Gelatinous and soft-bodied zooplankton in the Northeast Pacific Ocean: organic, elemental, and energy contents

Abstract

Gelatinous and soft-bodied zooplankton (GZ) have long been considered to have low energetic value (‘trophic dead end hypothesis’) and be insufficient to sustain higher trophic levels. However, the nutritional composition and energy content of GZ are often poorly known for entire groups, ignoring species-, size-, and stage-specific differences. In this study, organic matter and elemental composition (carbon and nitrogen) were measured for >1000 specimens from 34 GZ species collected from neritic and oceanic waters of the Northeast Pacific between 2014 and 2020. Species included 3 gastropods, 16 hydrozoans, 2 nude ctenophores, 6 scyphozoans, 3 tentaculate ctenophores, and 4 thaliaceans. Organic content and elemental composition were used to estimate energy content using published conversion factors and differed between and within taxonomic classes. Size-dependent variability was shown for several species. Differences in organic content and elemental composition by development stage were observed in a salp and scyphomedusa species, highlighting the need to consider life cycle stages separately. The relative energy values of GZ were generally low and highly variable, although some taxa were comparable to crustaceans. The findings of the present study emphasise the need for a more detailed consideration of GZ in marine food web models and time series analyses, to take into account their inter- and intraspecific variability.

Zooplankton functional group responses to environmental drivers off the west coast of Vancouver Island, Canada

“…Additionally, as zooplankton community composition changes, predators may have no choice but to utilize smaller copepods, other crustaceans and gelatinous zooplankton as an additional food source as a subsistence food since lipid-rich copepod prey would be limited (Mianzan et al, 2001;Parsons and Lalli, 2002;Lüskow et al, 2021).…”

“…Southern copepod species have been considered less lipid-rich than their northern subarctic NE Pacific counterparts (Tsuda et al, 2004;Yamada et al, 2016). A recent study has highlighted that many gelatinous zooplankton species do not have the same weight-specific energy content when compared to crustacean zooplankton species, with the exception of some Gastropoda and Tunicata species (Lüskow et al, 2021). In fact, Kiørbe (2013) found a bimodal distribution of zooplankton body composition where most zooplankton fall into a gelatinous or non-gelatinous category with respect to differences in water and carbon content.…”

“…In fact, Kiørbe (2013) found a bimodal distribution of zooplankton body composition where most zooplankton fall into a gelatinous or non-gelatinous category with respect to differences in water and carbon content. Therefore, additional comparisons of lipid storage type and amount would help better resolve their viability as an appropriate prey source for higher trophic levels, since past studies have indicated they usually contain less lipids than crustacean zooplankton (Ju et al, 2004;Kruse et al, 2010) as well as lower energy content (Lüskow et al, 2021) andcarbon (Kiørbe, 2013). Fatty acid analysis for zooplankton species along the WCVI have been restricted to a single species, Calanus marshallae (Bevan, 2015), whereas several crustacean zooplankton species from neighboring Strait of Georgia have been examined previously (El-Sabaawi et al, 2009, 2010Costalago et al, 2020).…”

Oceanic Fronts Shape Biodiversity of Gelatinous Zooplankton in the European Arctic

“…Unfortunately, the GZ is either completely absent from the local zooplankton time series, or the taxonomic resolution of their records is insufficient (Long et al, 2021), due to their fragile body structure that often damages when sampled harshly. From a broader perspective, the recent recognition of the GZ's trophic importance (Hays et al, 2018;Lüskow et al, 2021) as well as their diverse roles in the biogeochemical cycles (Wright et al, 2021) and the biological pump (Lebrato et al, 2019) renders understanding of the factors structuring their community pivotal for monitoring marine ecosystems and forecasting their climatemediated evolution.…”

Atlantification alters the reproduction of jellyfish Aglantha digitale in the European Arctic

“…Any conclusions on A. digitale phenology are hampered by the overwhelming lack of jellyfish data in planktonic time series (discussed in Long et al 2021), attributable mostly to the historical assumption of the low trophic importance of gelatinous animals (Lüskow et al 2021) that led to the identification of only more abundant, hard-bodied taxa from samples. Unfortunately, even when A. digitale was included in polar zooplankton time series, its population structure was unassessed (Weydmann et al 2014;Carstensen et al 2019), or routine sampling was too shallow (Ma nko et al 2020), which hampered having a thorough understanding of the fate of A. digitale in the European Arctic.…”