Taxonomic, Temporal, and Spatial Variations in Zooplankton Fatty Acid Composition in Puget Sound, WA, USA

Abstract

Fatty acid (FA) content and composition of zooplankton in Puget Sound, Washington (USA) was studied to investigate the nutritional quality of diverse zooplankton prey for juvenile salmon (Oncorhynchus spp.) in terms of their essential fatty acid (EFA) content. The study focus was on eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (ARA) as these are key FA needed to maintain growth and development of juvenile fish. The different zooplankton taxa varied in their FA composition. Much of the variation in FA composition was driven by 18:1ω9 (a biomarker of carnivory), ARA, DHA, and FA characteristic of diatoms, which are linked to zooplankton diet sources. Gammarid and hyperiid amphipods contained the highest amount of EFA, particularly the gammarid amphipod Cyphocaris challengeri, while shrimp and copepods had much lower EFA content. Crab larvae, which are important prey for juvenile salmon in Puget Sound, had intermediate EPA + DHA content and the lowest DHA/EPA ratio, and were rich in diatom biomarkers. Temporal and spatial trends in zooplankton lipids were less apparent than the taxonomic differences, although the EFA content increased from spring to summer in Cancridae zoeae and the amphipod C. challengeri. These results on taxon-specific EFA content provide baseline information on the nutritional quality of zooplankton that can be applied in food web models. Combining zooplankton fatty acid data (quality) with taxon-specific zooplankton biomass data (quantity) enables development of new, sensitive indicators of juvenile fish production to help assess recent declines in salmon production in the Pacific Northwest and predict future adult returns.

Dynamic coastal pelagic habitat drives rapid changes in growth and condition of juvenile sockeye salmon (Oncorhynchus nerka) during early marine migration

“…Large calanoid copepods, such as Neocalanus plumchrus and Calanus marshallae, and amphipods have higher DHA+EPA concentrations than other species. Our data showed that the JS zooplankton community was dominated by small copepod species, which tend to have low FA content (Hiltunen et al, 2021).…”

“…Large calanoid copepods, such as Neocalanus plumchrus and Calanus marshallae , and amphipods have higher DHA+EPA concentrations than other species. Our data showed that the JS zooplankton community was dominated by small copepod species, which tend to have low FA content (Hiltunen et al, 2021). Both the NSoG and QCS had a high abundance of larger copepods, euphausiids, and amphipods, with the latter two groups both having relatively large size (> 10 mm) and high DHA and EPA content (Hiltunen et al, 2021), i.e., prey was more nutritious in the NSoG and QCS than JS.…”

“…Both the NSoG and QCS had a high abundance of larger copepods, euphausiids, and amphipods, with the latter two groups both having relatively large size (> 10 mm) and high DHA and EPA content (Hiltunen et al, 2021), i.e., prey was more nutritious in the NSoG and QCS than JS. This observation supports prey quality as an important factor in the overall better nutritional health of fish in the NSoG and QCS.…”

“…Fish obtain DHA and EPA through their diet. In the case of zooplankton prey, variations in DHA and EPA can occur because of shifts in composition, with different species having different nutritional quality and fatty acid content (Hiltunen et al, 2021), or shifts in the nutrition of phytoplankton that the zooplankton feed on (Costalago et al, 2020; El-Sabaawi et al, 2009). (2009).…”

“…(2009). There is substantial variability in FA content among zooplankton species in the Salish Sea (El-Sabaawi et al, 2009; Hiltunen et al, 2021). However, analysis of zooplankton communities has shown that species composition in the NSoG did not differ between 2015 and 2016 (Mahara et al, 2019), indicating that this was not an important factor in zooplankton prey quality.…”