-intense blooming of a pelagic species of marine colonial gelatinous tunicate in the Thaliacean class, Pyrosoma atlanticum. We studied the seabed using a remotely operated vehicle (ROV) from 26 to 1,276 m, documenting jelly-C deposits and species of the megafaunal benthic community. Environmental variables from water column profiles at transects near our own off the Ivory Coast of West Africa were used in assessments. Jelly-C biomass peaked at 400 m (1,500 grC 100 m−2) and remained at the average (300 grC 100 m−2) through 1,276 m. Typically, in depth strata between 300 and 800 m, peaks in jelly-C biomass (500 to 1,500 grC 100 m−2) corresponded to areas with significantly reduced benthic megafaunal species abundances as well as diversity. From 800 to 1,276 m, we noted patchier jelly-C biomass deposits where individual megafauna species abundances and diversity correspondingly increased, yet total organism counts remained low. We observed 11 species from 5 phyla directly feeding on jelly-C and 10 single-species aggregations triggering megafaunal dominance events at various localized depth strata. Although such dynamics have been hypothesized and examined for some time with respect to phytodetritus biomass, they have been rarely described for jelly-C. Thus, our novel findings for jelly-C dynamics in the offshore regions can help to provide a better understanding of the ecological role that this component plays in marine benthic ecosystems and continental margins.

The cannonball jellyfish Stomolophus meleagris display colour variations from blue to purple, and different pigmentation patterns on the umbrella surface. Although these colour phenotypes are commo...

Blooms of stinging pelagic cnidarians have been causing increasing health problems for humans worldwide. Physalia physalis is among the worst stinging species in the Atlantic and Pacific oceans along the North and South American coasts. This siphonophore species has a large gas float and lives at the ocean surface, where its distribution is affected mainly by winds. P. physalis's strandings were observed in the southeastern Pacific Ocean for three consecutive years (2014 to 2016). Data of stranded P. physalis were gathered daily through a collaborative effort between the Chilean Navy and the Chilean Ministry of Health. The association between oceanographic variables and the stranded P. physalis was assessed using a generalized additive mixed model (GAMM) and cross-correlation analysis. The largest stranding occurred along more than 2600 km of coastline and totaled 44,683 colonies. Most of the strandings were along the central and south-central coast of Chile, where almost 200 people were stung, and more than 120 beaches were closed in summer 2016. The GAMM model showed that the oceanographic conditions of warmer temperatures during the winter periods and the weakening of the westerly winds associated with the Niño Southern Oscillation (ENSO) were the most likely causes for the arrival of transport from the colonies to the coast. Also, our analysis illustrates the utility of collaborations among scientists and public organizations to promote large-scale and long-term understanding and provide a model for predicting this dangerous species' arrival and warning for beaches and swimmers, which is of global importance for human health.

In Thailand, two species of rhizostome jellyfish, Rhopilema hispidum and Lobonemoides robustus, are commercially harvested. The cnidomes, nematocyst size and toxicities were compared between these species. Rhopilema hispidum and L. robustus each had four types of nematocysts on their oral arms. For R. hispidum, these nematocyst types included two types of isorhiza and two types of rhopaloid, while in L. robustus, there were three types of isorhiza and one type of rhopaloid. For R. hispidum, tubule lengths of the largest nematocyst type (large round isorhiza; mean ± SD = 313.8 ± 62.2 μm) were significantly longer than those of L. robustus (large ellipsoid rhopaloid; 162.1 ± 38.5 μm). Using the freshwater shrimp, Palaemon paucidens, in a bioassay, we determined that the lethal nematocyst concentrations for R. hispidum and L. robustus were 5705.3 ± 1118.1 and 3408.3 ± 1032.9 unit g−1 wet weight, respectively, and that these concentrations were significantly higher in the former than in the latter.

Since the mid-1980s, swarms of the rhizostome Rhopilema nomadica have been an annual phenomenon in Israeli Mediterranean coastal waters during the summer months. Despite its annual prominence and the potential impact on food webs and ecosystem services, studies concerning its feeding ecology and its interactions with other biota in the marine food web have not been conducted. During summer 2015 gut contents of 41 R. nomadica were analysed as well as ambient plankton assemblages. More than 60% of the medusae diet was found to consist of microzooplankton R. nomadica consumed faster swimming prey while smaller medusae relied more on the slower swimming taxa. The medusan diet reflected most of the ambient plankton taxa, but no statistically significant correlations between the relative abundance in diet and ambient plankton were found. As summer progressed, there was a gradual decrease in both mean medusa bell diameter (from 42.2–16 cm) and integrity of feeding structures. These findings suggest that R. nomadica, at least at the time of its appearance in Israeli coastal waters, may exert less predatory pressure on the plankton than we might otherwise expect.

