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"Jellyfish Blooms"
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Body size reduction under starvation, and the point of no return, in ephyrae of the moon jellyfish Aurelia aurita
Scyphozoan ephyrae need to start feeding before their endogenous nutritional reserves run out, and the success of feeding and growth is crucial to their recruitment into the medusa population. To evaluate starvation resistance in first-feeding ephyrae of the moon jellyfish Aurelia aurita s.l., we determined their point of no return (PNR50), i.e. days of starvation after which 50% of ephyrae die even if they then feed. PNR50 values were 33.8, 38.4 and 58.6 d at 15, 12 and 9°C, respectively. Before reaching PNR50, the ephyrae showed significant body size reduction: ca. 30 and 50% decrease in disc diameter and carbon content, respectively. These PNR50 values are nearly 1 order of magnitude longer than those of larval marine molluscs, crustaceans and fishes, which is attributable to the ephyra’s extremely low metabolic (i.e. respiration) rate relative to its copious carbon reserves. Such a strong endurance under prolonged starvation is likely an adaptive strategy for A. aurita ephyrae, the release of which is programmed to occur during the annual period of lowest temperatures, allowing them to cope with the concomitant seasonal food scarcity. Future studies are needed to identify causes of death for wild ephyrae, which are prone to starvation and/or predation, to forecast outbreaks prior to the season of medusa blooms.
Journal Article
Shorter, warmer winters may inhibit production of ephyrae in a population of the moon jellyfish Aurelia aurita
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.
Journal Article
Asexual Reproduction of Aurelia coerulea Polyps in situ on Settling Plates in Jiaozhou Bay, China
Jellyfish blooms are increasingly prevalent coastal phenomena, with
Aurelia coerulea
being a significant contributor. The complex life history of jellyfish, featuring a sessile polyp stage, is a key factor in bloom formation, yet it is challenging to study in the field. This study aimed to describe the asexual reproduction of
A. coerulea
polyps in Jiaozhou Bay, China, and to assess their ability to form sedentary colonies and their relationship with environmental factors. Using settling plates, we observed polyps
in situ
and documented three asexual reproduction modes: budding, strobilation, and podocyst formation. Environmental parameters including temperature, salinity, dissolved oxygen (DO), chlorophyll
a
(Chl
a
), and the biomass of phytoplankton and zooplankton were monitored. Budding was the predominant reproductive method, featuring stolon budding in autumn and direct budding during the winter and spring seasons. Strobilation took place in the colder months, releasing ephyrae between April and May. Polyp abundance was positively correlated with seawater temperature and negatively correlated with DO concentration. Polyps at 1.0 m depth showed higher survivorship and proliferation over 8 months, whereas those at 2.0 m depth experienced a steady decline and died within 4 months. The study enhances our understanding of the life cycle and asexual reproduction strategies of
A. coerulea
polyps in the field, with implications for predicting and managing jellyfish blooms. The findings underscore the importance of temperature and DO in polyp survival and suggest that initial polyp population proliferation is crucial for long-term survival.
Journal Article
Targeting metzincins to mitigate jellyfish blooms: a novel approach for conservation
IntroductionThe modification of the marine ecological environment has led to the frequent occurrence of jellyfish blooms, causing global hazards. The budding reproduction of jellyfish polyps is a critical factor in their population size, yet there is limited understanding of the molecular mechanisms involved in this process. This study aims to explore the intrinsic regulatory factors of the budding of jellyfish Aurelia coerulea (A. coerulea) polyps from the perspective of jellyfish biotoxin and to develop new strategies for the management of jellyfish abundance.MethodsThe main biological toxins of the A. coerulea polyp were screened through the integrated analysis of transcriptomic and proteomic data. The broad-spectrum metalloproteinase inhibitor, ethylenediaminetetraacetic acid (EDTA), was employed to treat polyps for observing its effect on the budding of A. coerulea polyps. Through conducting the detection of metzincin proteolytic activity, molecular docking and kinetic analysis, as well as transcriptomic analysis and RT-qPCR verification before and after EDTA treatment of the polyp, the key biological toxins and the mechanisms influencing polyp budding were clarified.ResultsFour types of the metzincin family of metalloproteinases constituted the main biotoxins in the A. coerulea polyp. Among them, astacins (NAS) were the predominant metzincins of the A. coerulea polyp. We discovered that EDTA significantly inhibited the activity of metzincins and the budding of A. coerulea polyps. EDTA was capable of stably binding to the zinc-binding active sites of the four major types of metzincins in the A. coerulea polyp and could down-regulate the expression levels of key metzincin molecules and enrich multiple pathways related to development.ConclusionThis study elucidates the effects of metzincins on the budding of jellyfish polyps, providing a potential target for mitigating jellyfish blooms.
Journal Article
Long-term time-series study of salp population dynamics in the Sargasso Sea
Salps are bloom-forming, pelagic tunicates with high grazing rates on phytoplankton, with the potential to greatly increase vertical particle flux through rapidly sinking fecal pellets. However, the frequency and causes of salp blooms are not well known. We quantified salps from day and night zooplankton net tows in the epipelagic zone of the North Atlantic subtropical gyre as part of the Bermuda Atlantic Time-series Study (BATS). Salp species and size were quantified in biweekly to monthly tows from April 1994 to November 2011. Twenty-one species of salps occurred at the BATS site over this time period, and the most common bloom-forming salps were Thalia democratica, Salpa fusiformis, Weelia (Salpa) cylindrica, Cyclosalpa polae, and Iasis zonaria. Five species of salps exhibited diel vertical migration, and salp abundances varied seasonally, with T. democratica, S. fusiformis, and C. polae blooms coincident with the spring phytoplankton bloom, and W. cylindrica blooms occurring more often in late summer. For T. democratica, mean annual biomass increased slightly over the time series and was elevated every 3 yr, and biomass increased in the presence of cyclonic mesoscale eddies. Decadal climate oscillations and biogeochemical conditions influenced multi-year trends in salp abundance and biomass. Both total salp and T. democratica abundance were positively correlated with primary production, total salp biomass was positively correlated with the North Pacific Gyre Oscillation, and T. democratica biomass was negatively correlated with the Pacific Decadal Oscillation. These salp bloom dynamics have important implications for planktonic food web interactions and biogeochemical cycling.
