ACUTE TOXICITY OF AMMONIA TO 4 SPECIES OF MARINE AMPHIPOD

Ammonia has been found to be toxic to many species of marine organisms, but little data address the toxicity of ammonia to benthic infaunal species such as amphipods. Organisms closely associated with marine or estuarine sediments may be exposed to higher ammonia concentrations than are found in the water column, especially when sediments are disturbed. In this study, four species of marine or estuarine amphipods (Rhepoxynius abronius, Eohaustorius estuarius, Ampelisca abdita and Grandidierella japonica) were exposed to ammonia in seawater, in the absence of sediment, under controlled laboratory conditions, to determine the concentrations of ammonia that would be acutely toxic to those species. A. abdita was found to be the most sensitive to ammonia, with a median lethal concentration (LC50) of 49.8 mg/liter total ammonia (0.83 mg/liter as un-ionized ammonia). R. abronius was also relatively sensitive: LC50 = 78.7 mg/liter total ammonia (1.59 mg/liter un-ionized ammonia). E. estuarius and G. japonica were less sensitive, with estimated LC50 values of 125.5 mg/liter and 148.3 mg/liter total ammonia, respectively (2.49 mg/liter and 3.35 mg/liter un-ionized ammonia). The absence of sediment did not appear to influence the response of the amphipods over the 96-h exposure period.