Although recent articles state that jellyfish populations are increasing, most available evidence shows that jellyfish abundances fluctuate with climatic cycles. Reports of increasing prob- lems with jellyfish, especially in East Asia, are too recent to exclude decadal climate cycles. Jellyfish are infamous for their direct negative effects on human enterprise; specifically, they interfere with tourism by stinging swimmers, fishing by clogging nets, aquaculture by killing fish in net-pens and power plants by clogging cooling-water intake screens. They also have indirect effects on fisheries by feeding on zooplankton and ichthyoplankton, and, therefore, are predators and potential competitors of fish. Ironically, many human activities may contribute to increases in jellyfish populations in coastal waters. Increased jellyfish and ctenophore populations often are associated with warming caused by climate changes and possibly power plant thermal effluents. Jellyfish may benefit from eutrophication, which can increase small-zooplankton abundance, turbidity and hypoxia, all conditions that may favor jellyfish over fish. Fishing activities can remove predators of jellyfish and zooplanktivorous fish com- petitors as well as cause large-scale ecosystem changes that improve conditions for jellyfish. Aquacul- ture releases millions of jellyfish into Asian coastal waters yearly to enhance the jellyfish fishery. Aquaculture and other marine structures provide favorable habitat for the benthic stages of jellyfish. Changes in the hydrological regime due to dams and other construction can change the salinity to favor jellyfish. Accidental introductions of non-native gelatinous species into disturbed ecosystems have led to blooms with serious consequences. In many coastal areas, most of these environmental changes occur simultaneously. We summarize cases of problem jellyfish blooms and the evidence for anthropogenic habitat disruptions that may have caused them. Rapid development in East Asia makes that region especially vulnerable to escalating problems. We conclude that human effects on coastal environments are certain to increase, and jellyfish blooms may increase as a consequence.

/pdf/anthropogenic-causes-of-jellyfish-blooms-and-their-direct-2yht76mdfl.pdf

Anthropogenic causes of jellyfish blooms and their direct consequences for humans: a review

In spite of being one of the most relevant components of the biosphere, the plank- ton-benthos network is still poorly studied as such. This is partly due to the irregular occurrence of driving phenomena such as gelatinous plankton pulses in this realm. Gelatinous plankters rely on their life cycles and histories to exploit temporarily abundant resources with an undeniable, but often overlooked, impact on marine food webs. Dramatic increases of gelatinous filter-feeders and/or carnivores (both native and nonindigenous species) are frequently observed, and explana- tions of these blooms alternatively invoke ecosystem variability, climate change, unspecified anthropogenic perturbation or removal of top predators from trophic networks. Gelatinous plank- ters, however, are not anomalies in plankton dynamics: the recognition of the ecological impor- tance of their pulses, based on their life cycle patterns (often involving benthic stages), is a critical breakthrough to understand the cycling diversity of plankton in space and time. The current study focuses on the many neglected aspects of the ecology and biology of gelatinous zooplankton, describes how life cycle patterns are central in marine ecology, as are the pulses of gelatinous organisms, and highlights how such a dramatic lack of knowledge can affect our understanding of the marine ecosystem as a whole.

https://www.int-res.com/articles/meps2008/356/m356p299.pdf

Gelatinous plankton: irregularities rule the world (sometimes)

http://www.everythingconnects.org/uploads/7/0/3/5/7035190/jellyfish_blooms_in_china.pdf

Jellyfish blooms in China: dominant species, causes and consequences.

