delta C-13, delta N-15, and C:N ratios as nutrition indicators of zooxanthellate jellyfishes: insights from an experimental approach

WOS:000500373400009International audienceSome jellyfish host zooxanthellae in their tissues (mostly from the family Symbiodiniaceae; Dinophyceae) and supplement their heterotrophic nutrition with their symbiont's photosynthates. The mixotrophy of zooxanthellate jellyfishes (as holobionts) renders the study of their nutrition, growth, and population dynamics complicated. Here, we used an experimental approach to assess how carbon and nitrogen stable isotopes (delta C-13 and delta N-15) as well as the elemental composition (C:N ratios) of zooxanthellate jellyfishes are affected by variations in nutrition sources: i.e. predation (heterotrophic) versus photosynthesis (autotrophic). Our laboratory experiment, conducted on the zooxanthellate jellyfish Cassiopea sp. medusae (including symbionts) in the presence or absence of light and prey during 24 days, showed conclusive results. Presence of light decreased delta N-15, increased delta C-13 and C:N ratios, whereas presence of prey increased delta N-15, and decreased delta C-13 and C:N ratios. The medusae incubated with both light and prey had intermediate delta N-15, delta C-13 and C:N ratios. Variations in zooxanthellate jellyfishes' nutrition sources (autotrophy vs. heterotrophy) are thus reflected by their isotopic and elemental composition. By disentangling the effects of autotrophy and of heterotrophy on zooxanthellate jellyfish isotopic and elemental compositions, these results would help to interpret the values of delta C-13, delta N-15 and C:N ratios that can be observed on these organisms in fieldwork studies