OSMOTIC BEHAVIOR IN AN INTERTIDAL LIMPET, ACMAEA LIMATULA

¹ Department of Biology, Rice University, Houston 1, Texas, and Department of Zoology, University of British Columbia, Vancouver 8, B. C.

1. Osmotic and air desiccation experiments were conducted on three populations of Acmaea limatula: Dike Rock, Scripps Institution of Oceanography; Todos Santos Bay, Punta Banda, Baja California; Papalote, Punta Banda, Baja California.

2. A. limatula does not osmoregulate over a range of salinities from 25 to 150% sea water. Mobile water calculations show that blood concentration changes in different external salinities are effected by salt as well as by water movement, particularly at lower external salinities.

3. Body water as percentage body weight decreased 28% in 150% sea water and increased 28% in 50% sea water in 24 hours.

4. Isotonicity of the blood with the medium is reached within three hours in hypertonic media; longer periods were necessary in hypotonic media.

5. Under identical conditions of exposure, the rate of rise of blood and extravisceral water concentration of animals on lava was faster and reached a higher concentration when compared with animals on sandstone.

6. The effect of removal of the extra-visceral water resulted in an increased concentration of both the extra-visceral water and the blood, when compared with limpets in which the extra-visceral water was not removed.

7. The two Punta Banda populations, under identical conditions of exposure, were different; the Bay population showed a more rapid increase in extra-visceral water and blood concentration than did the Open Coast population.

8. Under conditions of exposure, the extra-visceral water appears to function both in an osmotic and temperature buffering capacity.