THE ANNUAL REPRODUCTIVE AND NUTRITIONAL CYCLES IN TWO WESTERN SEA URCHINS

¹ Hopkins Marine Station, Pacific Grove, California

1. The degree of gonadal development in the purple sea urchin, Strongylocentrotus purpuratus, was measured by taking the gonad index, or ratio of volume of gonad to wet weight of urchin, every two weeks for a year (1953-54) in samples of 20 urchins obtained from each of two localities, Pescadero Point on the Monterey Peninsula, and Yankee Point, 10 miles south.

2. For S. purpuratus from both places, the average gonad index rose during the fall to a peak twice as high as that reached the previous year, and this peak was maintained at a fairly constant level from January through May.

3. Climatic factors, rather than ecological, are therefore thought to have the greater effect upon gonad growth. A clear-cut correlation was not established for any factor, but ocean temperature is known to have been higher during the winter of 1953-54 than in the previous year.

4. Determination of the gonad index for monthly samples of 10 specimens of the large western sea urchin, S. franciscanus, taken from below the tide pools of the Hopkins Marine Station, indicated a single reproductive cycle, but a much shorter breeding season, the peak of which was reached later than that of S. purpuratus.

5. Though males were found to have fertile gametes for a greater part of the year than females, no significant difference was found in the reproductive cycles of male and female urchins in either species, as measured by gonad index.

6. The great growth of gonads was not correlated with an increase in NPN (non-protein nitrogen) or RS (reducing sugar) in the body fluid of either species. However, greater mobilization, i.e., transport from gut to gonad, could not be determined by the methods used.

7. No seasonal variation of RS was found in either species. NPN was also invariant in S. purpuratus, but showed a marked increase in S. franciscanus during the summer.

8. In both species there was a much greater variability of RS than of NPN, suggesting no regulation of RS, but a degree of regulation of NPN. RS was skewly distributed, while NPN was normally distributed in nearly all samples, a fact which may be partially explained by the feeding habits of the animals.

9. Very small quantities of protein nitrogen of the order of 0.5 mg. per cent were found in the filtered body fluids of a few specimens of each species.