Trace element composition of Norway lobster (Nephrops norvegicus) in the proximity of fish farms

Abstract

The aquaculture industry in Norway is expected to grow with potential impact on the environment. The common seafood delicacy Norway lobster (Nephrops norvegicus) was studied to see how the vicinity to aquaculture might affect the trace element concentration. A total of 79 nephrops have been caught in four different locations in Romsdalsfjorden, Norway. Two locations (A and B) were in increasing distance from a fish farm, one location was considered a control group (C) several km from any fish farms, and the last location (D) was near, but upstream fish farms with potential effect. Hepatopancreas and muscle tissue have been analysed for the non-essential trace elements Cd, Hg, Pb, and As, in addition to the essential elements Cu, Zn, Fe, Mn and Se. The main objective of this study was to investigate the element composition of trace elements in this benthic invertebrate species in the vicinity of the fish farms. The trace elements were also investigated regarding distribution of concentration in the sampled organs (tail muscle and hepatopancreas) and differences between sexes.

The hepatopancreas samples showed significantly decreasing concentrations of Cu with increasing distance from aquaculture. The highest mean concentration was found closest to the fish farm (538.7 ± 106.4 mg/kg ww). Additionally, there were trends of the same elevation of concentration near fish farms in Zn concentration in the hepatopancreas, and for As, Cu, Se, and Zn in the muscle tissue. However, these trends were not statistically significant. The analysis of stable carbon and nitrogen isotopes in muscle tissue samples suggested a change in dietary niche of the nephrops close to the fish farm. Indications of a more specialized niche near the fish farm suggested that the nephrops have access to a more similar range of food, meaning they are likely directly or indirectly feeding on organic waste from the fish farm. When looking at all the collected individuals (irrespective of distance to fish farm), all the investigated elements were found to have higher concentrations in the hepatopancreas than in the muscle tissue. Different accumulation in the sexes were found, where females had significantly higher concentrations of Cd, Hg and Cu in the hepatopancreas samples and of Cd, Hg and Mn in the muscle samples. The males were found to have higher concentrations of Fe in the hepatopancreas samples, and higher concentration of As and Se in the muscle samples. In the muscle tissue, which is mainly what is eaten by humans, none of the trace elements were found to have higher values than the maximum legal limit. In the hepatopancreas, there were found elevated levels of Cd.