| Summary: | International audience A cryptic species complex encompasses morphologically indistinguishable species that are genetically divergent. Some of the most frequently used species in ecotoxicological assessment show evidence of cryptic diversity that may affect the results of a given test. Linking cryptic diversity to sensitivity of chemicals has rarely been investigated. Lithium (Li) is an alkali metal considered as one of the most important emerging pollutants under concern due to high demand for this compound essentially to produce rechargeable batteries. Li environmental concentrations are expected to increase in the next years and its effects on marine and coastal organisms remain relatively unrecognized. Here, we focused on two of six cryptic species of the estuarine copepod complex Eurytemora affinis, exposing natural populations on two continents. Our main objective was to characterize the differential sensitivity of these two-field collected E. affinis cryptic species (the European and the North-Atlantic clade) to Li using a larval bioassay. Ovigerous females of the North-Atlantic clade were sampled in the St. Lawrence estuary (Canada) and for the European clade in the Seine estuary (France) and incubated to recover early-stage larvae (nauplii). We assessed survival and growth of E. affinis nauplii exposed to a gradient of Li concentrations (1, 10, 50 and 100 mg.L-1) for 96 h at 5 PSU and 15°C. LC50 were estimated by using log-logistic model. LC50 for the nauplii from North-Atlantic and European clades of E. affinis were 243.42 (± 3.56) mg.L-1 and 241.41 (± 2.05) mg.L-1 at 24 h exposure and 86.31 (± 1.07) mg.L-1 and 72.78 (± 1.15) mg.L-1 respectively after 96 h. Li inhibit growth rate of nauplii at ≥ 50 mg.L-1 with an EC50 at 96 h of 60.19 (± 1.13) mg.L-1 for the North-Atlantic clade nauplii. The estimated EC/LC50 values were too high to cause extreme effects at environmental concentrations observed in Northern Hemisphere estuaries. No significant differences were observed in Li sensitivity between the ...
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