Jellyfish Outbreaks Research Articles

Environmental evidence that seasonal hypoxia enhances survival and success of jellyfish polyps in the northern Gulf of Mexico

Seasonal blooms of the scyphozoan jellyfish Aurelia sp. in the northern Gulf of Mexico broadly overlap with summer-fall hypoxia of the Louisiana–Texas shelf. It has been suggested previously that increased cultural eutrophication and hypoxia promote outbreaks of jellyfish by favoring the medusa stage of scyphozoans, since hypoxia affects their prey more than the jellyfish themselves. However, little information exists on what role hypoxia plays on the benthic polyp (scyphistoma) stage of the scyphozoan life-history. Understanding hypoxic effects on scyphozoan benthic stages is especially important in the northern Gulf of Mexico, since settlement and growth rates of its sessile benthic community are high and space is limited. Therefore, we used a combination of laboratory and field experiments to investigate the effect of low dissolved oxygen (DO) concentrations on the survival and growth of the polyps of the moon jellyfish Aurelia sp. and whether the general sessile community was relatively impacted by low DO to reduce spatial competition for hard substrate (i.e. if low DO might create transient openings in the sessile community for polyp settlement). We conducted a set of laboratory experiments that revealed low DO had a positive effect on planulae settlement. Greatest planulae settlement rates occurred under lowest DO concentrations (1.3mgl−1), indicating that reduced DO promotes settlement, perhaps as a signal of physiological stress on planula swimming. In a second set of experiments, survival of scyphistomae decreased only marginally under prolonged (56days) hypoxic conditions. Numerical growth due to asexual budding remained positive under prolonged hypoxia but at a rate significantly lower than the normoxic treatment. A third set of laboratory experiments showed that naturally seeded sessile community coverage was significantly reduced under similar levels of hypoxia when compared to normoxia. A field experiment placing polyp-seeded plates at different depths and oxygen concentrations off south-central Louisiana during seasonal hypoxia showed that polyps had higher survivorship in deeper, lower oxygen waters when compared to higher oxygen surface waters. Our data indicate that tolerance to the physiological stresses of hypoxia in the scyphozoan polyp stage and the reduction of sessile competition and predation in hypoxic areas may make these areas particularly vulnerable to jellyfish blooms.

A model for temperature control of jellyfish (Cotylorhiza tuberculata) outbreaks: A causal analysis in a Mediterranean coastal lagoon

Large outbreaks of jellyfish populations sporadically appear at the Mediterranean coasts without any self-evident cause creating public distress because of their impact on local ecosystems and economies. The exacerbated sensitivity of coastal societies has not been paralleled with comparable scientific understanding of the causal mechanisms controlling jellyfish population dynamics. Life-cycle and ecosystem complexities obscure the processes underlying medusa outbursts. Here we present evidence that helps explain population outbursts in a common Mediterranean species (Cotylorhiza tuberculata). Using a population-dynamics model and thermal forcing of its life cycle observed abundances of C. tuberculata could be reliably simulated within a coastal lagoon. Medusa populations fluctuate under the simple rule of “the warmer the better”, with collapses after polyp mortality in severe winters and peaks in years with mild winters and long summers. Cause and effect are here resolved to seize the mechanics of climate forcing on jellyfish dynamics, an understanding that can help to explain past and future fluctuations of abundance in a thermally changing ocean.

Greenhouse gas, upwelling‐favorable winds, and the future of coastal ocean upwelling ecosystems

