TP23 Environmental Hypoxia
Tuesday, 15 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(CAL-1117-835812) Copper tolerance of Monopylephorus rubroniveus and Streblospio benedicti under hypoxic conditions at different pH.

Calle, P², Holland, F¹, Dean, J², ² Belle W. Baruch Institute, University of South Carolina, Columbia, SC, USA¹ Hollings Marine Laboratory, Charleston, SC, USA

ABSTRACT- Non point source pollution impairs tidal creeks through chemical contamination and hypoxia. In South Carolina tidal creeks, the numerically dominant macrobenthic organisms are the oligochaete Monopylephorus rubroniveus, and the polychaete Streblospio benedicti. Monopylephorus rubroniveus is most abundant in areas with high levels of contaminants and frequent hypoxia. Streblospio benedicti is broadly distributed but is generally most abundant in creeks with lower levels of contamination and less frequent hypoxia. Study objectives were to determine if the distribution patterns of these species could in part be explained by tolerance information including: (1) hypoxia (< 7% saturation, 70 g of sediment), and (2) copper in seawater under a) normoxic conditions at pH 8.0, and b) hypoxic conditions at pH 7.6, 8.3, 8.9 for M. rubroniveus (< 7% saturation) and pH 7.7, 8.4, 8.7 for S. benedicti (< 20% saturation). Bioassays with three replicates were conducted (25 ppt, 22^oC, 10 organisms/500ml containers). Survival was determined daily for hypoxia exposures, and at 48 h for copper exposures. Bioassays demonstrated that M. rubroniveus is tolerant to hypoxia (LT₅₀ 12.3 days) and S. benedicti is sensitive to hypoxia (LT₅₀ 1.3 days). Copper bioassays indicated that under normoxic conditions M. rubroniveus and S. benedicti are relatively tolerant to copper (LC₅₀ 508 mg/l and LC₅₀ 307 mg/l respectively). Under hypoxic conditions tolerance to copper was inversely related to pH. Copper LC₅₀ for M. rubroniveus was 61 mg/l at pH 8.9, 131 mg/l at pH 8.3, and 259 mg/l at pH 7.6. Copper LC₅₀ for S. benedicti was 133 mg/l at pH 8.7, 129 mg/l at pH 8.4, and 242 mg/l at pH 7.7. Monopylephorus rubroniveus was more sensitive to copper at high pH than S. benedicti. Streblospio benedicti was more sensitive to hypoxic conditions. In conclusion, bioassay data contribute to explaining differences in distributional patterns of these organisms.

Key words: hypoxia, tolerance, copper, pH