There are indications that pelagic cnidarians and ctenophores (‘jellyfish’) have increased in abundance throughout the world, or that outbreaks are more frequent, although much uncertainty surrounds the issue, due to the scarcity of reliable baseline data. Numerous hypotheses have been proposed for the individual increases or outbreaks that are better documented, but direct experimental or manipulative studies at the ecosystem scale cannot be used for testing them. Thus, ecological modeling provides the best alternative to understand the role of jellyfish in large fisheries-based ecosystems; indeed, it is an approach consistent with new ecosystem-based fisheries management practices. Here, we provide an overview of online databases available to ecosystem modelers and discuss general aspects and shortcomings of the coverage of jellyfish in these databases. We then provide a summary of how jellyfish have been treated and parameterized by existing ecosystem models (specifically focusing on ‘Ecopath with Ecosim’ as a standard modeling toolset). Despite overall weaknesses in the parameterization of jellyfish in these models, interesting patterns emerge that suggest some systems, especially smaller and more structured ones, may be particularly vulnerable to long-term jellyfish biomass increase. Since jellyfish also feed on the eggs and larvae of commercially important food fish, outbreaks of jellyfish may ultimately imply a reduction in the fish biomass available to fisheries. On the other hand, jellyfish, which have been traditionally fished for human consumption in East and Southeast Asia, are now seen as a potential resource in other parts of the world, where pilot fisheries have emerged. It is also argued here that reduced predation on the benthic and pelagic stages of jellyfish, both a result of fishing, may be a strong contributing factor as well. For marine biologists specializing on jellyfish, this means that their research might become more applied. This implies that they would benefit from adopting some concepts and methods from fisheries biology and ecosystem modeling, and thus from using (and contributing to) online databases, such as SeaLifeBase and FishBase, developed to support such research. This would remedy the situation, documented here, wherein jellyfish are either infrequently included in food web models, typically constructed using the Ecopath with Ecosim software, or included as a single functional group with the characteristic of an ‘average’ jellyfish. Thus, jellyfish specialists could readily improve the jellyfish-related components of such models, and we show how they could do this. Also, it is suggested that when such improvement is performed, the resulting models can lead to non-intuitive inferences and hence interesting hypotheses on the roles of jellyfish in ecosystems. This is illustrated here through (a) an investigation of whether jellyfish are keystone species and (b) the identification of conditions under which (simulated) jellyfish outbreaks may occur.

/pdf/jellyfish-in-ecosystems-online-databases-and-ecosystem-hp3wdpbwaf.pdf

Jellyfish in ecosystems, online databases, and ecosystem models

Jellyfish (Cnidaria, Scyphozoa) blooms appear to be increasing in both intensity and frequency in many coastal areas worldwide, due to multiple hypothesized anthropogenic stressors. Here, we propose that the proliferation of artificial structures – associated with (1) the exponential growth in shipping, aquaculture, and other coastal industries, and (2) coastal protection (collectively, “ocean sprawl”) – provides habitat for jellyfish polyps and may be an important driver of the global increase in jellyfish blooms. However, the habitat of the benthic polyps that commonly result in coastal jellyfish blooms has remained elusive, limiting our understanding of the drivers of these blooms. Support for the hypothesized role of ocean sprawl in promoting jellyfish blooms is provided by observations and experimental evidence demonstrating that jellyfish larvae settle in large numbers on artificial structures in coastal waters and develop into dense concentrations of jellyfish-producing polyps.

/pdf/is-global-ocean-sprawl-a-cause-of-jellyfish-blooms-1os3cbueho.pdf

Is global ocean sprawl a cause of jellyfish blooms

A population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizo- stomeae) occurred in the Sea of Japan in 2002 and 2003, causing severe damage to fisheries. There was a further population explosion in 2004, but on a much smaller scale. In both years, young medusae began to appear in the Tsushima and Korea Strait in July and August, followed by a north- ward expatriation in the Tsushima Current to the northern Sea of Japan. We obtained scyphistomae of this species by artificial fertilization, and reared them to the young medusa stage in the laboratory. Asexual reproduction of scyphistomae occurred by means of podocyst formation. A thermal increase from 13 to 23°C induced strobilation, followed by liberation of 3 to 7 ephyrae from a strobila. The ephyrae developed to metephyrae having a complex canal system and characteristically possessing long reddish purple filiform appendages. By 40 d post-liberation, the metephyrae had grown to medusae in which the central mouth had closed and been replaced by numerous mouthlets on both oral wings and scapulets. The results from both laboratory-rearing experiments and field investiga- tions were combined to construct the seasonal life cycle and geographical distribution of N. nomurai in eastern Asian waters. Possible causes for the mass occurrence of N. nomurai, which has tended to be more frequent in the last decade, are discussed.

