1918] MACCAUGHEY—HAWAIIAN ALGAE 49 
of 18-24 inches. The difference between high and low tide is so 
small that there is almost a complete absence of the strongly 
developed tidal zonation so characteristic of many continental 
shores. However, on the broad platform reefs, like those near 
Pearl Harbor, Waialae, and Mauna-lua, this difference is sufficient 
to expose much of the reef surface at low tide. At this time the 
reef consists of an irregular series of pools, cut off from one another 
by the rocky platform, which has only 2-3 inches of water on it. 
Protruding areas of the reef are wholly exposed to the air, and on 
their knobs or knolls only the hardy species of algae can exist. 
Out toward the edge of the reef a shallow lagoon, or series of lagoons, 
may persist, unemptied by the lowest tides. This is the ideal time 
for collecting, as one can travel afoot far out to the rim of the reef 
and easily procure material which at high tide is hidden beneath 
the surf and foam. To get the full advantage of the low tide one 
customarily begins work when the tide is about half run out, and 
then follows the ebb out to its maximum. This gives a working 
period of 4~5 hours. 
Los CORALLINE ALGAE 
Highly important among the Hawaiian marine algae are the 
coralline or “stony” algae or nullipores. A number of genera 
(Lithothamnion, Corallina, Mastophora, and others) are abundant 
on the Hawaiian reefs, and have undoubtedly been highly effective 
in reef building. The importance of these lime-secreting algae was 
overlooked by the earlier students of the coral reefs, but is now 
beginning to receive adequate consideration. As MAYER‘ states: 
€ most striking feature which distinguishes the Pacific reefs is the 
development of a ridge which actually projects half a foot or more above low 
tide level and extends along the outer seaward edge of the reef-wall wherever ~ 
the breakers dash. In the Paumotus this ridge is dull reddish pink in color, 
and it is composed of a mass of stony seaweeds or nullipores of the sort called 
Lithothamnion, and also of bryozoa which are remarkable lime-secreting 
organisms related more closely to the worms than to any other form of the 
animal kingdom. 
This Lithothamnion ridge thrives only where the breakers strike in full 
force upon its living barrier, and it serves as the chief protector of the island, 
breaking the force of every wave that approaches the windward shore. 
* Popular Science Monthly 85: 209-231. 1914. 
