Who's Got Jellies in their Gut?

Gelatinous zooplankton, loosely termed as jellyfish, can be found throughout world’s oceans, known to cause large blooms. This group includes scyphozoan jellyfish, siphonophores, ctenophores, salps, pyrosomes, and appendicularians [1]. 

If we were asked who dines on these jellies, we might reserve the term ‘belly-full-of jelly’ to charismatic sea turtles (Dermochelys coriacea, Chelonia mydas) and the ocean sunfish (Mola mola). And it's indeed fitting since an adult leatherback turtle, for instance, ingests an average of 330-kg jellyfish wet mass per day or 73% of its body mass [1]. 

With the rise of new technologies in recent years, however, this exclusivity is no longer true: It turns out that not only such massive marine predators get a chunk of their diet from jellyfish. There’s a whole lot on the table, from birds to fishes to worms, joining the feast [1].

New approaches to study the diet of marine animals such as stable isotope analyses or SIA (getting animal tissues to estimate trophic level), animal-borne cameras, remotely operated vehicles or ROVs, and DNA metabarcoding support the finding that a diverse range of marine predators feed on jellies, not incidentally but targeted [1].  

SIA revealed that jellyfish forms a substantial part of the diet of bony fishes Chloroscombrus chrysurus, Thunnus thynnus, Euthynnus alletteratus, Tetrapterus belone, Xiphias gladius and the green sea turtle Chelonia mydas. 

Animal-borne cameras revealed 42.2% of prey capture for some species of penguins, consuming scyphozoans, salps and ctenophores [1]. 

Metabarcoding showed that jellies make up 20% of food DNA sequences of the two species of albatross, ahead of crustaceans in terms of importance. Meanwhile, next-generation sequencing showed that the endangered European eel Anguilla anguilla has got gelatinous zooplankton in its diet. Seen through powerful ROVs, deep-sea octopus (Haliphron atlanticus) and benthic animals, like echinoderms, crabs, shrimps, amphipods, sea anemones, and worms join the slew of jellyfish predators [1].

Hays et al. 2018 Figure 2A, showing a diverse group of predators worldwide feeding on jellyfish.

Overwhelming evidence of widespread jellyfish consumption throughout the world’s oceans means that jellyfish cannot be simply considered a bycatch, but targeted and opportunistically consumed by many marine predators. However, it's important to note that this shift may be influenced by changing ocean conditions [1]. 

Also, knowing that a growing number of marine life now relies on jellyfish for nutrition signifies their susceptibility to harm, or even death, for mistaking plastic wastes for food [1]. 

These findings are important given that jellyfish holds a huge fraction of the pelagic biomass and have recently increased their abundance worldwide [3]. The study also challenges the common notion that undermines the energetic gain from jellyfish consumption, thus the need to better understand its dietary value [1].

To know more about jellyfishes and other gelatinous zooplankton, visit SeaLifeBase. 

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[1] Hays, G. C., Doyle, T. K., & Houghton, J. D. (2018). A Paradigm Shift in the Trophic Importance of Jellyfish?. Trends in Ecology & Evolution 33(11):874-884. Retrieved from https://bit.ly/2DCvaY7

 [2] Lewis, A. (2011, January 5). Leatherback turtle feeding. YouTube. Retrieved from https://bit.ly/1vo1QO8