Marine Marine Biology 87,285-288 (1985) ==,BiOlOgy 9 Springer-Verlag 1985 Concentrations of Mn, Fe, Cu, Zn and Cd in the mesopelagic decapod Systellaspis debilis from the East Atlantic Ocean P. S. Ridout 1, A. D. Willcocks 2, R. J. Morris 1, S. L. White 3 and P. S. Rainbow 3 1 Institute of Oceanographic Sciences; Brook Road, Wormley, Godalming GU8 5UB, Surrey, England 2 Department of Oceanography, University of Southampton; Southampton SO9 5NH, England 3 School of Biological Sciences, Queen Mary College, University of London; Mile End Road, London E1 4NS, England Abstract Specimens of the oceanic decapod Systellaspis debilis were collected from six sites in the East Atlantic Ocean between 1970 and 1984, and were analysed for Mn, Fe, Cu, Zn and Cd. The data confirm that there are small but significant differences in mean metal concentrations from some sites which showed no obvious pattern in relation to geographic location of the samples. As a result, ranges of site means are quoted as "baseline" levels for each metal (jug g-1 dry wt): 2.3 to 2.9/~gMng -1, 31.2 to 77.8/~g Feg -1, 25.9 to 83.4/~gCug -1, 41.9 to 9 2 . 9 # g Z n g -~, 11.1 to 31.8/~gCdg-L The concentration of cadmium in S. debilis from all sites was raised relative to cadmium concentrations reported for coastal decapods, perhaps as a result of dietary enrichment. Metal accumulation may provide useful information for understanding the complex feeding behaviour of many oceanic animals. Introduction Increased awareness of marine pollution has given rise to many analyses of coastal and estuarine species (see Eisler, 1981), but data remain relatively sparse for oceanic animals. Most trace-metal concentrations in open-ocean water remain at low levels relative to many coastal sites (Jones and Jefferies, 1983), but metals can become concentrated in the marine organisms (Eisler, 1981). In general, open-ocean waters can be considered to provide "baseline" levels for the assessment of metal contamination in polluted coastal waters. Likewise, metal levels in oceanic organisms may provide such baselines at various trophic levels. These data could also be useful in the assessment of man's impact on the open ocean in the future (e.g. deepocean mining for metals). The reason for bioaccumulation of trace metals and the mechanisms by which it occurs are not fully understood. Although toxic in excess, iron, copper and zinc are known to have important biochemical roles and may be regulated, at least to some degree, within the organism (Bryan, 1979). The ability of decapods to regulate concentrations of essential trace metals has been investigated by a number of workers (e.g. Bryan, 1971; Martin, 1974; Wright, 1976; White and Rainbow, 1982, 1984 a, b). There is no known precise biochemical role for cadmium, although it does accumulate in some oceanic decapods (Leatherland etal., 1973). It has been shown that cadmium levels in decapods are not regulated (Dethlefsen, 1978; Jennings and Rainbow, 1979; White and Rainbow, 1982). Manganese is thought to be important in enzyme activity, although its biochemical role is poorly understood. Systellaspis debilis is an abundant and widely distributed member of the mesopelagic faunae in the East Atlantic Ocean. As an important member of the mesopelagic biota, it is an ideal species to study in an investigation of natural-product metaMevels within the oceanic ecosystem. In this study we have measured the concentrations of Mn, Fe, Cu, Zn and Cd in S. debilis in order to establish possible baseline levels for these metals in this species. Materials and methods Sampling Samples of Systellaspis debilis were collected from six East Atlantic sites (Fig. 1) between 1970 and 1984. All the decapods, trapped in good condition, were transferred immediately to polythene bags; air was excluded, and the decapods were deep-frozen (-20 ~ prior to analysis. During sampling, plastic implements were used as a precaution against metal-contamination. P, S. Ridout et aL: Mn, Fe, Cu, Zn and Cd in Systellaspis debilis 286 30 ~ W 40~ 20 ~ W lO~ I ......... ......... lO~ E 0~ [ ........ ,),,~ ..... ~_ 2 [2] 30~ - 20~N- 3E ~ ] 655). Corrections for any matrix interferences were made using the method of standard additions and for nonspecific absorption using a hydrogen continuum source. The data were analysed statistically for differences in mean metal concentrations using analysis of variance, both a priori to test for differences amongst all means, and a posteriori for differences between selected sites or groups of sites (Sokal and Rohlf, 1969). For all metals except manganese, the variance of the metal concentration varied with the mean, necessitating a logarithmic transformation of these data prior to the analysis of variance. All body metal concentrations are quoted in terms of k~g g-1 dry weight. D ~' 4 Results and discussion IO~ 5L_ ' 0 ~a m 6L___, Fig. 1. Six sites in the East Atlantic Ocean where Systellaspis debilis was collected Sample preparation and analysis Each individual decapod was rinsed with double-distilled water and then surface-dried in a stream of filtered air for approximately 5 rain. The decapods were overt-dried at 60~ to constant weight. This method of drying was compared with freeze-drying and found to be equally efficient for the metals studied (Willcocks, 1984). Dried samples were weighed into conical flasks (50 ml) with loose-fitting caps. Single dried individuals (0.2 to 0.5 g) were digested in acid using the following procedure, based on a system reported by Borg et al. (1981): (i) cold-soaked in concentrated HNO~ (1 ml) overnight; (ii) heated to 50 ~ (rain. = 4 h); (iii) heated to 120 ~ (min= 12 h); (iv) cooled and H202 (30%) added (2 ml); (v) heated to 160 ~ (5 to 6 h). All samples were made up to 10 ml vol with quartz-distilled water, transferred to plastic bottles, and stored at 4 ~C. Some modifications of the above methodology were used. Some material from Site 4 was digested fresh rather than dried, so the values were calculated on a dry weight basis using the average weight-loss value of 70%. Samples from Site 2 were sampled and analysed in an independent study which used a digest of nitric acid only (--~ 1 ml 0.3 g-1 dry material) at 100 ~ Analysis of the acid digests was carried out using atomic-absorption spectrophotometry with flame-atomization (Varian AA120 and Varian AA375) and electrothermal-atomization (Instrumentation Laboratory 151 / The relationship between the size (assumed equivalent to age) and trace-metal content in marine organisms has been investigated by a number of workers and reviewed by Phillips (1980). In the present study on Systellaspis debilis, grouped data from both total and individual sites, showed some correlation with size, for Mn, Fe and Cu, but not for Zn or Cd (Willcocks, 1984; White, unpublished data). In order to minimise any size/metal-content related effects, only results for individuals within a fixed size range (0.2 to 0.5 g dry wt) are reported. The weights and metal concentrations of the decapods collected from each site are shown in Table 1. A priori analysis of variance showed that, for all five metals there were small significant differences ~ < 0.001) between mean body metal concentrations at the six sites. A posteriori analysis of variance allowed, for each metal, the identification of groups of sites which showed no significant difference between means within the group but which differed significantly (p < 0.05) from other groups. Such groups are identified for each metal in Table 1, from which it can be seen that there are no discernible patterns of high or low metal concentrations in Systellaspis debilis from particular sites which are attributable to geographic position. Similarly, there is no evidence that a high or low mean concentration of one metal is correlated with a high or low mean concentration of another metal. Because of the results of the a priori analysis of variance, it is not valid to quote grand-mean concentrations for each metal in S. debilis from the East Atlantic. Therefore, in order to provide data on "baseline" metal level, ranges of metal concentrations are included in Table 1. In general it can be seen that, for each metal, the variation between the sites tMls within one standard deviation. The concentrations of manganese were lower than the majority of data available for coastal crustaceans (Eisler, 1981). Most body manganese is thought to be absorbed from the diet (Bryan and Ward, 1965), and the concentration of 3.6/~g g-1 reported for euphausiids (Martin and Knauer, 1973), a principal component of the diet of Systellaspis debilis (Roe, 1984), shows reasonable agreement with the values recorded in the present study.