the size distribution of the particles produced, and to compare these data with 

 the rate of production and size of particles produced by the rock-boring infauna 

 closely associated with the urchin bore holes. 



METHODS 



Urchin Population 



The distribution and abundance of E. lucunter adults (about 3 cm test 

 diameter) was determined by SCUBA divers off western Black Rock. Most of the 

 eastern side is sand, without urchins. Using a 0.25 m? PVC frame, the divers 

 counted the adult urchins within each frame (total of 35 frames) on three 

 separate transects that were continuous from the intertidal zone seaward until 

 no more urchins were found. The number of adult urchins was calculated for 

 each linear meter in a seaward direction. These numbers were extrapolated for 

 the lateral extent of the island to yield the total number of urchins. 



Sediment Yield 



Using chisels, SCUBA divers collected rocks, each containing one urchin in 

 its intact bore hole, from 2-3 m depths off western Black Rock. Similarly 

 sized rocks without urchins were collected for controls. Each rock was brushed 

 underwater to remove loose particles. The rocks were placed separately, without 

 exposure to air, in 20 1 plastic buckets. Each rock was placed on a styrofoam 

 pad and secured to the bottom of the bucket by criss-crossed rubber bands 

 latched onto plastic hooks attached inside the buckets. The buckets were 

 ventilated with 1150 cm? of 0.0625 mm nylon screen on the side and 72 cm? of 

 0.5 mm nylon screen at the top. Using an oxygen electrode, measurements made 

 at the start and end of an experimental run showed only a small decrease (maximum 

 decrease of 0.4 mg 1 _ 1) in dissolved oxygen within the bucket. Buckets were 

 secured to the seafloor at the collection site in various ways, all designed to 

 minimize movement of the rock within the bucket, which otherwise might have 

 produced sediment particles by abrasion (fig. 1A). Buckets were deployed for 

 43-50 hr during four separate cruises. Five control and eight experimental 

 buckets yielded thirteen usable measurements out of the twenty-four buckets 

 deployed. Some buckets were lost in squalls and others had rips in the nylon 

 mesh and therefore were not included. 



Figure 1 (opposite page). --(A) Buckets (20 1)' in situ at 2.5 m depth used for 

 urchin study; (B) SEM of limestone (eol ianit¥J wal 1 in Echinometra lucunter 

 bore hole. Upper right - encrusted with 1 ithothamnoid algae. Lower left - 

 algae-free area eroded by urchin and showing spherical grains in the limestone; 



(C) Fecal pellets from alimentary tract of E. lucunter . Bar = 0.5 mm; 



(D) Broken and partially regrown spine of E. lucunter ; (E) Abraded end of 

 tooth from Aristotle's lantern of E. lucunter ; (F) SEM close-up of fig. IE 

 (arrow), showing laminated microstructure of tooth tip visible from abrasion. 

 Tip pointing to right. 



153 



