Abstract
Jellyfish population play an important role in aquatic food chains, and many animals predate on this ‘mostly water containing’ organisms. However, what gelativores predators could gain from their prey is still poorly understood. This study provides insight into the nutritional value of the moon jelly (Aurelia aurita) by means of its fatty acid (FA) composition, while investigating seasonal variability and differences between its free-swimming life stages. A biweekly sampling was carried out in a temperate coastal ecosystem, the Kiel Fjord, Germany and during two consecutive years. FA profile of A. aurita showed significant seasonal variability, while mature medusae (due to reproductive tissues) possessed highest FA content. In addition, moon jelly contained several essential FAs (i.e. arachidonic acid, 20:4ω6; eicosapentaenoic acid, 20:5ω3; docosahexaenoic acid, 22:6ω3), which likely support predator’s vital physiological functions. Even though total FA contents proved to be low (7 × 10−3–34 × 10−3% per g dry weight), evidence supporting A. aurita’s capability to meet the dietary requirements of predators such as fish and crustaceans is provided. Finally, implications for gelativore and future food web configurations are discussed, while proposing that jellyfish are likely to be, and become, more than an opportunistic prey to many organisms.
Highlights
Whether or not jellyfish populations are increasing globally due to human-induced environmental changes has been a recurrent topic of debate over the past decades (Richardson et al, 2009; Condon et al, 2012)
89 ephyrae, 62 immature medusae and 10 mature medusae were caught between 18 March 2015 and 1 November 2016
One gonad sample was lost during sample preparation, resulting in a sample size of 9 for the reproductive tissue instead of the 10 as they were separated from the mature medusae
Summary
Whether or not jellyfish populations are increasing globally due to human-induced environmental changes has been a recurrent topic of debate over the past decades (Richardson et al, 2009; Condon et al, 2012). Regardless of the line of evidence, jellyfish blooms tend to maintain a negative reputation, fuelled by an array of complaints ranging from interfering with recreationists in coastal areas to outcompeting commercially important fish stocks (Purcell et al, 2007; Richardson et al, 2009). When looking beyond this human-centered perspective, jellyfish play an important role within marine ecosystems and we are only beginning to understand how complex their role within aquatic food webs is (Fleming et al, 2015; Choy et al, 2017). Many animals (e.g. a deep sea cephalopod, marine birds and various fish species), for instance, have been shown to predate on live gelatinous zooplankton (Hoving and Haddock, 2017; Thiebot et al, 2017; Hays et al, 2018), while their dead remains are thought to form an important organic carbon input into deep sea ecosystems (Sweetman et al, 2014; Lebrato et al, 2019)
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