366 



Abstract— We examined the diets and 

 habitat shift of juvenile red snapper 

 (Lutjanus campechanus) in the north- 

 east Gulf of Mexico. Fish were col- 

 lected from open sand-mud habitat 

 (little to no relief), and artificial reef 

 habitat (1-m 3 concrete or PVC blocks), 

 from June 1993 through December 

 1994. In 1994, fish settled over open 

 habitat from June to September, as 

 shown by trawl collections, then began 

 shifting to reef habitat — a shift that 

 was almost completed by December as 

 observed by SCUBA visual surveys. 

 Stomachs were examined from 1639 

 red snapper that ranged in size from 

 18.0 to 280.0 mm SL. Of these, 850 

 fish had empty stomachs, and 346 fish 

 from open habitat and 443 fish from 

 reef habitat contained prey. Prey were 

 identified to the lowest possible taxon 

 and quantified by volumetric measure- 

 ment. Specific volume of particular 

 prey taxa were calculated by dividing 

 prey volume by individual fish weight. 

 Red snapper shifted diets with increas- 

 ing size. Small red snapper (<60 mm 

 SL) fed mostly on chaetognaths. cope- 

 pods, shrimp, and squid. Large red 

 snapper (60-280 mm SL) shifted feed- 

 ing to fish prey, greater amounts of 

 squid and crabs, and continued feeding 

 on shrimp. We compared red snapper 

 diets for overlapping size classes (70- 

 160 mm SL) offish that were collected 

 from both habitats (Bray-Curtis dis- 

 similarity index and multidimensional 

 scaling analysis). Red snapper diets 

 separated by habitat type rather than 

 fish size for the size ranges that over- 

 lapped habitats. These diet shifts were 

 attributed to feeding more on reef prey 

 than on open-water prey. Thus, the 

 shift in habitat shown by juvenile red 

 snapper was reflected in their diet and 

 suggested differential habitat values 

 based not just on predation refuge but 

 food resources as well. 



Diet shifts of juvenile red snapper 



(Lutjanus campechanus) 



with changes in habitat and fish size 



Stephen T. Szedimayer 



Marine Fish Laboratory 



Department of Fisheries 



Auburn University 



8300 State Highway 104 



Fairhope, Alabama 36532 



E-mail address: sszedlmas'acesag auburn.edu 



Jason D. Lee 



Barry Vittor & Associates 

 8060 Cottage Hill Rd. 

 Mobile, Alabama 36695 



Manuscript approved lor publication 

 4 November 2003 by Scientific Editor. 



Manuscript received 20 January 2004 

 ..1 NMFS Scientific Publications Office. 



Fish. Bull. 102:366-375 (200 1 1 



Larval red snapper (Lutjanus cam- 

 pechanus) spend approximately 26 days 

 in the plankton, prior to metamorpho- 

 sis and first appearance on benthic 

 substrate. For the most part the fish 

 settle on open substrate, where peaks 

 in recruitment are observed in August 

 and September, after which they may 

 move to more structured habitat some- 

 time within the first year ( Szedimayer 

 and Conti, 1999). The apparent advan- 

 tage of this habitat shift would be 

 increased food resources and protec- 

 tion from predators. To help clarify the 

 value of increased food resources on 

 reef habitats, comparisons of diets from 

 the two habitats are necessary. Also, 

 because many fish species shift diets 

 with increasing size (Sedberry and 

 Cuellar, 1993; Burke, 1995; Rooker, 

 1995; Lowe et al., 1996), we need to 

 distinguish possible ontogenetic diet 

 differences from shifts that are due to 

 habitat. 



Previous red snapper diet studies 

 have focused on larger individuals and 

 on small sample sizes for fish <250 mm 

 SL (Camber, 1955; Moseley, 1966; 

 Bradley and Bryan, 1975). Camber 

 (1955) described the diets of 15 "small 

 red snapper" from Campeche Banks, 

 and reported that 14 of the 15 stom- 

 achs contained small penaeid shrimps. 

 Moseley ( 1966) described the diets of 45 

 "juvenile red snapper" collected off the 

 coasts of Texas, and 28 off Louisiana. 

 Louisiana fish fed on fishes, shrimps. 



detritus, and stomatopods, and Texas 

 fish fed on shrimps, crabs, and mysid 

 shrimps. 



Perhaps the most comprehensive red 

 snapper diet study to date has been 

 that of Bradley and Bryan ( 1975) which 

 described the diets, by season, of trawl- 

 collected (open sand-mud habitat) and 

 hook-and-line reef "rough bottom ar- 

 eas" fish off the Texas coast. They de- 

 scribed the diets of 258 open-habitat 

 and 190 reef red snapper and found 

 that juvenile red snapper (25-325 mm 

 FL) were dependent on shrimp, crabs, 

 and other crustaceans and that adults 

 (325-845 mm FL) were dependent on 

 fish, crabs, and other crustaceans. 

 They described a change in juvenile 

 red snapper diet as fish size increased, 

 "young red snapper depend almost 

 exclusively upon invertebrates," and 

 showed a gradual increase in verte- 

 brate prey with growth. However, they 

 did not separate out the proportions of 

 their "juvenile" red snapper that were 

 collected from reef versus open habi- 

 tat. Thus, the shift from open to reef 

 habitat is still poorly understood. If and 

 when this shift occurs and whether this 

 shift is accompanied with a diet shift 

 that is independent of fish-size effects 

 needs to be defined. 



The purpose of the present study- 

 is to describe the diet of red snapper 

 off the coast of Alabama — from the 

 juvenile stage (just after settlement I to 

 one-year old fish. We examined overall 



