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Abstract Ctenophores are numerically dominant members of oceanic epipelagic communities around the world. The ctenophore community is often comprised of several common, co-occurring lobate and cestid genera. Previous quantifications of the amount of fluid that lobate ctenophores entrain in their feeding currents revealed that oceanic lobates have the potential for high feeding rates. In order to more directly examine the trophic role of oceanic lobate ctenophores, we quantified the encounter and retention efficiencies of several co-occurring species (Bolinopsis vitrea, Ocyropsis crystallina, Eurhamphea vexilligera and Cestum veneris) in their natural environments. Encounters and predator–prey interactions were video recorded in the field using specialized cameras and SCUBA techniques. The lobate species encountered, on average, 2.4 prey per minute and ingested 40% of these prey. This translated to an estimated ingestion rate of close to 1 prey per minute. Cestum veneris and most of the lobate species retained prey as efficiently as the voracious coastal lobate predator Mnemiopsis leidyi, suggesting that these oceanic species have a similar predation impact in their environments as M. leidyi does in coastal ecosystems. Hence, quantified in situ predatory-prey interactions indicate that epipelagic ctenophores have a significant impact on oceanic ecosystems worldwide. 

Abstract Copepods are the dominant marine zooplankton and perform important functions in the marine food web. However, copepod traits have not been studied in many waters. We studied the copepod community under influence of the Mekong River and the Southern Vietnamese coastal upwelling, based on their functional traits, during the southwest monsoon period in 2016. Fourteen trait categories of four key functional traits (trophic-groups, feeding-types, reproductive-strategies and diel migration) of copepod data were analyzed to investigate how environmental gradients impact on their distribution and abundance among the four defined habitats: Mekong River (MKW), upwelling (UpW), nearshore (OnSW) and offshore waters (OSW). There were seven functional groups identified in the study waters based on multiple correspondence analysis of distribution, abundance and traits of 139 copepod species. Herbivorous, current-feeding and sac-spawning copepods were dominant in all habitats with the highest abundance in OSW. Specifically, herbivorous species dominated in MKW and UpW, whereas omnivorous species dominated in OnSW and OSW. Sac-spawners dominated in all habitats, but decreased from MKW and UpW to OnSW and lowest in OSW. Cruise feeders were 2-fold higher than ambush feeders in the UpW, but the opposite was observed in the other habitats. The results suggest that impacts of Mekong River and coastal upwelling led to distinctive copepod assemblages with specific functional traits.