MALACANTHUS PLUMIERI 



Along West Indian coral reefs, the sand tilefish Malacanthus plumieri 

 selectively builds nests that are roofed with coarse shell and coral 

 fragments. This fish may be largely responsible' for the distribution 

 of the coarse debris (shells 3-6 cm across and coral fragments 1-2 cm 

 in diameter and 5-10 cm long) , and thus a potentially significant 

 geologic agent. 



Several experiments were conducted to determine the extent to which 

 M. plumieri collects and segregates coarse shell and coral fragments 

 along the reef fronts. At a selected nest, fragments were removed 

 from the outer part, marked, and scattered within 2 meters of the 

 nest. Eight days later the outer part was again disassembled, and 

 the number of fragments restored to the nest tabulated. These 

 fragments were separated into groups containing equal assemblages of 

 fragments by size and shape. Each group was color coded and dropped 

 at specific intervals of 0-3, 3-6, 6-9, and 9-12 m from the nest. 

 The distance over which the fish restored fragments to the nest and 

 selectivity for shape of fragment could be established by inspecting 

 the color mark. In another experiment, 150 fragments were scattered 

 in a meter-square plot at two different sites near occupied 

 M. plumieri nests. In each plot, 50 of the fragments were irregular 

 pieces of coral (more than two forks) , 50 were simple cylindrical 

 coral rods (mostly Acropora cervicornis) , and 50 were shells taken 

 from M. plumieri nests elsewhere in the area. The number of shells 

 and fragments removed from the plots was checked periodically to 

 provide an estimate of the rate at which the fish collects different 

 types of fragments from the sea floor. 



Within the 8 days of the first experiment, the individual studied 

 returned 460 shells and pieces of coral from the 2-meter area. 

 During the second, he collected fragments over a distance from 

 the nest greater than 9 meters. In the preliminary stage of con- 

 struction, the fish selectively collects irregular cora] fragments 

 to form the "rafters" of his roof, then adds "shingles" in the 

 form of shells and more regularly shaped fragments. Tabulation 

 of marked shells and coral fragments collected by M. plumieri 

 during the time the nest was maintained, undisturbed from the two 

 plots that contained 150 fragments and shells each suggests that 

 he may selectively collect shells and irregular fragments of coral 

 in preference to simple coral cylinders. Mapping of M. plumieri 

 nests indicated the presence of 59 nests along a 250-meter stretch 

 of reef from southwest of the habitat. Twenty-four of these 

 showed evidence of occupation. With the given potential for a 

 single fish to transport and segregate coarse debris, the number 

 of fish present along the reef front is probably sufficient to 

 insure that most of the material in the 3 to lO-cm range is 

 concentrated in their nests. 



VI-24 



