Abstract. — Transplants of juve- 

 nile queen conch Strombus gigas L. 

 were conducted in the southern Ex- 

 uma Cays, Bahamas, to test the rela- 

 tionship between large-scale pat- 

 terns of distribution and differential 

 habitat quality (as indicated by conch 

 mortality and growth). One-year-old 

 conch (mean shell length 93 mm) 

 were transplanted to two locations 

 within known conch nursery habi- 

 tats, one with low and one with mod- 

 erate seagrass biomass. Transplants 

 were also made to six sites without 

 resident conch: two sites similar to 

 the moderate biomass site, two sites 

 similar to the low biomass site, one 

 site with heavy seagrass, and one on 

 bare sand. 



Mortality was low at stations with 

 natural conch populations and/or 

 moderate seagrass biomass. Mortal- 

 ity was high at all other sites, and in- 

 creased with time at the sand site 

 and at one of the low biomass sites. 

 Growth rate was high and relatively 

 constant through the experiment at 

 the stations with natural conch pop- 

 ulations and at one site with moder- 

 ate seagrass biomass and no resident 

 conch (C2). Rapidly declining growth 

 rates were found at all other sites 

 despite depth, sediment, and macro- 

 phyte characterisitics similar to sites 

 with resident conch. Data on stand- 

 ing crops of macrodetritus at the 

 beginning and end of the experiment 

 indicated food limitation at one site 

 where growth was low. Until the dis- 

 tribution of queen conch is under- 

 stood, small-scale transplanting will 

 provide a useful tool for evaluating 

 distributional mechanisms and a test 

 for habitats proposed for stock 

 enhancement. 



Experimental Analysis of 

 Habitat Quality for Juvenile 

 Queen Conch in Seagrass Meadows 



Allan W. Stoner 

 Veronique J. Sandt 



Caribbean Marine Research Center 



805 46th Place East. Vera Beach, Florida 32963 



Manuscript accepted 31 July 1991. 

 Fishery Bulletin, U.S. 89:693-700 (1991). 



Seagrass meadows are important 

 nursery habitats for many fishes and 

 invertebrates from high to low 

 latitudes (Thayer et al. 1975, Kikuchi 

 and Peres 1977, Weinstein and Heck 

 1979, Stoner 1983, Pollard 1984, 

 Robblee and Zieman 1984, Sogard et 

 al. 1987). The queen conch Strombus 

 gigas L. is a large gastropod mollusc 

 (to > 250 mm shell length) which uses 

 the seagrass habitat as a nursery 

 (Randall 1964, Weil and Laughlin 

 1984, Stoner and Waite 1990). Food 

 value makes the queen conch an im- 

 portant commercial species through- 

 out the Caribbean region (Brownell 

 and Stevely 1981, Berg and Olsen 

 1989). 



Hatchery data suggest that pelagic 

 larvae of the queen conch spend 

 18 to 40 days in the water column 

 (Brownell 1977, Davis et al. 1987, 

 Mianmanus 1988). The larvae settle 

 and metamorphose in the benthos 

 and live for the first several months 

 in places and in ways mostly un- 

 known at this time. Juveniles are 

 usually 35-40 mm shell length when 

 first observed on sandy shoals and in 

 shallow seagrass meadows (Stoner 

 and Sandt, unpubl. data). Primary 

 foods for juvenile stages are seagrass 

 detritus and algae (Stoner 1989a, 

 Stoner and Waite 1991). In seagrass 

 beds of the Bahama, Turks, and 

 Caicos Is., Virgin Is., Cuba, and 

 Venezuela, juvenile queen conch den- 

 sities of 1 to 2 animals/m 2 are com- 

 mon (Alcolado 1976, Hesse 1979, 

 Weil and Laughlin 1984, Iversen et 



al. 1987, Stoner 1989a). Recent in- 

 vestigations in the Bahamas show 

 that highest densities of juvenile 

 queen conch are associated with sea- 

 grass beds of intermediate shoot den- 

 sity (Stoner and Waite 1990). Older 

 juveniles move to deeper water (Weil 

 and Laughlin 1984), and sexual 

 maturity is attained at approximate- 

 ly 3.5 to 4.0 years (Randall 1964, Ap- 

 peldoorn 1988). 



Large seagrass habitats (hundreds 

 of hectares) are found near Lee 

 Stocking I., in the Exuma Cays, 

 Bahamas. Much of this habitat ap- 

 pears to be appropriate for juvenile 

 queen conch (depth, sediments, 

 macrophyte cover); however, conch 

 are associated with certain geo- 

 graphic areas within the seagrass 

 meadows. Five discrete juvenile 

 populations have been observed in 

 particular localities near Lee Stock- 

 ing I. from 1984 to the present (Wick- 

 lund et al. 1988, Stoner, unpubl. 

 data). 



Reported here are the results of ex- 

 perimental transplants designed to 

 examine qualities of seagrass mea- 

 dows which provide optimal habitat 

 for juvenile queen conch. The follow- 

 ing two hypotheses were tested using 

 conch survivorship and growth as in- 

 dicators of habitat quality: (1) habi- 

 tat quality is directly related to 

 seagrass biomass; and (2) Habitats 

 with similar depth, sediments, and 

 macrophyte biomass have equivalent 

 qualities as nurseries for juvenile 

 conch. 



693 



