Abstract
Standard model species are commonly used in toxicity tests due to their biological and technical advantages but studying native species increases the specificity and relevance of results generated for the potential risk assessment to an ecosystem. Accounting for intraspecies variability and other factors, such as chemical and physical characterization of test medium, is necessary to develop a reproducible bioassay for toxicity testing with native species. In this study, larval stage I American lobster (Homarus americanus), a commercially important and native species of Atlantic Canada, was used as the test species. Toxicity tests were first conducted by exposing lobster larvae to a reference toxicant of copper sulphate (CuSO4) and then to physically and chemically (using Corexit 9500A) dispersed oil (WAF and CEWAF, respectively). The effect on larval survival was estimated by calculating the 24-h median effect concentration (24-h EC50), and there was no difference between WAF or CEWAF exposure when the results are reported on a total petroleum hydrocarbon (TPH) basis. The 24-h EC50s ranged from 2.54 to 9.73 mg TPH/L when all trials (n = 19) are considered together. The HC5 (hazardous concentration for 5 per cent of the population) value was 2.52 mg TPH/L and similar to the EC50 value when all trials were pooled. To evaluate the reproducibility of the lobster toxicity tests, inter-trial variability was determined, and the resultant coefficients of variation (%CV) were compared to those reported for two standard test species, mysid shrimp (Americamysis bahia) and inland silverside (Menidia beryillina). This comparison showed that the %CV for the lobster toxicity tests were lower than those for the standard species tests indicating that the described larval lobster toxicity bioassay produces reliable and repeatable results.
Highlights
A common approach to minimize the impact of biological variability on the outcome of toxicity tests is to rely on laboratory cultures of standard test species, where a reduction, or exclusion, of genetic diversity serves to reduce experimental variability
American lobster (Homarus americanus) is not a standard test species; due to its economic and ecological importance in eastern North America, it is prudent to characterize its risk from exposure to environmental contaminants, such as those associated with an oil spill
The toxicological responses of American lobster exposed to petroleum hydrocarbons are less well understood compared to other crustaceans, such as the mysid shrimp (Americamysis bahia) a standard marine test organism
Summary
A common approach to minimize the impact of biological variability on the outcome of toxicity tests is to rely on laboratory cultures of standard test species, where a reduction, or exclusion, of genetic diversity serves to reduce experimental variability. The standard model species (e.g. Daphnia magna, Oncorhynchus mykiss, Danio rerio, Americamysis bahia, Menidia beryllina) generally meet certain technical criteria, such as easy and inexpensive maintenance in the laboratory, genetic tractability, and availability of a broad spectrum of experimental and methodological tools (Segner and Baumann 2015). These species meet some biological criteria, such as fast growth, high reproductive potential, sensitivity to pollutants, abundance, replenishment ability, and/or captive rearing capabilities (Hughes et al 2005). The 1996 grounding of the North Cape barge off the southwestern coast of Rhode Island (USA) resulted in an estimated 2700 metric tons of fuel oil entering into the shallow near shore waters, killing approximately 9 million lobsters (French-McCay 2003)
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