National Geographic : 1927 Jan
LIFE ON A CORAL REEF The Fertility and Mystery of the Sea Studied Beneath the Waters Surrounding Dry Tortugas BY W. H. LONGLEY, M. A., PH. D. S EVENTY miles west of Key West lie seven low bars of shell and coral sand, the Dry Tortugas Islands, west ernmost of the Florida Keys (see map, page 4). They owe their name to Ponce de Le6n, who on the night of their discov ery in June, 1513, captured 170 tortoises there, tortugas being the Spanish word for tortoises. In 1565 that redoubtable Elizabethan, Captain John Hawkins, homeward bound from a profitable voyage in forbidden Spanish waters, knew them by their pres ent name and visited them. He loaded his pinnace with birds of species that still breed there by thousands, took of the flesh and eggs of great sea turtles, and set down in his log notes that read like a page from Robinson Crusoe. As Hawkins found them, so essentially the islands remain. Their permanent population includes only the three keepers, with their families, of the tall Loggerhead Light, guarding the western entrance to the perilous Straits of Florida. Three months in the year a sun-baked resident warden, living alone in the babel of birds' cries and hissing wings, protects the terns on Bird Key during their breed ing season, or their colony would probably have disappeared with the turtles, which are almost extinct (see pages 63 and 66). For three months, too, the Marine Lab oratory of the Carnegie Institution houses a small group of biologists busily engaged in research. Otherwise only the spread ing bulk of old Fort Jefferson (see illus trations, pages 63 and 67), with the hurri cane-twisted tangle of coaling machinery beside it on Garden Key, hints at changes that have occurred since Hawkins' visit and links the present with the more stir ring past. FAMOUS PRISONER FOUGHT YELLOW SCOURGE IN FORT JEFFERSON The fort, dismantled and decaying, has played no important part in military story. No enemy gun was ever directed against it; but within its moated wall death has stalked as horribly as through the ranks of any beleaguered garrison. Yellow fever appeared in August, 1867. Both ways it spread from the bed of the first patient. The whole side of the fort in which it broke out was evacuated and closed off from the remainder by par titions. Right and left of the abandoned gallery the men nearest the partitions next fell ill, and the plague renewed its march. Hos pital facilities were overtaxed; deaths oc curred daily and burial followed at once with little ceremony. All officers, including the surgeon, suc cumbed, and for a time all direction of medical affairs rested with a prisoner, the unfortunate Dr. Samuel A. Mudd, an al leged conspirator in the assassination of President Lincoln; for it was Dr. Mudd who, when awakened in the dead of night, at his home beside the Potomac River, miles below Washington, set the broken leg of John Wilkes Booth, the assassin. STARTLING CHANGE IN FEW FEET ELEVATION The land surface of the group as it stands is a scant square mile, but Tortugas undersea is far more imposing. If the sea bottom were elevated twenty feet, twenty square miles of land would emerge, the existing islands would grow much greater, and several of the family group lost within a century would reappear. New ones ris ing would form with the old an imposing atoll ten miles long and five wide, with three chief ship channels and several smaller ones connecting the lagoon with the open sea. Such an atoll seems to have existed in the past, for the outer face of the great Tortugas Bank is scored at many points with submerged, but unmistakable, sea-cut cliffs of an old shore line, within which lies the ocean field where I have ranged freely in my diving hood, cultivating in particular the acquaintance of fishes that live there.