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Marine Biology 90,317-326 (1986) Duration of the planktonic larval stage of one hundred species of Pacific and Atlantic wrasses (family Labridae) B. C.Victor Department of Biological Sciences and Marine Science Institute, University of California at Santa Barbara: Santa Barbara, California 93106. USA Abstract tity for both ecological and biogeographical studies. Both Sale (1980) and Anderson et al. (1981) have agreed that the The planktonic larval durations of a preliminary sample of scale on which community ecological studies of reef as- one hundred species of wrasses from both the Pacific and semblages should be performed depends directly on the Atlantic Oceans were estimated with the use of the daily larval dispersal distance. In addition, it is possible that otolith-increment aging-technique. Larval durations were varying dispersal abilities could account for many of the determined by counting the number of daily increments complex patterns characteristic of coral-reef fish bio- between the center of the otolith and the mark correspond- geography. ing to settlement. The duration of the planktonic larval Estimates of the duration of the larval life of reef fishes phase of wrasses appears to be extremely variable between are difficult to derive without an accurate aging technique. species, ranging from 15 d in Diproctacanthus xanthurus to Randall (1961) estimated the planktonic larval duration of 121 d in a specimen of Thalassoma ballieui. Larval dura- a surgeonfish in Hawaii by measuring the difference in tions within species were also variable, especially in species timing between the seasonal onset of spawning and the with relatively long durations. Congeners tended to have subsequent influx of settlers. This method depends on the similar larval durations and similar otolith-increment presence of distinct seasonal cycles of spawning and settle- characteristics. Hawaiian and Eastern Pacific species had ment and requires that incoming larvae originate from the longer larval durations than their Caribbean or Western local population. The discovery of daily incremental marks Pacific congeners. Similarly, Hawaiian populations had on the otoliths of many fishes has greatly simplified the significantly longer larval durations than their Western Pa- process (Panella, 197 1; Brothers et al., 1976). It is possible cific conspecifics. The implications of these findings for to use this technique to make extremely precise and accu- biogeographical studies are discussed. rate measurements of the age of individual fishes. There are two methods by which one can derive an estimate of the planktonic larval duration using the daily otolith-in- crement technique. One method is to capture larval Introduction recruits as they settle onto the reef and count the number of daily increments on their otoliths (Brothers et a/., 1983; Coral-reef fishes, diverse in most other respects, are no- Victor, 1983 b). Alternatively, if there is a mark on the oto- tably consistent in having a planktonic larval stage. Virtu- lith that can be demonstrated to be associated with settle- ally all of the thousands of species native to coral reefs ment, one can then estimate the planktonic larval duration have larvae which spend some time adrift in the plankton for any settled individual by counting the number of daily (Sale, 1980). This phase of their life history can play an im- increments between the center of the otolith ard the settle- portant, perhaps crucial, role in determining the distri- ment mark (Brothers and McFarland, 1981; Victor, 1982, bution, abundance, and dynamics of reef-fish populations 1983 b). (Williams, 1980; Doherty, 1983; Victor, 1983a, 1984, and The wrasse family (Labridae) is, at present, unique in press). There is, nevertheless, very little known about among coral-reef fishes in that there is direct experimental even the most basic aspects of the larval life of coral-reef evidence demonstrating the existence of both daily in- fishes (Sale, 1980). The distance over which these larvae crements and a distinct mark on their otoliths correspond- are able to disperse, presumably a function of the du- ing to settlement (Victor, 1982, 1983 b). This family is, fur- ration of the larval phase, is a particularly important quan- thermore, one of the most speciose of reef-fish families 8.C.Victor: Planktonic larval duration oiwr;ls\es (with about 400 species, second only to the gobies), and is without further preparation, but some of the larger and less unparalleled in diversity of both form and habit (Nelson, clear needed to be ground before their daily increment se- 1976). Wrasses also exhibit a great variety of distributional quence could be counted. Grinding was performed by patterns, with some species endemic to single islands and hand on a glass plate with Carborundum 600 grit in im- others found throughout the Indian and Pacific Oceans. mersion oil. For these reasons, this family is particularly suitable for