Lunar Periodicity 221 



director of the Bermuda Biological Station for Research, took a special 

 interest in studying the swarming of this marine polychaete. He 

 found that swarming and luminescence began at about 55 minutes 

 after sunset and lasted for half an hour. On one occasion when Pro- 

 fessor Mark was traveling to Bermuda he realized that he would ar- 

 rive on a day when the fireworms were due to appear. He interested 

 his fellow passengers in the phenomenon, telling them that the timing 

 was so exact that one could set one's watch by it and invited a large 

 group of people to come to the shore that evening. When the moment 

 arrived for the beginning of the display, not a worm was in sight, 

 nor was there after 5 minutes, 10 minutes, and more. Soon people, 

 feeling that they had been hoodwinked, began moving away, but 20 

 minutes after the appointed time the worms appeared in great num- 

 bers and a spectacular demonstration was given for the visitors who 

 still remained. Not until the next day was Dr. Mark's embarrassment 

 relieved when it was discovered that during the winter Bermuda 

 time had been changed from local sun time to zonal time, resulting 

 in setting the Bermuda clocks ahead 19 minutes. 



Perhaps the most fascinating of all the responses of animals to the 

 lunar or tidal cycle is that exhibited by the grunion or California 

 smelt. On the three or four days after the spring tides from April to 

 June the grunion swims in on the beaches of southern California to 

 lay its eggs in the sand. During this period the higher of the daily 

 high tides comes at night. About an hour after the water reaches its 

 highest level on each of these nights the fish allow themselves to be 

 carried up on the beach by the waves. As each wave recedes, an 

 observer can discern hundreds or thousands of fish left behind, wrig- 

 gling in the wet sand (Fig. 6.19). Within a few seconds the females 

 have burrowed tail first into the sand where they deposit the eggs 

 while the males curl around them discharging the sperm. When the 

 next wave comes in, the fish are washed out to sea once more. Since 

 the eggs have been discharged during the period of descending tides 

 after the highest spring tides and during the hours following high 

 tide each night, the waves do not reach them again during the next 

 two weeks. The eggs are thus left undisturbed to develop in the 

 warm, moist sand. When the next spring tide occurs, the eroding 

 surf of the rising tide uncovers the eggs, now ready to hatch out, and 

 the young larvae swim away. In order for this complicated relation- 

 ship between the life cycle of the fish and the tides to be carried out, 

 the fish, which ordinarily remain in the waters offshore, must be 

 stimulated in some way to move in to the beach on the proper day 

 and to allow themselves to be stranded on the shore by the waves 



