Reviews and syntheses: Insights into deep-sea food webs and global environmental gradients revealed by stable isotope (<i>δ</i><sup>15</sup>N, <i>δ</i><sup>13</sup>C) and fatty acid trophic biomarkers

Abstract

Abstract. Biochemical markers developed initially for food-web studies of terrestrial and shallow-water environments have only recently been applied to deep-sea ecosystems (i.e., in the early 2000s). For the first time since their implementation, this review took a close look at the existing literature in the field of deep-sea trophic ecology to synthesize current knowledge. Furthermore, it provided an opportunity for a preliminary analysis of global geographic (i.e., latitudinal, along a depth gradient) trends in the isotopic (δ15N, δ13C) and fatty acid composition of deep-sea macro- and megafauna from heterotrophic systems. Results revealed significant relationships along the latitudinal and bathymetric gradients. Deep-sea animals sampled at temperate and polar latitudes displayed lower isotopic ratios and greater proportions of essential ω3 long-chain polyunsaturated fatty acids (LC-PUFAs) than did tropical counterparts. Furthermore, δ15N and δ13C ratios as well as proportions of arachidonic acid increased with increasing depth. Since similar latitudinal trends in the isotopic and fatty acid composition were found in surface water phytoplankton and particulate organic matter, these results highlight the link across latitudes between surface primary production and deep-water communities. Because global climate change may affect quantity and quality (e.g., levels of essential ω3 PUFAs) of surface primary productivity, and by extension those of its downward flux, the dietary intake of deep-sea organisms may likely be altered. In addition, because essential ω3 PUFAs play a major role in the response to temperature variations, climate change may interfere with the ability of deep-sea species to cope with potential temperature shifts. Importantly, methodological disparities were highlighted that prevented in-depth analyses, indicating that further studies should be conducted using standardized methods in order to generate more reliable global predictions.

Integrating siphonophores into marine food‐web ecology

“…Biochemical techniques such as fatty acid and stable isotope analyses have become widely-used approaches to complement GCA in ecological studies (Nielsen et al 2018;Parzanini et al 2019). Stable isotope values can provide trophic position estimates of siphonophores, and information about the trophic structure of zooplankton communities independent of GCA.…”

Stable Isotopic Evidence of Mixotrophy in Xylophagaids, Deep-Sea Wood-Boring Bivalves

“…POM from our collection localities are not available. Globally, average deep-sea heterotrophic animals have isotopic values ranging from 10-13 for δ 15 N and −17 to −21 for δ 13 C, depending on latitude (reviewed in Parzanini et al, 2019). POM data from the literature show elevated values compared with nitrogen fixed by bacteria.…”

“…Deep-sea nitrogen particulates may have comparatively high δ 15 N signatures (Sigman and Casciotti, 2001). Globally, deep-sea heterotrophic animals have average δ 15 N isotopic values from 10 to 13 depending on latitude (reviewed in Parzanini et al, 2019). Montoya et al (2002) found POM δ 15 N increases rapidly to 6-8 in the first 300 m in the tropical Atlantic.…”

The important role of sponges in carbon and nitrogen cycling in a deep‐sea biological hotspot

“…Fatty acids can provide complementary information on deep-sea food web functioning (Colaço et al, 2007;Parzanini et al, 2019), particularly for unravelling the transfer of organic matter from sponges to the wider food web. Sponges contain specific fatty acids that can serve as a biomarker, like mid-chain-branched fatty acids containing single methyl groups between the ω5 and ω9 positions, which are unique microbial markers of the associated microbiota of sponges that are typically not found in the environment ( de Kluijver, Nierop, et al, 2021;Thiel et al, 2002).…”

“…Compound‐specific‐isotope analyses of amino acids can be used to unravel trophic positions and food web interactions based on differential fractionation of amino acid nitrogen isotopes from food source to consumer (Chikaraishi et al, 2009; McClelland & Montoya, 2002). Fatty acids can provide complementary information on deep‐sea food web functioning (Colaço et al, 2007; Parzanini et al, 2019), particularly for unravelling the transfer of organic matter from sponges to the wider food web. Sponges contain specific fatty acids that can serve as a biomarker, like mid‐chain‐branched fatty acids containing single methyl groups between the ω5 and ω9 positions, which are unique microbial markers of the associated microbiota of sponges that are typically not found in the environment (de Kluijver, Nierop, et al, 2021; Thiel et al, 2002).…”