Recovery from hypoxia with and without sulfide in Saduria entomon: potassium, ATP and behavior

The contribution of potassium pumping, tissue ATP levels and locomotory activity to the oxygen debt was studied in the Baltic brackish water isopod Saduria entomon recovering from hypoxic and sulfidic conditions. The isopods were exposed (8 h; 9C; salinity 10 ppt) to hypoxia (0.3 kPa) and to hypoxia (1 kPa) with sulfide (45 M) and allowed to recover from hypoxia (8 h) and sulfide (28 h). When exposed to hypoxia the hemolymph and tissue K+ concentrations decreased significantly. When allowed 8 h recovery, normoxic K+ concentration was restored in the tissue but not in the hemolymph. After exposure to sulfide the hemolymph K+ was not different from the normoxic level but tissue K+ decreased significantly. When allowed 28 h of recovery the tissue K+ concentration was restored but the hemolymph K+ was significantly decreased as compared to the normoxic value. The ATP level in the normoxic control showed a significant decrease with time, indicating a general decrease in metabolic activity. The ATP level was significantly decreased after exposure to both hypoxia and sulfide. When allowed to recover, the ATP level in sulfide was significantly increased as compared to the normoxic value, indicating the occurrence of repair processes. During recovery from hypoxia and sulfide S. entomon showed no increase in locomotory activity. In terms of oxygen equivalents, re-establisment of potassium concentration contributed approximately 25 and 20% to the oxygen debt paid after exposure to hypoxia and sulfide, respectively. The results are discussed in relation to their contribution to the oxygen debt in S. entomon recovering from hypoxic and sulfidic exposure and possible processes not yet identified.