ABSTRACT: The detection of high concentrations of methylmercury in the sub-thermocline low oxygen seawater indicates a potential for enhanced bioaccumulation of mercury in such environments not yet explored. Here we present mercury concentrations in 8 fish species of low trophic level in relation to their vertical distribution. Fish species were selected to cover a wide range of vertical distributions, from epipelagic (<200 m) to mesopelagic (>300 m) environments in the sub-tropical mid-North Atlantic. Mean mercury concentrations in the study species ranged from 57 to 377 ppb dry wt and were significantly and positively correlated with median daytime depth. Concentrations increased by 4-fold from epipelagic to mesopelagic species with no further increases with depth among mesopelagic species down to about 1200 m. Such enhanced mercury bioaccumulation in the marine mesopelagic compartment seems to be determined proximately by levels in food and ultimately by water chemistry that controls mercury speciation and uptake at the base of the food chain. We conclude that this is the best explanation for high and yet poorly understood mercury concentrations found in deep-sea predators.

KEY WORDS: Mercury · Methylation · Fish · Accumulation · Epipelagic · Mesopelagic

Published in MEPS Vol. 141 (1996) on October 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996