Integrating siphonophores into marine food‐web ecology

Hetherington, Elizabeth D.; Damian‐Serrano, Alejandro; Haddock, Steven H. D.; Dunn, Casey W.; Choy, C. Anela

doi:10.1002/lol2.10235

Cited by 20 publications

(23 citation statements)

References 64 publications

(116 reference statements)

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“…The published records on the diets of siphonophores appear to differ in prey-type composition between epi-and deep-pelagic habitats [8]. However, the different methodological limitations inherent to each visual method (small prey underestimated by submersibles, soft-bodied prey underestimated by gut content inspections) are hypothesized to be responsible for such differences [8].…”

Section: Plos Onementioning

confidence: 99%

“…A review of the literature on siphonophore diets revealed significant differences between the diets of epipelagic and deep-dwelling siphonophore species [8]. Gelatinous prey appeared to be more prevalent in deep-sea observations while small crustaceans appeared to be the predominant prey in shallow gut content samples.…”

Section: Introductionmentioning

confidence: 99%

“…The subset of the pelagic food web involving gelatinous fauna has been referred to as the "jelly web" [2]. Among the most abundant [5,6] and trophically-connected [4] gelatinous predators are siphonophores-mid-trophic organisms that feed on a broad variety of prey such as medusae, salps, crustaceans, molluscs, and fishes [4,7,8]. Siphonophores are sitand-wait, non-visual, ambush predators that rely on prey encountering their tentacles and tentilla [9].…”

Section: Introductionmentioning

confidence: 99%

“…The diets of some epipelagic siphonophores have been examined through gut content analyses of SCUBA-collected colonies [7,13], and have been reviewed in Hetherington et al [8]. Recent studies based on ROV observations have shed some light on the diets of deep midwater siphonophores [4,8]. However, these approaches are limited by their biases.…”

Section: Introductionmentioning

confidence: 99%

“…ROVs can observe feeding on gelatinous prey before they become digested. However, ROV observations are skewed towards large prey items that can be easily identified from the camera screen (such as large medusae, ctenophores, crustaceans, or fishes), and can overlook important prey items such as copepods and larvae [8]. In addition, prey are relatively scarce in the open ocean, especially in the deeper regions [2], thus it is infrequent to find specimens capturing prey or carrying visually-identifiable prey in their guts [7].…”

Section: Introductionmentioning

confidence: 99%

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Characterizing the secret diets of siphonophores (Cnidaria: Hydrozoa) using DNA metabarcoding

et al. 2022

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Siphonophores (Cnidaria: Hydrozoa) are abundant and diverse gelatinous predators in open-ocean ecosystems. Due to limited access to the midwater, little is known about the diets of most deep-dwelling gelatinous species, which constrains our understanding of food-web structure and nutrient flow in these vast ecosystems. Visual gut-content methods can rarely identify soft-bodied rapidly-digested prey, while observations from submersibles often overlook small prey items. These methods have been differentially applied to shallow and deep siphonophore taxa, confounding habitat and methodological biases. DNA metabarcoding can be used to assess both shallow and deep species’ diets under a common methodological framework, since it can detect both small and gelatinous prey. We (1) further characterized the diets of open-ocean siphonophores using DNA metabarcoding, (2) compared the prey detected by visual and molecular methods to evaluate their technical biases, and (3) evaluated tentacle-based predictions of diet. To do this, we performed DNA metabarcoding analyses on the gut contents of 39 siphonophore species across depths to describe their diets, using six barcode regions along the 18S gene. Taxonomic identifications were assigned using public databases combined with local zooplankton sequences. We identified 55 unique prey items, including crustaceans, gelatinous animals, and fish across 47 siphonophore specimens in 24 species. We reported 29 novel predator-prey interactions, among them the first insights into the diets of nine siphonophore species, many of which were congruent with the dietary predictions based on tentilla morphology. Our analyses detected both small and gelatinous prey taxa underrepresented by visual methods in species from both shallow and deep habitats, indicating that siphonophores play similar trophic roles across depth habitats. We also reveal hidden links between siphonophores and filter-feeders near the base of the food web. This study expands our understanding of the ecological roles of siphonophores in the open ocean, their trophic roles within the ‘jelly-web’, and the importance of their diversity for nutrient flow and ecosystem functioning. Understanding these inconspicuous yet ubiquitous predator-prey interactions is critical to predict the impacts of climate change, overfishing, and conservation policies on oceanic ecosystems.

