![]() ![]() This study raises the issue of essential element composition as another determinant of food quality, and the risk associated with changes in forage species' availability for the proper functioning of marine food webs and ecosystems. Neritic common dolphins and harbour porpoises but also minke whales were thus mainly supplied by the Se‐enriched nutritional group composed of small (pelagic) schooling fish (including sandeels, (horse) mackerel and also some Clupeids), while the diets of pilot whales or Risso's dolphins that mostly consume benthic cephalopods were clearly Cu‐enriched. We revealed contrasting diets in terms of exposure to elements. Mean concentrations of each element in the diet of eight cetacean species was finally calculated, as well as the importance of each nutritional group (as defined by HCA including all elements) for each predator species. The 78 forage species were then classified by hierarchical clustering analysis (HCA) into different nutritional groups, based on their composition in eleven elements. Some elements (As, Cu or Se) were more variable than others, especially in fish for Cu and Se. We showed a broad range of elemental composition values across forage species, partly driven by taxonomy (fish versus crustaceans/cephalopods) or their habitat (coastal versus oceanic, pelagic versus benthic). Elements included two essential macro‐minerals (nitrogen and phosphorous) and nine trace elements (arsenic (As), cobalt, copper (Cu), chromium, iron, manganese, nickel, selenium (Se), zinc). Species encompassed jellyfish, crustaceans, cephalopods, cartilaginous and bony fish. We analysed 78 forage species from the Bay of Biscay, NE Atlantic, for their concentrations in various chemical elements with a documented biological role (i.e. While large differences in energy densities have been demonstrated among these species, other determinants of their quality remain poorly explored. All trace element pairs were positively correlated in fishes suggesting regulation processes.īy transferring energy and nutrients from plankton to top predators, forage species play a major ecological role in marine food webs. No relationships were found between trace element concentrations and δ¹⁵N values of micronekton (except cobalt which decreased with increasing δ¹⁵N values), since most trace elements are not biomagnified in food webs due to regulation and excretion processes within organisms. ![]() When significant, negative relationships were found between micronekton body size and trace element concentrations, which can possibly be attributed to differing metabolic activity in young and old individuals, dietary shifts and/or dilution effect of growth. ![]() The difference in cadmium, copper and zinc concentrations between micronekton broad categories reflected differing metabolic and storage processes. Myctophids were associated with high concentrations of arsenic at La Pérouse and MAD-Ridge seamounts, and with lead and manganese at MAD-Ridge and in the Mozambique Channel. Trace elements and δ¹⁵N values were analysed in micronekton (crustaceans, fishes and squids) sampled in the south-western Indian Ocean. panamense play a major role in trace element transfer to higher trophic levels in the pelagic food web of the Gulf of California. These diel vertical migrators are crucial in the energy transfer between the deep-sea and epipelagic zones (and vice-versa), and the estimation of the Biomagnification Factor (based on Cu, Zn, Cd and Pb) levels revealed that both T. panamense, and these differences seemed to be related to inherent physiological and/or ecological traits rather than environmental element availability. mexicanus exhibited significantly higher concentrations of Cr, Cu, Zn and Pb in comparison to B. mexicanus the less abundant trace element was Ni (0.332 µg.g−1 dw) and for B. mexicanus presented 39.8 µg.g−1 dw and B. Zinc (Zn) was the most common trace element for both species, T. Therefore, the trace elemental composition (Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd and Pb) of Triphoturus mexicanus and Benthosema panamense specimens was determined. They play a central role in oceanic food webs and are known to perform diel vertical migrations, crossing the thermocline and reaching the oxygen minimum zone, however, very scarce information exists on trace element content in these organisms. Myctophids are key members of mesopelagic communities with a world biomass estimated at 600 million tons.
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