a The otoliths were examined under a compound micro- detailed and comprehensive study of planktonic larval du- scope using transmitted light at magnifications of 400 to rations. In the present study, I document the duration of 1000X. A rotatable polarizing filter placed between the the planktonic larval stage for a hundred species of wrasses light source and the slide was used to accentuate the marks from both the Pacific and Atlantic Oceans using the daily on the otolith. Increment sequences were clearer on oto- otolith-increment aging-technique. I also examine some of liths that had remained in oil for more than a few weeks or the problems inherent in otolith-aging of coral-reef fish lar- months. Each daily increment consists of a light line fol- vae and discuss the implications of these preliminary find- lowed by a narrower dark line. The light line corresponds ings for biogeographical studies of coral-reef fishes. to a mostly crystalline growth zone. while the dark line consists of a zone comprised mainly of a protein matrix (Watabe etul.. 1982). The settlement mark was identified Materials and methods as a band with increments that were wide and very ?dint (V~ctor,1982. 1983 b). The dark iines within this band are The wrasses from the Caribbean Sea were collected in often not apparent and the settlement mark then looks like January and February of 1983 from Aguadargana Reef in a band without increments at all. The settlement mark is the San Blas Islands of Panama in the southern Caribbean usually quite conspicuous because increments at the end of Sea. The large number of bluehead wrasses, Thalussomu bi- the larval sequence often have highly contrasting light and fasciaturn, were obtained between 1980 and 1984 from dark lines making up each increment. various reefs at the western edge of the San Blas Islands. The number of daily increments between the center of The wrasses from the western Pacific were collected during the otolith and the settlement mark was counted and re- July and August of 19S3 from Palau in the Caroline 1s- corded for each individual captured. Otolith increments lands. Most specimens were captured on Augulpelu reef on have been experimentally demonstrated to be daily for two the east coast of Palau near Koror, while the remainder species of tropical wrasse juveniles (Victor, 1982. 1983 b). were collected in the Ngel Channel and in Malakal Har- These studies also demonstrated that a distinct settlement bor. The Hawaiian wrasses were collected from the Wainae mark is produced on the otoliths of these species when the coast of Oahu and the Kona coast of Hawaii in May 1981. planktonic larva first settles onto the reef. Direct exper- The wrasses from the eastern tropical Pacific were collected imental evidence for the production of daily increments on around the island of Pacheca. the northermost of the Perlas the otoliths of planktonic larvae in the field (as opposed to Islands in the Gulf of Panama in November 1982 and in settled juveniles) has not yet been obtained for any fish. It November 1984. The eastern Pacific temperate wrasses is therefore assumed in this study that (1) the increments were obtained from Southern California in July 1985. The observed on larval otoliths are also daily, and (2) the daily north Atlantic wrasses were collected along the Mas- increments and settlement marks demonstrated in the two sachusetts coast in May 1985. species of wrasses are common to all wrasses. Wrasse oto- Most of the samples consisted ofjuvenile wrasses which liths appear within a day or two of fertilization in tropical I subdued with the anaesthetic Quinaldine and then cap- waters (Victor. unpublished data). I therefore added two tured with an aquarium dipnet. Larger individuals were days to the number of pre-settlement increments to arrive shot with various sized spears. 'Those fish small enough to at an estimate of the entire planktonic larval duration. be conveniently preserved in the field were immediately put into 95% ethanol (formalin dissolves otoliths), while the otoliths were removed directly from the larger fishes. Results Two of the three pairs of otoliths (the sagittae and the la- pilli) were used in this study. The largest pair, the sagittae. Otolith increments often exhibited clear increments and thus were usually se- lected for examination. In many cases, the lapilli, the mid- Incremental marks were found on all the otoliths exam- sized pair. proved to have clearer increments than the ined. In many of the species examined, there was only one sagittae. In those species with vely narrow otolith in- array of increments and the counting was therefore crements, however, the sagittae were always used since in- straishtfonvard. However, on the otoliths of many other crements on the lapilli often become too uarrow to detect. species there appeared to be more than one type of repeat- ?he otoliths were obtained by first removing the top of the ing incremental mark.

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