The glacial relict Saduria (Mesidotea) entornon (L.) (Crustacea: Isopoda) lives buried in sandy/muddy bottoms in the Baltic. During hypoxia Saduria remains buried until oxygen tension (P,Oz) has decreased to < 5 Torr (8°C; 7 % S). Respiration rate (MO2) for buried Saduria was lower than for other crustaceans of similar size. Saduria is able to maintain a stable MO2 with decreasing P,Oz down to < 5 to 10 Torr, i.e. in practice over the entire P , 0 2 range. After exposure to severe hypoxia for many hours a respiratory overshoot was sometimes found. Only small amounts of haemolymph lactate had accumulated at P,02 = < 5 Torr; up to 30mg 100ml-' after 144 h exposure. The presence of anaerobic endproducts other than lactate is suggested. Patterns of heartbeat frequency (fh) and gill ventilation (6) changed considerably, but gradually, with time in buried Saduria. Normoxic fh varied from 0 to 120 beats min-' in a cyclic sequence lasting 5 to 6 min. f, varied in a similar way although with different rates. At P,Oz = < 10 Torr the acute ventilatory response was a high stroke frequency, but after some hours the ventilatory pattern changed to the same cyclic sequence as at higher P,,02, f, retained the same cyclic sequence in hypoxia as in normoxia but without cardiac arrests. Cardiac output remained constant over the entire P, O: ! range but ventilatory efficiency increased with decreasing P,02. Respiratory independence is governed by changes in ventilatory pump flow and in behaviour in order to facilitate the transfer of oxygen from the often hypoxic Baltic bottom water to respiratory tissues.

The Baltic clam Macoma balthica, a predominant species of macrofauna in the Gulf of Gdansk (Poland), is exposed to high concentrations of hydrogen sulphide at many locations in this bay. When oxygen is available, the species is able to detoxify penetrating sulphlde mainly by oxidizing it to non-toxlc thiosulphate. Sulphide influx rato can be quantified by calculation of the diffusion coefficient for total sulphide. A relatively low apparent diffusion coefficient of about 2 X 10 cm' S' l indicates that M. balthica is able to reduce sulphide dlffuslon by temporary valve closure. During oxic-sulphidic incubation, an equilibrium between sulphide diffusion and detoxification is established at a specific internal sulphide concentration, c,, which can be calculated by the following equation: c, = cn e '': '" where c, = Internal sulphide equilibrium concentration, c. = external sulphide concentration, k = apparent detoxificatlon constant, r,. = effective radius, and D = apparent diffusion coefficient. The ainount of accumulated sulphide in the tissues is strongly dependent on individual size. This IS confirmed by experiments as well as by fleld studies. After specific sulphide ~ncubatlons, only low internal sulphide concentrations are found In large clams, whereas small clams accumulate much more sulphide in the tissues. Field studies show a distinct reduction in numbers of small clams In high sulphidic areas. We conclude that efficient sulphide detoxificatlon seems possible only if the body slze exceeds a certain minimal value.

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Anaerobic metabolic strategy of the glacial relict isopod Saduria (Mesidotea) entomonLars ~a g e r m a n ' , Anna szaniawska2' Marine Biological Laboratory, Strandpromenaden 5, DK-3000 Helsingsr, Denmark * Oceanographical Institute, Gdansk University, Al. Czolgistow 46,81-378 Gdynia, Poland ABSTRACT: The glacial relict isopod Saduria (fidesidotea) entomon (L.) was kept under anoxia for u p to 300 h (S, 7 ?h; T, 8 "C). Glycogen was found in normoxic concentration of 20 to 30 wmol g-' dry wt; it decreased rapidly in anoxia for the first 100 h, after whlch the decrease slowed. The glycolytlc flux decreased after 100 h by a factor of 10. Blood glucose increased dunng the period of hlgh glycolytic flux, but, corresponding to the decrease in glycolytic flux after 100 h , it decreased agaln, remaining however above normoxic values. S, entomon forced to be active under anoxla accumulated lactate, but when quiescent showed practically no increase in lactate. Quiescent S. entomon showed a steady accumulation of alanine, which inhibits the activity of pyruvate klnase and is thus responsible for the reduction in glycolytic flux. This anaerobic strategy, which makes it possible to survive extended periods of anoxia, is unique among crustaceans.