Essential element (micro-nutrient) concentrations in 78 coastal to oceanic forage species sampled in the Bay of Biscay, Northeast Atlantic, between 2002 and 2008

The dataset contains the concentrations of 11 essential elements (micro-nutrients) analysed in whole bodies of 78 forage species sampled on the continental shelf or in the canyons of the Bay of Biscay, North-East Atlantic. The species encompass jellyfish, crustaceans, cephalopods, cartilaginous and bony fish from coastal to oceanic and deep-sea waters. The elements include two macro-minerals (nitrogen and phosphorous) and nine trace elements (arsenic, cobalt, chromium, copper, iron, manganese, nickel, selenium, and zinc). Most of the specimens were collected during the annual EVHOE fishery campaigns (“Evaluation Halieutique de l'Ouest de l'Europe”; https://doi.org/10.18142/8) conducted each autumn by the “Institut Français de Recherche pour l'Exploitation de la Mer” (Ifremer) on R/V Thalassa, between 2002 and 2008, by benthic trawling with marge vertical opening or by pelagic trawling. Some species were additionally sampled during the same period from opportunistic fishing boats. As far as possible, the size range of these forage species was selected to match published prey sizes for cetacean predators in the Bay of Biscay.
All the material was frozen immediately after collection and kept at –20°C until being processed. In the laboratory, whole organisms were briefly thawed. To reduce inter-individual variability, few to hundreds of individuals (depending on the size of species) were grouped for each species (i.e. constitution of pools) and homogenized using a stainless-steel knife mill, carefully rinsed with ultrapure water between each sample. These pools of whole specimens (corresponding to analytical samples) were frozen again –20°C, freeze-dried and reduced into fine powder until further analyses. A total of 115 samples was finally analysed. The process of organisms and samples (brief thawing, homogenization, freeze-dried and reduction into powder) was done within a maximum of two years after at-sea collection, and the samples (powders) were stored in a clean and dry place until analyses. Total element analyses on samples were then all conducted at the same date (in 2016).
Total nitrogen (N) concentrations were determined following the Kjeldahl method (AOAC, 1990). Briefly, this method consists in digesting the samples with sulfuric acid to transform all N present into ammonium sulfate. The solution is then alkalized and the resulting ammonia is determined by distillation into a known volume of boric acid, the excess of which (corresponding to the amount of nitrogen in samples) is finally determined by titration.
For all other elements, aliquots of samples (~200 mg dry weight of homogenised powder) were digested using a 6:2 (v/v) mixture with nitric acid (HNO3 69%, Trace Metal Grade®, FisherScientific) and hydrochloric acid (HCl, 34%, Trace Metal Grade®, FisherScientific). Acidic digestion of the samples was performed overnight at room temperature and then in a microwave oven (START-D, Milestone). Total concentrations of the micro-mineral phosphorus (P) and of the essential trace elements arsenic (As), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), selenium (Se) and zinc (Zn) were determined by inductively coupled plasma atomic emission spectrometry (ICP-OES, Vista-Pro Varian) and/or mass spectrometry (ICP-MS, X Series 2 Thermofisher Scientific). The quality assurance of these elemental analyses relied on blank and internal standard controls, and on the accuracy and reproducibility of data relative to the certified reference materials (CRMs) used in each analytical run. The CRMs used were TORT-3 (lobster hepatopancreas, National Research Council of Canada/NRCC) and DOLT-4 (dogfish liver, NRCC). Blank values were systematically below the detection limits and CRM values concurred with certified concentrations, with recovery rates ranging between 83% and 116% depending on the elements and on the CRM. Limits of quantification (LOQ) were calculated for each sample, depending on the mass of the aliquot analysed. The few concentrations below LOQ were replaced by half of the LOQ for each sample of concern. Specifically, this concerned 19 and 2 samples out of the 115 analysed for Cr and Ni respectively, corresponding to about 15% of values (for Cr) or much less than 15% (for Ni), in which cases this method of replacing non-detects by half the LOQ may be applied for data analysis (U.S. Environmental Protection Agency, 2000).
All elemental concentrations given on a dry weight basis can be converted on a wet weight basis according to the average percentages of moisture given for each species.

