Reports

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SR-2002-013

Metazoan Parasite Community Structure in Bluegill (lepomis macrochirus) as an Indicator of the Impact of Urbanization on 2 streams in San Antonio, Texas

M. Bhuthimethee, N. O. Dronen, W. H. Neill

Our project explored the possibility of using metazoan fish parasites as an indicator of deleterious effects on stream biota due to non-point source pollution, which is associated with urbanization and development. Experiments were conducted in the late summers of 1999 and 2000. We chose 2 major streams in the upper San Antonio River Basin in Bexar County, Texas, known to be non-point source polluted and hazardous for human and wildlife use. We constructed wire mesh cages, anchored them in the stream channels at middle and lower watershed sites, and placed bluegill (Lepomis macrochirus) obtained from a local aquaculturist in the cages for 20 days to expose them to stream conditions and to allow parasite communities to become established. Fish were collected and examined for metazoan parasite load. Water samples were taken at each of the sites to assess water quality. During the 1999 field season, values of Shannon's diversity index indicated a greater diversity of bluegill parasites at the upper watershed sites for both streams (1.142, 1.144), compared with lower sites (0.48, 0.75). Equitability followed the same pattern, with upper watershed sites having higher values (0.64, 0.64) than the lower sites (0.27, 0.42). The August 2000 data reflected similar patterns. Dissolved nitrate values ranged from 0.28 to 9.1 mg/L in 1999, and from 0.19 to 4.8 mg/L in 2000. Spearman's rank correlation was used to evaluate trends between parasite diversity, water quality parameters, and trace metal concentrations between sites. Low parasite diversity was associated with high nitrate levels for both years. This study contributes to the developing field of using bio-indicators of environmental quality in stream habitats.

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