CAUSES INFLUENCING THE GROWTH OF CORAL ZOOPHYTES. 59 



3. Causes influencing the Growth of Coral Zoophytes. 



Marine zoophytes generally require pure ocean water, and they 

 abound especially in the broad inner channels among the reefs, 

 or the large lagoons, and in the shallow waters outside of the 

 breakers. In these channels at the Feejee Group, there are spe- 

 cies of every genus, and they grow in the greatest luxuriance, 

 exceeding in profusion and display, all that was elsewhere seen 

 in the Pacific. Here are found the huge Astraea domes, the Me- 

 andrinas, Pontes, the leafy clusters of the Merulinae, numerous 

 Madrepores; — indeed nearly all the Pacific corals described in 

 the Report on Zoophytes, exclusive of those from the Tahitian 

 and Hawaiian Islands, were obtained from the inner reefs of the 

 Feejees.* It is therefore an assertion wide from the fact that 

 only smaller corals grow in the lagoons and channels, though 

 true of lagoons and channels of small size, or of such parts of 

 the larger channels as immediately adjoin the mouths of fresh- 

 water streams. 



There are undoubtedly species especially fitted for the open 

 ocean ; but as peculiar conveniences are required for the collec- 

 tion of zoophytes outside of the line of breakers, we have not the 

 facts necessary for an exact list of such species. From the very 

 abundant masses of Astraeas, Meandrinas, Pontes, and Madre- 

 poras thrown up by the waves on the exposed reefs, it was evi- 

 dent that these genera were well represented in the outer seas. 

 In the Paumotus, the single individuals of Pontes lying upon 

 the shores were at times six or eight feet in diameter. Around 

 the Duke of York's Island the bottom was observed to be covered 

 with small branching and foliaceous Madrepores, (Manoporae,) as 

 delicate as any of the species in more protected waters. 



Species of the same genera grow in the face of the breakers, 

 and some are identical with those that occur also in deeper waters. 

 Numerous Astraeas, Meandrinas and Madreporas grow at the outer 

 edge of the reefs where the waves come tumbling in with their 

 full force. There are also many Milleporas and some Porites and 

 Pocilloporas in the same places. But the weaker Manoporas, ex- 

 cepting incrusting species, are found in stiller waters either deep 

 or shallow. The Nullipores, properly calcareous vegetation, 

 flourish best along the line of breakers and form thick accumula- 

 tions upon the reef.f 



Again, the same genera occur in the shallow waters of the 

 reef inside of the breakers. Astraeas, Meandrinas and Pocil- 



* The author's observations on the species of corals were not commenced till 

 reaching the Feejees, where we were among the inner reefs. Previous to that 

 time, this department in Zoology was in the hands of Mr. J. P. Couthouy. 



f Porites and Milleporfe, according to Mr. Darwin, prevail on the surf-reef of 

 Keeling's Island. Chamisso states that the large Astraeas live and grow in the 

 breakers. 