The catostylid jellyfish,Crambionella annandaleiwas originally described by Rao (1932) based on a preserved specimen collected from the Andaman Sea. Since then, no detailed taxonomic studies have been conducted and the species is often misidentified. Here, we provide a detailed morphological re-description ofC. annandaleifrom fresh material collected at a variety of locations along the east coast of India. The species can be distinguished from its congeners by a combination of morphological characters, the most important of which are the proportion of terminal club length to oral arm length (0.48 ± 0.031), the proportion of the distal portion of the oral arm to naked proximal portion (7.25 ± 0.268) and the body colour. The occurrence of intra-specific colour variation in fresh specimens was also observed in the present study.

Marine lakes represent a unique aquatic environment. Here, we tested if prokaryotic communities of water, sediment, jellyfish, mussel and sponge biotopes differed in composition, higher taxon abundance and diversity. All of these proved to differ significantly among biotopes. In addition to this, we also observed significant differences in composition and diversity in mussel populations from different marine lakes. Diversity was particularly low in jellyfish populations, which were dominated by a single OTU, assigned to the genus Endozoicomonas, although individual samples also contained relatively abundant OTUs assigned to other phyla (e.g., Tenericutes). In contrast to jellyfish, Brachidontes mussels from different lakes housed highly distinct prokaryotic communities in terms of diversity and composition. An OTU assigned to the genus Endozoicomonas dominated mussels from a lake with limited connection to the open sea. Prokaryotic communities in mussels from a more connected marine lake were, in contrast, much more diverse. Sponges housed prokaryotic communities that were similar, but still distinct, to those found in water. Our results show that benthic and pelagic communities of marine lake organisms house distinct prokaryotic communities. Future research should focus on the functional implications of these differences and how they contribute to maintaining a healthy lake environment.

Jellyfish population play an important role in aquatic food chains, and many animals predate on this ‘mostly water containing’ organisms. However, what gelativores predators could gain from their prey is still poorly understood. This study provides insight into the nutritional value of the moon jelly (Aurelia aurita) by means of its fatty acid (FA) composition, while investigating seasonal variability and differences between its free-swimming life stages. A biweekly sampling was carried out in a temperate coastal ecosystem, the Kiel Fjord, Germany and during two consecutive years. FA profile of A. aurita showed significant seasonal variability, while mature medusae (due to reproductive tissues) possessed highest FA content. In addition, moon jelly contained several essential FAs (i.e. arachidonic acid, 20:4ω6; eicosapentaenoic acid, 20:5ω3; docosahexaenoic acid, 22:6ω3), which likely support predator’s vital physiological functions. Even though total FA contents proved to be low (7 × 10−3–34 × 10−3% per g dry weight), evidence supporting A. aurita’s capability to meet the dietary requirements of predators such as fish and crustaceans is provided. Finally, implications for gelativore and future food web configurations are discussed, while proposing that jellyfish are likely to be, and become, more than an opportunistic prey to many organisms.

Ctenophora are important components of marine ecosystems. However, the South-western Atlantic and Sub Antarctic region are still one of the least studied region in the world. We report the species ...

Jellyfish (JF) swarms impact human wellbeing and marine ecosystems. Their global proliferation is a matter of concern and scientific debate, and the multitude of factors affecting (and affected by) their density and distribution merits long-term monitoring of their populations. Here we present an eight-year time series for Rhopilema nomadica, the most prominent JF species swarming the Eastern Mediterranean Sea. Reports were submitted by the public and within it a group of trained participants via an internet website between June 2011 and June 2019. Data collected included species, size, location, ranked amount and stinging. Swarms of R. nomadica prevailed in July and ended in August but were also prominent in winter from January to March. Both observations deviate from past swarming patterns described in the late 1980s, when summer swarms persevered until October and winter swarms were not documented. Climate change (increasing water temperature) and the westwards up-current spread of R. nomadica are discussed as possible explanations for this phenological shift. We further demonstrate how data obtained by Citizen Science is used to develop a swarming indicator and monitor JF in time and space, and propose a forecast based on these observations.

