Fish rely on scyphozoan hosts as a primary food source: evidence from stable isotope analysis

Predation of fish on their scyphozoan hosts has not been clearly defined using analysis of gut contents because gelatinous prey are difficult to visually detect and are dissolved by fixative solutions. Therefore, scyphomedusae have been generally considered not relevant in fish diet. To determine the contribution of their scyphozoan host tissue to the assimilated diet of age-0 Chloroscombrus chrysurus, we determined δ[sup.13]C and δ[sup.15]N of fish, their hosts (scyphomedusae Aurelia sp. and Drymonema larsoni) and their potential prey--small plankton (200 µm)--in the coastal waters of Alabama, USA. The diet of C. chrysurus was defined using the Bayesian mixing model Stable Isotope Analysis in R (SIAR). Models indicated that the scyphozoan hosts contributed on average ~90 % to fish assimilated diet. In contrast with previous dietary assessments based on analysis of gut contents, these results highlight that scyphozoans are important to the diet of fish associated with them. Because several ecologically and economically important fish species live in association with scyphomedusae, a redefinition of trophic links in marine food webs may be needed in light of the findings in this study.
Introduction Interactions between fish and jellyfish (Phylum Cnidaria, Class Scyphozoa) are complex. Jellyfish can consume fish eggs and larvae, and they potentially compete with fish for plankton prey (reviewed in [...]