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

Abstract

<p><strong>Abstract.</strong> 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 (δ<sup>15</sup>N, δ<sup>13</sup>C) and fatty acid composition of deep-sea taxa. 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-PUFA) than did tropical counterparts. Furthermore, δ<sup>15</sup>N and δ<sup>13</sup>C 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 PUFA) 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 PUFA 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.</p>

Feeding habitat and silvering stage affect lipid content and fatty acid composition of European eel Anguilla anguilla tissues

“…While eels store fat in both muscle and liver (Burgos et al ., 1989; Otwell & Rickards, 1981), liver is also the main site of lipid metabolism and energy mobilization (Hansen & Abraham, 1983; Tocher, 2003). As liver is characterized by higher biochemical turnover rates than white muscle, it is typically the less preferred tissue choice in long‐term dietary studies (Parzanini et al ., 2019). For the eyes, contradictory results have been reported regarding diet effects on FA composition ( e.g ., Brodtkorb et al ., 1997; Li et al ., 2014; Navarro et al ., 1997).…”

Trophic ecology of deep-sea megafauna in the ultra-oligotrophic Southeastern Mediterranean Sea

“…Knowledge of food web structure and dynamics is key to our understanding of ecological communities and their functioning (Polis and Strong, 1996;Winemiller and Polis, 1996). This fundamental information is, however, lacking in many oceanographic regions, including the Southeastern Mediterranean Sea (hereafter, SEMS) (Parzanini et al, 2019) – one of the most oligotrophic, nutrient-impoverished marginal basin, worldwide (Kress et al, 2014). The SEMS provides a miniature model of processes occurring in vast oligotrophic gyres, an ideal location to study food web structure and functioning under sever nutrient limitation.…”

Trophic Ecology of Deep-Sea Megafauna in the Ultra-Oligotrophic Southeastern Mediterranean Sea

“…Knowledge of food web structure and dynamics is key to our understanding of ecological communities and their functioning (Polis and Strong, 1996;Winemiller and Polis, 1996). This fundamental information is, however, lacking in many oceanographic regions, including the Southeastern Mediterranean Sea (hereafter, SEMS) (Parzanini et al, 2019) -one of the most oligotrophic, nutrient-impoverished marginal basin, worldwide (Kress et al, 2014). This basin exhibits extremely low open water primary production (~60 g C m −2 y −1 ) merely half of that measured in other oligotrophic areas of the ocean (Hazan et al, 2018), resulting in limited energy sources to its deep-sea habitats (Rahav et al, 2019).…”