Addressing assumptions: variation in stable isotopes and fatty acids of marine macrophytes can confound conclusions of food web studies

Dethier, Megan N.; Sosik, Elizabeth A.; Galloway, Aaron W. E.; Duggins, David O.; Simenstad, Charles A.

doi:10.3354/meps10310

Cited by 72 publications

(85 citation statements)

References 64 publications

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“…These results show that FA signatures and MSI values of organisms are generally a function of their environment. Site differences in biomarker signatures are not unexpected (Guest et al 2010;Dethier et al 2013). Nevertheless, to our knowledge, the finding of consistent changes in FA and MSI values between conspecifics across a depth gradient is novel.…”

Section: Discussionmentioning

confidence: 89%

“…The combination of FA and MSI in this study ultimately suggested diagenesis as a mechanism for the consumer patterns, an explanation that may have been missed with MSI alone. The results also highlight the importance of considering primary producer aging, and subsequent biochemical changes that affect conclusions drawn of trophic relationships using mixing models (Sosik 2012;Dethier et al 2013), an area of potential variation that is often overlooked.…”

Section: Discussionmentioning

confidence: 99%

“…The deep areas sampled in the SJA have Britton-Simmons et al 2012). The main species contributing to the drift are relatively enriched kelps (Laminariales) that have average (6 SD) d 13 C signatures of 215.9 6 3.7 (n 5 75 replicates across four kelp taxa, multiple seasons, and the same three sites) or seagrasses (e.g., Zostera [Anthophyta]) that have d 13 C signatures of 210.9 6 1.9 (n 5 20 replicates in two seasons at the same three sites; data from Dethier et al 2013). The degradation and resuspension of this material could be contributing disproportionately to deep benthic food webs.…”

Section: Discussionmentioning

confidence: 99%

“…Britton-Simmons et al (2012) used a remotely operated vehicle to show that detached macrophytes (drift) are abundant at all depths surveyed below the photic zone (30-170 m) in the San Juan Channel and are associated with large aggregations of consumers, including shrimp. Furthermore, previous research in our system showed that MSI signatures of macrophytes can differ among sites (Dethier et al 2013; among-site FA signatures not evaluated). Because site-level differences in MSI and FA signatures were found in invertebrate consumer tissues in other systems (e.g., Tasmania; Guest et al 2010), we explicitly designed our study to capture potential variation at multiple sites.…”

Section: Methodsmentioning

confidence: 99%

“…Because site level variation is potentially significant for biomarker signatures (Guest et al 2010;Dethier et al 2013), to analyze our fundamental question about differences between depths we first pooled sites in one-way analyses on the factor depth. We also performed two-way PERMANOVAs (for both FA and MSI) to investigate site 3 depth interactions, which were present in most tests (see Results).…”

Section: Methodsmentioning

confidence: 99%

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Fatty acid and stable isotope biomarkers suggest microbe‐induced differences in benthic food webs between depths

Galloway

Lowe²,

Sosik

et al. 2013

Limnology & Oceanography

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Benthic marine consumers inhabiting the subphotic zone rely on subsidies of energy synthesized by macrophytes and phytoplankton in the photic zone. The effects of this energy subsidy on the trophic ecology of deep invertebrates are generally unknown. We used fatty acids (FA) and multiple stable isotopes (MSI) as trophic biomarkers to compare tissues from conspecifics of primary and secondary consumers in photic and subphotic habitats (15 and 100 m depth) at three sites in the San Juan Archipelago, Washington. FA composition differed across depths for all five species and MSI differed across depths for six of seven species. We found a general pattern of enrichment in d 13 C from shallow to deep for all consumers. d 15 N was consistently enriched in deep herbivores and suspension feeders, but did not differ in predators. Total v-3 FA were lower in deep primary consumers, whereas predator v-3 FA did not differ between depths. Total bacterial marker FA were lower in deep suspension feeders but higher in deep predators. The results suggest a possible mechanism for the differences in FA and enrichment between habitats: deep consumers potentially ingest detritus that has been biochemically altered by microbes during transport. We found support for this hypothetical mechanism in an algal aging experiment. Aged algae colonized by microbes responded with increases in bacterial FA, and decreases in v-3 FA. This study highlights the power of combining FA and MSI biomarkers, and provides evidence for the importance of organic matter degradation to food web studies.

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Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Fatty acid and stable isotope biomarkers suggest microbe‐induced differences in benthic food webs between depths

Galloway

Lowe²,

Sosik

et al. 2013

Limnology & Oceanography

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Tracing trophic pathways through the marine ecosystem of Rapa Nui (Easter Island)

Zapata‐Hernández

Sellanes

Letourneur

et al. 2021

Aquatic Conservation

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Stable isotope‐based trophic structure of pelagic fish and jellyfish across natural and anthropogenic landscape gradients in a fjord estuary

Naman

Greene

Rice

et al. 2016

Ecology and Evolution

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Identifying causes of structural ecosystem shifts often requires understanding trophic structure, an important determinant of energy flow in ecological communities. In coastal pelagic ecosystems worldwide, increasing jellyfish (Cnidaria and Ctenophora) at the expense of small fish has been linked to anthropogenic alteration of basal trophic pathways. However, this hypothesis remains untested in part because baseline description of fish–jellyfish trophic dynamics, and the environmental features that influence them are lacking. Using stable isotopes of carbon (δ13C) and nitrogen (δ15N), we examined spatiotemporal patterns of fish and jellyfish trophic structure in greater Puget Sound, an urbanizing fjord estuary in the NW United States. We quantified niche positions of constituent species, niche widths and trophic overlap between fish and jellyfish assemblages, and several community‐level trophic diversity metrics (resource diversity, trophic length, and niche widths) of fish and jellyfish combined. We then related assemblage‐ and community‐level measures to landscape gradients of terrestrial–marine connectivity and anthropogenic influence in adjacent catchments. Relative niche positions among species varied considerably and displayed no clear pattern except that fish generally had higher δ15N and lower δ13C relative to jellyfish, which resulted in low assemblage‐level trophic overlap. Fish assemblages had larger niche widths than jellyfish in most cases and, along with whole community trophic diversity, exhibited contrasting seasonal patterns across oceanographic basins, which was positively correlated to landscape variation in terrestrial connectivity. In contrast, jellyfish niche widths were unrelated to terrestrial connectivity, but weakly negatively correlated to urban land use in adjacent catchments. Our results indicate that fish–jellyfish trophic structure is highly heterogeneous and that disparate processes may underlie the trophic ecology of these taxa; consequently, they may respond divergently to environmental change. In addition, spatiotemporal variation in ecosystem connectivity, in this case through freshwater influence, may influence trophic structure across heterogeneous landscapes.

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Addressing assumptions: variation in stable isotopes and fatty acids of marine macrophytes can confound conclusions of food web studies

Abstract: Resale or republication not permitted without written consent of the publisher Biomarker signatures in intertidal and subtidal macroalgae and seagrasses may vary considerably in space and time.

Cited by 72 publications

References 64 publications

Fatty acid and stable isotope biomarkers suggest microbe‐induced differences in benthic food webs between depths

Fatty acid and stable isotope biomarkers suggest microbe‐induced differences in benthic food webs between depths

Tracing trophic pathways through the marine ecosystem of Rapa Nui (Easter Island)

Stable isotope‐based trophic structure of pelagic fish and jellyfish across natural and anthropogenic landscape gradients in a fjord estuary

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