THE MIGRATORY HABITS OF THE MARINE GRIBBLE LIMNORIA TRIPUNCTATA MENZIES IN SAN DIEGO HARBOR, CALIFORNIA ,

Abstract

1. L. tripunctata undergoes a definite seasonal migratory period which reaches its height approximately during the season of highest water temperatures. This differs from the earlier migratory season usually shown for L. lignorum. 2. The attack on new wood is about equally severe on floating and submerged blocks. 3. A comparison of the percentage composition of the 30-day test-block populations shows that about 97% of the migrants are sexually mature animals as contrasted with piling populations where 50% consisted of newly hatched immature animals and only about 28% sexually mature. The piling population remains fairly constant in its composition. 4. None of the females is gravid at the time of migration. Pairing takes place after establishment on the test blocks. 5. As with L. lignorum the factors influencing migration are probably a combination of approach to a reproductive phase and population pressure due to overcrowding in old established populations. 6. Water temperature is important in influencing migration in that the higher temperatures hasten the rate of growth and attainment of sexual maturity, production of eggs, and shorten the incubation period. Gravidity (per cent gravid females) in L. tripunctata evidently reaches its peak between 17° and 19° C. as contrasted with about 10° C. for L. lignorum. 7. The brood size of piling populations is about ½ that found in uncrowded testblock populations. 8. A single female probably produced three or more broods during the year. 9. Using size as a criterion, most migrant females appear to have produced a brood prior to migration. 10. In extrapolating the test-block data to the piling populations, there is indicated a marked population increase during the months of maximal migration.