Accurately predicting how marine biota are likely to respond to changing ocean conditions requires accurate simulation of interacting stressors, exposure regimes and recovery periods. Jellyfish populations have increased in some parts of the world and, despite few direct empirical tests, are hypothesised to be increasing because they are robust to a range of environmental stressors. Here, we investigated the effects of contaminated runoff on a zooxanthellate jellyfish by exposing juvenile Cassiopea sp. medusae to a photosystem II (PSII) herbicide, atrazine and reduced salinity conditions that occur following rainfall. Four levels of atrazine (0ngL⁻¹, 10ngL⁻¹, 2μgL⁻¹, 20μgL⁻¹) and three levels of salinity (35 ppt, 25 ppt, 17 ppt) were varied, mimicking the timeline of light, moderate and heavy rainfall events. Normal conditions were then slowly re-established over four days to mimic the recovery of the ecosystem post-rain and the experiment continued for a further 7 days to observe potential recovery of the medusae. Pulse-amplitude modulated (PAM) chlorophyll fluorescence, growth and bell contraction rates of medusae were measured. Medusae exposed to the combination of high atrazine and lowest salinity died. After 3 days of exposure, bell contraction rates were reduced by 88% and medusae were 16% smaller in the lowest salinity treatments. By Day 5 of the experiment, all medusae that survived the initial pulse event began to recover quickly. Although atrazine decreased YII under normal salinity conditions, YII was further reduced when medusae were exposed to both low salinity and atrazine simultaneously. Atrazine breakdown products were more concentrated in jellyfish tissues than atrazine at the end of the experiment, suggesting that although bioaccumulation occurred, atrazine was metabolised. Our results suggest that reduced salinity may increase the susceptibility of medusae to herbicide exposure during heavy rainfall events.

Chemical pollutants, such as pesticides, often leach into aquatic environments and impact non-target organisms. Marine invertebrates have complex life cycles with multiple life-history stages. Exposure to pesticides during one life-history stage potentially influences subsequent stages; a process known as a carry-over effect. Here, we investigated carry-over effects on the jellyfish Aurelia coerulea. We exposed polyps to individual and combined concentrations of atrazine (2.5 μg/L) and chlorpyrifos (0.04 μg/L) for four weeks, after which they were induced to strobilate. The resultant ephyrae were then redistributed and exposed to either the same conditions as their parent-polyps or to filtered seawater to track potential carry-over effects. The percentage of deformities, ephyrae size, pulsation and respiration rates, as well as the metabolic profile of the ephyrae, were measured. We detected a subtle carry-over effect in two metabolites, acetoacetate and glycerophosphocholine, which are precursors of the neurotransmitter acetylcholine, important for energy metabolism and osmoregulation of the ephyrae. Although these carry-over effects were not reflected in the other response variables in the short-term, a persistent reduction of these two metabolites could have negative physiological consequences on A. coerulea jellyfish in the long-term. Our results highlight the importance of considering more than one life-history stage in ecotoxicology, and measuring a range of variables with different sensitivities to detect sub-lethal effects caused by anthropogenic stressors. Furthermore, since we identified few effects when using pesticides concentrations corresponding to Australian water quality guidelines, we suggest that future studies consider concentrations detected in the environment, which are higher than the water quality guidelines, to obtain a more realistic scenario by possible risk from pesticide exposure.

Recurrent jellyfish blooms and their impacts on ecosystem deliverables of coastal habitats have become a major ecological concern. In view of this, repercussions of a surge in the jellyfish population on the plankton community were studied in Cochin estuary (CE), the largest tropical estuary along the southwest coast of India. Evaluation of hydrographic attributes and plankton community of the CE during early and late pre-monsoon revealed a marked disparity in its hydrography which favoured an increase in jellyfish abundances during late pre-monsoon, eliciting distinct impacts on the plankton community. The escalation in the jellyfish abundance and their subsequent predation on the crustacean plankton released the phytoplankton community from the grazing pressure resulting in a trophic cascade in the planktonic food web. The indiscriminate feeding of jellyfishes on the ichthyoplankton, decapod larvae, and Copepoda, the primary diet component of forage fishes evoked a potent threat to the fishery potential of CE.

Blooms of the non-toxic dinoflagellate Prorocentrum donghaiense are common in the East China Sea; however, the in situ impacts of these blooms on zooplankton community functions have not yet been conducted in this area. Using functional trait-based methods, we found that P. donghaiense bloom significantly changed the zooplankton community structure and functions in the coastal water of the East China Sea. Zooplankton species richness and biodiversity increased after the bloom. Based on body length, feeding type, trophic group and reproductive mode, we categorized zooplankton into four functional groups and characterized their dynamics. Before and after the bloom, the zooplankton community was dominated by herbivorous- and free-spawner- lineages represented by copepods and tunicates, while during the bloom, the zooplankton community was dominated by carnivorous- and egg-brooding- lineages represented by small jellyfish, chaetognaths and copepods.

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.

