Pearse: Fauna of the Rock Beaches 
11 
1913 ] 
1. The Rocks above High Tide Mark 
Perhaps the most characteristic animal in this region of bare 
rock was the fly, Parydra sp. (?).- Spiders and ants commonly 
foraged here, beetles were not infrequent, and occasionally Ani - 
solabia or a myriapod was seen skulking into a fissure. Where 
boulders afforded shelter rats were often seen to come out to feed 
at low tide. Besides Parydra , butterflies, dragon-flies, mosqui- 
toes, and damsel-flies frequented the air above. 
The little pools in the hollows of the rock often supported an 
abundant fauna. Corixa , Notonecta, Culex larvae, toad tadpoles, 
amphipopods, cladocera, copepopods, and chironomid larvae fre- 
quently occurred in great numbers with Enteromorpha or Clado- 
phora in fairly fresh water. Parydra bred in these puddles and 
collected on the surface in such numbers that it formed rafts 
several inches across. Near the ocean where spray collected in 
depressions, barnacles, Littorina, Mytilus , Corallina and other 
marine organisms obtained a foothold and maintained them- 
selves. 
In some cases there was a definite stratification of the water 
in rock depressions and both marine and fresh water animals 
were able to exist in the same pool. Toad tadpoles, Corixa , 
Chironomid and Culex larvae were found in the same basin with 
living barnacles, rock crabs and Littorina. The stratification leads 
to curious temperature relation for when the sun shines on the 
rock, the heavier salty water at the bottom is raised to a higher 
temperature than that near the surface. In one pool ten inches 
deep the top and bottom temperatures (of the water — -the ther- 
mometer was not permitted to rest on the bottom) were 15.7° C. 
and 23.5° C. respectively; in another, 17.7° C. and 24.0° C. At 
Station 6 (fig. 1) where fresh water seeped through the rocks 
there were several pools just above high tide mark which had a 
typically marine fauna at the bottom (. Littorina , Corallina, Car - 
cinides, Balanus, Jaera), and freshwater animals above (tadpoles, 
Corixa , dipterous larvae). In pools in the barnacle zone just 
below these there were few or no barnacles for about one inch 
below the surface of the water, though they were abundant on 
the rocks above and in the deeper parts of the pools. 
The bare rocks above the limits of high tide are clearly under 
