islands that are near the outer edge of the Indo- 

 Pacific coral region. 



Barrier reefs consist of lines of reefs paralleling a 

 mainland but separated from it by a lagoon channel 

 deep enough to accommodate large ships. These are 

 not well developed in the Indian Ocean but in the 

 Pacific are found at the Society Islands, the Fiji Is- 

 lands, New Caledonia, to the southeast of New 

 Guinea, and at many other spots. The largest and 

 best-known of barrier reefs is the Great Barrier Reef 

 of northeastern Australia, which parallels the coast 

 of Queensland for 1250 miles, though it is inter- 

 rupted by many passages. 



Atolls are the coral islands that romantic dreams 

 are made of. These ring-shaped or horseshoe-shaped 

 islands, surrounding a central lagoon with sheltering 

 palm trees and mangroves, are dotted litce oases over 

 the vast Indian and Pacific oceans in waters thou- 

 sands of feet deep. 



Below the depths at which there is sufficient light 

 for the photosynthesis carried on by their content of 

 plantlike cells, reef corals cannot live. They grow 

 best near the surface and are most abundant in the 

 upper 60 feet of water, though many extend through 

 the water layers down to 150 feet. Only a few man- 

 age to grow as low as 270 feet. 



The best-developed reefs of the Bahamas, Ja- 

 maica, and Florida, according to Norman Newell, a 

 leading student of Atlantic and other reefs, usually 

 have three coral zones, which are determined by 

 differences in depth and turbulence of water: an 

 outer zone of massive corals, especially of yellow- 

 brown Montastrea annularis lying at depths of thirty 

 to sixty feet; a middle zone of brownish yellow stag- 

 horn corals, Acropora pahnata. at five to thirty feet; 

 and an inner rocky shoal rising to low-tide level. 

 This last zone is characterized by the velvety yellow- 

 orange or brown "stinging coral," Millepora alcicor- 

 nis (not a true stony coral but a hydrozoan coral), 

 encrusting coralline algae, sea fans, and small 

 rounded corals. In the Indo-Pacific many reefs re- 

 ceive much greater contributions of limestone from 

 the coral-secreting algae, and also in certain places 

 from hydrozoan reef-builders like the organ-pipe 

 coral and blue coral. 



THE ZOANTHIDS 



Without skeletons and with a marginal circlet of 

 unbranched tentacles, zoanthids superficially resem- 

 ble small anemones, except that most of them are 

 colonial and are united at their bases. This is a small 

 group, found in both shallow and deep waters and in 

 cold and warm latitudes, but especially in warm 

 shallow seas. Most zoanthids regularly grow on the 

 surfaces of other animals, often on very specific 

 hosts. Certain species of Epizoanthits occur only on 

 particular glass sponges; others fasten to the shells 



inhabited by hermit crabs, dissolving away the crab's 

 shell and finally coming to enclose the crab directly. 

 Other genera live on sponges, hydroids, gorgonians, 

 corals, bryozoans, and worm tubes (Plate 30). 



THE BLACK CORALS 



The black or thorny corals, or antipatharians, are 

 slender, branching, attached colonies of plantlike 

 form ranging from an inch to several feet high. Most 

 are known to biologists only as preserved specimens 

 dredged from deep or abyssal waters, especially of 

 the tropics and subtropics. The horny internal 

 skeleton is black or brown and beset with thorns. 

 According to Russel and Yonge, in the excellent ac- 

 count of products of the sea which concludes their 

 book The Seas, the skeletons of certain black corals 



The star coral, Montastrea, grows into yellow-brown 

 boulder-like masses, 5 feet or more across, in Florida, 

 the Bahamas, Bermuda, and the West Indies. Tbe 

 individual cups are only a fraction of an inch across 

 and show the ridges supporting the internal parti- 

 tions. (Fritz Goro: Life ^Iagazine) 