Worldwide catches of cannonball jellyfish Stomolophus meleagris (Cnidaria: Scyphozoa) have increased during the last years; nevertheless, this species still lacks updated biological knowledge for its management. This research proposes that the individual growth pattern for jellyfish can be estimated in the absence of age readings through cohort follow-up over time and by multi-model inference approach (MMI). Length data were obtained during 2010–2011 in Gulf of California to obtain cohort information using a multinomial analysis and then assign age; growth model selection was based on MMI. Three cohorts were identified and the von Bertalanffy model suitably described their growth. The species has an accelerated growth with a short life cycle; cohorts one and two reached their asymptotic length, and the third one barely reached the length-at-first sexual maturity. Growth variations among cohorts could be explained by their different biological strategies where the first two prioritized asymptotic length and the third one reproduction length. The three cohorts shared a common goal for medusoid phase, which was sexual reproduction. This information could be used for estimating harvest rates or assessing their capacity for redoubling as an invasive population in coastal ecosystems. The proposed methodology may be applied in other jellyfish species around the world.

Almost nothing is known about the historical abundance of the ocean sunfish. Yet as an ecologically and functionally important taxa, understanding changes in abundance may be a useful indicator of how our seas are responding to anthropogenic changes including overfishing and climate change. Within this context, sightings from a coastal bird observatory (51.26$$^\circ$$ ∘ N, 9.30$$^\circ$$ ∘ W) over a 47 year period (from April to October 1971–2017) provided the first long-term index of sunfish abundance. Using a general linear mixed effect model with a hurdle to deal with imperfect detectability and to model trends, a higher probability of detecting sunfish was found in the 1990s and 2000s. Continuous Plankton Recorder (CPR) phytoplankton color indices and the annual mean position of the 13 $$^{\circ }$$ ∘ C sea surface isotherm were significantly correlated with the probability of detecting sunfish. An increase in siphonophore abundance (as measured by the CPR) was also documented. However, this increase occurred 10–15 years after the sunfish increase and was not significantly correlated with sunfish abundance. Our results suggest that the observed increase in sunfish sightings is evidence of a range expansion because it was significantly correlated with the mean position of the 13 $$^{\circ }$$ ∘ C isotherm which moved northwards by over 200 km. Furthermore, the observed increase in sunfish occured 10 years before sunfish sightings are documented in Icelandic and Norwegian waters, and was concurrent with well-known range expansions for other fish species during the 1990s. This study demonstrates how sustained citizen science projects can provide unique insights on the historical abundance of this enigmatic species.

High throughput low-density SNP arrays provide a cost-effective solution for population genetic studies and monitoring of genetic diversity as well as population structure commonly implemented in real time stock assessment of commercially important fish species. However, the application of high throughput SNP arrays for monitoring of invasive species has so far not been implemented. We developed a species-specific SNP array for the invasive comb jelly Mnemiopsis leidyi based on whole genome re-sequencing data. Initially, a total of 1,395 high quality SNPs were identified using stringent filtering criteria. From those, 192 assays were designed and validated, resulting in the final panel of 116 SNPs. Markers were diagnostic between the northern and southern M. leidyi lineages and highly polymorphic to distinguish populations. Despite using a reduced representation of the genome, our SNP panel yielded comparable results to using a whole genome re-sequencing approach (832,323 SNPs), recovering similar values of genetic differentiation between samples and detecting the same clustering groups when performing Structure analyses. The resource presented here provides a cost-effective, high throughput solution for population genetic studies, allowing to routinely genotype large number of individuals. Monitoring of genetic diversity and effective population size estimations in this highly invasive species will allow for the early detection of new introductions from distant source regions or hybridization events. Thereby, this SNP chip represents an important management tool in order to understand invasion dynamics and opens the door for implementing such methods for a wider range of non-indigenous invasive species.

