SETTLEMENT AND LARVAL METAMORPHOSIS PRODUCE DISTINCT MARKS ON 

 THE OTOLITHS OF THE SLIPPERY DICK, HALICHOERES BIVITTATUS 



Benjamin C. Victor 

 Department of Biological Sciences and Marine Science Institute 

 University of California, Santa Barbara, California 93106 



ABSTRACT 



Early in the sequence of daily increments on wrasse otoliths 

 there is a transition from clear increments to a band of very 

 faint, often indecipherable, wide increments. After about five of 

 these wide increments clear increments resume. Planktonic larvae 

 do not have the transition on the edge of their otoliths, while 

 newly-metamorphosed juveniles have both the transition and the 

 subsequent band on theirs. Experiments showed that metamorphosis 

 takes about five days, during which the larva remains buried in 

 sand. The transition therefore corresponds to settlement of the 

 planktonic larva onto the reef, and the band is formed during the 

 process of metamorphosis. These findings demonstrate that 1) it 

 cannot be assumed that newly-appeared fish on the reef settled that 

 day and 2) experiments are necessary to ascertain the meaning of 

 marks on the otolith. 



INTRODUCTION 



Reef fish ecologists have only recently begun to focus their 

 attention on the early life history of reef fishes. These fishes 

 are unusual in that virtually every one of the many thousands of 

 species that live on coral reefs has a planktonic larval stage. 

 The interest in the ecology of larvae and the process of 

 recruitment is indeed timely, for it is becoming increasingly 

 apparent that many of the patterns of diversity and abundance of 

 coral reef fishes are being determined by processes occurring in 

 the plankton. Several studies have demonstrated that reef fish 

 populations are limited by the supply of larval recruits, rather 

 than by some resource on the reef (Wi 11 iams , 1980; Doherty , 1983 ; 

 Victor , 1983) . Furthermore, some of my recent findings (in prep) 

 indicate 1) that species-specific larval behaviors determine 

 when successful recruitment occurs in some Caribbean wrasses and 

 thus promote the coexistence of species on the reef, and 2) that 

 the duration of the planktonic larval stage affects the 

 distribution of wrasse species in the Indo-Pacific and may well 

 account for the differing degree of speciation that has occurred 

 within wrasse genera. 



Much of the progress that has been made on this subject is a 

 result of the power of the daily otolith increment aging technique 

 (Brothers, 1981; Brothers & McFar land , 1981 ) . Because there are 

 both daily increments and a mark corresponding to the settlement of 

 the planktonic larva on wrasse otoliths (Victor , 1982) , the date of 

 settlement for any individual can be calculated by subtracting the 



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