Contrasting food web factor and body size relationships with Hg and Se concentrations in marine biota

Abstract

Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by δ(15)N) and degree of pelagic feeding (measured by δ(13)C). Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans.

Figure 1. Variability in Hg and Se content in finfish and invertebrates.

Hg content is more variable within and across taxa, compared with Se.

Figure 2. Relationships between Hg (left), Se (right) and Hg:Se molar ratios in fish (top) and invertebrates (bottom).

Hg content is more strongly related to Hg:Se molar ratios than Se content. The range of the axes varies among panels. Shark taxa are shown as triangles. Hg and Hg:Se relationships are described by the equation for fish: Log₁₀(Hg:Se)  = 0.17+1.0*Log₁₀(Hg), R² = 0.98, P<0.0001, F_1,10 = 410 and invertebrates Log₁₀(Hg:Se)  = −0.22+0.87*Log₁₀(Hg), R² = 0.78, P = 0.0006, F_1,8 = 29.

Figure 3. Mean mercury concentrations in Long Island fish (top) and invertebrates (bottom) were within the range, but generally lower than those summarized from a database of Hg concentrations in U.S. commercial seafood [Seafood Hg Database, 12].

Database taxa matched Long Island taxa except for bay anchovy (database values for all anchovies were used), long-finned squid (database values for all squid were used), angelwing clam, surf clam and razor clam (database values for all clams were used), ribbed mussels and blue mussels (database values for all mussels were used).

Figure 4. PCA biplot on mean values across taxa.

Hg content is more strongly, positively related to body size and trophic level (δ¹⁵N). Invertebrates are indicated by a plus sign, shark species are indicated by a triangle, all other finfish are indicated by a circle.