98 
Abstract — Measurements of 18 0/ 16 0 
and 13 C/ 12 C ratios in the carbonate 
of juvenile gray snapper (Lutjanus 
griseus ) sagittal otoliths collected 
during 2001-2005 from different 
southern Florida regions indicated 
significant variations in the ratios 
between Florida Bay and surrounding 
areas. Annual differences in isoto- 
pic composition were also observed. 
Classification accuracy of individual 
otoliths to a region averaged 80% 
(63% to 96%), thereby enabling the 
probability of assigning an unknown 
individual to the appropriate juve- 
nile nursery habitat. Identification 
of isotopic signatures in the otoliths 
of gray snapper from Florida Bay and 
adjacent ecosystems may be important 
for distinguishing specific portions 
of the bay that are crucial nursery 
grounds for juveniles. Separation of 
gray snapper between geographic 
regions and nursery sites is possible 
and has the potential to establish 
a link between adult gray snapper 
present on offshore reefs and larvae 
and juveniles at nursery habitats in 
Florida Bay or adjacent areas. 
Manuscript submitted 4 December 2008. 
Manuscript accepted 6 November 2009. 
Fish. Bull. 104:98-105 (2010). 
The views and opinions expressed 
or implied in this article are those 
of the author (or authors) and do not 
necessarily reflect the position of the 
National Marine Fisheries Service, 
NOAA. 
Variation in the isotopic signatures 
of juvenile gray snapper ( Lutjanus griseus ) 
from five southern Florida regions 
Trika Gerard (contact author) 
Barbara Muhling 
Email address for contact author: tnka.gerard@noaa.gov 
National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Southeast Fisheries Science Center 
75 Virginia Beach Dr. 
Miami, Florida 33149 
Identification of nursery habitats is 
important for effective management 
of coral reef fishes. Many reef fish are 
commercially, recreationally, and eco- 
logically important and are believed to 
migrate to reefs from juvenile nursery 
areas such as seagrass and mangrove 
habitats. Little is known about the 
nature of these nursery areas or the 
migration corridors that exist between 
nursery areas and coral reefs. Otolith 
microchemistry is a proven method for 
determining the early stage habitats 
of juvenile fishes, particularly if tag- 
ging studies are not feasible (Gao et 
al., 2004). Trace elements and stable 
isotopes obtained from the otoliths 
of teleost fish have been well docu- 
mented as useful tools for providing a 
wealth of information on environmen- 
tal variations and stock structure of 
fish throughout their life history (Ste- 
phenson et al., 2001). New research 
has shown that the stable isotopic 
composition of otoliths provides a way 
of identifying fish that have inhab- 
ited different water masses, therefore 
serving as a tracer for distinguishing 
various nursery habitats of fish popu- 
lations (Ashford and Jones, 2006). 
The application of the stable isoto- 
pic composition of otoliths as a natu- 
ral chemical tag can help in the eval- 
uation of the significance of estuaries 
as nursery grounds for coral reef fish, 
and determine which habitats, such 
as seagrass beds, mangrove islands, 
and mangrove shorelines, within an 
estuary are most important as nurs- 
ery areas for producing adult coral 
reef fish. Each of these habitats 
supplies juvenile reef fish with nu- 
trition and shelter from predators. 
Gray snapper ( Lutjanus griseus) ju- 
veniles are often present in a variety 
of estuarine ecosystems with soft and 
hard bottom habitats and with a wide 
range of temperatures and salinities 
(Bortone and Williams 1 ). 
Gray snapper are an economically 
important Florida reef fish. They 
make up a large proportion of the 
commercial and recreational fin- 
fish landings for the state and are 
the most popular game fish, with 
the highest recreational landings in 
Florida Bay (Starck and Schroeder, 
1971; Lara et al., 2008). After spawn- 
ing, larvae spend approximately 
20-35 days as pelagic plankton at 
sizes ranging from 10-20 mm stan- 
dard length (SL). They then settle as 
early juveniles in seagrass beds at 
sizes of approximately 40-50 mm SL 
(Richards et al., 2005) and migrate to 
coral reef habitats as adults. 
The goal of this study was to 
analyze and assess the spatial and 
temporal variation of stable isotopic 
carbon and oxygen composition in 
the otoliths of juvenile gray snapper 
from southern Florida. This analysis 
will help determine the importance 
of Florida Bay as a nursery ground 
1 Bortone, S., and J. Williams. 1986. Spe- 
cies profiles: Life histories and environ- 
mental requirements of coastal fishes and 
invertebrates (South Florida) — gray, lane, 
mutton, and yellowtail snappers. U. 
S. Fish and Wildlife Service Biol. Rep. 
82(11.52), 18 p. 
