AN EXPERIMENTAL FIELD-STUDY OE WARNING COLORATION 

 CORAL-REEF FISHES.^ 



By Jacob Reighard. 



I. INTRODUCTION. 



The islands of the Tortugas group rise gently from a submerged plateau 

 many square miles in extent. To the southeast, at a distance of about 3 

 miles, is the outer reef, and beyond this deep water. Immediately about 

 the islands the bottom is overlaid by the gray-white or yellow-white coral 

 sand and, except where traversed by the few tortuous channels, it is covered 

 with water from 8 to 15 or 20 feet in depth. From this bottom the inner 

 reefs rise sheer. These vary in size from isolated coral heads of a square 

 yard or two in area to small reefs of a few square rods or a fraction of an 

 acre. The upper surfaces of these reefs are sometimes exposed at low tide, 

 and at all tides one may readily wade over them. (See plates in Saville- 

 Kent, 1893, of the Great Barrier Reef of Australia.) Although nearly level 

 on top, the reefs are penetrated in every direction by chasms, fissures, and 

 tortuous covered passages which intercommunicate so as to form veritable 

 labyrinths. Structurally the whole is not unlike a mass of small boulders 

 carelessly piled and roughly cemented together (plate i ; plate 2, fig. 3 ; plate 

 4, fig. 8). On its upper surface and for a short distance downward into 

 the larger fissures each reef is clothed with living coral, massive or branched ; 

 beneath this is dead coral and coral rock. 



The crevasses of the coral reefs harbor many species of teleostean fishes. 

 The smaller species and the younger individuals of the larger species are 

 never seen at a distance from this shelter. On the reef and in its imme- 

 diate neighborhood they find their food ; when disturbed they scurry to the 

 reef and vanish into its protecting mazes. As the disturbance subsides they 

 slowly emerge, in the inverse order of their timidity, and gradually resume 

 their wonted activities. 



The larger individuals of those species that reach a considerable size 

 may wander from the reef to a distance of some rods, protected from 

 piscivorous fish of their own size apparently by their bulk. Thus Abudcfditf 



' Contributions from the Zoological Laboratory of the University of Michigan, 

 No. 116. 



261 



