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PACIFIC SCIENCE, Vol. II, July, 1948 
Tide pools remained warmer than the air for 
the first few nocturnal hours, which accounts 
partially for the intense activity in the pools 
in the early evening. Later in the night, the 
crabs wandered out of the tide pools and ledges 
to forage areas higher on the strand. The air 
temperatures were, at this time, relatively low; 
consequently, the foraging animals moved quite 
slowly. The foregoing data indicate that tem¬ 
perature must be added to the factors which 
exert a regulatory effect on these crabs. 
In addition to temperature changes, the 
periodic fluctuation of activity created by the 
changing tide must be considered in any dis¬ 
cussion concerning the behavior of a littoral 
species. The subsistence of P. crassipes in the lit¬ 
toral zone subjects the animal to regular 
changes of exposure and submersion, with the 
result that the sum total of its activities tends 
to be placed on a rhythmical basis. Its elevated 
position on the strand has succeeded in remov¬ 
ing some of the restrictions on activity and in¬ 
activity imposed upon species located lower in 
the littoral area; nevertheless, the tidal influence 
was clearly manifested. The relative inactivity 
of the crabs during high tide, and the activity 
shown throughout the hours of exposure, fur¬ 
nished evidence of a behavior pattern which 
seldom deviated from the standard; indeed, it 
tended to be stereotyped. The life of this crab 
seems to approach a monotony of repetitions, a 
seldom-changing series of actions and reactions. 
The Influence of the Ocean on P. crassipes 
Drezwina (1908) studied the influence of 
the ocean on C. maenas in some detail; she con¬ 
cluded that the crabs showed a tropic response 
to the sea, which she designated "hydrotropism.” 
The wind, slope of the land, and amount of 
light were demonstrated to have no bearing 
on the response which repeatedly occurred in 
the same manner without regard to external 
conditions. None of the crabs traveled in a 
direction opposite to the sea, and the crabs with 
painted eyes oriented themselves no differently 
from normal ones. Time did not permit a study 
of these behaviorisms in great detail for P. cras¬ 
sipes, but the results of some simple field obser¬ 
vations tend to confirm the findings of Drez¬ 
wina with some modification. 
Sixty-one crabs were released high on the 
beach behind a rocky outcrop which shielded 
the sea from the sight of the crabs. The writer 
stood 10 feet to seaward from the point of re¬ 
lease. Many small rocks were strewn about the 
area, both in a direction away from the sea 
and toward it. Approximately one-half of the 
crabs immediately started toward the ocean, 
disregarded rock refuges in the vicinity, trav¬ 
eled around the rocky outcrop, and went down 
the inclined beach for several feet before con¬ 
cealing themselves in ledges situated there. After 
a momentary stop, most of them continued to¬ 
ward the water until damp crevices or small 
tide pools were reached. Of the remaining half, 
many traveled parallel to the ocean and halted 
momentarily at each rock encountered. Although 
the water was visible, several crabs traveled 
at least 20 feet in a lateral direction before they 
moved toward the ocean. The remaining crabs 
went away from the sea and took refuge below 
rocks higher on the strand, a behavior in notable 
contrast to that of C. maenas (Drezwina, 1908). 
In some individuals the stimulus for conceal¬ 
ment apparently overcame the desire to seek 
the ocean water. Within an hours time the 
crabs high on the beach gradually moved from 
rock to rock in a direction toward the sea. At 
the close of a 2-hour observation period, all 
had either reached the edge of the water or were 
secluded in moist crevices. Although the innate 
tendency of all crabs to react in a like manner 
was evident, the response was more pronounced 
in some individuals than it was in others. It 
is barely possible that some of these crabs, 
which were collected during the night on their 
high foraging area, were representatives of low 
tide-pool areas, while others may have chosen 
a higher level in the rocks as their usual habitat. 
Perhaps concealment in the high, dry crevices 
would suffice for the latter crabs, whereas the 
former would have a stronger tendency to seek 
