Abstract. — a study was con- 

 ducted on shallow banks near Lee 

 Stocking Island, Bahamas, to deter- 

 mine habitat associations of queen 

 conch Stromhus gigas L. within sea- 

 grass meadows of Thalaiisia testudi- 

 num. Transect data showed that 

 conch density and biomass increased 

 directly with increasing macrophyte 

 cover up to an optimal level of 

 moderate-density seagrass (608-864 

 shoots/m^), after which conch den- 

 sity decreased sharply. Up to the op- 

 timal level, conch density and bio- 

 mass were closely correlated with 

 seagrass and detritus biomass, shoot 

 density, and depth. Seagrass shoot 

 density was the best predictor of 

 conch abundance. Results of habitat 

 choice experiments showed that two 

 different juvenile size classes (75-100 

 mm and 12.5-150 mm shell length) 

 are proficient in detecting and choos- 

 ing habitats with moderate seagrass 

 density over bare sand, low or high 

 seagrass density. Larger conch ap- 

 pear to prefer habitat with higher 

 shoot density than conch of smaller 

 size classes; adult conch were less 

 specialized in their habitat associa- 

 tion. These results provide data on 

 one of the key environmental vari- 

 ables, seagrass structure, which will 

 be useful in predicting conch distri- 

 butions in the field and for planning 

 conch outplanting. 



Distribution and Behavior of 

 Queen Concli Strombus gigas 

 Relative to Seagrass Standing Crop 



Allan W. Stoner 

 Janice M. Waite 



Caribbean Manne Research Center, 100 E 1 7th Street 

 Riviera Beach, Florida 33404 



and 

 Lee Stocking Island, Exuma Cays, Bahamas 



Manuscript accepted 14 May 1990, 

 Fishery Bulletin, U.S. 88:.573-58.5. 



Seagrass meadows, common in pro- 

 tected shallow waters, are known to 

 be important sources of food and 

 shelter for numerous fishes and in- 

 vertebrates from high to low lati- 

 tudes (Kikuchi 1980, Ogden 1980, 

 Virnstein et al. 1984). Living sea- 

 grasses are consumed by a few 

 animals such as surgeonfishes, 

 halfbeaks, parrotfishes (Randall 

 1964, Ogden 1980), urchins (Law- 

 rence 1975), green sea turtles (Ogden 

 1980), and sirenia (Bertram and Ber- 

 tram 1968); however, most nonpre- 

 daceous fauna of seagrass meadows 

 consume seagrass epiphytes or 

 detritus (Zimmerman et al. 1979, 

 Leber 1983, Fry 1984, Howard 1984, 

 Kitting et al. 1984, Van Montfrans et 

 al. 1984). Sheltering from predation 

 has been shown experimentally for 

 many seagrass inhabitants, par- 

 ticularly crustaceans (Nelson 1979, 

 1981; Heck and Thoman 1981; Coen 

 et al. 1981; Stoner 1982; Leber 1985; 

 Wilson et al. 1987). 



The queen conch Strombus gigas L. 

 is a large gastropod mollusc which 

 derives both food and shelter from 

 seagrass beds of the Caribbean 

 region (Bermuda and southeastern 

 Florida to Brazil). After the first year 

 of life, of which little is known, queen 

 conch juveniles emerge from the sedi- 

 ment and feed epibenthically in sea- 

 grass meadows where there are large 

 quantities of algal and detrital foods 

 (Randall 1964). Juvenile queen conch 

 are important grazers of seagrass 



detritus, and conch densities may be 

 limited by food abundance (Stoner 

 1989). Recent experiments conducted 

 in the Bahamas have shown that 

 seagrasses reduce predation rates on 

 juvenile conch in nursery areas (Mar- 

 shall and Lipcius, In review). 



Throughout its geographic range, 

 the queen conch is an important 

 commercial species which has been 

 severely depleted in many areas 

 (Adams 1970, Brownell et al. 1977). 

 For this reason, there is increas- 

 ing interest in improving the man- 

 agement of conch, and seeding of 

 depleted areas with hatchery- 

 reared juveniles has been proposed 

 (Berg 1976, Brownell and Stevely 

 1981, Laughlin and Weil 1983, 

 Coulston etal. 1987). Successful 

 management of the fishery and/ 

 or outplanted populations will re- 

 quire detailed information on the 

 relationships between queen conch 

 and environmental variables. This 

 study was conducted to examine the 

 role of macrophyte cover in the 

 distribution of juvenile conch in 

 two nursery areas of the Exuma 

 Cays, Bahamas. In addition to sea- 

 grass shoot density and biomass, 

 abundance of detritus, sediment 

 characteristics, and depth were con- 

 sidered for their potential influence 

 on the density, distribution, and 

 biomass of conch. Field experiments 

 were conducted to determine the role 

 of habitat selection in natural conch 

 distributions. 



573 



