Spiked exposure, continuous flow toxicity tests using the oil dispersant Corexit 9527® were performed during the early life stages of four California marine species. Test chambers containing sensitive life stages of the giant kelp (Macrocystis pyrifera), the red abalone (Haliotis rufescens), a kelp forest mysid (Holmesimysis costata), and the topsmelt (Atherinops affinis) were inoculated with concentrated dispersant, then allowed to flush with clean, filtered seawater Spectrophotometric monitoring of tests showed dispersant levels diminishing to below detection limits within 5 to 6 h or less Results showed Hahotis to be the most sensitive species tested, with Atherinops being least sensitive in terms of no‐observed effect concentration (NOEC) and Holmesimysis being least sensitive in terms of median effect concentration, Macrocystis was intermediate in both measures. When spiked exposure toxicity results were compared to those of previously reported constant‐exposure tests, no consistent conversion factor that might relate spiked‐ and constant‐exposure toxicity data was found.

Continuous‐flow toxicity tests using the oil dispersant Corexit 9527s̊ were performed on the early life stages of four California marine species. Newly released zoospores of the giant kelp, Macrocystis pyrifera, embryos of the red abalone, Haliotis rufescens, 4‐d‐old juveniles of the mysid, Holmesimysis costata and 10‐d‐old larvae of the topsmelt, Atherinops affinis, were all used in triplicate 48‐ and 96‐h tests. Quantitative verification of dispersant concentrations using UV spectrophotometry was performed twice daily during testing. Results indicated growth of kelp gametophytes was significantly reduced at <2.4 ppm after a 48‐h exposure. Of the three animals tested, developing red abalone were the most sensitive (NOEC = 0.63 to 1.50 ppm; LC50 = 1.60 to 2.20 ppm). Mysid juveniles were intermediate in sensitivity (NOEC = 1.66 to 4.20 ppm; LC50 = 4.26 to 7.26 ppm), whereas topsmelt larvae were the least sensitive (NOEC = 12.27 to 14.18 ppm; LC50 =25.51 to 40.63 ppm). Reproducibility of test data was very high (coefficient of variation = 15.7 to 27.1%).

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Continuous-flow toxicity tests using the oil dispersant Corex~t 9527° were performed on the early life stages of four California marine species. Newly released zoospores of the giant kelp, Macrocystispyrifera, embryos of the red abalone, Haliotis rufescens, 4-d-old juveniles of the mysid, Holmes~mysis costata and 10-d-old larvae of the topsmelt, Athermops affinis, were all used in triplicate 48-and 96-h tests. Quantitative verification of dispersant concentrations using UV spectrophotometry was performed twice daily during testing. Results indicated growth of kelp gametophytes was significantly reduced at <2.4 ppm after a 48-h exposure. Of the three animals tested, developing red abalone were the most sensitive (NOEC = 0.63 to 1.50 ppm; LC50 = 1.60 to 2.20 pprn). Mysid juveniles were intermediate in sensitivity (NOEC = 1.66 to 4.20 ppm; LC50 = 4.26 to 7.26 ppm), whereas topsmelt larvae were the least sensitive (NOEC = 12.27 to 14.18 ppm; LC50 = 25.51 to 40.63 ppm). Reproducibility of test data was very high (coefficient of variation = 15.7 to 27.1%).