Humans cause ocean-wrecking jellyfish plague! Or maybe not …

How many jellyfish are there really? ImipolexG/Flickr

It seems that every day you read in the scientific literature and global media about the human destruction of our oceans, through impacts such as climate change, eutrophication, overfishing and urban sprawling of our coasts. In many cases, human activity has clearly affected marine ecosystems.

Dredging, oil spills and introduced species are cases where the impact is immediately apparent. The combination of these impacts has led many scientists to conclude, perhaps prematurely, that the health of our oceans is in jeopardy. They predict a series of “plagues” – including disease, outbreaks of harmful algal blooms and a rise in the number of jellyfish.

Emerging evidence, however, suggests the above claims about jellyfish may be not be supported.

At first glance, claims of a global rise in jellyfish numbers might seem reasonable. Blooms, or proliferations, of jellyfish have created a substantial, visible impact on humans and coastal populations – clogging nets for fishermen, stinging tourists, even choking intake lines for power plants. In fact, science and media reports about jellyfish have increased exponentially over the past two decades and typically portray a rise in the prevalence of jellyfish blooms.

Carlos Duarte

But a multitude of evidence suggests the opposite. The Ancient Minoans painted jellyfish blooms on their pottery in 4000 BCE. Fossilised jellyfish strandings are found at excavation sites. Even Captain Cook’s First Fleet voyages noted “swarms” of jellyfish in Port Jackson.

Collectively, these observations provide evidence that jellyfish blooms are not a modern-day, but rather an ancient phenomenon. Blooms are a characteristic feature of the ecology of these animals.

A paradigm describes ecological processes and puts them in the context of the global ecosystem. In contrast, myths in science can start from cultural perceptions from within a small part of the community; they are accentuated throughout ecological literature at the global level.

Myths can easily become paradigms, especially when spread by colleagues outside the field of particular research, either through dialogue or in print. However, a true paradigm should always be based on scientific data, observation and controlled experimentation using rigorous statistical analyses.

So where did the paradigm about global increases in jellyfish begin? The original paradigm was built on a paper published in 2001 in Science by coral reef ecologist Jeremy Jackson and his colleagues. This paper concluded that a “litany” of human insults to the sea would initiate severe outbreaks of jellyfish.

The scientific reasoning behind the authors’ “Rise of Slime” hypothesis is based on a prediction that opportunistic groups, such as jellyfish, will emerge in estuaries as a result of overfishing and “microbialization” of food webs. But the manuscript provides no data on jellyfish to support this hypothesis. In fact, as the sole support for this assertion, it cites a paper that does not discuss jellyfish.

Published in a high-profile journal, this paper has been widely cited by scientists (over 2,600 times, according to Google Scholar) and echoed by the global media. More pertinent examples based on empirical data but published in lower-ranking journals are largely ignored, aiding the formation of a false paradigm.

Mike Kingsford

Science is not entirely to blame. The media has clearly perpetuated the perception of a global rise in jellyfish. For every scientific publication since 1990 there are 20 more global media reports, usually portraying jellyfish in a negative context – after all, positive stories don’t sell newspapers.

The emergence of new jellyfish blooms or increases in their magnitude or extent can be misinterpreted. Or they may be a case of loss of collective memory. For example, the injury or death of one person may lead to the closure of large lengths of coastline, creating the misperception that jellyfish are widespread.

There are also multiple examples from the early-mid 1900s of media reporting “hordes of jellyfish” in a region, only to have the same media outlet claim that “unprecedented” blooms have occurred again decades later. Outreach education and adequate retrospective analyses of jellyfish blooms are key in rectifying this misconception.

Science has a clear responsibility to make sure the correct message is communicated to the media and public. The entire basis of credibility within global media reports depends on the quality of information which it receives mainly from scientists.

But there is much discord, even among jellyfish researchers, about whether jellyfish have increased globally. Scientists must word their answers to journalists carefully and have the confidence to say “I don’t know”, when conclusive evidence is not yet available. Knowing there are gaps in our knowledge provides the impetus to formulate research questions and address them on the basis of robust data and analyses.

Carlos Duarte

There is also an inherent bias in the peer-review process towards publishing positive results. We must encourage scientific journal editors to consider null results with equal weighting.

This is a challenging, but important time for jellyfish researchers. There are many serious implications and outcomes of jellyfish blooms for fisheries and ecosystem managers, as well as tourism. Long-term datasets will provide the most compelling evidence for evaluating jellyfish blooms. No one has attempted a global synthesis and analysis, but it is essential to answer the question about potential global increases in jellyfish.

Now is the time to build unity and community spirit to enable a cohesive and collective analysis on jellyfish blooms, to build trust in the scientific method, and to establish the correct paradigm rather than myths.

This article was co-authored by Rob Condon, a Research Senior Marine Scientist at the Dauphin Island Sea Lab, Alabama, USA.

All authors are co-founders and representatives of the Global Jellyfish Group based at the National Center for Ecological Analysis and Synthesis, California, USA.

The opinions expressed in this article are elaborated in greater detail in “Questioning the Rise of Jellyfish in the World’s Oceans”, published in the February 2012 edition of BioScience.