Oecologia (1998) 115:268±277 Ó Springer-Verlag 1998 Laura Gutie rrez Habitat selection by recruits establishes local patterns of adult distribution in two species of damsel®shes: Stegastes dorsopunicans and S. planifrons Received: 27 May 1997 / Accepted: 4 January 1998 Abstract Local patterns of adult distribution in organ- Introduction isms that disperse young as pelagic larvae can be de- termined at the time of recruitment through habitat The population dynamics of species with open popula- selection or, shortly thereafter, through post-recruit- tions, such as many nearshore marine organisms which ment processes such as dierential juvenile survivorship possess a planktonic larval stage, has received much and interspeci®c competition. This study addresses the attention over the last decade (Roughgarden et al. 1985, importance of habitat selection by recruits in establish- 1988; Victor 1986; Underwood and Fairweather 1989; ing the local pattern of adult distribution in two Gaines 1992). Variable recruitment can in¯uence the sympatric Caribbean damsel®sh species, Stegastes patterns and processes of local community structure. dorsopunicans and S. planifrons. Both species inhabit For example, an abundant supply of larvae can increase shallow reefs but show little overlap in their distribu- population density and consequently the intensity of tion; S. dorsopunicans predominates in the reef crest and biological interactions (e.g., competition and predation) S. planifrons occurs primarily on the reef slope. Fur- within the community, whereas a limited supply of lar- thermore, S. dorsopunicans is associated with rocky vae may have the opposite eect (Pacala and Silander substrate, while S. planifrons occupies live coral. The 1985; Roughgarden et al. 1988; Pacala 1989). Thus, local substrate cover follows a similar pattern with coral patterns of adult distribution in marine organisms which being much less common on the reef crest than on the disperse primarily during a larval stage will be estab- reef slope. Monitoring recruitment every other day in lished either at settlement through habitat selection, or reciprocal removal experiments and arti®cial reefs indi- thereafter through processes such as dierential preda- cates that the observed pattern of local adult distribu- tion, competition, and/or habitat selection through tion is a product of habitat selection for both species. migration (Raimondi 1991). The presence or absence of conspeci®cs did not in¯uence It is important to distinguish between settlement and recruitment patterns for either species. Stegastes dorso- recruitment since these two events give complementary, punicans recruited primarily to shallow, rocky areas, but dierent insights into the processes structuring appearing to cue on both substratum type and depth. communities. Settlement is the initial establishment of Stegastes planifrons recruited exclusively to coral sub- larvae onto the substratum. Recruitment, on the other stratum independent of depth. These results indicate hand, is the ®rst record of the settled larvae (sensu that local adult patterns of distribution can be explained Keough and Downes 1982). While a settler's age is zero, by habitat selection at recruitment, and that substrate the age of a recruit can vary from hours (Raimondi type and depth may be important cues. 1991) to months (Doherty and Fowler 1994). A pattern of distribution and abundance described at settlement Key words Habitat selection á Distribution á Damsel®sh á re¯ects only larval processes; if it is described at re- Recruitment á Coral-reef ®shes cruitment, it also includes the eects of post-settlement processes. As in many marine organisms, the life cycle of most coral reef ®shes involves a dispersive planktonic larval phase (Sale 1980). Hence, abundance and distribution L. Gutie rrez Department of Biology, University of Houston, patterns of ®shes on the reef can be determined by both Houston, TX 77204-5513, USA settlement and post-settlement processes. Much atten- Fax: (713)743-2636; e-mail: [email protected] tion has been given to post-settlement processes. In the 269 past, competition was considered to be the major pro- functionally important members of coral reef ®sh communities. cess structuring ®sh communities (references in Sale Damsel®shes of the genus Stegastes are relatively small territorial ®sh (Itzkowitz 1977; Robertson et al. 1981, Robertson 1984). These 1980). Predation has received attention more recently territories are utilized for food, shelter, and nesting (Thresher (Hixon 1991). The focus on recruitment has been di- 1976). Most adult damsel®shes grow a dense algal mat within their rected primarily to its role in regulating the abundance territories from which they feed. They control the species