CIRCULATORY ADAPTATIONS TO THE OXYGEN MINIMUM LAYER IN THE BATHYPELAGIC MYSID GNATHOPHAUSIA INGENS

¹ Department of Biological Sciences and Marine Science Institute, University of California, Santa Barbara, California 93106

1. The anatomy of the blood circulatory system in G. ingens is similar to that in other crustacea, although proportionately both the heart and arterial channels are quite large.

2. G. ingens gill surface area ranges from 5-15 cm²/g wet body weight. These gill surface areas are as large as the greatest areas measured in other, much larger crustaceans. A large gill surface area relative to a low oxygen consumption rate permits an increased oxygen diffusion across the gills despite a low oxygen gradient.

3. The generalized intra-ventricular blood pressure in G. ingens is 24/19 cm H₂O. Mean arterial pressure matches the systolic pressure. These pressures are comparable to those in the large brachyuran Carcinus maenas.

4. Blood velocities of from 0.54 to 4.71 cm/sec occur in the heart and arterial system of G. ingens. Under normoxic conditions (PO² = 6 mm Hg) heart rates average 42 b/m and arterial velocities average 1-2 cm/sec.

5. The circulation of blood in G. ingens, when compared to other crustaceans on the basis of minute volume, cardiac output and turnover time, appears to be remarkably effective. It is suggested that this effectiveness explains, in large part, the unique ability of G. ingens to remove large percentages of the available oxygen while moving large volumes of water over the gills.