ZONES OF THE SEA-WHERE THEY LIVE 23 



fauna. A comprehensive list of the fauna given by Hesse, and others (1951), 

 and Ekman (1953) includes a few crustaceans, several hydroids, a few worms, 

 brvozoans, two barnacles, a tunicate, some snails, a sea spider, a pipefish, and 

 the extraordinarv sargassum fish. All of these live directly on the weed most or 

 all of their lives. Sargassum also forms a nesting place for flying fishes. The 

 young of many tropical fish use the weed as a place of protection. 



THE CORAL REEF 



Most of us, if given free choice of places to dive, would pick the coral reef 

 for several reasons. It possesses by far the gaudiest, most varied, and most 

 luxurious fauna of any place where life is found on the earth. In its never- 

 ending nooks and crannies, innumerable animals make their homes, animals 

 which quite frequently have extraordinary habits. 



Coral reefs owe their existence to groups of animals and plants which deposit 

 calcium around themselves as a protective skeleton. This building of lime 

 progresses best in tropical waters for two reasons: (1) the chemical reaction 

 which forms calcium carbonate is fastest at temperatures of 68° Fahrenheit 

 and above, and (2) calcium is more soluble, and hence more abundant, in 

 warm waters than in cold. 



Though the name "coral reef" is given to a limy reef built largely by stony 

 or madreporite coral, these little colonial animals are not the only reef builders. 

 On almost all reefs the stinging, hydroid millepores, called "fire corals," are 

 very common and, to go farther afield, foraminiferans, calcareous algae such as 

 Halhneda, and calcareous bryozoans play a dominant part. In fact, the madre- 

 porite corals sometimes even take third place behind foraminiferans and algae 

 in the building of some reefs. Still, the tropical madrepores are the dominant 

 and most spectacular builders of reefs. 



Temperature is important; a minimum of 68° Fahrenheit is necessary for 

 the building of coral reefs. The temperature also determines the abundance and 

 variety of corals, for at the marginal temperature of 68°, coral becomes rather 

 depauperate. It takes higher temperatures of about a minimum of 74° to 

 introduce large branching corals to a reef. Borderline waters of 68° such as 

 those off Bermuda, have a noticeably depauperate coral fauna. Hesse, and 

 others (1951), compare Bermuda's 12 coral species to the Red Sea's 125. On 

 the other hand, coral can stand very high temperatures of up to 132° Fahren- 

 heit when uncovered by low tides for short periods. Stony corals do exist in 

 cool temperate waters, incidentally, but reefs are never formed. 



Temperature is not the only limiting factor for the growth of coral reefs. 

 Moving water must be present, and it must move at the right speed, not so 

 fast as to break the coral or to prevent the coral larvae from gaining a foothold 

 and not so slow as to prevent the distribution of enough planktonic food and 

 oxygen to keep the coral animals alive. 



Coral must have firm substrate to which to attach itself. It is poor or lacking 

 if hard bottom is scarce. Such is the case on the otherwise adequate southeastern 

 coast of Florida. 



Coral is usually poor in areas of cold upwelling waters. The eastern Pacific 

 has a poor coral fauna for that reason. 



