CHANGES IN THE TISSUE CHLORIDE OF THE CALIFORNIA MUSSEL IN RESPONSE TO HETEROSMOTIC ENVIRONMENTS

¹ From the Scripps Institution of Oceanography, La Jolla, California

1. Experiments indicate that the adult mussel Mytilus californiaus is heterosmotic, yet potentially euryhaline to a considerable degree, although sperm, eggs and larvae are highly stenohaline toward dilution of the environment.

2. The tissue-chloride content is close to 1 per cent by wet weight, varying only slightly with season. Mature males show slightly higher chloride values than do the mature females, due to the higher chloride content of testicular tissues than of ovarian tissues.

3. Mussels can survive for indefinite periods the sudden and continued exposure of their tissues to sea water diluted by 50 per cent (Cl conc. 0.94 per cent) or water concentrated to half again its normal value (Cl conc. 2.73 per cent to 2.8 per cent). Below or above these two respective extremes, sudden immersion is fatal.

4. Within the limits of the physiologically tolerated range indicated, the concentrations of tissue chloride are adjusted to concentrations of chloride in the environment, with maintenance of an approximate value of 1: 1.60, calculated as grams per 100 ml. of internal and external water.

5. Considerable individual differences exist in the rate of establishment of equilibrium between environmental and tissue chloride concentrations, when mussels are exposed to the indicated dilute and concentrated solutions.

6. While sudden immersion in solutions of sea salts below or above the respective limits resulted fatally, it was possible for mussels to survive in solutions considerably beyond such limits, i.e. in water diluted to as low as 0.62 per cent Cl, or concentrated to 3.48 per cent Cl, if the concentrations were altered by gradual steps.

7. Mussels surviving in sea water, gradually diluted to a chlorinity of 0.625 per cent Cl, underwent a fall in their tissue chloride to values of about 0.26 per cent to 0.38 per cent; animals kept in sea water gradually concentrated to a chlorinity of 3.48 per cent underwent a rise in their tissue chloride to average values of 2.25 per cent; at these respective points animals were at their threshold of tolerance and showed incipient sluggishness. Animals of such extreme chloride levels, however, recovered placed in running sea water, and readily underwent therein a restoration of their tissue chlorides to normal values.

8. Exposure of mussels to the diluted or concentrated solutions results in migrations of both water and chloride between internal and external media.