Abstract
Understanding the relationship between metal level in predators and their prey is an important issue, and is usually difficult to determine because animals eat a variety of organisms. However, shorebirds that stop over during spring migration along Delaware Bay (New Jersey) stay for only 2–3 weeks, and eat mainly horseshoe crab (Limulus polyphemus) eggs. In this paper, we examine the relationship between metal levels in horseshoe crab eggs, and blood and feather levels of metals in red knot (Calidris canutus rufa; n = 30), sanderling (Calidris alba; n = 20) and semipalmated sandpiper (Calidris pusilla; n = 38) from Delaware Bay. There is a rich literature on metal levels in feathers. For all three species, the levels of arsenic, cadmium, chromium, lead and mercury in blood were highly correlated with the levels of metals in the eggs of horseshoe crab (17 pooled samples). This indicates that the levels in the blood of these shorebirds quickly reflect levels in their prey (horseshoe crab eggs), while metals in the feathers were not correlated with the levels in eggs. Semipalmated sandpipers had the lowest levels of arsenic in blood and the highest levels of arsenic in feathers, compared to the other species. At Delaware Bay, semipalmated sandpipers have a diet higher in marsh invertebrates than the other species, which may account for the differences. The levels of cadmium and chromium in blood were significantly higher in knots than other species; knots only ate horseshoe crab eggs. For all of the metals except arsenic, the ratio of levels in blood/feathers was similar among species. For arsenic, the ratio of levels in blood/feathers were significantly lower in semipalmated sandpipers than in the other species, by an order of magnitude.
Highlights
Government agencies, conservationists, and the public are interested in levels of heavy metals in wildlife that could prove detrimental to the organisms themselves, or to those that eat them.Heavy metals in biota can be used to indicate information about the levels in the foods they eat.Coastal birds are often used as bioindicators of contamination because they live in a variety of habitats, occupy different trophic levels, and are exposed to a range of chemicals [1,2,3]
There were significant interspecific differences in the levels of cadmium in blood; red knots had the highest levels of cadmium compared to the other species
The levels of heavy metals in the blood of all three species were positively correlated with the levels in horseshoe crab eggs, their primary food while they are in Delaware Bay
Summary
Government agencies, conservationists, and the public are interested in levels of heavy metals in wildlife that could prove detrimental to the organisms themselves, or to those that eat them.Heavy metals in biota can be used to indicate information about the levels in the foods they eat.Coastal birds are often used as bioindicators of contamination because they live in a variety of habitats, occupy different trophic levels, and are exposed to a range of chemicals [1,2,3]. Government agencies, conservationists, and the public are interested in levels of heavy metals in wildlife that could prove detrimental to the organisms themselves, or to those that eat them. Heavy metals in biota can be used to indicate information about the levels in the foods they eat. Coastal birds are often used as bioindicators of contamination because they live in a variety of habitats, occupy different trophic levels, and are exposed to a range of chemicals [1,2,3]. Levels are often higher in coastal areas because of the runoff from rivers [4,5], as well as atmospheric deposition [6,7]. Metals can be sequestered in bottom sediments of bays and estuaries, to be released by storms or strong tides.
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