Jellyfish as Prey: Frequency of Predation and Selective Foraging of Boops boops (Vertebrata, Actinopterygii) on the Mauve Stinger Pelagia noctiluca (Cnidaria, Scyphozoa)

Abstract

In recent years, jellyfish blooms have attracted considerable scientific interest for their potential impacts on human activities and ecosystem functioning, with much attention paid to jellyfish as predators and to gelatinous biomass as a carbon sink. Other than qualitative data and observations, few studies have quantified direct predation of fish on jellyfish to clarify whether they may represent a seasonally abundant food source. Here we estimate predation frequency by the commercially valuable Mediterranean bogue, Boops boops on the mauve stinger jellyfish, Pelagia noctiluca, in the Strait of Messina (NE Sicily). A total of 1054 jellyfish were sampled throughout one year to quantify predation by B. boops from bite marks on partially eaten jellyfish and energy density of the jellyfish. Predation by B. boops in summer was almost twice that in winter, and they selectively fed according to medusa gender and body part. Calorimetric analysis and biochemical composition showed that female jellyfish gonads had significantly higher energy content than male gonads due to more lipids and that gonads had six-fold higher energy content than the somatic tissues due to higher lipid and protein concentrations. Energetically, jellyfish gonads represent a highly rewarding food source, largely available to B. boops throughout spring and summer. During the remainder of the year, when gonads were not very evident, fish predation switched towards less-selective foraging on the somatic gelatinous biomass. P. noctiluca, the most abundant jellyfish species in the Mediterranean Sea and a key planktonic predator, may represent not only a nuisance for human leisure activities and a source of mortality for fish eggs and larvae, but also an important resource for fish species of commercial value, such as B. boops.

Trophic relationships between the large scyphomedusa Chrysaora plocamia and the parasitic amphipod Hyperia curticephala

“…Thus, the size range available to assess these relationships in mesoglea was between 9 and 39 cm, whereas for gonad tissue, it was between 15 and 39 cm. Alternatively, this could be related to our finding of no significant differences in δ 13 C and δ 15 N values between gonad and mesoglea tissues, which is surprising because previous studies have shown that scyhozoan gonads are lipid rich and have therefore lower δ 13 C than other tissues (Milisenda et al 2014;D'Ambra et al 2015). Conversely, our comparison of C:N ratios in the two tissues indicates that at the time of sampling, lipid contents were similar.…”

The giant deep-sea octopus Haliphron atlanticus forages on gelatinous fauna

“…Fully establishing that there is a feeding relationship beyond the behavioral association requires more than just witnessing the association, and we believe that the combined evidence supports that the octopus feeds upon the medusa, at least initially in the relationship: Our five specimens and the published record of gelatinous remains in the stomachs of net-caught Haliphron specimens13 complements our in-situ observation that the oral arms and stomach of the medusa were missing from within the bell. This is similar to how fish21 and sea turtles22 feed on medusae, by initially targeting their more energy-dense oral arms and gonads.…”

The influence of invasive jellyfish blooms on the aquatic microbiome in a coastal lagoon (Varano, SE Italy) detected by an Illumina-based deep sequencing strategy

“…In spite of considerable evidence for predation on jellyfish tissues (e.g. Arai 2005;Milisenda et al 2014), jellyfish are usually considered to be a lowvalue biomass not easily available to higher trophic levels and dependent on the microbial loop for recycling (Condon et al 2011). Overall, the observed differences in the bacterial community might be interpreted as an ecosystem response to allow adaptation of metabolic pathways to the jellyfish-derived organic carbon substrate.…”