Fatty acid biomarkers in coldwater eelgrass meadows: elevated terrestrial input to the food web of age-0 Atlantic cod Gadus morhua

Abstract

Lipid classes, fatty acids (FAs), and stable carbon isotopes of FAs were used to investigate dietary sources of organic carbon for juvenile Atlantic cod Gadus morhua during settlement into eelgrass Zostera marina. Primary producers, epibenthic prey, zooplankton, and fish were collected from August to November 2002 in shallow (<10 m) eelgrass in Bonavista Bay, Newfoundland, Canada. Lipid data indicated that zooplankton (> 80 µm) were associated with fresh organic material, while seston (5-80 µm) had high levels of bacterial FA and non-acyl lipids, typical of sedimentary material. Zooplankton, mysids, and amphipods showed a seasonal decrease in 22:6n-3 with a concomitant increased in the ubiquitous terrestrial indicators 18:2n-3 and 18:3n-3. Based on essential FA composition of prey, there was a decrease in the quality of food available to juvenile fish from August until November. Earlier (August) pelagic juveniles had higher levels of marine-sourced FA (22:6n-3) than late (November) arrivers. Further, in October and November settled juveniles had higher proportions of terrestrial FA biomarkers than pelagic cod, indicating an increased dietary terrestrial input at settlement. Isotopic evidence demonstrated that eelgrass was the most enriched (-14 ‰) source of organic carbon and supported multivariate FA analysis, confirming that eelgrass was not incorporated into the food web of juvenile cod. Increased terrestrial input of organic carbon coupled with low proportions of dietary essential FAs indicate that the functional significance of this habitat is refuge and not nutrition.

Revealing organic carbon sources fueling a coral reef food web in the Gulf of Mexico using stable isotopes and fatty acids

“…When all sources were considered together (uncorrected data by SIAR output contribution) to compute the trophic retention factor, the regression for essential FAs showed that there is a mechanism for ''trophic magnification,'' not just for 22:6v3 as proposed for cold seas (Parrish et al 2009), but for 20:4v6 and 20:5v3 within the coral reef food web. In the Gulf of Mexico coral reef food web, the EPA and DHA ratio is close to one in phytoplankton, the principal source of DHA (Table 3); however, TRF of DHA was 3.5 compared with EPA with TRF of 1.5, confirming that there is a preferential trophic accumulation for DHA.…”

“…Trophic retention factor-FA biomarker tracers may provide an additional advantage for studying food webs in that their signals may persist through multiple trophic transfers (Hall et al 2006;Copeman et al 2009). The most important long-chain (C 20 -C 22 ) HUFAs in fish are ARA, EPA, and DHA (Sargent et al 1999).…”

“…ARA . EPA, considered as essential dietary nutrients as well as essential metabolites sensu Parrish (2009).…”

Carbon isotopic fractionation in eider adipose tissue varies with fatty acid structure: implications for trophic studies

“…Free-ranging eiders would not normally consume such high levels of 18:2n-6, with that FA typically present in proportions <12% in most marine bivalve species (Table1) (Joseph, 1982), as well as aquatic insects (Goedkoop et al, 2000;Sushchik et al, 2003) and plants (e.g. Copeman et al, 2009). Known diet items for free-ranging eiders would also be expected to have low lipid contents, so that 18:2n-6 would make very little contribution to total FA consumed.…”

Lipids in Marine Ecosystems

“…This multivariate technique handles a large amount of variables simultaneously, and has been used by organic geochemists to determine organic matter sources and degradation of suspended and sinking particles in the oceans [110,111]. We have used PCA to determine marine, terrestrial, and anthropogenic organic inputs, and trophic relationships (e.g., [100,102,104,[112][113][114]). Fatty acid PCA continues to have a strong following [115][116][117], but more sophisticated multivariate statistical analyses are emerging too (see below).…”