. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ALVINELLID EXTRACELLULAR HEMOGLOBINS 371 experimental conditions (Table III), 2 to 10 times higher than that of the lugworm which has a Hb affinity for O2 that is already quite high (for a comparison with other annelid Hbs. see Weber, 1980). In the extreme conditions of low temperature (10°C) and high pH (), the O: af- finity of .-1. potnpejana Hb was so high (P5I, lower than mm Hg, with 1 mm Hg = Pa) that it could not be measured with the Hemox technique. Hbs with high O2 affinities are generally considered ver
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ALVINELLID EXTRACELLULAR HEMOGLOBINS 371 experimental conditions (Table III), 2 to 10 times higher than that of the lugworm which has a Hb affinity for O2 that is already quite high (for a comparison with other annelid Hbs. see Weber, 1980). In the extreme conditions of low temperature (10°C) and high pH (), the O: af- finity of .-1. potnpejana Hb was so high (P5I, lower than mm Hg, with 1 mm Hg = Pa) that it could not be measured with the Hemox technique. Hbs with high O2 affinities are generally considered very adaptive in spe- cies lacking an efficient, specialized respiratory organ (see Weber, 1978). But alvinellid gills are characterized by the highest specific surface areas yet measured in polychaetes. low diffusion distances between the external seawater and the blood, and a branchial circulatory system with a com- plexity comparable to that of the fish gill (Jouin and Gaill. 1990). Hbs with high O: affinity can also be advantageous to species living in a poorly oxygenated environment (Weber, 1980). But what do the alvinellids actually breathe? Ac- cording to Desbruyeres el al. (1982) and Arp and Childress (in Terwilliger and Terwilliger, 1984), a mild to warm (up to 50°C), hypoxic water: , a mixture of the very hot, anoxic vent water and the cold, oxygenated local bottom seawater. But the oxygen concentration of this water mix has never been directly measured in aim. and the only direct evidence for low O2 concentrations inside and out- side hydrothermal vent community come from the Rose Garden vent field in the Galapagos Rift (Johnson et al., 1986), where the O2 content is always below 'A of the saturation at one atmosphere hydrostatic pressure. How- ever, alvinellids have never been seen at the Rose Garden site, and the conditions there are quite different from those at the 13°N site. The hypothesis that alvinellids breathe hypoxic water must be considered, but is as
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