Human-induced stresses of overfishing, eutrophication, climate change, translocation and habitat modification appear to be promoting jellyfish (pelagic cnidarian and ctenophore) blooms to the detriment of other marine organisms. Mounting evidence suggests that the structure of pelagic ecosystems can change rapidly from one that is dominated by fish (that keep jellyfish in check through competition or predation) to a less desirable gelatinous state, with lasting ecological, economic and social consequences. Management actions needed to stop such changes require tactical coping strategies and longer-term preventative responses based on fundamental and targeted research on this understudied group.

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The jellyfish joyride: causes, consequences and management responses to a more gelatinous future

Although there are various indications and claims that jellyfish (ie, scyphozoans, cubozoans, most hydrozoans, ctenophores, and salps) have been increasing at a global scale in recent decades, a rigorous demonstration of this has never been presented Because this is mainly due to scarcity of quantitative time series of jellyfish abundance from scientific surveys, we attempt to complement such data with non-conventional information from other sources This was accomplished using the analytical framework of fuzzy logic, which allows the combination of information with variable degrees of cardinality, reliability, and temporal and spatial coverage Data were aggregated and analyzed at the scale of Large Marine Ecosystem (LME) Of the 66 LMEs defined thus far that cover the world’s coastal waters and seas, trends of jellyfish abundance after 1950 (increasing, decreasing, or stable/variable) were identified for 45, with variable degrees of confidence Of those 45 LMEs, the majority (28 or 62%) showed increasing trends These changes are discussed in the context of possible sources of bias and uncertainty, along with previously proposed hypotheses to explain increases in jellyfish

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Increasing jellyfish populations: trends in Large Marine Ecosystems

Effects of ocean sprawl on ecological connectivity: impacts and solutions

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.

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Is global ocean sprawl a cause of jellyfish blooms

Large population fluctuations of jellyfish occur over a variety of temporal scales, from weekly to seasonal, inter-annual and even decadal, with some regions of the world reported to be experiencing persistent seasonal bloom events. Recent jellyfish research has focussed on understanding the causes and consequences of these population changes, with the vast majority of studies considering the effect of changing environmental variables only on the pelagic medusa. But many of the bloom-forming species are members of the Scyphozoa with complex metagenic life cycles consisting of a sexually reproducing pelagic medusa and asexually reproducing benthic polyp. Recruitment success during the juvenile (planula, polyp and ephyrae) stages of the life cycle can have a major effect on the abundance of the adult (medusa) population, but until very recently, little was known about the ecology of the polyp or scyphistoma phase of the scyphozoan life cycle. The aim of this review is to synthesise the current state of knowledge of polyp ecology by examining (1) the recruitment and metamorphosis of planulae larvae into polyps, (2) survival and longevity of polyps, (3) expansion of polyp populations via asexual propagation and (4) strobilation and recruitment of ephyrae (juvenile medusae). Where possible, comparisons are made with the life histories of other bentho-pelagic marine invertebrates so that further inferences can be made. Differences between tropical and temperate species are highlighted and related to climate change, and populations of the same species (in particular Aurelia aurita) inhabiting different habitats within its geographic range are compared. The roles that polyps play in ensuring the long-term survival of jellyfish populations as well as in the formation of bloom populations are considered, and recommendations for future research are presented.

Jellyfish life histories: role of polyps in forming and maintaining scyphomedusa populations.

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

T. Parsons

Papers

Gelatinous plankton: irregularities rule the world (sometimes)