Spatial and temporal variation in results of purple urchin (Strongylocentrotus purpuratus) toxicity tests with zinc

Purple urchins (Strongylocentrotus purpuratus) were maintained in year-round spawning condition in the laboratory for use in fertilization and larval development experiments designed to assess temporal variability in response to zinc. Results of these tests were compared to those from tests using gametes obtained from a field-collected population. Fertilization and larval development tests were also conducted comparing field-collected purple urchins from three geographically distinct groups on the West Coast of the United States. Fertilization tests conducted to assess temporal variability produced variable median effects concentrations (EC50s) ranging from 4.1 to >100 μg/L zinc. Larval development tests produced more consistent EC50s, which averaged 107.4 ± 21.9 μg/L zinc for laboratory purple urchins and 97.2 ± 19.2 μg/L zinc for field-collected purple urchins. Larval development tests did not demonstrate significant differences in response to zinc between geographically distinct purple urchin populations. Fertilization test variability was examined in terms of sperm concentration and sperm collection method during two seasons. Reduced variability was found with dry sperm collection in tests conducted in March 1995 but increased again in tests conducted in June 1995, regardless of sperm collection method. Increased variability in response to zinc may be caused by seasonal temperature effects.