An Analysis of Possible Genotoxic Exposure in Adultand Juvenile Royal Terns in North Carolina, USA TERRI J. MANESS AND STEVEN D. EMSLIE Department of Biological Sciences, University of North Carolina, Wilmington, NC 28405 USA Internet: manesst@uncwil.edu Abstract.-We studied possible genotoxic exposure in Royal Terns (Sterna maxima) by collecting blood from adults and juveniles at five breeding colonies in coastal North Carolina in 1999. These colonies are located in three estuarine systems (Core Sound, Pamlico Sound, and Cape Fear River), each subjected to different contaminant loads. DNA in red blood cells was analyzed using the comet assay to determine levels of DNA strand breaks, a tech- nique previously not applied to birds. In addition, we weighed each bird and estimated its fat reserves as an indica- tion of nutritional health. Gross health assessments showed no significant differences between study sites, both for adult and juvenile terns. The comet assay indicated that blood cells from the adult andjuvenile terns from two Core Sound colonies, Wainwright and Sand Bag Islands, had significantly higher levels of apparent DNA damage than the remaining study sites. Based on previously published studies of sediment contaminants, the Core Sound colo- nies have relatively low overall pollutant loads, a finding contrary to the expected result based on the DNA damage. Plausible explanations for these finding are that birds from the Core Sound are exposed to an undetected genotox- ic contaminant(s) or that birds from the more polluted sites have had an adaptive response to the contaminant ex- posure. Received 30 October 2000, accepted 25 March 2001. Key Words.-Royal Terns, genotoxins, North Carolina, comet assay, environmental pollutants. Waterbirds 24(3): 352-360, 2001 We investigated the potential effect of genotoxic exposure in Royal Terns (Sterna maxima) while breeding in estuaries along the coast of North Carolina. Genotoxins are pol- lutants that damage DNA and can accumulate through the food chain rendering high trophic-level feeders particularly at risk (Gard- ner et al. 1991; French et al. 1996; Boon et al. 1998; White et al. 1998). Seabirds are known bioindicators of the health of marine ecosys- tems (Bourne 1976; Furness and Camphuysen 1997) and top predators such as terns and gulls are potentially excellent indicator spe- cies for the assessment of genotoxic exposure. Royal Terns were selected for this study because they breed in three areas of North Carolina that are known to receive different levels of pollutants that cause genotoxic damage, a large number of known-age birds exist in these colonies, thereby providing a unique opportunity to assess contaminant exposure over time and, in the early 1990s, juvenile birds from one colony were ob- served with foot and bill deformities (T. Aug- spurger, pers. comm.). Moreover, the Royal Terns in North Carolina have been declining over the past 23 years. According to Parnell et al. (1997), there were 9,755 Royal Tern nests in North Carolina in 1977. This num- ber increased in the 1980's, but by 1999 the number dropped to 12,519 (NC Colonial Waterbird Database, unpublished data). The number of breeding terns can fluctuate from year to year depending on weather con- ditions and nest site availability. However, ten-year averages beginning in 1977 indicate that there has been a 13% drop in Royal Tern numbers in the last decade. To assess possible genotoxic exposure, blood was collected from adult and juvenile Royal Terns at five colonies in three estua- rine systems in North Carolina. The blood was analyzed by the comet assay in order to determine levels of DNA strand breaks. Comet assays have been used to assess DNA damage, both in laboratory and field studies, and on a variety of cell types (for a review see Fairbairn et al. 1995). Previous studies using the comet assay on other organisms have indicated that the amount of strand breaks correlates well with exposure to genotoxic agents (Theodorakis et al. 1994; Shugart 1988; Meyers-Schone et al. 1993; Mitchelmore and Chipman 1998a, b; Leroy et al. 1996; Collins et al. 1997; Fairbairn et al. 1995; Nacci et al. 1996; Pandrangi et al. 1995). The biological effects of genotoxic agents are mutations, altered gene expres- 352