Survival of the copepod Acartia tonsa following egg exposure to near anoxia and to sulfide at different pH values

The impact of near anoxia (1.78 x 10(-3) to 3.56 x 10(-3) mmolO(2) l(-1)) and anoxia/sulfide (similar to1 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 greater than or equal to15 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).