Highlights: • Sightings of non-native of range expanding marine species in the SW Baltic Sea • Novel approach for classification of hydrographic conditions in the SW Baltic Sea • Linking sightings of species to hydrographic environmental anomalies Abstract: The Baltic Sea, located in northern Europe, is one of the largest brackish water bodies in the world. Salinity levels range from fresh water conditions in the northeast to full strength saline waters at its transition zone to the North Sea in the west. Most of the water exchange happens in the SW Baltic Sea, the Belt Sea, where fresh water exits the Baltic Sea at the surface, while high saline, oxygen rich water is entering the Baltic at depth. Due to the extended salinity gradient of the Baltic Sea, a variety of species occur at the limit of their physiological tolerance and preference, i.e. in areas and habitats not representing their marine or fresh water origin. Additionally, the Baltic Sea is known for its high share of non-indigenous species, which have established. In this study, we compiled extraordinary sightings of transient, non-native or potentially range expanding species in the SW Baltic Sea for a period from 2001 to 2018. We focused on jellyfish, squid, fishes and marine mammals and linked their occurrences to the local hydrography. Hydrographic conditions, such as water temperature and salinity, were obtained from a high spatio-temporally resolved hydrodynamic Baltic Sea model, covering a daily resolved 40-year time series. We investigated that changes in the occurrence of exceptional species reflect the dynamics of water mass exchange between the Kattegat/Skagerrak and the SW Baltic Sea. Our analyses show that these changes could be related to the presence of anomalously high saline water masses. However, only a minor part of the sightings was caused by major Baltic inflow events, which are important to sustain oxygen rich deep water in the central Baltic Sea. This documents that the hydrographically highly dynamic SW Baltic Sea needs special attention for monitoring of non-indigenous species, as (i) high saline and warm water intrusions are more frequent than currently believed and ii) can be linked to sightings of exceptional species in the SW Baltic Sea. Additionally, most of the recent sightings occurred during anomalously warm periods. This supports the hypothesis, that the Baltic Sea is presently a predominant receiver area for non-indigenous species from warmer regions of the world.

Made available in DSpace on 2020-12-10T19:46:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-20 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Feeding strategies provide essential information to help understand symbiotic relationships and resource competition as well as environmental integrity. This study examined the feeding ecology of the spider crab Libinia ferreirae, which is commonly associated with the jellyfish Lychnorhiza lucerna during part of its life cycle, especially the juvenile stage. In the adult phase, the crab is a host for many epibionts that live on its carapace. The crabs were collected in 1 year, and the stomach contents were analyzed by the percentage points and the frequency of occurrence of the food items. We identified ten food items (food in the advanced stage of digestion was unidentifiable) and microplastic particles in the gastric contents of the crabs. The food items with high abundances were sediment, crustaceans, and cnidarians. We found niche partitioning of the spider crab's diet during the benthic (free-living) and planktonic (L. lucerna association) phases. The fact that microplastic is part of the diet of L. ferreirae is concerning and shows how environmental contamination with plastic material has been incorporated into the marine food chain as a whole. Sao Paulo State Univ, Grp Studies Crustacean Biol Ecol & Cultivat NEBEC, Zool Dept, Inst Biosci Botucatu, BR-18618970 Sao Paulo, Brazil Sao Paulo State Univ, Grp Studies Crustacean Biol Ecol & Cultivat NEBEC, Zool Dept, Inst Biosci Botucatu, BR-18618970 Sao Paulo, Brazil CAPES: CIMAR II 23038.004310/2014-85 FAPESP: 2010/50188-8 FAPESP: 2014/13770-1 FAPESP: 2018/01659-0 CNPq: 303371/2011-0 CNPq: 311034/2018-7

Within the Eastern Bering Sea, the jellyfish Chrysaora melanaster has fluctuated widely over recent decades. We examined the role of C. melanaster as an ecosystem-structuring agent via application of ecosystem models representing inner-, mid-, and outer-shelf regions of comparable areal coverage. Chrysaora melanaster utilize 1% of total mid-shelf consumer production, or 1/4th the energy required by forage fish (capelin Mallotus villosus, Pacific herring Clupea pallasii, age-0 Pacific cod Gadus macrocephalus, age-0 walleye pollock Gadus chalcogrammus). Model simulations show the impacts of C. melanaster are broadly distributed across consumer groups with increasingly negative impacts with higher jellyfish biomass. Age-0 pollock represent the greater part of the forage fish biomass, and observed pollock biomass during low jellyfish years (2004–2007) was significantly greater than during high jellyfish years (2009–2014). However, sensitivity among consumer groups to observed jellyfish variability is small, within 5% of baseline (2004–2015) conditions. Estimates using similar models for the Coastal Gulf of Alaska (CGoA) and Northern California Current (NCC) suggest large differences in the role of scyphozoans among northern Pacific shelf ecosystems. Only 0.1% of total summer consumer production is required to support CGoA Chrysaora, while the coastal NCC population uses 19%.

