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Long-term anaerobiosis was studied in the priapulid Haljcryptus spinulosus and the bivalves Astarte borealis and Arctica island~ca, species with an extremely high resistance to lack of oxygen, from Kiel Bight. This shallow, brackish environment is frequently affected by extended periods of oxygen deficiency. Animals were experimentally subjected to anoxia for up to 60 d. Glycogen was the most important substrate during long-term anaerobiosis, although it amounts to only 5 to 12 O/ O of soft tissue dry weight. Succinate, acetate and propionate were produced from glycogen degradation by anaerobic metabolic pathways. Succinate accumulation wth in tissues attained the highest concentrations found so far in marine invertebrates, and depended on duration of exposure to anoxia. Most H. spinulosus remained active during the first 3 or 4 wk of anoxia. They contained only low levels of aspartic acid, which seems to be of minor importance a s a substrate during long-term anaerobiosis. The activity of lactate dehydrogenase was low and lactate formation was also negligible. In A. borealis, activities of lactate, alanopine, and strombine dehydrogenases were low under anoxia and only small amounts of alanopine and strombine were produced. Volatile fatty acids were produced by all 3 species; in A borealis, acetate reached maximum concentrations during the transition phase from aerobic to anaerobic metabolism, whereas propionate was detected only after 2 d of anoxic incubation. Acetate and proplonate concentrations remained low, the excess being excreted. A. islandica, on the other hand, produced propionate immediately at the onset of anoxic conditions, and accumulated high concentrations of acetate and propionate. Propionate excretion was nearly negligible. Calorimetric measurements on the bivalves showed that they reduced their metabolism by up to 40 % during the first day of oxygen lack when they turned to anaerobic metabolism. After prolonged anoxia, energy release decreased to less than 1 ",o of aerobic rates. These are the lowest rates found in marine invertebrates so far. A. lslandica is able to undergo periods of self-induced anaerobiosis, and can reduce its glycogen consumption drastically, as can be calculated from calorimetric measurements. Thls behaviour may help it to withstand adverse environmental condltlons.

marine ecology. progress series

Long-term anaerobiosis in sublittoral marine invertebrates from the Western Baltic Sea: Halicryptus spinulosus (Priapulida), Astarte borealis and Arctica islandica (Bivalvia)