348 "ALBATROSS" TEOPICAL PACIFIC EXPEDITION. 



deeper water, corals no longer find propitious conditions for growth, and 

 even on the lee side of the patches corals are killed by the silt. Corals 

 growing on the slope of the patches extend generally down to fifteen or 

 eighteen fathoms. 



The corals on the flats have all disappeared at a depth of twenty fathoms, 

 where nothing but silt and a mud bottom are found. According to the prox- 

 imity of the coral patches to the belt of mangroves, the depth to which 

 they reach varies from ten to fifteen or twenty fathoms. We found 

 growing among the corals Alcyonarians, sponges, and large Actinians. 

 The corals were mainly huge heads of Millepores, Madrepores, Goniastreas, 

 Porites, Pavonias, and also Fungia. Nowhere in the Pacific have we 

 found more magnificent corals than in the Carolines, reminding us of 

 those which flourish on the Great Barrier Reef of Australia, where the 

 sponges, Alcyonarian and Actinarian masses play such an important part 

 in the physiognomy of the coral reefs. A few Mseandrinas also occur, the 

 first we have seen for a long time; between the heads grow large masses 

 of Sabella. The coloring of the corals is also much more brilliant than 

 that of the coral reefs to the eastward. The corals I have mentioned 

 form huge masses of pink, purple, yellow, and brown ; they alternate with 

 green sponges, with the many variegated, banded, and striped Alcyona- 

 rians, and with the large masses of purple Actinians which grow to an 

 enormous size among the coral heads over the more exposed parts of 

 the flats. A coating of Nullipores has gradually spread over the dead 

 corals. It is mainly on the slopes of openings and channels leading into 

 the barrier reef lagoon that corals are most flourishing, sheltered as they 

 are to a certain extent from the encroaching silt. The Porites heads grow- 

 ing near the inner edge of the mangrove flats are the first to be killed. 

 Near the outer edge of the reef flat the tops of the coral patches are 

 killed by the loose material thrown in by the action of the sea, and this 

 loose material is in its turn cemented by a coating of Nullipores. As we 

 approach the inner mangrove belt of the muddy reef flat, the bottom 

 becomes covered by volcanic silt, the water becomes dirtier and dirtier, 

 the corals have all been killed, excepting those which live on the upper 

 slopes of knolls or are attached to the sides of large heads. 



