561 



Abstract — Age-based analyses were 

 used to demonstrate consistent dif- 

 ferences in growth between popula- 

 tions of Acanthochromis polyacanthus 

 (Pomacentridae) collected at three dis- 

 tance strata across the continental 

 shelf (inner, mid-, and outer shelf) 

 of the central Great Barrier Reef 

 (three reefs per distance stratum). 

 Fish had significantly greater max- 

 imum lengths with increasing dis- 

 tance from shore, but fish from all 

 distances reached approximately the 

 same maximum age, indicating that 

 growth is more rapid for fish found 

 on outer-shelf reefs. Only one fish col- 

 lected from inner-shelf reefs reached 

 >100 mm SL, whereas 38-67% offish 

 collected from the outer shelf were 

 >100 mm SL. The largest age class of 

 adult-size fish collected from inner- 

 and mid-shelf locations comprised 

 3-4 year-olds, but shifted to 2-year- 

 olds on outer-shelf reefs. Mortality 

 schedules iZ and S) were similar irre- 

 spective of shelf position (inner shelf: 

 0.51 and 60.0%; mid-shelf: 0.48 and 

 61.8%; outer shelf: 0.43 and 65.1%, 

 respectively). Age validation of captive 

 fish indicated that growth increments 

 are deposited annually, between the 

 end of winter and early spring. The 

 observed cross-shelf patterns in adult 

 sizes and growth were unlikely to be 

 a result of genetic differences between 

 sample populations because all fish 

 collected showed the same color 

 pattern. It is likely that cross-shelf 

 variation in quality and quantity of 

 food, as well as in turbidity, are fac- 

 tors that contribute to the observed 

 patterns of growth. Similar patterns 

 of cross-shelf mortality indicate that 

 predation rates varied little across 

 the shelf. Our study cautions against 

 pooling demographic parameters on 

 broad spatial scales without consid- 

 eration of the potential for cross-shelf 

 variability. 



Patterns of growth, mortality, and size 



of the tropical damselfish 



Acanthochromis polyacanthus across 



the continental shelf of the Great Barrier Reef 



Michael J. Kingsford 



Julian M. Hughes 



Reef and Ocean Ecology Laboratory 



School of Marine Biology and Aquaculture 



James Cook University 



James Cook Drive 



Townsville, Queensland, Australia 4811 



E-mail address (for M J Kingstord) Michael Kingsforda<|cii edu au 



Manuscript submitted 10 June 2004 

 to the Scientific Editor's Office. 



Manuscript approved 30 March 2005 

 by the Scientific Editor. 



Fish. Bull. 103:561-573 120051. 



Coral reefs are spatially diverse and 

 heterogeneous marine environments. 

 The Great Barrier Reef (GBR) is the 

 largest reef system and represents a 

 near-continuous matrix of over 2400 

 individual reefs spanning a distance 

 of some 2000 km along the coast of 

 Queensland, eastern Australia (Fig. 

 1). Coral reef habitats are subject to 

 the influences of environmental (e.g., 

 exposure and proximity to coastlines), 

 as well as biotic processes (e.g., avail- 

 ability of food). Strong cross-shelf abi- 

 otic and biotic gradients (Wilkinson 

 and Cheshire, 1988) have the potential 

 to influence patterns of abundance 

 and demographic characteristics of 

 fishes associated with coral reefs. Sev- 

 eral studies have examined the broad- 

 scale abundance and distribution of a 

 wide variety of organisms across the 

 continental shelf of the GBR, includ- 

 ing hard corals (Done, 1982), soft 

 corals (Dinesen, 1983), crustaceans 

 (Preston and Doherty, 1990, 1994), 

 algae (McCook et al., 1997), and reef 

 fishes (Williams, 1982, 1983; Wil- 

 liams and Hatcher, 1983; Russ, 1984a, 

 1984b; Newman and Williams, 1996; 

 Newman et al., 1997; Gust et al., 2001, 

 2002). Great cross-shelf differences in 

 abundance are common within and 

 among taxa. Although environmental 

 gradients have often been implicated 

 as causing these patterns and it is also 

 known that environmental features 



influence demographic characteris- 

 tics (e.g., growth), there have been few 

 comparisons of demographic charac- 

 ters by geography and spatial scale. 



Demographic measures are cru- 

 cial to understanding population 

 dynamics. Population demographics 

 of a number of many fish species have 

 been shown to vary at spatial scales 

 ranging from 100's of m to 100's of km 

 (Gillanders, 1995; Meekan et al., 

 2001; Gust et al., 2002). With the ex- 

 ception of data on a few commercially 

 important taxa (Munro and Williams, 

 1985; Williams et al., 2003) and some 

 others (e.g., acanthurids and scarids; 

 Choat and Axe, 1996), there are few 

 data on demographic parameters of 

 coral reef fishes and even less on 

 spatial variation within these para- 

 meters. Variation in demographics 

 may be common across the shelf. 

 For example, significant differences 

 in the size frequency, growth, mor- 

 tality, and longevity in populations 

 of three scarids (Scarus frenatus, S. 

 niger, and Chlorurus sordidus) and 

 an acanthurid (Acanthurus lineatus) 

 have been shown between mid- and 

 outer-shelf locations on the northern 

 GBR (Gust et al., 2001, 2002). Dud- 

 geon et al. (2000) found evidence that 

 high levels of genetic exchange oc- 

 curred between populations of these 

 fishes on mid- and outer-shelf reefs 

 and concluded that observed differ- 



