CONOR and CONOR: BEHAVIOR IN LARVAL PORCELLANID CRABS 



Turbulence caused a few animals to undergo 

 feeding behavior even when food was absent. 

 When food was present, there usually was some 

 "feeding activity in still water. When the water 

 was agitated and food was present, feeding be- 

 havior greatly increased. In the presence of 

 food, water movement, although not essential 

 for the initiation of feeding, favors both the 

 initiation and maintenance of feeding activity, 

 probably because turbulence suspends the par- 

 ticles so that they can readily be filtered. The 

 results suggest that there is a periodicity to feed- 

 ing activity, but the experiment was too brief to 

 clearly demonstrate this. No effect of daylight 

 or darkness on feeding behavior was observed. 



Locomotory behavior gradually changed 

 throughout the megalopa stage. The numbers 

 of megalopae available for observation at dif- 

 ferent ages are indicated in Table 2, which gives 

 the age of the megalopae in days since the molt 

 from the second zoeal stage. Adultlike locomo- 

 tory behavior slowly evolved as the megalopa 

 grew older. Newly metamorphosed megalopae 

 were strongly planktonic, swimming almost con- 

 tinuously by means of the pleopods, with the 

 walking legs and chelipeds extended forward. 

 After spending some time (1-4 days) as truly 

 planktonic animals, the megalopae became more 

 quiescent and began to demonstrate clinging 

 tendencies. Small stones, to which the settling 

 megalopae could cling, were introduced into the 

 culture flasks at this point. 



The megalopae which are just beginning to 

 settle show no signs of recognizing a substrate 

 suitable for settling. If a larva encounters a 

 rock while swimming forward, it continues 

 swimming motions, pushing against the obstacle 

 with the extended chelipeds but not moving for- 



Table 2. — Number and age in days of megalopae avail- 

 able for behavioral observations. 



ward. However, if megalopae of this age are 

 artificially introduced to a rough surface, walk- 

 ing legs first, by means of turbulence or by di- 

 rect placement, they cling readily and will usu- 

 ally remain on that surface unless disturbed. As 

 the megalopae increase in age, they appear to 

 develop the ability to recognize a suitable sub- 

 stratum. Larvae of 2 weeks or older were seen 

 to collide head on with a rock, stop swimming, 

 and put the walking legs down. They then 

 turned around and backed onto the piece of 

 gravel. 



In the laboratory, recently settled megalopae 

 can be induced to leave an apparently suitable 

 substrate if the water is stirred vigorously or 

 if the larvae are touched. In addition, when a 

 settling megalopa encounters a stone that is al- 

 ready occupied, it will remain there only if it can 

 do so without contacting the other occupant. If 

 the stone is too small to allow this, the settling 

 megalopa will usually cling only momentarily 

 and then resume swimming. In a few cases, 

 however, the settling megalopa forced the ori- 

 ginal occupant to leave its stone and begin swim- 

 ming. 



A specialized form of behavior was observed 

 in advanced megalopae of Petrolisthes eriomer- 

 iis. After locating a stone, a swimming meg- 

 alopa will settle on it and then elevate and lower 

 both chelipeds simultaneously several times. If 

 the megalopa then moves a short distance over 

 the rock, the cheliped elevation sequence is often 

 repeated. This activity was observed only in 

 individuals that had just arrived on a substrate 

 and was exhibited whether or not another meg- 

 alopa was. present on the rock. 



An advanced behavior was observed in still 

 older animals (30-33 days in Pachycheles pubes- 

 cens) . These megalopae could not be induced 

 to use their pleopods when swimming, even when 

 they were so disturbed that they would finally 

 leave their rocks. Instead, a disturbed animal 

 would bob up and down in the water, clumsily 

 clapping the abdomen to the thorax. The 

 presence of the four pairs of fully developed 

 pleopods prevented effective swimming by this 

 action. Adult porcelain crabs, whose pleopods 

 are reduced in size and often in number, swim 

 only by clapping the abdomen to the thorax. The 



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