Abstract
AbstractGelatinous zooplankton can be present in high biomass and taxonomic diversity in planktonic oceanic food webs, yet the trophic structuring and importance of this “jelly web” remain incompletely understood. To address this knowledge gap, we provide a holistic trophic characterization of a jelly web in the eastern tropical Atlantic, based on δ13C and δ15N stable isotope analysis of a unique gelatinous zooplankton sample set. The jelly web covered most of the isotopic niche space of the entire planktonic oceanic food web, spanning > 3 trophic levels, ranging from herbivores (e.g., pyrosomes) to higher predators (e.g., ctenophores), highlighting the diverse functional roles and broad possible food web relevance of gelatinous zooplankton. Among gelatinous zooplankton taxa, comparisons of isotopic niches pointed to the presence of differentiation and resource partitioning, but also highlighted the potential for competition, e.g., between hydromedusae and siphonophores. Significant differences in spatial (seamount vs. open ocean) and depth‐resolved patterns (0–400 m vs. 400–1000 m) pointed to additional complexity, and raise questions about the extent of connectivity between locations and differential patterns in vertical coupling between gelatinous zooplankton groups. Added complexity also resulted from inconsistent patterns in trophic ontogenetic shifts among groups. We conclude that the broad trophic niche covered by the jelly web, patterns in niche differentiation within this web, and substantial complexity at the spatial, depth, and taxon level call for a more careful consideration of gelatinous zooplankton in oceanic food web models. In light of climate change and fishing pressure, the data presented here also provide a valuable baseline against which to measure future trophic observations of gelatinous zooplankton communities in the eastern tropical Atlantic.
Highlights
Associate editor: Kelly Benoit-Bird phytoplankton in the sunlit surface layer
We conclude that the broad trophic niche covered by the jelly web, patterns in niche differentiation within this web, and substantial complexity at the spatial, depth, and taxon level call for a more careful consideration of gelatinous zooplankton in oceanic food web models
We provided the first dedicated trophic assessment of the jelly web within the planktonic food web of the eastern tropical Atlantic based on stable isotope analysis
Summary
Associate editor: Kelly Benoit-Bird phytoplankton in the sunlit surface layer. The resulting phytoplankton-based organic matter is utilized by microbial communities and by herbivorous zooplankton, which are in turn consumed by carnivores such as gelatinous zooplankton, chitinous zooplankton, ichthyoplankton, planktivorous fishes, and juvenile squids (Robison 2009). The same study observed that tunicates, siphonophores, hydromedusae, and ctenophores could serve as prey items for other predators such as narcomedusae In their function as both predator and prey, feeding interactions between gelatinous zooplankton groups, and between gelatinous and non-gelatinous zooplankton groups were relevant. Trophodynamics of many individual gelatinous zooplankton taxa have been revealed via experimental studies and field observations These studies have highlighted the range of diets, possible functional roles, and trophic positions covered by different specific gelatinous zooplankton groups. A combined view of trophic niches of a large range of gelatinous zooplankton taxa would in turn reflect the overall trophic niche space covered by the jelly web within planktonic oceanic communities and reveal patterns in resource partitioning and competition (Boecklen et al 2011), in line with community ecology studies on other systems. A holistic view reflecting the range of roles and interactions involving gelatinous zooplankton in oceanic food webs is mostly lacking, which is reflected in an often oversimplified or inaccurate representation of gelatinous zooplankton in food web models as illustrated and acknowledged by Pauly et al (2009)
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