Metal levels in eggs of common terns (Sterna hirundo) in New Jersey: temporal trends from 1971 to 2002

Abstract

Managers and public policy makers require information on the status of and trends in contaminant levels in organisms to assess ecosystem health. Seabirds are excellent bioindicators because they are long-lived, feed at different trophic levels, and are at the top of the food chain, and many are abundant and widely distributed. They can reveal spatial or temporal trends in contaminant levels. In this paper, we examine temporal trends in the levels of cadmium, chromium, lead, manganese, mercury, and selenium in eggs from common terns (Sterna hirundo) nesting on several salt marsh islands in Barnegat Bay, New Jersey. We test the null hypothesis that there are no temporal differences in levels of cadmium, lead, and mercury from 1971 to 2002 and in chromium, manganese, and selenium from 1992 to 2002. Arsenic was also analyzed in recent years. Levels were highest for manganese, followed by selenium, mercury, arsenic, lead, chromium, and cadmium. The eggs of Barnegat Bay common terns show a decline in levels of cadmium, chromium, and lead. Mercury declined from 1971 to 1982, increased dramatically in 1999, and declined thereafter. Manganese, an essential element, showed a decline (except for 2001), and selenium declined initially, but then remained stable. The data indicate that common terns can serve as useful bioindicators of temporal trends in exposure and that some of the metals of concern in estuarine environments (lead, cadmium) have declined over the past 30 years, although mercury levels are higher than in the early 1980s. The spike in 1999 is unexplained.