compo- of ®sh populations (Doherty and Williams 1988; Do- sition of these algal turfs, and defend them against other herbivores herty 1991). Little attention has been paid to its function such as ®sh and sea urchins (Myrberg and Thresher 1974; Thresher 1976). In order to provide substratum for this algal mat, some adult in the establishment of local patterns of distribution; for damsel®shes may kill live coral within their territories, thus, af- example, through habitat selection. fecting the benthic algal and coral communities (Brawley and Adey Habitat selection, the active choice of a living site by 1977; Kaufman 1977; Lobel 1980; Williams 1980; Robertson et al. an individual, may limit the distribution of species yet 1981; Wellington 1982; Hixon and Brosto 1983; Foster 1987; Knowlton et al. 1990). Their territories also serve as shelter, con- allow potentially competing individuals or species to taining holes or crevices where the ®sh hide from predators. These coexist. Habitat selection may occur at settlement or shelters are defended against other diurnal ®shes (Robertson and anytime thereafter. Because recruitment patterns pro- Sheldon 1979). Finally, all damsel®shes lay benthic eggs. Females vide a static snapshot of a perhaps dynamic process, deposit eggs inside the male territory, and males aerate the nest and defend it against piscivores until hatching (Thresher 1984). they can be used to study habitat selection at settlement, Several studies have shown habitat partitioning among dam- provided recruitment is censused frequently. sel®sh species (Itzkowitz 1977; Williams 1978; Waldner and Rob- Many coral reef ®shes disperse only during the ertson 1980; Robertson 1984; Wellington 1992). Six species of the planktonic phase assuming a sedentary, sometimes genus Stegastes occur on Caribbean reefs: S. diencaeus, S. dorso- territorial existence soon after settlement. Numerous punicans, S. leucostictus, S. partitus, S. planifrons, and S. variabilis. The two species chosen for this study (three-spot damsel®sh, studies on coral reef ®sh have revealed the importance of S. planifrons, and dusky damsel®sh, S. dorsopunicans) are common habitat characteristics to ®sh survivorship and growth, throughout the Caribbean and easily distinguishable on the basis of for example, dierent reefs (Aldenhoven 1986), depths their coloration both as juveniles and adults. The depth range of (Jones 1986; Shapiro 1987; Wellington 1992), densities S. planifrons is broader including both shallow and deep reefs, and S. dorsopunicans inhabits shallow reefs (0.5±5 m). Even on shallow (Jones 1987; Forrester 1995; Hixon and Beets 1993) and reefs, however, these two species show little overlap in their substrata (Jones 1988; Booth 1992; Wellington 1992). distribution (Waldner and Robertson 1980; Robertson 1984). The These results indicate that there should be strong selec- extent of the overlap seems to be related to the steepness of the tive pressure for ®sh to choose the proper habitat at, or transition between the reef crest and the reef slope (personal ob- servation). Thus, these two damsel®shes provide an ideal system to soon after, settlement. In fact, many studies have shown examine the recruitment and post-recruitment processes establish- habitat selection in reef ®shes (Shulman et al. 1983; ing local adult distributions. Sweatman 1983; Holbrook and Schmitt 1988; Carr 1991; Levin 1991; Booth 1992; Wellington 1992; Danilowicz 1996). Some ®sh species have been shown to cue on Study site habitat complexity (Carr 1991; Levin 1991), as well as on abundance of predators (Shulman et al. 1983), conspe- The study was carried out at the Smithsonian Tropical Research ci®cs and congeners (Sweatman 1985, 1988; Booth Institute ®eld station in the San Blas Comarca, Panama. Shallow reefs in this area are dominated by Millepora complanata on the 1992), or speci®c substrata (Sale 1971; Marliave 1977; crest and Agaricia spp. on the slope, with Porites porites, P. furcata, Danilowicz 1996). Few studies, however, have attempted P. astreoides and Montastraea spp. also being common. to relate habitat selection to community structure The study area was composed of four shallow (0.5±5 m) patch (Wellington 1992). Habitat selection at, or soon after, reefs at Punta de San Blas (Fig. 1) diering in coral cover, wave action, etc. These reefs are separated from each other by 100±400 m settlement may determine local adult patterns of dis- of sand which minimizes the possibility of ®sh migration between tribution. Wellington (1992) showed that Stegastes reefs. Thus, individual reefs were considered independent repli- leucostictus and S. variabilis settlement was con®ned to cates. Stegastes planifrons and S. dorsopunicans are the most conspeci®c adult habitats. common