Stable isotope and biochemical fractionation in the marine pelagic food chain: the jellyfish Pelagia noctiluca and net zooplankton

TLDR: Isotopic and biochemical evidence indicate that, though collected in nearshore waters, P. noctiluca depended on autochthonous marine organic matter, indicating a greater loss of carbon relative to nitrogen and phosphorus along the passage to a higher trophic level.

Abstract: In our field study we analyzed the C and H isotopic and biochemical (C, N, P, protein, lipid, carbohydrate) composition of the jellyfish Pelagia noctiluca (collected from the Gulf of Trieste in 1985 to 1986) and its presumed diet-net zooplankton. The mean δ 13C (-18.8‰) and δ D (-58.4‰) ratios of P. noctiluca showed enrichment in heavy isotopes relative to net zooplankton (∼2‰ for carbon and ∼30‰ for hydrogen). Both the jellyfish and net zooplankton were characterized by a linear correlation between δ 13C and δ D. C. N, P, protein, lipid, and carbohydrate contents of P. noctiluca were low on a dry weight basis as compared to net zooplankton. Significantly lower C:N and C:P ratios were found in jellyfish indicating a greater loss of carbon relative to nitrogen and phosphorus along the passage to a higher trophic level. Isotopic and biochemical evidence indicate that, though collected in nearshore waters, P. noctiluca depended on autochthonous marine organic matter.