The mercury content of mullets and black mojarras of Urías lagoon (NW Mexico) were determined every second month from November 2012 to September 2013, to determine differences related to season or to trophic levels. The Hg contents of the muscle were significantly higher in mojarras, confirming that Hg contents tend to increase along the food chain, while the levels in liver were higher in mullets, suggesting different Hg storage strategies of these species. In mullets, the content of muscles did not vary seasonally and was significantly lower than in the liver. In black mojarras there were no significant differences between muscle and liver, and the lowest mean values were in May in both tissues. Given the low Hg contents, both species are safe for human consumption, but care should be taken in traditional fishing communities.

Oysters of Urías lagoon (NW M exico) were collected every second month from November 2012 to September 2013, to determine the variations of their mercury (Hg 2+ ) content and assess their suitability for human consumption. Concentrations were significantly higher in November than in M arch and M ay, which indicates that variability does not depend on the alternation of dry and rainy seasons, and is probably related to the reproductive cycle of this species. In view of the low apparent seafood consumption in M exico and given the low mean H g 2+ concentrations (0.07-0.26 µg g -1 , dw), consumption of this oyster does not seem to pose risks to the largest part of the population, but the local fishing communities are the ones most likely to be at risk, because of their higher seafood consumption.