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Fishery Bulletin 96(4), 1 998 
simply by fine-scale hydrodynamic relationships as- 
sociated with seagrasses and macroalgae, as observed 
for certain other invertebrates including mollusks 
(Eckman, 1987; Harvey et al., 1993, 1995). In fact, 
conch larvae settled in approximately equal densi- 
ties across the seagrass gradient at transect D which 
spanned only 250 m. Therefore, the structure pro- 
vided by macrophytes appears not to influence settle- 
ment of conch larvae even though older juveniles 
prefer seagrass habitats and are associated with an 
optimal shoot density (Stoner and Waite, 1990). 
Although accumulation of competent larvae near 
the Shark Rock nursery is the most parsimonious 
explanation for the observed settlement and recruit- 
ment patterns, earlier experiments indicate that 
seemingly similar seagrass beds offer different quali- 
ties that have significant effects on larval and juve- 
nile conch. Laboratory experiments have shown that 
macrophytes collected from stations within the Shark 
Rock nursery (B, C3, D3, D4) induced significantly 
higher metamorphosis than the same types of sub- 
strata collected outside the general nursery area (sta- 
tions A, F) (Davis and Stoner, 1994). Growth rates of 
newly settled conch (1.2 mm) fed seagrass detritus 
from the different sources reflected metamorphic 
responses on the same substrata (Stoner et al., 
1996a), and when 1 -yr-old juvenile conch were trans- 
planted to stations A and F, growth rates were low in 
comparison with those in the Shark Rock nursery 
(Stoner et al., 1994). It is clear, therefore, that the 
nursery area is trophically unique, despite visual 
similiarity to surrounding areas. 
Micro-organism films that coat the sediment in 
soft-bottom communities are known to be important 
inducers of metamorphosis in conch and other in- 
vertebrates, most likely because they are associated 
with favorable nutritional requirements for postlar- 
vae (Scheltema, 1961; Gray, 1974; Davis and Stoner, 
1994; Stoner et al., 1996a). Characteristics that make 
the Shark Rock nursery an attractive location for 
settling larvae and an ecologically suitable habitat 
for juveniles probably stem from hydrodynamic prop- 
erties of the location that affect nutrient cycling and 
productivity patterns in certain algal foods for conch 
(Stoner et al., 1994, 1996b). Field manipulations will 
be needed to distinguish direct effects of hydrody- 
namics (i.e. larval transport and retention) from in- 
direct effects such as hydrographic mediation of bio- 
logical productivity, habitat choices, and postsettle- 
ment processes. 
Postlarval conch recruited to the same habitats 
traditionally occupied by 1- and 2-yr-old animals. 
This association is probably not the result of conspe- 
cific attraction because settlement was equally high 
at stations with and without older conspecifics. This 
result corroborates an earlier laboratory study show- 
ing that cues associated with previously settled ju- 
veniles (slime trails, feces, and the older conch them- 
selves) did not elicit larval metamorphosis (Davis and 
Stoner, 1994). 
The role of micropredators 
on conch recruitment 
Although settlement of queen conch was relatively 
independent of habitat features other than location, 
predator distributions were highly correlated with 
seagrass shoot density, detrital abundance, and sedi- 
ment organics and grain size. Numerous studies have 
shown that animal abundances in seagrass beds are 
correlated with certain measures of habitat complex- 
ity such as seagrass blade density or biomass, detri- 
tal biomass, leaf characteristics, or rhizome struc- 
ture (Orth et al., 1984; Stoner and Lewis, 1985). The 
association between benthic macrofauna and physi- 
cal structure may be related to food abundance or 
predation, or both. There is abundant experimental 
evidence that the physical structure provided in 
seagrass beds reduces predation rates on inverte- 
brates (Heck and Wilson, 1987; Heck and Crowder, 
1991). Potential conch predators dredged in this 
study were prey species themselves, and they un- 
doubtedly derived some measure of protection or 
nutrition from the habitat, or both. 
Predation on early postsettlement stages can be 
an important process affecting the number of inver- 
tebrate settlers that survive to recruit into a popula- 
tion (Thorson, 1966; Keough and Downes, 1982; 
Osman and Whitlach, 1995). Heavy losses to 
micropredators during the first days or weeks after 
settlement can severely diminish or eliminate a prey 
species, and even regulate community composition 
(Osman et al., 1992; Osman and Whitlatch, 1995). It 
is apparent from the length frequency of dead conch 
collected in this study that very high mortality oc- 
curs immediately after settlement, when conch are 
<5-mm shell length. Queen conch have many preda- 
tors at this size (Ray-Culp et al., 1997), and one of 
the most important is probably the xanthid crab 
Micropanope sp., which was the most abundant in- 
vertebrate counted in dredge samples. The crab is 
capable of killing conch that are up to 0.5 times its 
own carapace width ( Ray-Culp et al. 2 ). Although a 
large proportion of the xanthids collected were too 
small (mode=1.5 mm) to kill even newly settled conch 
2 Ray-Culp, M., M. Davis, and A. W. Stoner. 1998. Escaping 
the xanthid crab gauntlet — the role of size, density and habitat 
for newly-settled queen conch. Caribbean Marine Research Cen- 
ter, 805 E. 46th Place, Vero Beach, FL 32963. Unpubl. manuscr. 
