885 
Settlement and recruitment of queen 
conch, Strombus gigas, in seagrass 
meadows: associations with habitat 
and micropredators 
Allan W, Stoner 
Melody Ray-Culp 
Sheila M. O'Connell 
Caribbean Marine Research Center 
805 E. 46th Place 
Veto Beach, Florida 32963 
Present address (for A. W. Stoner) Northeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
74 Magruder Road, Highlands, New Jersey 07732 
E-mail address (for A. W. Stoner): al.stoner@noaa.gov 
Abstract.-A suction dredge survey 
was conducted in the Bahamas in a 
tidal flow field system which contained 
a nursery ground for the economically 
significant gastropod Strombus gigas 
(queen conch). Settlement of larval 
conch within the system was associated 
with the specific location of the nurs- 
ery and positively correlated with sub- 
sequent recruitment to the juvenile 
population ( <45 mm shell length). 
Settlement was relatively independent 
of habitat features including depth, 
sediment characteristics, and macro- 
phytes. Conversely, densities of micro- 
predators (small crabs, shrimp, and 
predaceous gastropods) capable of con- 
suming early postsettlement conch 
were often correlated with habitat fea- 
tures such as seagrass shoot density, 
seagrass detritus, and organic content 
of the sediment. The density of small 
xanthid crabs (mode=1.5 mm carapace 
width) was positively correlated with 
density of live postsettlement conch 
(mean <4/m 2 ), suggesting that conch 
settle in predator-prone areas or that 
the crabs respond numerically to small 
conch (or both). Densities of xanthids 
were very high (to >200/m 2 ), and the 
crabs probably represent an important 
source of mortality for small conch in 
the primary nursery ground. Shells of 
dead conch indicated that molluscan 
and asteroid predators probably caused 
most of the predatory mortality on 
young conch that settled outside the 
nursery. Because critical settlement and 
recruitment habitats for queen conch are 
associated with particular hydrographic 
conditions, these habitats cannot be iden- 
tified or predicted simply by mapping 
obvious features such as seagrass cover, 
depth, or sediment type. An understand- 
ing of dynamic processes, such as larval 
transport and retention, selective settle- 
ment mechanisms, and trophic ecology, 
will be required to identify critical nurs- 
ery habitats. 
Manuscript accepted 13 January 1998. 
Fish. Bull. 96: 885-899 < 1998). 
Distribution of marine species with 
planktonic larvae is a function of 
both pre- and postsettlement pro- 
cesses. Location of reproductive 
sources, physical and oceanographic 
processes, duration and survivor- 
ship of larval stages, and larval be- 
havior combine to determine settle- 
ment location, whereas predation, 
suitable habitat, and the behavior 
of early juveniles affect the number 
of individuals that survive to repre- 
sent juvenile recruitment (Keough 
and Downes, 1982; Luckenbach, 
1984; Connell, 1985). Experiments 
conducted in the laboratory with a 
large variety of species have shown 
that settlement in the field is prob- 
ably a nonrandom process for the 
majority of marine invertebrates, 
and settlement behavior is usually 
assumed to place juveniles in habi- 
tats most suitable for growth or sur- 
vival (or both) (Hadfield and Scheuer, 
1985; Butman and Grassle, 1992; 
Grassle et al., 1992; Davis and 
Stoner, 1994; Stoner et al., 1996a). 
Despite an abundance of data and 
experiments on settlement, rela- 
tively little is known about the rela- 
tive importance of settlement rate 
and postsettlement predation in 
controlling local recruitment of 
most species to juvenile stages 
(Osman and Whitlatch, 1995). Be- 
cause early postsettlement juve- 
niles of many benthic species, espe- 
cially those associated with soft sedi- 
ments, are difficult to survey, quan- 
titative data related to recruitment 
often depend upon observations of the 
smallest juveniles that can be de- 
tected easily. The result is a relatively 
poor understanding of the crucial 
period between settlement and first 
detection in the benthos ( Keough and 
Downes, 1982; Luckenbach, 1984). 
Queen conch ( Strombus gigas) is 
a large gastropod that has great 
economic significance throughout 
the Caribbean and adjacent regions 
(Appeldoorn, 1994). Despite the 
wealth of information now available 
for conch larvae (Davis, 1994; 
Stoner and Davis, 1997), juveniles 
in year class 1 (e.g. Marshall, 1992; 
Iversen et al., 1987; Appeldoorn, 
1994), and adults (Appeldoorn, 
1988; Stoner and Sandt, 1992), little 
is known about larval settlement 
and the early postsettlement stage. 
Newly settled queen conch ( <10 mm ) 
are cryptic, often buried (Iversen et 
al., 1989; Sandt and Stoner, 1993), 
and are readily preyed upon by 
micropredators such as xanthid 