Concepts in microplastics studies are not well established due to the emerging nature of microplastic research, especially in jellyfish. We conducted experiments to test whether ephyrae would ingest more microbeads via trophic transfer than direct ingestion and whether medusae would ingest more aged microbeads than virgin microbeads. We exposed ephyrae of Aurelia coerulea to two treatments, aged microbeads and Artemia nauplii that had ingested microbeads. We found that the ephyrae ingested 35 times more microbeads via trophic transfer than by direct ingestion. In the second experiment, medusae of A. coerulea were exposed to virgin microbeads and microbeads in seawater under a 12/12 light/dark cycle or constant darkness. Ingestion rates of microbeads from the light incubation were greater than those from the dark incubation or virgin microbeads, suggesting the likely presence of photosynthetic organisms in biofilms from the light incubation increased the palatability of the microbeads and promoted their ingestion.

Jellyfish are abundant in coastal waters across broad latitudinal ranges and are often considered pests and a group that can cause phase shifts in marine ecosystems. Recent studies have highlighted their potential as biomonitors of contaminants including metals, herbicides and nutrients. Traditionally, sedentary organisms like molluscs and annelid worms have been used, but some jellyfish have similar characteristics of localised distributions and in some cases sedentary behaviour. Broad gradients in contaminant accumulation have been shown for a number of planktonic jellyfish species. An alternative biomonitoring candidate is the tropical/sub-tropical upside-down jellyfish (Cassiopea spp.). In laboratory and field deployments, Cassiopea accumulate measurable contaminants over days to weeks, making them ideal for detecting short-term pulses. Furthermore, the decay curve of contaminants varies temporally post-exposure and contaminant type. This can provide an estimate of the timing of exposure. Cassiopea, along with other jellyfish, have the potential to be an interesting and valuable group of organisms for monitoring coastal impacts.

Peripheral marine ecosystems can harbor endemic diversity and attract tourism attention, yet are generally not included in conservation management plans due to their remoteness or inland positioning. A case study in Raja Ampat of seven landlocked marine lakes containing golden jellyfish (Mastigias spp.) was conducted to address the lack of fundamental insights into evolutionary, ecological and social contexts of these ecosystems. An interdisciplinary approach was taken towards identifying the jellyfish lakes as distinct management units in order to incorporate them into existing Marine Protected Areas. Mastigias papua populations showed strong genetic (ϕST: 0.30–0.86) and morphological (F = 28.62, p-value = 0.001) structure among lakes, with putative new subspecies. Risks arising from rapid increase in tourism to Raja Ampat (30-fold since 2007) warrant restrictions on jellyfish lake use. Recommendations are provided for adaptive management and science-based conservation policies for jellyfish lakes across Indonesia.

A hypoxia event occurred in the nearshore of the northern Yellow Sea in summer 2016, and a bloom of small jellyfish occurred in June of this year. As a key copepod species in the Yellow Sea, Calanus sinicus exhibits early recruitment mainly in this nearshore area. Therefore, this study assessed the effects of these two phenomena on C. sinicus especially on their early recruitment. Sampling in nearshore waters was performed every month from May to December, except for October 2016. The numerical abundance of eggs and nauplii (E + N), copepodites and adults (C + A) of C. sinicus was determined in relation to environmental factors. Results showed that dissolved oxygen (DO) concentrations decreased from June on, attaining a minimum in August, and showed a significant positive relationship with C. sinicus E + N abundance. This suggested that decreasing DO had potential negative effects on early recruitment of C. sinicus. The abundance of small jellyfish, dominated by Sugiura chengshanense (Hydromedusa), also showed a significant positive relationship with C. sinicus E + N abundance, indicating a potential predator-prey relationship between them. Spatial relationships were also examined between E + N abundance and DO concentration in July and with small jellyfish abundance in June. Both bottom DO (B-DO) and E + N abundance in inshore waters were significantly lower than those in offshore water in July, indicating a potential negative effect of low B-DO (<6 mg L⁻¹) in nearshore water. Spatial variation of small jellyfish abundance showed no correlation with C. sinicus abundance in June, but the non-overlapping patchy distribution also suggested their potential predator-prey relationship. Together, both the seasonal and spatial results indicated that low DO and a small jellyfish bloom in nearshore waters had detrimental effects on early recruitment of C. sinicus. These negative effects thus have the potential to indirectly impact the trophodynamics of fishery resources in the northern Yellow Sea.

Gelatinous zooplankton including jellyfishes, pyrosomes, and salps serve as important prey items for a number of marine species; however, relatively few studies have examined contaminant concentrations in these animals. Scyphozoans (Aurelia sp., Chrysaora colorata, C. fuscescens, and Phacellophora camtschatica) and Thaliaceans (Pyrosoma sp.) were collected from 2009 to 2011 from Monterey Bay National Marine Sanctuary and analyzed for total mercury and selenium concentrations. In general, mercury (0.0001–0.0016 μg/g wet weight) and selenium (0.009–0.304 μg/g wet weight) concentrations of the sampled organisms were low; however, the two Pyrosoma sp. had total mercury and selenium concentrations that were one order of magnitude higher than the Scyphozoans. There was a significant positive relationship between mercury and selenium concentrations in jellyfishes and pyrosomes, suggesting a potential detoxification mechanism in these lower trophic level organisms. This study provides evidence that trophic transfer of mercury and selenium likely occurs through ingestion of gelatinous prey.