Aquatic invertebrate resting egg sensitivity to glutaraldehyde and sodium hypochlorite.

Ballast tank treatment technologies are currently in development to reduce the risk of acquiring or transporting viable aquatic organisms that could be introduced to ecosystems and become invasive. Aquatic invertebrate resting eggs represent a challenge to such technologies because of morphological and biochemical adaptations to stress that also protect eggs from artificial stressors. To evaluate the potential efficacy of chemical biocides for ballast tank treatment, the present study examined the acute toxicity of glutaraldehyde and sodium hypochlorite on resting eggs of the freshwater cladoceran Daphnia mendotae and marine brine shrimp (Artemia sp.). Glutaraldehyde was toxic to resting eggs of Artemia sp., as indicated by a lethal concentration to 90% of organisms (LC90) of 95% confidence interval (226 +/- 10 mg/L). Daphnia mendotae, in contrast, displayed erratic responses to glutaraldehyde. Sodium hypochlorite was similarly toxic to resting eggs of Artemia sp. and D. mendotae, which displayed LC90s of 86.5 +/- 3.0 and 78.3 +/- 1.6 mg/L, respectively. Burial in sediment protected resting eggs from toxicants. The present results corroborate those from previous investigations of resting egg sensitivity to artificial stressors, supporting the conclusions that resting eggs are less sensitive than other life stages to artificial stressors and that chemical biocide concentrations effective against other life stages may be ineffective against resting stages.

Sensitivity of aquatic invertebrate resting eggs to SeaKleen (Menadione): a test of potential ballast tank treatment options.

The introduction of aquatic species in resting life stages by the release of ballast water is a less well-known but potentially important invasive species vector. Best-management practices designed to minimize transport of ballast water cannot eliminate this threat, because residual water and sediment are retained in ballast tanks after draining. To evaluate the potential efficacy of chemical treatment of residual material in ship ballast tanks, the present study examined the acute toxicity of the proposed biocide SeaKleen (menadione; Garnett, Watkinsville, GA, USA) on resting eggs of Brachionus plicatilis (a marine rotifer), a freshwater copepod, Daphnia mendotae (a freshwater cladoceran), and Artemia sp. (a marine brine shrimp). SeaKleen was toxic to resting eggs of all taxa. Daphnia mendotae resting eggs encased in protective ephippia were the least sensitive, as indicated by a 24-h lethal concentration of toxicant to 90% of organisms of 8.7 mg/L (95% confidence interval, +/- 0.1 mg/L). SeaKleen induced teratogenic effects in D. mendotae and Artemia sp. Exposure to sunlight quickly degraded SeaKleen, which lost all toxicity after 72 h outdoors. SeaKleen increased in toxicity slightly after 72 h in darkness. Burial of D. mendotae ephippia in natural lake sediment reduced SeaKleen toxicity by a factor of 20. Reduced toxicity in the presence of sediment raises serious doubts as to the potential for this, or any, chemical biocide to kill aquatic invertebrate resting stages buried in sediment retained in ship ballast tanks.