Mercury biomagnification in the Atlantic spotted dolphin (Stenella frontalis) food chain, using nitrogen stable isotope as an ecological tracer

Abstract

An assessment of mercury (Hg) concentrations and nitrogen stable isotope (15N) was conducted in the food chain of the Atlantic spotted dolphin (Stenella frontalis), including phytoplankton, zooplankton, planktivorous fish and its major prey (predatory fish and a single species of cephalopod), that compose a tropical trophic chain of the Brazilian southeastern coast. Tissue concentrations of Hg in a voracious predator fish, the largehead hairtail (Trichiurus lepturus), one of the dolphin’s prey, were 9.8 times lower than median concentrations found in dolphin tissues. 15N values in predatory fish were found to be lower to those of its predator the spotted dolphin. Isotopic data suggested significant differences for 15N along the trophic chain, with the top predator (dolphin) exhibiting heavier value, followed by the voracious predator fish and the benthonic carnivorous fish, the whitemouth croaker (Micropogonias furnieri). Phytoplankton displayed the lightest 15N, followed by zooplankton and the planktophagous fish, the lebranche mullet (Mugil liza). This fish species and the cephalopod showed the lowest median Hg concentration. All links of the entire trophic chain presented trophic transfer of Hg with a biomagnification factor higher than 1. A significant relationship was found between the log Hg concentration and trophic level (TL) of all evaluated species, with a positive slope (= 0.87). The calculated trophic magnification factor (TMF= 7.44) indicates that Hg concentration increased per TL, and also that the entire coastal food chain from the South Atlantic Ocean presented a biomagnification power of Hg within a range previously reported for tropical coastal ecosystems.