number of daily increments between the settlement mark and the edge 

 of the otolith from the date of capture. The duration of the 

 planktonic larval period can also be estimated by counting the 

 number of increments between the center of the otolith and the 

 settlement mark. The settlement mark appears under the microscope 

 as a transition where the previously prominent dark lines that 

 delineate each increment abruptly disappear. Regular increments 

 only reappear after a band without clear increments is formed 

 (see Fig. 1C) . It is, however, often possible to discern several 

 (usually five) faint increments making up this band in some areas 

 of the otolith. The aim of this study is to clarify which events 

 during the process of settlement account for the transition and the 

 subsequent settlement band on the otoliths of the slippery dick, 

 Halichoeres bivi ttatus , one of the most abundant wrasses in the 

 Caribbean. 



METHODS 



Planktonic larvae of the slippery dick were captured at a 

 nightlight with an aquarium dipnet on Ukubtupo reef in the San Bias 

 Islands of Panama. They were identified both by fin ray counts and 

 by raising in an aquarium. Only larvae that had their full 

 complement of fin rays and were of a size ready to settle were 

 present at the nightlight. Some of those captured were preserved 

 in ethanol immediately, while others were transferred to a 

 ten-gallon aquarium containing sand and sea-water. Collections of 

 juvenile slippery dicks also were made on Ukubtupo reef about the 

 same time. 



The otoliths of all individuals captured were obtained by first 

 removing the top of the cranium and then extracting the larger 

 pair, the sagittae, from the base of the skull and the smaller 

 pair, the lapilli, from the sides of the skull with fine forceps. 

 The otoliths were then cleaned and dried and placed in a drop of 

 immersion oil on a glass slide. They were subsequently examined 

 under a compound microscope with transmitted light and a polarizing 

 filter at magnifications of 400X to 1000X. 



RESULTS 



All twenty of the slippery dick larvae captured at the 

 nightlight and preserved immediately had no settlement transition 

 on their otoliths. In these fish the alternating light and dark 

 lines that make up daily increments continued all the way out to 

 the edge of the otolith (Fig. 1A) . 



Those larvae that were put into an aquarium had all disappeared 

 into the sand at the bottom of the tank by the next morning. After 

 a number of days these fish emerged from the sand and after some 

 exploring took up residence in a corner or near some rubble. 

 During those days in the sand they had lost the transparency and 

 the melanophore pattern of larvae and developed the stripes, spots, 

 and colors typical of juveniles of this species. The juvenile 

 slippery dicks usually emerged on the fifth day (mean of 5.5, n=17, 



48 



