Species and element-specific associations of trace elements with body size in mesopelagic fish and crustaceans from the North-East Atlantic

We explored the association between standard body length and whole-body element concentrations of As, Cd, Cu, Fe, Hg, Mn, Se, V, and Zn in four common mesopelagic species collected from fjord and offshore locations of the North-East Atlantic. These included Silvery lightfish (Maurolicus muelleri), Glacier lanternfish (Benthosema glaciale), Northern krill (Meganyctiphanes norvegica), and Arctic red prawn (Eusergeses arcticus), and a large size-range was covered for each species. We found that the concentrations of most elements changed with size in the fish species and E. arcticus, and to a lesser degree in M. norvegica, likely due to its large growth variability which might have blurred the accumulation and dilution patterns. For the fjord samples, more elements were significantly associated with body length than for the offshore samples. Essential elements were mostly showing significant decreases in concentration with body size and growth dilution was suggested to be an important factor; however, further research is advised. For M. muelleri, Hg concentrations and δ¹⁵N increased with size, while for B. glaciale, neither Hg concentrations nor δ¹⁵N clearly increased with size in offshore locations, suggesting an association between Hg concentrations and trophic position. Regarding food safety, Cd concentrations might be of concern for direct consumption of whole individuals for M. muelleri and B. glaciale caught in offshore locations, as more than half of the individuals, meaning the smallest ones, exceeded the European legal maximum level. Our findings provide useful information on nutritional content and safety of these species as food and feed, and on their role in element cycling.