Ctenophores are a highly impactful predatory guild in open oceanic ecosystems.

Abstract

The emergence of optical plankton sampling techniques has revealed that gelatinous zooplankton predators are considerably more numerous than previously observed.^1,2 This recognition of the widespread presence of gelatinous zooplankton challenges our understanding of oceanic food-web dynamics because gelatinous zooplankton have traditionally been viewed as only minor players in oceanic biogeochemical cycles, which are critical in regulating atmospheric carbon dioxide.^3,4,5,6,7,8 Ctenophores (commonly called comb jellies) can be numerically dominant predators in these gelatinous communities but are severely under-sampled due to their extremely delicate gelatinous bodies.^9,10,11,12 To better understand their trophic impact, we used novel, non-invasive SCUBA techniques to document prey ingestion patterns of four widespread oceanic ctenophore species. We found that these ctenophores, on average, ingested 32 prey/h and up to 50 prey/h. At these rates, lobate and cestid ctenophores consume prey at similar rates to their highly impactful coastal relative, Mnemiopsis leidyi, and are likely the most impactful planktonic predator in the open oceans. Further, we showed that although major dietary components overlapped, different oceanic ctenophore species appear to consume different members of the plankton. Since these oceanic ctenophore species frequently co-occur, they comprise a powerful predatory guild with synergistic impacts. Consequently, epipelagic ctenophores have much greater trophic effects on material cycles over broad areas of the open ocean than previously considered.