The abundance and distribution of plastic debris at the sea surface shows considerable variability over different spatial scales. Some of the oceanographic processes at small (n= 11 sites with slicks) in the coastal waters of Rapa Nui (Easter Island) during two campaigns in austral summer (January 2018) and autumn (April 2019). In general, passive particles, including plastics, exuviae, eggs and foraminiferans, were found more frequently inside than outside the slicks. In some cases, motile zooplankton organisms such as chaetognaths, vertically migrating crustaceans and early developmental stages (EDS) of fish were also more common within the slicks. In addition, a positive relationship was found between plastics and planktonic organisms such as foraminiferans, snails and jellyfish (e.g.,Velella velella), although a strong correlation was also found with fish EDS and chaetognaths. These results suggest that surface slicks are areas of aggregation for both passive particles and active organisms, thus playing an important ecological role in food retention and particle concentration where the risk of plastic ingestion by fish and seabirds is enhanced.

Phenomena such as global warming, rising sea temperatures and extreme weather and climate anomalies such as floods and heat waves have been shown to alter absolute salinity values. While affecting marine and estuarine population dynamics, these scenarios may also favour the invasion and proliferation of opportunistic and potentially harmful species in new geographical areas—such as blooming jellyfish. These organisms are one of the less studied taxa, particularly the proliferative asexual benthic phase, to which effects of in situ and experimental global change scenarios are poorly addressed. Acclimation and plasticity to global change scenarios were individually assessed through life history and physiological responses (survival, settlement time, time until maturity, feeding activity, asexual reproduction and behaviour) of laboratory-reared ciliated buds and polyps (= scyphostomae) of the invasive Phyllorhiza punctata (Cnidaria: Rhizostomeae). The present study evaluated the effects of two temperature levels (21 °C—current thermal scenario, or 25 °C—warming scenario) and six salinity regimes resembling estuarine and marine conditions (15, 20, 25, 30, 35 or 40) during 21 days. Under warming, P. punctata scyphostomae showed faster development and budding rates upon estuarine-like salinities, but higher mortality and reduced development under marine-like conditions—an ecological niche trade-off since at 21 °C such pattern was not found. Overall, our results suggest that global changes might prompt P. punctata proliferation through polyp colonisation mainly in estuarine areas and potentially increase blooming events with further implications at local and regional scales.

With the continuous development of jellyfish fisheries and food products around the world, an effective traceability system has become increasingly prominent. This study provides insight into the origin traceability and authentication of two commercially important jellyfish species, flame jellyfish Rhopilema esculentum and Nomura’s jellyfish Nemopilema nomurai, while investigating the intra- and inter-specific variation in fatty acid (FA) profiles and carbon and nitrogen stable isotope ratios (δ13C and δ15N). Results showed significant differences in FA profiles and isotopic values in fresh bell tissues between wild and farmed R. esculentum and among geographic origins, possibly due to different food sources, nutritional status, and energy costs that each group experiences at a given location. The linear discriminant analysis indicated that δ13C, δ15N, C16:0, C17:0, C18:0, C16:1n7, and C20:5n3 were suitable discriminatory variables with a high rate of correct classification for distinguishing origins of R. esculentum. In addition, inter-specific FA profiles/biomarkers, combined with isotopic values, suggests the variety of dietary sources and trophic positions of sympatric similar-sized R. esculentum and N. nomurai and the potential use of biomarkers, especially stable isotope analysis, for distinguishing sympatric jellyfish species. These results highlighted the complementarity of FA and stable isotope analyses and provide an alternative approach for improving the origin traceability and authenticity evaluation of untreated edible jellyfish. Furthermore, this study adds new information regarding the biochemical compositions of jellyfish species.

