424 



THE AMEBIC AN NATURALIST [Vol.LII 



LithotDunuiion, CoraUina. Mastophora, and others— are 

 abundant on the reefs, and undoubtedly have been active as 

 reef -builders. The importance of the lime-secreting algae 

 was overlooked by the earlier students of coral reefs, but 

 is now receiving adequate consideration. Howe 5 shows 

 that these forms work effectively at greater depths and 

 at lower temperatures than do the true corals, and that 

 they are much more generally and widely distributed 

 than the latter. 



The Hawaiian coralline algse inhabit the shallow waters, 

 as well as occurring at considerable depths. In the 

 former situations they form beautiful rose, purple and 

 lavender incrustations. On the faces of cliffs that are 

 washed by the sea these incrustations appear as con- 

 spicuous bands, extending from high- tide mark or the up- 

 permost wash of the surf down to the zone of minimum 

 illumination. The lower margin of the coralline zone has 

 not been investigated in the Hawaiian Islands, but in 

 other island groups they flourish at 1,000 ft. depth. In 

 the coralline zone are also many of the calcareous hydro- 

 zoa. 



Sponges of many species, sizes and colors abound in all 

 protected portions of the reefs, but have never been made 

 the subject of critical taxonomic study. They range from 

 tiny, fragile forms, the size of a shoe-button, up to coarse 

 horny masses as large as a man's head. The lesser 

 species are common on the coral-rock litter in the lagoons. 

 The larger forms inhabit the deeper waters, and are torn 

 from their anchorage only by the occasional severe storms. 

 After a period of southerly storms, for example, the lee- 

 ward beaches are littered with these large, tough sponges, 

 which average eight inches in diameter. 



The range of color is bizarre and striking. In a single 

 afternoon's collecting one may pick up, in the shallow 

 water, species of bright red, pale yellow, rich purple, dull 

 brown, creamy white, green, and dead black pigmentation. 

 Dredging reveals others which add to the chromatic series. 

 Most of the sponges are of the encrusting type, the body 



5M. A. Howe, "Building of Coral Reefs," Science, 36: 837-842, 1912. 