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Section: Plos Onementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Characterizing the secret diets of siphonophores (Cnidaria: Hydrozoa) using DNA metabarcoding

et al. 2022

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Mid‐summer fish behavior in a high‐latitude twilight zone

Kaartvedt

Christiansen

Titelman

2023

Limnology & Oceanography

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The behavior of the mesopelagic fish Benthosema glaciale was studied at 60°N in mid‐summer. We hypothesized that diel vertical migration (DVM) is constrained by short and dusk nights (surface illumination > 10−2 μmol m−2 s−1) and that individuals are active at depth during the long summer days. Submerged echosounders provided high‐resolution data throughout the water column. During the day, a part of the population ascended toward the increasing daylight. Short vertical relocations were followed by minutes of vertical inactivity. Swimming included horizontal turns and loops associated with the vertical steps. Normal DVM was initiated ~ 4 h before sunset and reflected independent individual decisions. The fish initially ascended stepwise but switched to mostly straight upwards swimming attaining 3–4 cm s−1. Their vertical speed was faster than the slow ascent of isolumes and even the deepest living fish potentially could reach upper layers shortly after sunset. However, many individuals aborted their ascent and returned to depth before the darkest time of the night, while others returned downward closer to sunrise. The daytime swimming and individual variability in diel migration behavior have implications for encounters with prey and predators in the twilight zone and the biological carbon pump. A principal conclusion is that mesopelagic fishes can modify their behavior and migration patterns to suit a wide range of changing conditions.

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Vertical trophic structure and niche partitioning of gelatinous predators in a pelagic food web: Insights from stable isotopes of siphonophores

Hetherington,

Close,

Haddock

et al. 2024

Limnology & Oceanography

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Gelatinous zooplankton are increasingly recognized as key components of pelagic ecosystems, and there have been many recent insights into their ecology and roles in food webs. To examine the trophic ecology of siphonophores (Cnidaria, Hydrozoa), we used bulk (carbon and nitrogen) and compound‐specific (nitrogen) isotope analysis of individual amino acids (CSIA‐AA). We collected samples of 15 siphonophore genera using blue‐water diving, midwater trawls, and remotely operated vehicles in the California Current Ecosystem, from 0 to 3000 m. We examined the basal resources supporting siphonophore nutrition by comparing their isotope values to those of contemporaneously collected sinking and suspended particles (0–500 m). Stable isotope values provided novel insights into siphonophore trophic ecology, indicating considerable niche overlap between calycophoran and physonect siphonophores. However, there were clear relationships between siphonophore trophic positions and phylogeny, and the highest siphonophore trophic positions were restricted to physonects. Bulk and source amino acid nitrogen isotope (δ15N) values of siphonophores and suspended particles all increased significantly with increasing collection depth. In contrast, siphonophore trophic positions did not increase with increasing collection depth. This suggests that microbially reworked, deep, suspended particles with higher δ15N values than surface particles, likely indirectly support deep‐pelagic siphonophores. Siphonophores feed upon a range of prey, from small crustaceans to fishes, and we show that their measured trophic positions reflect this trophic diversity, spanning 1.5 trophic levels (range 2.4–4.0). Further, we demonstrate that CSIA‐AA can elucidate the feeding ecology of gelatinous zooplankton and distinguish between nutritional resources across vertical habitats. These findings improve our understanding of the functional roles of gelatinous zooplankton and energy flow through pelagic food webs.

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Integrating siphonophores into marine food‐web ecology

Cited by 20 publications

References 64 publications

Characterizing the secret diets of siphonophores (Cnidaria: Hydrozoa) using DNA metabarcoding

Characterizing the secret diets of siphonophores (Cnidaria: Hydrozoa) using DNA metabarcoding

Mid‐summer fish behavior in a high‐latitude twilight zone

Vertical trophic structure and niche partitioning of gelatinous predators in a pelagic food web: Insights from stable isotopes of siphonophores

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