Lindeman and Snyder Nearshore hardbottom fishes of soutfieast Florida 



519 



(0 



regation among life stages of many grunt 

 and snapper species from other regions as 

 well; early demersal stages appear to most 

 commonly use shallow habitats (Starck, 

 1970; Dennis, 1992). Similar ontogenetic 

 differences in distribution and abundance 

 exist for many other taxa that utilize 

 nearshore hardbottom habitats. 



Determining if the availability of habitat 

 structure limits survival of early stages is 

 important in assessing nursery value. Ab- 

 sences of habitat structure can result in 

 increased predation or lowered growth 

 (Hixon, 1991). In southeast mainland 

 Florida, many natural nearshore marine 

 habitats outside of coastal lagoons and be- 

 tween 25°30'N and 26°20'N (Dade and 

 Broward Counties) are sand plains lacking 

 hardbottom and substantial three-dimen- 

 sional structure (ACOE, 1996). Although 

 large stretches of nearshore hardbottom 

 exist between 26°20'N and 27°50'N (Palm 

 Beach, Martin, St. Lucie, and Indian River 

 Counties) these habitats are often separated 

 by kilometers of sand plains. There are no 

 other natural habitats in the same near- 

 shore areas that can support equivalent 

 abundances of early life stages. These con- 

 ditions could promote a demographic bottle- 

 neck that limits local adult populations 

 owing to limited habitat availability for 

 early stages. 



Despite their shallow depth, nearshore 

 hardbottom reefs are positioned within cur- 

 rent and tide regimes that can support con- 

 siderable larval abundances. The occur- 

 rence of presettlement larvae in these ar- 

 eas is reflected by the abundances of newly settled 

 stages in the present study and larvae in nearshore 

 zones of Gulf of Mexico barrier islands (Ruple, 1984; 

 Ross et al., 1987). Newly settled individuals were not 

 recorded during any surveys of pure sand habitats 

 in the present study. However, the presence of 

 nearshore hardbottom promoted substantial coloni- 

 zation of shallow outcrops by larvae of many spe- 

 cies, including haemulids, lutjanids, sparids, labrids, 

 gerreids, sciaenids, and scarids. Ecotones with high 

 vertical relief (e.g. hardbottom-sand interfaces near 

 ledges) sometimes had large aggregations of newly 

 settled stages of these taxa. However, microhabitat- 

 scale distributions of fishes on nearshore hardbottom 

 remain unquantified. 



Use of nearshore hardbottom reefs as nurseries 

 may be bidirectional across the shelf Both inshore 

 and offshore migrations during differing ontogenetic 



I I Coral Cove (control) 



u 



|TT 



A 



i 



! 



Carlin Park (impact) 



AMJ JASONDJ FMAMJ JASONDJ 



I I I I I 

 FMAMJ 



1994 



1995 



1996 



20 -r 



15 - 



10 



5 - 



10 - 



15 

 20 



I 



11 



f! 



I 



h 



Coral Cove 



il 



|i 



I 



! 



I 



A 



SSI 



ts 



Carlin Park 



AMJ JASONDJ FMAMJ 



"T \ ] 1 I ! [ : ' \ ! r" 

 JASONDJ FMAMJ 



Figure 9 



Mean numbers of individuals and species at control and impact sites 

 m Jupiter, FL. Arrows indicate timing of dredge burial of hardbottom 

 reef 



stages can be facilitated by habitats positioned cen- 

 trally on the shelf Nearshore hardbottom may serve 

 a primary nursery role for incoming early life stages 

 that would undergo increased predation mortality 

 without shelter. Nearshore hardbottom may also 

 serve as secondary nursery habitat for juveniles that 

 emigrate out of inlets towards offshore reefs. This 

 pattern is seen in gray snapper and bluestriped grunt 

 which often settle inside inlets and primarily use 

 nearshore hardbottom as older juveniles. In addition, 

 some species use these structures as resident nurs- 

 eries, settling, growing-out, and maturing sexually 

 as permanent residents (e. g. pomacentrids, labri- 

 somids). A secondary nursery role may also result 

 from increased growth because of higher food avail- 

 abilities in structure-rich environments. The inter- 

 mediate cross-shelf positioning and other attributes 

 reviewed above suggest nearshore hardbottom rep- 



