Stoner et a I.: Recruitment of Strombus gigas 
897 
( 1.2 mm), xanthids up to 10 mm were far more abun- 
dant than conch, and they undoubtedly play a major 
role in conch mortality. The high positive correlation 
between live conch and xanthids suggests that conch 
settle in areas prone to high predator abundance. 
However, with typical summer growth rates, men- 
tioned earlier, conch would escape predation by 
xanthids in about 10 days when they reach 5 mm 
shell length. Consequently, predator-prey relation- 
ships associated with the early postsettlement stages 
may be highly dynamic, with suites of predators shift- 
ing rapidly over time. 
There was an increase in conch survivorship from 
bare sand to moderate density seagrass over both 
cross-channel transects. A similar trend was obtained 
experimentally when year-class 0 and 1 juveniles 
were tethered over an analogous seagrass gradient 
near transect D (Ray and Stoner, 1994, 1995). High- 
est mortality occurred on bare sand and in highest 
seagrass biomass whereas lowest mortality occurred 
in moderate biomass. It appears that a certain 
amount of seagrass structure provides protection, but 
too much is detrimental. However, in the down flow 
field dimension, survivorship was highest within the 
traditional nursery ground, and distribution is clearly 
related to both settlement and survivorship in this 
dimension. 
Identifying critical habitats 
Our findings have important management implica- 
tions for queen conch and other species associated 
with seagrass beds. First, it may not be possible to 
determine the value of a particular site for a species 
on the basis of simple habitat maps. Even descrip- 
tions of the beds that include seagrass species com- 
position, biomass, and shoot density do not provide 
adequate information to identify critical habitats for 
conch. Value of specific seagrass bed locations also 
depends upon hydrography, larval retention, larval 
settlement, predator abundance, and the related 
survivorship. Persistence in the locations of queen 
conch nurseries near Lee Stocking Island (Stoner et 
ah, 1996b; Jones, 1996) indicates that these factors 
are relatively constant over periods of several years, 
and that the specific locations may be as “critical” as 
habitat type. Only certain seagrass beds are suitable 
for queen conch; these must be identified and pro- 
tected. Furthermore, in many areas of the Caribbean, 
conch populations have been devastated by overfish- 
ing, and there is an intense interest in rehabilitat- 
ing them through releases of hatchery-reared juve- 
niles. Transplant experiments have shown that ju- 
venile conch will survive and grow only in very spe- 
cific locations, and releases must be made in loca- 
tions that ensure economically acceptable survivor- 
ship (Stoner, 1994). Clearly, thorough knowledge of 
distributional mechanisms is necessary to make pre- 
dictions on the habitat requirements of queen conch 
and other managed species. 
Acknowledgments 
This research was supported by a grant from the 
National Undersea Research Program of NOAA (U.S. 
Department of Commerce). We thank C. Bolton, D. 
Carlin, L. Cowell, M. Davis, C. Kelso, J. Lally, and P. 
Monaghan for assistance in the field, laboratory sort- 
ing, and sediment analysis. B. Bower-Dennis drafted 
Figure 1. J. Lin and anonymous reviewers helped to 
improve the manuscript. 
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