Journal Article
Transgenerational acclimation influences asexual reproduction in Aurelia aurita jellyfish polyps in response to temperature
Climate change events and anthropogenic activities (e.g. translocation of nonindigenous 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.
Journal Article
Associations of large jellyfish distributions with temperature and salinity in the Yellow Sea and East China Sea
Climate change may contribute to the increasing frequency and intensity of jellyfish blooms around the world. To test the null hypotheses that distributions did not differ among species of jellyfish or according to temperature salinity, we sampled large jellyfishes using bottom trawl surveys during 2006–2007 in the Yellow Sea (YS) and East China Sea (ECS). The total biomass of large jellyfish in the YS was low in April 2006 in cool waters, increased with warming waters, peaked in early September 2006 (22,891 ± 25,888 kg km
–2
), and then decreased with cooling to minimal biomass during March 2007. During its peak early September 2006,
Nemopilema nomurai
was relatively eurythermal and distributed throughout the YS.
Cyanea
spp. occurred in warmer waters and attained maximum biomass in May 2007 in the ECS. Ulmaridae, which preferred colder temperatures, reached maximum biomass in October 2006 and occurred mainly in the central YS.
Aequorea
spp. usually occurred in colder waters, with maximum biomass in May 2007 mainly north of 30°N. Our analyses suggest that environmental preferences of the large jellyfish may enable prediction of jellyfish population sizes and distributions in Chinese waters, which is essential in order to address ecological problems caused by large jellyfish blooms in East Asia Waters.
Journal Article
Intraguild predation by polyps of three scyphozoan jellyfish: Nemopilema nomurai, Aurelia coerulea, and Rhopilema esculentum
Jellyfish blooms occur worldwide and have resulted in serious problems in tourism, fisheries, coastal industries, and the marine ecosystem. The life cycle of scyphozoan jellyfish consists of a pelagic medusa stage and a benthic polyp stage. Success of asexual reproduction of the polyps determines directly the number of medusae; thus, the polyp stage is the key to understanding the population dynamics of medusae.
Nemopilema nomurai, Aurelia coerulea
, and
Rhopilema esculentum
are three scyphozoan jellyfish commonly inhabit in Chinese coastal waters. Polyps of
A. coerulea
are easily visible, while those of
N
.
nomurai
and
R. esculentum
remain yet to be found in the wild. However, distribution of the medusa indicates that the polyps of all three species may occur together. To evaluate the distribution pattern of polyps of the three species and explore intraguild predation by the polyps, we conducted a laboratory experiment that considered the attachment sequence and size relationship of calyx diameter of the polyps. We found that the polyps of
A. coerulea
preyed on polyps of the other two species in all treatments, except when polyps of
R. esculentum
were bigger than those of
A. coerulea
. The polyps of
R. esculentum
preyed on the polyps of
N. nomurai
only when polyps of
R. esculentum
attached first and were bigger than those of
N. nomurai
. Colonies of
N. nomurai
polyps were rarely found in the places inhabited by
A. coerulea
polyps. In addition,
A. coerulea
polyps are known to inhabit at depths of less than 20 m in coastal sea, thus, we speculate that
N. tnomurai
polyp colonies might occur at depths of more than 20 m. Therefore, our finding that polyps of
A
.
coerulea
aggressively preyed on polyps of other species may help understand other such systems of jellyfish bloom in the world.
Journal Article
Natural predators of polyps of three scyphozoans: Nemopilema nomurai, Aurelia coerulea, and Rhopilema esculentum
Jellyfish blooms have become a hot research topic in recent decades because they pose a serious threat to fisheries, coastal industries, tourism, and the marine ecosystem. The life cycle of scyphozoan jellyfish consists of a pelagic medusa stage and a benthic polyp stage, where asexual reproduction and strobilation of the polyps directly affect the abundance of ephyra and subsequently medusa abundance. The dynamics of polyps are affected by both environmental and biological factors, and predation by natural predators is one of the most important biological factors.
Nemopilema nomurai
,
Aurelia coerulea
, and
Rhopilema esculentum
are three scyphozoan species that are commonly found in Chinese coastal waters, and previous studies reported that the survivorship of polyps differs among the three species when they are exposed to the same benthic community. To identify potential natural predators of polyps of these three species in Chinese coastal waters and to determine whether the predation rates on polyps of the three species differ, we collected 39 species of macrozoobenthos from the Bohai Sea, Yellow Sea, and East China Sea from May 2014 to June 2016 and conducted predation tests and predation rate measurements. We found that the nudibranchs
Pleurobranchaea novaezealandiae
,
Okenia plana
, and
Chromodoris tinctoria
and the sea anemones
Paracalliactis sinica
,
Calliactis japonica
,
Anthopleura incerta
, and
Anthopleura midori
could prey on the polyps of all three scyphozoan species. The predation rates increased with the body length of the predators. The predations rates were also related to the polyp species, although the different predators showed no consistent preference for a particular species of polyp. Our results indicate that introducing predators to locations inhabited by polyps might be a way to control the benthic polyp populations and prevent subsequent jellyfish blooms.
Journal Article