/pdf/unusual-population-explosion-of-the-giant-jellyfish-33ikt2atfo.pdf

Unusual population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae) in East Asian waters

Since marine medusae and ctenophores harbor a wide variety of symbionts, from protists to fish, they con- stitute a unique community in pelagic ecosystems. Their symbiotic relationships broadly range from simple, facultative phoresy through parasitisim to complex mutualism, although it is sometimes difficult to define these associations strictly. Phoresy and/or commensalism are found in symbionts such as pycnogonids, decapod larvae and fish juveniles. Parasitism and/or parasitoidism are common in the following symbionts: dinoflagellates, ciliates, anthozoan larvae, pe- dunculate barnacles, anuropid isopods, and hyperiid amphipods. Mutualism is established between ctenophores and gymnamoebae, and between rhizostome medusae and endosymbiotic dinoflagellates. More information on symbiotic apostome ciliates, anthozoan larvae and hyperiid amphipods is definitely needed for further studies in consideration of their high prevalence and serious damage they can inflict on their hosts. The present paper briefly reviews previously published data on symbionts on these gelatinous predators and introduces new information in the form of our unpub- lished data.

http://www.plankton.jp/PBR/issue/vol04_1/0401_001.pdf

Symbionts of marine medusae and ctenophores

The life cycle of Lychnorhiza lucerna (Scyphozoa: Rhizostomeae) and the settlement preferences of its larvae were studied using laboratory-based rearing experiments. Mature medusae of L. lucerna were collected from the beach of the Rio de la Plata estuary, Argentina. This species displayed the typical metagenetic, (i.e. medusoid and polypoid), life cycle reported for other rhizostomes. The fertilized eggs developed into motile and short lived planulae. The majority of planulae settled on the air-water interface (p   0.05). No planulae settled on stones. Several hours after planulae settled, they metamorphosed into sessile four-tentacled scyphistomae. Most scyphistomae attached onto the air-water interface. At 19–22°C, the scyphistomae grew up to 22 tentacles and reached 1,500 μm height. The scyphistomae increased their numbers by means of formation of podocysts from which new polyps emerged and strobilated. Strobilation occurred 46 days after settlement. Only polydisk strobilation was observed and each strobila always produced three ephyrae. After releasing ephyrae, strobilae returned to normal scyphistomae and were capable of repeating strobilation. A single founder polyp was estimated to produce up to 60 ephyrae over 4 months. Ephyrae developed into metephyrae 15 days after release at 19–22°C. In this paper we describe the morphological and some behavioural features of L. lucerna in the polypoid and early medusoid stages.

Life cycle of the jellyfish Lychnorhiza lucerna (Scyphozoa: Rhizostomeae)

/pdf/bloom-or-non-bloom-in-the-giant-jellyfish-nemopilema-nomurai-1cq1jpdc7x.pdf

Bloom or non-bloom in the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae): roles of dormant podocysts

Three edible jellyfish Rhopilema hispidum, R. esculentum and Nemopilema nomurai are virulent to humans. We monitored one patient that was stung sequentially by these three species of jellyfish. The first species caused a persistent eruption, the second produced significant pruritus and the last induced only cutaneous symptoms rather than severe systemic disorders reported for its Chinese counterpart. The lesions of these jellyfish species are characteristic and common in workers harvesting medusae. There is no significant incidence of symptoms by ingesting these animals. r 2006 Elsevier Ltd. All rights reserved.

Masato Kawahara

Papers

Unusual population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae) in East Asian waters

Symbionts of marine medusae and ctenophores

Life cycle of the jellyfish Lychnorhiza lucerna (Scyphozoa: Rhizostomeae)

Bloom or non-bloom in the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae): roles of dormant podocysts

Short communication Stings of edible jellyfish (Rhopilema hispidum, Rhopilema esculentum and Nemopilema nomurai) in Japanese waters