The impact of near anoxia (1.78 × 10 -3 to 3.56 × 10 -3 mmol O 2 l -1) and anoxia/sulfide (~1 mmol l -1 ) on hatching and viability of eggs of the planktonic copepod Acartia tonsa was evaluated. Since the equilibrium concentration of the sulfide species is influenced by pH and the different species have different capacities to enter cells, the impact of sulfide was analyzed at pH 8.2 and 6.5. The consequences of egg exposure for growth and survival of the hatched organisms were also studied. Subitaneous eggs, spawned by laboratory-reared organisms, were incubated in near anoxia or anoxia/sulfide for different periods (1, 4, 15 and 32 d) and then transferred to normoxic conditions. Short exposure to near anoxia or anoxia/sulfide did not affect egg viability and subsequent growth and survival. Exposure times ≥15 d caused significant declines in hatching and strong reductions in life expectancy. No significant differences between the effects of near anoxia and anoxia/sulfide (at both pHs) were observed following incubation for 15 d. After 32 d incubation, the hatching success of eggs exposed to anoxia/sulfide at pH 8.2 was significantly higher than that of eggs exposed to near anoxia or to anoxia/sulfide at pH 6.5, and life expectancy was also less reduced. The results indicate that long exposure of eggs to anoxia/sulfide is less detrimental to A. tonsa than near anoxia alone when the pH is in the range of natural seawater (7.9 to 8.3). It seems to be more detrimental when pH is as low as that reached in pore waters (6.0 to 6.5). KEY WORDS: Near anoxia · Sulfide · pH · Acartia tonsaResale or republication not permitted without written consent of the publisher

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The availability of standardized protocols for both organism culture and bioassay with ecologically relevant species is of great concern in ecotoxicology. Acartia tonsa represents an important, often dominant, member of zooplankton communities and meets all the practical criteria suggested for model species. New standardized procedures for laboratory culturing of the copepod A. tonsa and standardized methods for acute (24- and 48-h) and semichronic (7-d, static-renewal) toxicity tests with the nauplius stage are described. In both cases, eggs are the starting stage, and nauplius immobilization is the endpoint. The methods were the object of an intercomparison test involving nine laboratories, and nickel was the reference toxicant. Relative reproducibility was 24, 25, and 34% for 24-h, 48-h, and 7-d tests, respectively.

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