FISHERY BULLETIN: VOL. 76, NO. 1 



water column, D. reticulatus and A. curacao were 

 the only deep-bodied forms. Other diurnal plank- 

 tivores were more sparse. The more prominent of 

 these were species ofChromis that usually stayed 

 within 2 m of the reef. Chromis caerulea,^ mostly 

 juveniles, generally hovered in small aggrega- 

 tions above heads of the coral Pocillopora, but C. 

 agilis and C. margaritifer more often were solitary 

 or in groups of just a few. At night all of these 

 fishes were under reef shelter, and we saw no evi- 

 dence of them feeding at that time. 



Despite the relative paucity of adult diurnal 

 planktivores in this habitat, planktivorous juve- 

 niles and larvae of at least several fish species 

 frequently were numerous and fed by day. An out- 

 standing example was the juveniles of Apogon 



3 At the distances that most of our observations were made, we 

 were unable to consistently distinguish Chromis caerulea from 

 the very similar C. atripectoralis , and so referred all observa- 

 tions to the former. Significantly, however, the behavior attri- 

 buted to this species is consistent with that in all individuals 

 observed. 



gracilis, well under 50 mm long, which hovered in 

 large, umbrella-shaped aggregations above coral 

 heads in open sand (Figure 4). Dense schools of 

 larval fishes, 7 to 10 mm long, (often taken on first 

 glance as mysid swarms) were sometimes promi- 

 nent, but so close to the reefs that our net sampled 

 only an occasional outlier. 



Although adult diurnal planktivores were com- 

 paratively sparse in this habitat, their nocturnal 

 counterparts tended to be especially numerous. 

 During daylight, dense, inactive concentrations of 

 Myripristis spp. abounded at openings of reef cre- 

 vices. Prominent as these concentrations were, 

 they represented only a small part of the tremend- 

 ous numbers of their species packed into the reef 

 interstices. We became fully aware of the immen- 

 sity of these populations when, about 30 min after 

 sunset, they abruptly streamed into the open and 

 entered the water column. Shortly after emerging, 

 most individuals of one species, M. murdjan, ap- 

 parently moved elsewhere, because though they 

 were numerous initially, relatively few were seen 

 during the night, and their numbers did not in- 



FIGURE 4. — Juvenile cardinal fish, Apogon gracilis, approximately 25 to 30 mm long, feeding on plankton by day where currents are 



weak. 



138 



