Habitat-related differences in the responses to oxygen deficiencies in Idotea baltica and Idotea emarginata (Isopoda, Crustacea)

Two apparently ecologically similar sublittoral isopod species, Idotea balt ica and Idotea emarginata, were studied with respect to their abilities to cope with deficiencies in environmental oxygen concentration. In a first se ries of experiments, respiration rates of both species were measured, at di fferent temperatures (5, 10, 15 degrees C), as a function of oxygen partial pressure. Whereas I. baltica showed the characteristics of an oxyconformer , I. emarginata regulates oxygen consumption from normoxia down to distinct hypoxic conditions. In a second series of experiments, anoxia survival tim es (LD50) were determined for different types of individuals of both specie s (mancas, juveniles, adult females, adult males). In both species, surviva l times increased with developmental stage. Adult males were more resistant to anoxia than adult females. In all types of individuals, the LD50 values of I. emarginata were significantly higher than those of I. baltica. The i nterspecific differences are clearly adaptive, correlating with respective habitat differences. Idotea baltica is associated with seaweed drifting at the water surface where oxygen is in the normoxic range. In contrast, I. em arginata lives among accumulations of macroalgal debris an the seabed where hypoxia is common. The different abilities of the species to sustain perio ds of hypoxia may contribute to the maintenance of habitat segregation. (C) 1999 Elsevier Science B.V. All rights reserved.