Funding: The publication of this manuscript was kindly funded by the state of Bremen. JL acknowledges financial support through Postgraduate Research Scholarships awarded by Griffith University. Many pigments, such as melanins, are widely distributed throughout the animal kingdom. Others have arisen as novelties in particular lineages, for example, the Green Fluorescent Protein (GFP) found in cnidarians. While GFPs, widely used as fluorescent tags in biomedical research, are the most famous cnidarian example, other novel proteins have also been identified within this phylum. A blue protein that contains a Kringle (KR) domain inserted within a Frizzled cysteine-rich domain (Fz-CRD) was previously described from the jellyfish Rhizostoma pulmo (named rpulFKz1), however little is known about this pigment’s evolution or distribution among cnidarians. We performed a systematic search for homologs of this protein in published genomes and transcriptomes of 93 cnidarians. Phylogenetic analyses revealed eight predicted proteins that possess both domains in the same arrangement and that fall within the same clade as rpulFKz1. The sequence of one of these proteins contains motifs that match sequenced peptides of Cassio Blue, the blue pigment from Cassiopea xamachana. Another one of these proteins belongs to Stomolophus meleagris, and chemical studies on blue pigments that may occur in this genus have shown similarities to rpulFKz1 and Cassio Blue. Therefore, we hypothesize that the eight rpulFKz1 homologs identified are also pigment precursors. All precursors identified were exclusive to jellyfish in the order Rhizostomeae, so we herein name this new pigment family “rhizostomins.” Not all rhizostomes analyzed are blue, however, so these rhizostomin proteins may also be responsible for other colors, or perform other biochemical and biophysical roles. Previous studies have hypothesized that cnidarian pigments are photoprotective, and this study serves as basis for future investigations not only on the function of rhizostomins, but also on potential biotechnological applications for these proteins. Publisher PDF

Despite the diversity and oftentimes large biomass of jellyfish in marine systems, their ecological role remains poorly understood. We here provide the first systematic review of studies on jellyfish trophic ecology in the Baltic Sea (a regional marine system under strong multiple global and regional anthropogenic pressures). In total, we identified 57 peer-reviewed publications, with notable taxonomic bias towards two species (Aurelia aurita; non-indigenous Mnemiopsis leidyi) and spatial bias towards five areas (Bornholm Basin, Kiel Bight, Kertinge Nor, Lim- and Gullmarsfjord). The studies provide evidence for diverse trophic roles of jellyfish as predators and as competitors of other jellyfish, zooplankton and fish species. In combination, the studies also highlight potentially large impacts via top-down (grazing) and bottom-up (nutrient excretion) effects, but also, strong spatio-temporal variability in the magnitude of these effects, depending on the occurrence of jellyfish blooms. Studies on the role of jellyfish as prey for fish, seabirds or marine mammals, and for benthic systems via food-falls, were limited or lacking for the Baltic Sea, despite increasing focus on these topics globally. Improved understanding of the temporal (seasonal, inter-annual, long-term) and spatial variability of blooms and corresponding trophic effects, would provide more systematic understanding of the ecological role of jellyfish in the spatio-temporally variable Baltic Sea. A broader spatial coverage, inclusion of more jellyfish taxa and under-studied early life history stages, as well as the implementation and continuation of long-term data series would represent important steps towards this goal.

The supply of nutrients for agricultural production faces enormous challenges as food security and sustainability goals have to be ensured. Processing of marine biomass has high potential to provide nutrients for agricultural purposes in coastal areas. One underexplored resource are jellyfish, which occur as blooms and by-catch of the fishing industry. In this context, a pot experiment investigated the effects of jellyfish as a fertilizer on biomass accumulation of annual ryegrass (Lolium multiflorum), and its effect on the important greenhouse gas N2O as a sustainability indicator of novel fertilizers. Dried and ground jellyfish was applied [3 species: Aurelia aurita (AA), Cyanea capillata (CC), Periphylla periphylla (PP)] and compared with an unfertilized and a mineral fertilized (calcium-ammonium-nitrate, CAN) treatment. Dried jellyfish and CAN were applied at equal N rates of 5 g N per m2. The N2O-fluxes from soil were measured over 56 days after fertilizer application. Grass dry matter yields, when using CC and PP treatments, were not significantly different to the CAN treatment (p > 0.05). After reducing its salinity, AA also showed no differences to CAN on plant growth and the lowest coefficient of variation for dry matter yield as an indicator for yield stability. Accumulated N2O-emissions were lowest in the control and were 3-times higher in AA and CC compared to CAN (p < 0.05). If salinity levels are moderate, jellyfish application to soil can compete with artificial mineral fertilizers in terms of N-supply for above- and belowground yield response, regardless of jellyfish species used. However, elevated N2O-emissions are likely to affect its suitability for large-scale application. Nevertheless, if energy-efficient methods of drying and desalination of jellyfish can be developed, in coastal areas dried jellyfish is a valuable fertilizer in coastal areas, particularly in situations where nutrient supplies for agriculture are limited.

