Fatty acid trophic markers and trophic links among seston, crustacean zooplankton and the siphonophore &lt;em&gt;Nanomia cara&lt;/em&gt; in Georges Basin and Oceanographer Canyon (NW Atlantic)

Sergio Rossi,Xènia Garrofé,Marsh J Youngbluth,Francesc Pagès,Charles A Jacoby

doi:10.3989/scimar.2008.72n2403

Abstract

Fatty acid concentrations expressed as percentages of total fatty acid pools in seston, stage V copepodites of Calanus finmarchicus , adults of the euphausiid Meganyctiphanes norvegica , and the physonect siphonophore Nanomia cara were used to elucidate trophic links in Georges Basin and Oceanographer Canyon in September 2003. Seston at both locations was refractory and comprised mainly of saturated fatty acids. Phytoplankton did not contribute significantly to the fatty acid composition of seston or higher trophic levels. Only four fatty acids, i.e. 14:0, 16:0, 16:1 (n–7) and 18:1 (n–7), were transferred from seston to C. finmarchicus or M. norvegica , which suggested weak trophic interactions. Fatty acids transferred from the two species of crustaceans to N. cara included the same four fatty acids, along with three polyunsaturated fatty acids found in relatively high concentrations in both crustaceans, i.e. 20:3 (n–6), 20:5 (n–3) and 22:6 (n–3). In addition, 18:1 (n–9), which occurred in relatively high concentrations only in M. norvegica , and 18:0 and 18:2 (n–6), which were found in low concentrations in both crustaceans, also appeared to be transferred to N. cara . Overall, fatty acid trophic markers proved useful for identifying trophic links to N. cara .

Highlights

Gelatinous zooplankton function as herbivores, carnivores, omnivores or detritivores in all oceans from surface waters to the deep sea (Hartman and Emery, 1956; Pugh, 1975; Biggs et al, 1981; Pagès and Kurbjewit, 1994; Patriti, 1995; Gorsky et al, 2000)
Summary: Fatty acid concentrations expressed as percentages of total fatty acid pools in seston, stage V copepodites of Calanus finmarchicus, adults of the euphausiid Meganyctiphanes norvegica, and the physonect siphonophore Nanomia cara were used to elucidate trophic links in Georges Basin and Oceanographer Canyon in September 2003
Fatty acids transferred from the two species of crustaceans to N. cara included the same four fatty acids, along with three polyunsaturated fatty acids found in relatively high concentrations in both crustaceans, i.e. 20:3 (n–6), 20:5 (n–3) and 22:6 (n–3)

Summary

Introduction

Gelatinous zooplankton function as herbivores, carnivores, omnivores or detritivores in all oceans from surface waters to the deep sea (Hartman and Emery, 1956; Pugh, 1975; Biggs et al, 1981; Pagès and Kurbjewit, 1994; Patriti, 1995; Gorsky et al, 2000). The roles of gelatinous zooplankton in food webs mainly have been determined from the stomach contents of specimens caught in nets. Such sampling can bias estimates of prey consumption because gelatinous zooplankton may feed on prey concentrated in cod ends, digest stomach contents during tows, or regurgitate prey (Youngbluth and Båmstedt, 2001). In situ observations provide reliable data on gut contents of gelatinous predators, but such observations are limited (Robison, 2004)

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Discussion

Conclusion