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Mercury (Hg) transference through an established and defined food web from an urbanized subtropical coastal lagoon (SE Gulf of California) was examined by using carbon and nitrogen stable isotope and Hg analyses. Concentrations of Hg in seawater (0.045-0.078 μg L(-1)), predominantly incorporated to the particulate fraction (60% of total), were lower than those found in highly contaminated coastal areas around the world (0.18-16 μg L(-1)). Although levels of Hg available for the biota (e.g., associated to the reactive and pyrite fractions; 0.11-0.15 μg g(-1)) were within of effects range-low (ER-L, 0.15-0.71 μg g(-1)) these concentrations represented from 46.6 to 67.0% of the total Hg pool that may be transferred through food web. The sequence of bio-accumulation of Hg in studied species was according with their functional guild: tertiary consumer (0.85-1.15 μg g(-1)) > secondary consumers (0.084-0.168 μg g(-1)) > primary consumers (0.014-0.160 μg g(-1)) > primary producers (0.016-0.056 μg g(-1)). Hg concentrations increased for each successive trophic position estimate through δ(15) N isotopic values, although these relationships showed differences between dry and rainy seasons (R(2) = 0.37 and R(2) = 0.39 between δ(15) N vs. Hg in organisms, respectively). We concluded that Hg is being positively transferred (biomagnification factor >1) through the studied food web probably enhanced by the favorable environmental conditions for Hg-methylation (e.g., fine sediments rich in organic matter, and environmental conditions changes of the redox, pH, and temperature) found in this urbanized coastal water, however, the study of processes methlylation and biomagnifcation of Hg need further investigations., (Copyright © 2011 Wiley Periodicals, Inc.)

The objective of this investigation was to assess the transfer of lead (Pb) along an experimental, four-level food chain: Tetraselmis suecica (phytoplankton) → Artemia franciscana (crustacean, brine shrimp) → Litopenaeus vannamei (crustacean, white shrimp) → Haemulon scudderi (fish, grunt). T. suecica was exposed to a sublethal dose of Pb in solution and then used as the base of a marine food chain. Significant differences in Pb concentrations were found between exposed organisms of the different trophic levels and the control. Particularly, Pb concentrations in fish of the simulated trophic chain were two-to three times higher in the exposed specimens than in the control. Levels of Pb in phytoplankton showed a substantial increase with respect to the solution (level I), with bioconcentration factors averaging from 930 to 3630. In contrast, a strong decrease in Pb concentration from phytoplankton to zooplankton (level II) and from zooplankton to shrimp tissues (level III) was evidenced by bioaccumulation factors <1. Despite the decrease in the assimilation efficiency of metal transfer observed in these two predators, Pb concentration in the grunt fish (level IV) was higher than in the shrimp (level III) (bioaccumulation factor >1.0). Some of the added Pb is transferred from the phytoplankton along the food chain, thus producing a net accumulation of Pb mainly in fish and, to a lesser extent, in shrimp tissues. Because Pb is one of the most pervasive contaminants in coastal ecosystems, its transference by way of diet and potential net accumulation in higher predators is of ecologic importance for marine life. In addition, because shrimp and adult Haemulon scudderi are commercially important resources, this issue is of particular relevance to the safety of marine products.

This investigation sought to assess the biological responses to Pb along a simplified four-level food chain, from the primary producer, the microalgae Tetraselmis suecica, grown in a control medium with < 1 µg/L of Pb and exposed to a sublethal dose (20 µg/L of Pb) and used as the base of a simulated food chain, through the primary-, secondary-, and tertiary-level consumers, namely, the brine shrimp, Artemia franciscana; the white-leg shrimp, Litopenaeus vannamei; and the grunt fish, Haemulon scudderi, respectively. Growth of Pb-exposed T. suecica was 40% lower than that of the control cultures, and survival of A. franciscana fed this diet was 25 to 30% lower than the control. No differences in the growth rates of Pb-exposed and control shrimp and fish and no gross morphological changes were evident in the exposed specimens. However, the exposed shrimp and fish had 20 and 15% higher mortalities than their controls, respectively. In addition, behavioral alterations were observed in exposed shrimp and fish, including reduction in food consumption or cessation of feeding, breathing air out of the water, reduction of motility, and erratic swimming. The negative correlation between Pb concentration in whole body of shrimp and fish and Fulton's condition factor suggested also that the exposed organisms were stressed because of Pb accumulation., (Copyright © 2011 SETAC.)

Trophic relationships and heavy metal transference in a coastal subtropical lagoon marine food web were investigated through the use of stable isotopes in food sources and biota. A selective extraction scheme was applied to the surface sediments as an indirect way to evaluate the potential of toxicity of metals. Results showed that cadmium, copper, lead and zinc concentrations were within sediment quality guidelines criteria. Concentrations of these metals in organisms varied widely among functional groups and within the same and closely related taxa. delta(13)C values varied significantly among organisms from different functional groups, while the delta(15)N values varied according with their feeding habits. Cd, Cu, Pb, and Zn were not positively transferred (biomagnification factor <1) through entire food web. However, a partial positive transference was observed for Cu and Zn involving three trophic levels (from the phytoplankton to crab as secondary consumer).