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Abstract Oceanic ctenophores are widespread predators on pelagic zooplankton. While data on coastal ctenophores often show strong top-down predatory impacts in their ecosystems, differing morphologies, prey capture mechanisms and behaviors of oceanic species preclude the use of coastal data to draw conclusion on oceanic species. We used high-resolution imaging methods both in situ and in the laboratory to quantify interactions of Ocyropsis spp. with natural copepod prey. We confirmed that Ocyropsis spp. uses muscular lobe contraction and a prehensile mouth to capture prey, which is unique amongst ctenophores. This feeding mechanism results in high overall capture success whether encountering single or multiple prey between the lobes (71 and 81% respectively). However, multiple prey require several attempts for successful capture whereas single prey are often captured on the first attempt. Digestion of adult copepods takes 44 min at 25 °C and does not vary with ctenophore size. At high natural densities, we estimate that Ocyropsis spp. consume up to 40% of the daily copepod standing stock. This suggests that, when numerous, Ocyropsis spp. can exert strong top-down control on oceanic copepod populations. At more common densities, these animals consume only a small proportion of the daily copepod standing stock. However, compared to data from pelagic fishes and oceanic medusae, Ocyropsis spp. appears to be the dominant copepod predator in this habitat.
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Ctenophores are direct developers that reproduce continuously beginning very early after hatching
A substantial body of literature reports that ctenophores exhibit an apparently unique life history characterized by biphasic sexual reproduction, the first phase of which is called larval reproduction or dissogeny. Whether this strategy is plastically deployed or a typical part of these species’ life history was unknown. In contrast to previous reports, we show that the ctenophore Mnemiopsis leidyi does not have separate phases of early and adult reproduction, regardless of the morphological transition to what has been considered the adult form. Rather, these ctenophores begin to reproduce at a small body size and spawn continuously from this point onward under adequate environmental conditions. They do not display a gap in productivity for metamorphosis or other physiological transition at a certain body size. Furthermore, nutritional and environmental constraints on fecundity are similar in both small and large animals. Our results provide critical parameters for understanding resource partitioning between growth and reproduction in this taxon, with implications for management of this species in its invaded range. Finally, we report an observation of similarly small-size spawning in a beroid ctenophore, which is morphologically, ecologically, and phylogenetically distinct from other ctenophores reported to spawn at small sizes. We conclude that spawning at small body size should be considered as the default, on-time developmental trajectory rather than as precocious, stress-induced, or otherwise unusual for ctenophores. The ancestral ctenophore was likely a direct developer, consistent with the hypothesis that multiphasic life cycles were introduced after the divergence of the ctenophore lineage.
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- PAR ID:
- 10405680
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 18
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2122052119
