Metal levels in horseshoe crabs (Limulus polyphemus) from Maine to Florida

Abstract

There is considerable concern for the health of spawning populations of horseshoe crabs (Limulus polyphemus) along the east coast of North America because of an increase in the harvest, an apparent decrease in population levels, and the dependence of migrating shorebirds on a superabundant supply of horseshoe crab eggs during their migratory stopover on Delaware Bay. In addition to overfishing, population declines could be caused or recovery slowed, by pollution. In this paper, we examine the levels of metals (arsenic, cadmium, chromium, lead, manganese, mercury, and selenium) in the eggs, leg muscle, and apodeme of 100 horseshoe crabs collected at nine sites from Maine to Florida. Arsenic levels were the highest, followed by manganese and selenium, while levels for the other metals averaged below 100ppb for most tissues. Arsenic and mercury levels were highest in the leg muscle; cadmium, lead, manganese, and selenium levels were highest in eggs; and chromium levels were highest in the apodeme. There were significant geographical differences for all metals in all three tissues. No one geographical site had the highest levels of more than two metals. Arsenic, with the highest levels overall, was highest in Florida in all the three tissues. Manganese levels were highest in Massachusetts for eggs and apodeme, but not leg, which was highest in Port Jefferson, New York. Selenium was highest in apodeme from Florida, and in eggs and leg muscle from Prime Hook, Delaware. The patterns among locations and tissues were not as clear for the other metals because the levels generally averaged below 100ppb. The levels of contaminants found in horseshoe crabs, with the possible exceptions of arsenic in Florida, and mercury from Barnegat Bay and Prime Hook, were below those known to cause adverse effects in the crabs themselves or in organisms that consume them or their eggs. Our results indicate that site-specific data are essential for managers to evaluate the potential threat from contaminants to both the horseshoe crabs and those that consume them.