“Transparent, low in carbon, and a pain to work with!"
With this description, Cornelia Jaspers introduces ICES Annual Science Conference 2022 audience to what has so far been her life's work – gelatinous zooplankton. Jaspers, leader of the Centre for Gelatinous Plankton Ecology & Evolution at the Danish National Institute of Aquatic Resources (DTU Aqua), has been researching gelatinous zooplankton (i.e. jellyfish, comb jellies, and pelagic tunicates) in Denmark, the US, and Germany since her M.Sc. days.
And she feels that the time has come for jellies to no longer remain unacknowledged: instead of existing as the elephant in the marine science room, Jaspers asks the entire ICES community to include gelatinous plankton in wider ecosystem discussions. In response to ICES General Secretary's Opening remarks at ICES ASC 2022, where Alan Haynie called for “big ideas", Jaspers sets out hers. “If we are to understand ecosystem changes that are due to global changes, these are key players that we cannot avoid anymore."
Changes in plankton community composition and size ranges can have wide-ranging consequences for food-web structure, carbon flow, and secondary production potential, which will impact fisheries and human welfare. Jaspers took the audience on her research journey to show them both the observed and the anticipated changes, exploring if an increase of gelatinous plankton under global change can be expected, and how this might translate into future ocean productivity.
Many believe gelatinous zooplankton, especially jellyfish, to be the beneficiaries of global change, increasing in number throughout overfished ecosystems while being a trophic dead end. Jaspers wants to expel these paradigms. But science is not about beliefs. “We lack a mechanistic understanding and need to include jellies systematically in ecosystem assessments and fisheries investigations to understand and be able to predict what will happen to our oceans' in the near future", she points out, “as jellies are systematically disregarded from most food web studies so far".
A distinction that Jaspers was quick to make was that between native and invasive non-indigenous species. The latter she identifies as the troublemakers. “We have a suite of invasive gelatinous zooplankton species that are of concern, and not only in European waters". This has implications for human activities such as fisheries, aquaculture, and tourism.
Jaspers used the example of Rhopilema nomadica an invasive jellyfish species in the Mediterranean since the 1970s and Blackfordia virginica, a smaller-sized jellyfish which is widespread in estuaries worldwide and now likely to expand into the Baltic Sea. The "rock star" of the invasive gelatinous species is the comb jellyfish Mnemiopsis leidyi or the Sea Walnut. Its invasion is associated with the collapse of commercial fisheries in the Black Sea during the late 1980s. This raises the scientific and societal awareness that, although largely ignored until now, the role of gelatinous zooplankton in coastal and oceanic ecosystems cannot be ignored any longer.
Using spread dynamics of the invasive Sea Walnut as an example, Jaspers shows how the ocean currents in the North Sea act almost as a conveyor belt, spreading pelagic animals from warm pockets to colonize and re-colonize areas even following local extinctions. Jaspers' research on Mnemiopsis has also shown how the animal can adapt to and survive in unfavourable conditions.
Therefore, Jaspers asks ICES community to consider this connectivity in invasion risk assessments, along with phenotype, ocean currents, genetic make-up, and habitats, taking a holistic approach to halting species introductions.
Far from being a dead end in the food chain, Jaspers presents gut analysis, molecular analysis, and stable isotope analysis as evidence of many species feeding on jellies: Atlantic bluefin tuna, European Eel leptocephali, Atlantic mackerel and Baltic cod among them. "Given their high water content and fast digestion, it is challenging to find gelatinous zooplankton in the gut contents, but if you search for them, you find that they are much more widespread in the diet of fish, also fast swimming fish such as tuna, than currently acknowledged".
"If we do not systematically look, it's too late", Jaspers replied when asked about the expected population development of jellies in the Arctic.
Anticipating being resource-poor as the counter-arguments to monitoring, Jaspers highlights US datasets from bottom trawl surveys and recent publications that highlight cost-effective ways of doing so. The inclusion of jellies in fisheries surveys – both macro in trawls and micro in ichthyoplankton surveys – is already being carried out in some fisheries monitoring programs. Still, it needs to be coordinated and supported. Jaspers is adamant that ICES is the right arena for this coordination and systematic recognition of jellies.
She is hopeful that the upcoming generation of scientists have a different mindset and are more open to leaving current paradigms behind.
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Cornelia Jaspers, leader of the Centre for Gelatinous Plankton Ecology & Evolution at DTU Aqua.