本数据集涵盖东北大西洋比斯开湾大陆架及峡谷海域采集的78种饵料生物全躯体的11种必需元素（微量营养素，micro-nutrients）浓度检测数据。该批次物种涵盖从近岸到远洋及深海水域的水母、甲壳类、头足类、软骨鱼与硬骨鱼。所检测元素包含2种大量矿物质（氮与磷）以及9种微量元素（砷、钴、铬、铜、铁、锰、镍、硒、锌）。多数标本采集于2002至2008年间每年秋季，由法国海洋开发研究院（Institut Français de Recherche pour l'Exploitation de la Mer, Ifremer）在"塔拉萨"号科考船（R/V Thalassa）上开展的年度EVHOE渔业调查项目（全称"Evaluation Halieutique de l'Ouest de l'Europe"; https://doi.org/10.18142/8）完成，采样方式为垂直开度可调的底拖网或中层拖网。部分物种同期通过临时作业渔船补充采集。采样时尽可能选取与比斯开湾海域已发表的鲸类捕食者猎物尺寸匹配的饵料生物个体尺寸范围。

所有采集的样本均在采集后立即冷冻，并保存于-20℃环境直至实验室处理。实验室中，将全躯体生物样品进行短暂解冻。为降低个体间差异，按物种将少量至数百个个体（依物种体型而定）混合为混合样本（即样本池），并使用不锈钢刀式研磨机进行均质处理，每批次样品间均用超纯水仔细冲洗研磨机。这些全躯体混合样本（即分析用样品）再次冷冻保存于-20℃，经冷冻干燥后研磨为细粉，以待后续检测。最终共完成115份样本的检测分析。从海上采集至完成样品处理（短暂解冻、均质、冷冻干燥及研磨制粉）的全过程最长不超过两年，制备好的粉末样品保存于洁净干燥环境直至检测。所有样品的元素检测均于2016年同期完成。

总氮（N）浓度按照凯氏定氮法（Kjeldahl method, AOAC, 1990）进行测定。该方法简要流程为：用硫酸消解样品，将样品中所有氮转化为硫酸铵；随后对溶液进行碱化处理，通过蒸馏将生成的氨导入已知体积的硼酸溶液中，最后通过滴定法测定过量的硼酸（其消耗量与样品中的氮含量相对应）。

对于其余元素，称取约200mg干重的均质粉末样品，使用体积比6:2的硝酸（HNO3 69%, Trace Metal Grade®, FisherScientific）与盐酸（HCl, 34%, Trace Metal Grade®, FisherScientific）混合溶液进行消解。样品的酸性消解先在室温下静置过夜，随后置于微波消解仪（START-D, Milestone）中完成。常量矿物质磷（P）以及必需微量元素砷（As）、钴（Co）、铬（Cr）、铜（Cu）、铁（Fe）、锰（Mn）、镍（Ni）、硒（Se）与锌（Zn）的总浓度，通过电感耦合等离子体原子发射光谱法（inductively coupled plasma atomic emission spectrometry, ICP-OES, Vista-Pro Varian）和/或电感耦合等离子体质谱法（inductively coupled plasma mass spectrometry, ICP-MS, X Series 2 Thermofisher Scientific）进行测定。本次元素检测的质量控制依托空白对照与内标质控，以及各分析批次中使用的标准参考物质（certified reference materials, CRMs）来保证数据的准确性与可重复性。本次使用的标准参考物质为TORT-3（加拿大国家研究委员会NRCC出品的龙虾肝胰腺标准物质）与DOLT-4（NRCC出品的角鲨肝标准物质）。所有空白值均低于检测限，标准参考物质的测定值与认定浓度一致，元素的加标回收率介于83%至116%之间，具体数值依元素与标准参考物质类型而异。针对每份样品，根据分析所用的称样量计算其定量限（limits of quantification, LOQ）。少量低于定量限的浓度值，采用对应样品定量限的一半进行替代。具体而言，115份分析样本中，铬（Cr）有19份、镍（Ni）有2份的浓度低于定量限，占比分别约为15%与远低于15%；此种情况下可采用将未检出值替换为定量限一半的方法进行数据分析（美国环境保护署，2000）。

所有以干重计的元素浓度，可根据各物种的平均含水率换算为湿重计浓度。