Factors affecting toxicity test endpoints in sensitive life stages of native Gulf of Mexico species

Indigenous species are less commonly used in laboratory aquatic toxicity tests compared with standard test species due to (1) limited availability lack of requisite information necessary for their acclimation and maintenance under laboratory conditions and (2) lack of information on their sensitivity and the reproducibility of toxicity test results. As part of the Natural Resource Damage Assessment aquatic toxicity program in response to the Deepwater Horizon Oil incident (2010), sensitive life stages of native Gulf of Mexico species were evaluated in laboratory toxicity tests to determine the potential effects of the spill. Fish (n = 5) and invertebrates (n = 2) selected for this program include the following: the Florida pompano (Trachinotus carolinus), red drum (Sciaenops ocellatus), spotted sea trout (Cynoscion nebulosus), cobia (Rachycentron canadum), red porgy (Pagrus pagrus), blue crab (Callinectes sapidus), and the common moon jellyfish (Aurelia aurita). Initially in the program, to establish part of the background information, acute tests with reference toxicants (CdCl2, KCl, CuSO4) were performed with each species to establish data on intraspecies variability and test precision as well as identify other factors that may affect toxicity results. Median lethal concentration (LC50) values were calculated for each acute toxicity test with average LC50 values ranging from 248 to 862 mg/L for fish exposures to potassium chloride. Variability between test results was determined for each species by calculating the coefficient of variation (%CV) based on LC50 values. CVs ranged from 11.2 % for pompano (96-h LC50 value) to 74.8 % for red porgy 24-h tests. Cadmium chloride acute toxicity tests with the jellyfish A. aurita had the lowest overall CV of 3.6 %. By understanding acute toxicity to these native organisms from a compound with known toxicity ranges and the variability in test results, acute tests with nonstandard species can be better interpreted and used appropriately when determining risk.