Presentation Abstract

Despite the low energy content, the contribution of gelatinous zooplankton (GZ; medusae, siphonophores, ctenophores, pelagic tunicates, pelagic gastropods) to predator energy budgets might be much greater than traditionally assumed (trophic dead end hypothesis). Feeding on GZ does, in fact, hold several advantages for the predator, including fast digestion, low capture and handling costs, easy access during blooms. Selective feeding on the more energy-rich tissues and organs can enhance prey attractivity for predators. Results of new analytical approaches have revealed that GZ around the world’s oceans are frequently consumed by a diverse set of marine predators. Nevertheless, GZ are infrequently included in food web models. Wet weights (standard for fish and other invertebrate biomass estimation) are inappropriate for GZ given their high water content. Rather, energy units per unit volume should be applied. However, required GZ energy content baseline data are lacking for many species and regions. In this study, we aimed to establish such baseline data for the Northeast Pacific. More than 30 GZ species (about 700 specimens) were collected on 7 cruises in 2014, 2015, and 2019 using vertical net deployments in the upper 1,000 m (but mostly 250 m) in the Salish Sea, north and west of Vancouver Island, and in the Gulf of Alaska. Caloric value, organic content, and C/N ratio were measured. Analysis results and literature values strongly suggest that not all GZ and soft-bodied species are equal in their energetic value for higher trophic levels and even though most often less ‘valuable’ than crustacean zooplankton, GZ pose a huge energy reservoir that might become more relevant for predators in changing ocean conditions. Information, however, on seasonality, sex and stage differences of various GZ energy contents are still missing after this study and remain to be determined for improving future food web models.

Session Title

Track: Trophic Interactions - Zooplankton, Phytoplankton, Salmon, Forage Fish & Invasive Species – Posters

Conference Track

Trophic Interactions - Zooplankton, Phytoplankton, Salmon, Forage Fish & Invasive Species

Conference Name

Salish Sea Ecosystem Conference (2020 : Online)

Document Type

Event

SSEC Identifier

2020_abstractID_3351

Start Date

21-4-2020 9:00 AM

End Date

22-4-2020 4:45 PM

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.

Language

English

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Apr 21st, 9:00 AM Apr 22nd, 4:45 PM

Squishy but not useless for energy balance: Energetic value of gelatinous zooplankton from the Salish Sea and adjacent waters

Despite the low energy content, the contribution of gelatinous zooplankton (GZ; medusae, siphonophores, ctenophores, pelagic tunicates, pelagic gastropods) to predator energy budgets might be much greater than traditionally assumed (trophic dead end hypothesis). Feeding on GZ does, in fact, hold several advantages for the predator, including fast digestion, low capture and handling costs, easy access during blooms. Selective feeding on the more energy-rich tissues and organs can enhance prey attractivity for predators. Results of new analytical approaches have revealed that GZ around the world’s oceans are frequently consumed by a diverse set of marine predators. Nevertheless, GZ are infrequently included in food web models. Wet weights (standard for fish and other invertebrate biomass estimation) are inappropriate for GZ given their high water content. Rather, energy units per unit volume should be applied. However, required GZ energy content baseline data are lacking for many species and regions. In this study, we aimed to establish such baseline data for the Northeast Pacific. More than 30 GZ species (about 700 specimens) were collected on 7 cruises in 2014, 2015, and 2019 using vertical net deployments in the upper 1,000 m (but mostly 250 m) in the Salish Sea, north and west of Vancouver Island, and in the Gulf of Alaska. Caloric value, organic content, and C/N ratio were measured. Analysis results and literature values strongly suggest that not all GZ and soft-bodied species are equal in their energetic value for higher trophic levels and even though most often less ‘valuable’ than crustacean zooplankton, GZ pose a huge energy reservoir that might become more relevant for predators in changing ocean conditions. Information, however, on seasonality, sex and stage differences of various GZ energy contents are still missing after this study and remain to be determined for improving future food web models.