142 scientific publications have been reviewed on the characteristics of the scyphozoans with respect to their ability to develop blooms and the most significant environmental characteristics that determine them. Special attention was paid to depth, temperature, salinity, chlorophyll concentration, and the habitat of the 39 registered blooming genera. After the review, we find that over the past decades, the number of scyphozoan blooming-species is higher than previously recorded, increasing from circa 14% to 25% of the class. Species that inhabit depths less than 27.1 m are prone to produce blooms, particularly in semienclosed areas with low rates of water renewal and high thermal amplitudes. Temperature appears as the main environmental factor controlling blooms, but food availability is essential to sustain the proliferations. Interspecies variability in the response to environmental factors observed in this work suggest that bloom predictive models should be constructed species-habitat-specific.

The characterization of the internal microenvironment of symbiotic marine invertebrates is essential for a better understanding of the symbiosis dynamics. Microalgal symbionts (of the family: Symbiodiniaceae) influence diel fluctuations of in host O2 and pH conditions through their metabolic activities (i.e., photosynthesis and respiration). These variations may play an important role in driving oxygen budgets and energy demands of the holobiont and its responses to climate change. In situ measurements using microsensors were used to resolve the O2 and pH diel fluctuations in the oral arms of non-calcifying cnidarian model species Cassiopea sp. (the “upside-down jellyfish”), which has an obligatory association with Symbiodiniaceae. Before sunrise, the internal O2 and pH levels were substantially lower than those in ambient seawater conditions (minimum average levels: 61.92 ± 5.06 1SE μmol O2 L–1 and 7.93 ± 0.02 1SE pH units, respectively), indicating that conditions within Cassiopea’s oral arms were acidified and hypoxic relative to the surrounding seawater. Measurements performed during the afternoon revealed hyperoxia (maximum average levels: 546.22 ± 16.45 1SE μmol O2 L–1) and internal pH similar to ambient levels (8.61 ± 0.02 1SE pH units). The calculated gross photosynthetic rates of Cassiopea sp. were 0.04 ± 0.013 1SE nmol cm–2 s–1 in individuals collected at night and 0.08 ± 0.02 1SE nmol cm–2 s–1 in individuals collected during the afternoon.

Causes and consequences of jellyfish bloom formation are subject to controversial discussions worldwide. While medusae have been studied to a broader extent, the knowledge on polyp stages of scyphozoans is limited thus hampering reliable prediction of jellyfish bloom formation. This study describes the occurrence, abundance, habitat characteristics and interactions of scyphozoan Aurelia sp. polyp colonies with other fouling organisms in intertidal and subtidal sectors of Trondheimsfjorden (Norway). In total, 982 polyps were found on 70 substrata of varying material types during a field survey in spring-summer 2018 along a longitudinal gradient within and outside Trondheimsfjorden. The polyps were identified as Aurelia sp. based on molecular species identification. Most polyps were found in bays with macroalgae canopy on the down facing side of artificial and natural substrata (rocks, concrete, iron) and inside rock cracks. Polyp microhabitats included the surface of Ascidia mentula (solitary ascidian), increments of Pomatoceros triqueter (polychete) tubes and dead Balanus balanoides (barnacle) shells. Based on the deployment of settling plates, abundance of Aurelia sp. polyps ranged from 1.2 (± 0.7) to 0.12 (± 0.07) polyps cm–2. Settlement occurred either directly on the PVC settling plates or as epibionts on the ascidian Ascidia mentula and on barnacle shells of Balanus balanoides. This study provides insights into the potential of local Aurelia sp. polyps contributing to the seasonal occurrence and abundance of Aurelia sp. in fjord systems, where intensive blooms occur annually.