Gelatinous zooplankton can be present in high biomass and taxonomic diversity in planktonic oceanic food webs, yet the trophic structuring and importance of this "jelly web" remain incompletely understood. To address this knowledge gap, we provide a holistic trophic characterization of a jelly web in the eastern tropical Atlantic, based on δ 13 C and δ 15 N stable isotope analysis of a unique gelatinous zooplankton sample set. The jelly web covered most of the isotopic niche space of the entire planktonic oceanic food web, spanning > 3 trophic levels, ranging from herbivores (e.g., pyrosomes) to higher predators (e.g., ctenophores), highlighting the diverse functional roles and broad possible food web relevance of gelatinous zooplankton. Among gelatinous zooplankton taxa, comparisons of isotopic niches pointed to the presence of differentiation and resource partitioning, but also highlighted the potential for competition, e.g., between hydromedusae and siphonophores. Significant differences in spatial (seamount vs. open ocean) and depth-resolved patterns (0-400 m vs. 400-1000m) pointed to additional complexity, and raise questions about the extent of connectivity between locations and differential patterns in vertical coupling between gelatinous zooplankton groups. Added complexity also resulted from inconsistent patterns in trophic ontogenetic shifts among groups. We conclude that the broad trophic niche covered by the jelly web, patterns in niche differentiation within this web, and substantial complexity at the spatial, depth, and taxon level call for a more careful consideration of gelatinous zooplankton in oceanic food web models. In light of climate change and fishing pressure, the data presented here also provide a valuable baseline against which to measure future trophic observations of gelatinous zooplankton communities in the eastern tropical Atlantic.

Understanding the interaction between organisms' life history traits and environmental factors is an essential task in ecology. In spite of the increasing appreciation of jellyfish as an important component in marine ecosystem, there are still considerable gaps in understanding how the phase transition from the benthic polyp to the pelagic medusa stage is influenced by multiple environmental factors, including nutrition. To investigate survival, growth, and phase transition of Aurelia aurita polyps, we designed a factorial experiment manipulating food quantity (20 μg C, 5 μg C and 1.5 μg C polyp -1 every other day), food quality (Artemia salina and two dietary manipulated Acartia tonsa), and temperature (13 °C, 20 °C, and 27 °C). Temperature was the key factor determining phase transition of polyps and negatively affecting their survival rate and

Many marine invertebrates including ctenophores are capable of extensive body regeneration when injured. However, as for the invasive ctenophore Mnemiopsis leidyi, there is a constant subportion of individuals not undergoing whole body regeneration but forming functionally stable half-animals instead. Yet, the driving factors of this phenomenon have not been addressed so far. This study sheds new light on how differences in food availability affect self-repair choice and regeneration success in cydippid larvae of M. leidyi. As expected, high food availability favored whole-body regeneration. However, under low food conditions half-animals became the preferential self-repair mode. Remarkably, both regenerating and half-animals showed very similar survival chances under respective food quantities. As a consequence of impaired food uptake after injury, degeneration of the digestive system would often occur indicating limited energy storage capacities. Taken together, this indicates that half-animals may represent an alternative energy-saving trajectory which implies self-repair plasticity as an adaptive trade-off between high regeneration costs and low energy storage capacities. We conclude that self-repair plasticity could lead to higher population fitness of ctenophores under adverse conditions such as in ships’ ballast water tanks which is postulated to be the major vector source for the species’ spreading around the globe.

Abstract 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.

