Use of Geochemical Tracers to Elucidate Life History Trajectories of Gray Snapper within South Florida's Marine Ecosystems
David L. Jones
Univ. of Miami-RSMAS, Miami, FL
Monica R. Lara
Univ. of Miami-RSMAS-CIMAS, Miami, FL
John T. Lamkin
NOAA-NMFS-SEFSC, Miami, FL
The snappers inhabiting South Florida's marine ecosystems are a commercially, recreationally, and ecologically important group of higher trophic level carnivores. The larvae of a number of species are believed to settle in seagrass and mangrove habitats of Florida Bay where they spend their juvenile phase before migrating to the reef tract as young adults. Trace elements incorporated into the otoliths of fish during growth vary in composition and proportion depending on the environmental conditions fish were previously exposed to. Technological developments have recently become available to detect the microchemical constituents of fish otoliths and determine trace elemental signatures. These signatures can differ among stocks exposed to different water masses and environmental conditions allowing them to serve as natural tags for tracking fishes.
The elemental composition of otoliths extracted from juvenile gray snapper (Lutjanus griseus) collected in and around Florida Bay were examined using solution based Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in order to determine the existence of a unique "Florida Bay Signature". Juvenile Gray snapper were obtained from waters in and around Florida Bay using a variety of collection gears from Jan-2001 to Aug-2002. Specimens were kept frozen until dissection of otoliths was performed. All dissection, cleaning, and drying of otoliths was performed under Class-100 clean room conditions using acid washed glass instruments and polyethylene storage capsules. Samples were transported to the Laboratory for Isotope and Trace Element Research (LITER) at Old Dominion University where they were decontaminated, weighted, and dissolved in acid. Samples were processed using a double focusing sector field Finnigan MAT Element-2 ICP-MS using internal and external standardization and method blanks.
The selection of elements to use as natural tags was based on their known occurrence in seawater and usefulness for stock discrimination in previous work. A suite of Rare Earth elements was included in the analysis since they lack biological activity and should more readily reflect environmental conditions in otolith chemistry. Additionally, Rare Earths are indicative of freshwater (riverine) input and anthropogenic effects. A total of 32 elements were targeted for analysis: Li, Na, Rb, Mg, Sr, Ba, Sc, Y, Lu, Cr, Mn, Fe, Cu, Zn, Cd, Hg, Pb, and P; a suite of rare earth elements (La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb) and the actinoids Th and U.
Nonparametric (permutation-based) forms of MANOVA and Canonical Discriminant Analysis were used in the analysis of otolith trace elemental data in order to test for differences in elemental signatures within and among collection sites and across habitat types. Our results indicates a tentative "Florida Bay signature" can be defined by this technique, based primarily on the Rare Earth components of the elemental suite examined. This "Bay signature" allows high resolution spatial separation of collection sites, on the order of 10 km, with additional, significant variation attributed to habitat type.
Our ultimate goal is to employ multivariate pattern matching techniques comparing the juvenile portion of adult otoliths from the reef tract to our "Bay signature" in order to assess the proportion of adults on the Reef that used the Bay as a nursery habitat. The ability to reconstruct the environmental history of individual fish is a significant advancement in our ability to describe life histories and habitat requirements. These results are believed to offer new tools to fisheries managers and may have important implications regarding connectivity, establishment of marine protected areas, and designation of essential fish habitat.
David, Jones, University of Miami-RSMAS, 4600 Rickenbacker CWSY, Miami, FL, 33149, Phone: 305-361-4246, Fax: 305-361-4478, , Question 5