AbstractCoastal ocean upwelling ecosystems generally represent the most productive large marine ecosystems of the world's oceans, in terms of both primary production rates and tonnages of exploitable fish produced. The Peruvian upwelling system, in particular, stands out as a major factor in world fish production. The Pacific trade winds have traditionally been considered to be the primary driving force for the upwelling system off Peru, but are projected to weaken as climate change proceeds. This leads to concern that the upwelling process in the Peru system, to which its productivity is linked, may likewise weaken. However, other mechanisms involving greenhouse‐associated intensification of thermal low‐pressure cells over the coastal landmasses of upwelling regions suggest general intensification of wind‐driven ocean upwelling in coastal upwelling regions of the world's oceans. But although certain empirical results have supported this expectation, it has not been consistently corroborated in climate model simulations, possibly because the scale of the coastal intensification may be small relative to the scales that are appropriately reflected in the standard models. Here we summarize available evidence for the intensification mechanism and present a proxy test that uses variations in water vapor, the dominant natural greenhouse gas, to offer multiple‐realization empirical evidence for action of the proposed mechanism in the real world situation. While many potential consequences to the future of marine ecosystems would codepend on climate change‐related changes in the thermocline and nutricline structures, an important subset, involving potential increased propensities for hypoxia, noxious gas eruptions, toxic red tide blooms, and/or jellyfish outbreaks, may depend more directly on changes in the upwelling‐favorable wind itself. A prospective role of fisheries in either mitigating or reinforcing this particular class of effects is suggested.

Jellyfish in ecosystems, online databases, and ecosystem models

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.

Environmental effects on asexual reproduction rates of the scyphozoan Aurelia labiata

Problem outbreaks of jellyfish and warming of the Earth's climate are both being reported at unprecedented rates. Models forecast continued changes in temperature, salinity, and solar radiation (insolation) in the world's oceans as consequences of global warming. Many species with a swimming jellyfish stage also have a benthic stage that asexually produces buds and new jel- lyfish (ephyrae). This perennial benthic stage probably determines the numbers of jellyfish in the population. In this study, polyps of the moon jellyfish Aurelia labiata from Puget Sound, Washington, USA, were tested in 9 combinations of temperature (7, 10, 15°C) and salinity (20, 27, 34) in the dark, and in 9 combinations of photoperiod (12, 8, and 4 h d -1 ) and light intensity (1 screen, 2 screens, opaque) at ambient salinity (27) and temperature (15°C). Another experiment tested polyps in treat- ments of 10, 15, and 20°C. Survival of the initial polyps in all treatments was high (83 to 100%). Tem- perature, salinity, and their combination dramatically affected the numbers of ephyrae produced (from nearly 0 at 7°C to 42 ephyrae polyp -1 at 15°C), the percentages of ephyrae out of total asexual reproduction (≤12% at 7°C to 89% at 20°C), and the delay before ephyra production (> 81 d at 7°C but only 39 to 46 d at 15°C). Thus, all results showed that more jellyfish were produced with increasing temperature. Long photoperiod and highest light intensity greatly accelerated strobilation, with polyps in 12 h light strobilating 30 to 40 d before those in other treatments. Polyps receiving the most light strobilated most frequently. In situ conditions showed that light increased much more rapidly than temperature before strobilisation, suggesting that light may be the more important signal. I sug- gest that the light-sensitive hormone melatonin, or a precursor like serotonin, coordinates the timing of strobilation in A. labiata with the seasonal light cycle.

North Atlantic climate and northwestern Mediterranean plankton variability

Climate variability across three distinct spatial scales and the interannual changes of planktonic copepods and jellyfish were studied from November 1966 to December 1993. The results obtained identified a cascade of links between the large-scale climate pattern playing out in the North Atlantic and the local climate variability governing the Ligurian Sea, northwestern Mediterranean. The chain of events appeared driven by the long-term temperature anomalies that in turn played a key role in the relationship between copepods and jellyfish. Indeed, the increase in jellyfish outbreaks during the 1980s was largely favored by high positive anomalies observed in climate at large (North Atlantic), regional (Ligurian Sea), and local (Villefranche Bay) spatial scales and in water temperature. Linked to jellyfish abundance, the dynamics of the relationship between copepods and jellyfish showed a strong modification during the middle-late 1980s, which highlight the top-down effect exerted by jellyfish on copepods. The warming temperatures and the observed ecological changes, high abundance of jellyfish, and marked drop in the abundance of copepods are discussed in the framework of a potential change in the functioning of the planktonic ecosystem indicative of a more regeneration-dominated production system in the Ligurian Sea. Overall, the cascade of links identified by these results should be considered and integrated into the assessment and modeling studies of pelagic ecosystem and biogeochemical fluxes in the northwestern Mediterranean Sea.

Predicting Jellyfish Outbreaks AroundShetland Using MIKE 3

Predicting Jellyfish Outbreaks AroundShetland Using MIKE 3