Resistance to freshwater exposure in White Sea Littorina spp. I: Anaerobicmetabolism and energetics

Anaerobic metabolism and changes in the osmotic concentration of extravisce ral fluid were studied in the White Sea periwinkles (Littorina littorea, Li ttorina saxatilis and Littorina obtusata) during freshwater exposure. Resis tance to hypoosmotic stress increased in the order; L. obtusata < L. saxati lis < L. littorea. Our data suggest that osmotic shock is not a primary rea son for mortality of the periwinkles under these conditions. During, enviro nmental anaerobiosis, considerable succinate accumulation (up to 10-19 mu m ol g(-1) wet weight), and depletion of phosphagen and ATP pools were found in the studied species. Other metabolic end products (alanopine, strombine, lactate, acetate or propionate) were not detected. Succinate accumulation and net ATP breakdown were the fastest in the least resistant species, L, o btusata. and slowest in the most resistant, L. littorea. Rate of ATP turnov er decreased during freshwater exposure in L. littorea and L. saxatilis, bu t not in L. obtusata. Our data suggest that differential resistance of thre e studied Littorina spp. to extreme hypoosmotic stress may be related to th eir different abilities to reduce metabolic rate and ATP turnover during su stained anoxia. Species-specific variations in anaerobic capacity of Littor ina spp. are discussed in relation to their vertical distribution, size and ecology.