10. Mercury Biomagnification in the Food Web of Tropical Andean Stream

Increasing release of mercury (Hg) through gold amalgamation, and deforestation have been major concerns in South America. Volcanic sources have also contributed to the natural emission of Hg from the Andes Mountains. Hg not only exhibits biomagnification through aquatic food webs, but it is also neurotoxic and impacts the reproductive capacity of fish. Many studies have assessed Hg biomagnification from areas of gold mining and erosion, but ours is one of the first to examine Hg contamination in a relatively undisturbed area. We used stable nitrogen () and carbon (13C) isotopes to characterize the food web of Río Las Marías, Venezuela, and examine Hg biomagnification trends. Representative fish species from Río Las Marías were collected during January‐February 2004, including detritivores, herbivores, invertivores, parasites, piscivores, and carnivores. Nitrogen isotope results indicate that parasitic catfish (Ochmancanthus alternus) ( = 12.2‰), carnivorous stingrays (Potamotrygon orbignyi) ( =11.4‰) and piscivorous redeye piranhas (Serrasalmus rhombeus) ( =10.9‰) act as top consumers in the web. Detritivorous characins (Steindachnerina argentae) (=6.8‰), and invertivorous knifefish (Apteronotus albifrons) ( =7.9‰) were located at the bottom of the food web. Although the highest value was observed from Ochmancanthus alternus due to its unusual diet of fish mucus, we predict that piscivorous species will exhibit higher Hg concentrations by consuming the muscle tissue where Hg is stored. Our assessment of Hg patterns in Río Las Marías will clarify the extent of Hg contamination in undisturbed areas, and will offer a valuable comparison to rivers that are influenced by gold mining activities.3