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The impacts of biochemicals driving food web processes are under investigation for just the last few decades. In addition, as jellyfish are drawing increasing attentions because of their mass developments and of their potential capacity of driving food web structures and energy flow by "top-down" and "bottom-up" controls. We here show that the provision with the biochemical complex thiamin (vitamin B 1 ) to the common phytoplankton Rhodomonas baltica altered its fatty acid (FA) pattern toward ω3-highly-unsaturated FAs (ω3-HUFA) and that this pattern was further transferred up to the zooplankton consumer, the copepod Acartia tonsa. However, polyps of the Jellyfish Aurelia aurita feeding on A. tonsa only had a low relative ω3-HUFA content, especially due to a reduction in 22:6ω3 (DHA), but elevated levels of 20:4ω6 (ARA). The high proportion of the ω-6 HUFA, ARA in polyps may provide evidence for preferential conversion of ARA in polyps, eventually from DHA in a so far unknown pathway. In contrast to A. tonsa, newly hatched A. salina nauplii used as food for A. aurita polyps were almost devoid of HUFA, but contained high levels of C 18 polyunsaturated FAs (C 18 -PUFA). Consequently, polyps feeding on them contained few HUFA, while high levels of C 18 -PUFA predominated. This suggests that A. aurita polyps cannot efficiently convert ω3 C 18 -PUFA to ω3-HUFA. In addition, besides a decrease in saturated FAs, especially an increase in HUFA in A. aurita polyps with decreasing temperature was observed, for which the dietary provision with HUFA seemed to be critical. Altering the FA pattern as a response of temperature reflects an adaptation to seasonal changes and may be related to their life history plasticity.

Aurelia coerulea, a type of scyphozoan jellyfish, has massively appeared in the coastal waters of China in recent years and caused great damage, but the asexual reproduction of A. coerulea polyp predicted by local temperature could not correspond well to the field abundance of jellyfish in summer. To understand the influence of winter and spring conditions on the reproductive process and to provide the basis for jellyfish population prediction, A. coerulea polyps, originally reared from planula larvae of medusae collected from Jiaozhou Bay (120.2°E, 36.1°N), were investigated at orthometric 3 overwintering temperatures (2, 5, and 8°C), 3 spring warming speeds (1°C increment every 5 days, 7.5 days, and 10 days), and 3 feeding frequencies (once per 9 days, 6 days, and 3 days), representing the range of environment conditions in winter and spring where they exist. Polyps had earlier strobilation, higher strobilation frequency, and more ephyra and bud production during warmer winter, but had intensive strobilation after colder winter when the temperature began to rise in spring. When warming speed was fast in spring, the percentage of the first strobilation was higher and ephyrae were released more intensively. However, when warming speed was slow in spring, the polyp could conduct secondary strobilation, resulting in higher strobilation frequency and more ephyrae with a longer period. High feeding frequency helped polyps accumulate more energy and promote asexual reproduction, especially beneficial to the second strobilation. This experiment shows that winter and spring temperature in addition to food availability has a significant effect on the asexual reproduction of polyp. However, these may not be only factors necessarily lead to jellyfish outbreaks in the natural environment. In the context of global warming, whether reproduction of polyps will eventually lead to the outbreak of jellyfish needs to be multifacetedly analyzed based on the complex situation in the field, such as the concentration and timing of jellyfish appearance, and their interactions with other species.

Understanding the life history strategy of organisms is key to predicting their population dynamics. The population of scyphozoan jellyfish has displayed an increasing trend in recent decades, yet its life history strategy is not fully understood. To interpret the reproduction strategy of scyphozoan jellyfish from an evolutionary ecology perspective, we dissected 10 asexual generations of Aurelia coerulea polyps to investigate the relationships between transgenerational effects on their budding reproduction and strobilation. Our results reveal that a polyp’s average budding reproduction rate declined 32.82% through asexual generations within the experimental time. Furthermore, a longer culture duration counteracted the transgenerational effects on budding rates and strobilation afterward. Thus, this effort provides insight into the necessity of sexual reproduction in organisms involving a metagenic life cycle, i.e., to renew the asexual reproduction ability of a population. Besides this, we suggest taking note that it is necessary to know the “asexual age” of polyps when performing experimental studies and mathematical modeling to explore their population dynamics. Our results also present a valuable data set to interpret the evolution of the scyphozoan jellyfish’s life history strategy under multifactorial environments.