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

Abstract

Scyphozoan jellyfish develop dramatic population blooms, which may significantly alter marine food webs. In turn, hyperiid amphipods parasitising jellyfish can occur in such great numbers that they represent an important trophic link to diverse species of fish, and may contribute to the decline of their host populations. Therefore, there is an urgent need to assess the trophic function and energy transfer through jellyfish and their parasites. We studied the isotopic composition (i.e. δ13C and δ15N) of Chrysaora plocamia, the largest and most abundant scyphozoan jellyfish in the Humboldt Current System of Chile and Peru, and of its associated hyperiid parasite Hyperia curticephala. The isotopic composition of C. plocamia changed with body size, suggesting that that the diet of this species may include both pelagic and benthic prey as a consequence of the vertical distribution patterns observed. Although the density and intensity of infection of the parasite H. curticephala changed with the size of the host, their isotopic composition showed little variation, suggesting no shifts in the use of resources by the parasite. In contrast to other hyperiid parasites, reported to shift to a benthic mode of life when their hosts are lacking or in low abundance, the isotopic composition of H. curticephala revealed that their food source is mainly pelagic.