LARVAL TRANSPORT AND RECRUITMENT
Recruitment pathways in the Florida Keys:
We have been actively investigating the physical processes contributing to the recruitment of fishes to the Florida Keys. Although the Florida Keys is the only coral reef system in the contiguous U.S., relatively little is known about how populations of reef organisms are replenished and sustained over time. We have conducted several time series collections of larval arrival along the Florida Keys which have shown that (1) near-reef larval fish assemblages differ markedly from offshore assemblages and their abundance is strongly event-related (Sponaugle et al. 2003), (2) very large multi-taxa pulses of settlement stage fish occur in association with the nearshore passage of mesoscale Florida Current eddies, and (3) such mesoscale eddies can also flush larvae out of the system (Sponaugle et al. 2005a, D'Alessandro et al. 2007).
Reef fish recruitment to the Florida Keys:
Without fundamental data on patterns of recruitment, it is difficult to examine the underlying processes creating such pattern. My lab began a year-round monthly reef fish recruitment survey in 2003, which now forms a 7 yr + baseline time series on recruitment magnitude and timing. Monthly underwater SCUBA-based surveys are conducted across the upper Florida Keys shelf encompassing replicate fringing reef, patch reef, seagrass, and mangrove sites. Students have incorporated portions of the recruitment dynamics of particular species into their research (Paddack & Sponaugle 2008, Rankin 2010), including comparison of larval supply and recruitment among protected (reserve) and non-protected sites in the Florida Keys National Marine Sanctuary (Grorud-Colvert & Sponaugle 2009). We are in the process of using our 7-yr time series of recruitment to examine taxon-specific differences in recruitment to marine reserves and non-reserves.
POPULATION CONNECTIVITY
Larval linkages: an interdisciplinary approach
The degree to which populations of marine organisms are connected via the dispersal of larval propagules is a central unanswered ecological and oceanographic question. The complex oceanography of marine systems, and high mortality and diffuse concentrations of larvae make direct measurement of larval sources generally not feasible, particularly for marine populations distributed along open coastlines. Furthermore, ecological population connectivity is not only a function of the physical transport of the larvae, but also the interaction of factors influencing larval growth, survival, and condition at settlement (Pineda et al. 2007; Cowen & Sponaugle 2009). A major ongoing effort in my lab is our research into connectivity of reef fishes in the Florida Keys. This collaborative, interdisciplinary National Science Foundation -sponsored project designed to integrate intensive field sampling with biophysical modeling to begin to define dispersal kernels for reef fish populations in oceanographically dynamic regions. High-resolution shipboard ichthyoplankton and physical oceanographic sampling along and upstream of the Florida Keys are linked to simultaneous reef-based sampling of larval supply and juvenile recruitment. Fishes are “tracked” across this transitional period by analysis of their otolith growth trajectories. We are testing whether larval growth varies with distance to shore and water mass (specifically, larval encounter with mesoscale eddies). These empirical data are being incorporated into a coupled biophysical model (a comprehensive three-dimensional hydrodynamic model [see http://coastalmodeling.rsmas.miami.edu/ ] coupled with a Lagrangian particle tracking model [see http://www.rsmas.miami.edu/personal/cparis/ ], which will be run iteratively to quantify the relative contribution of local (near-field) and upstream (far-field) larval sources. Co-PIs on this project are Robert Cowen (MBF/RSMAS), Claire Paris (AMP/RSMAS), and Villy Kourafalou (MPO/RSMAS). Field, laboratory, and shipboard efforts are coordinated by Senior Research Associates Kristen Delano Walter and Cedric Guigand. Morgan Witman, a high school science teacher, was selected by the National Science Foundation ARMADA program to participate in our second cruise in 2007. Her experience is fully documented in her online journal at http://www.armadaproject.org/journals/2007-2008/hardwick-witman/7-29-30.htm
Other fish movement studies:
A collaborative Sea Grant funded project with Jiangang Luo (RSMAS) and Joe Serafy (NOAA/NMFS Miami Lab) focused on the older stages of gray snapper ( Lutjanus griseus ) and involved tracking the diel and seasonal movement of gray snapper among nearshore habitats of the Florida Keys. We used conventional, acoustic, and archival tagging techniques as well as video observations to directly track snapper within and among mangroves, seagrasses, and coral reefs near Biscayne Bay (Luo et al. 2009 ).
GROWTH AND SURVIVORSHIP OF EARLY STAGES
Reef fishes:
Successful settlement of reef fishes is more than successful larval transport between spawning sites and juvenile habitat. My lab is actively involved in quantifying aspects of larval growth and survivorship for several model reef fishes. The analysis of fish otoliths is a central tool in this research as a method for comparing relative growth rates and condition among individuals (Sponaugle 2009, 2010). Building upon previous work on the relationship between variation in early life history traits and survival of fishes in Barbados (Searcy & Sponaugle 2000, 2001), and the effect of distinct physical oceanographic features on larval growth and transport (Sponaugle & Pinkard 2004a,b), we have been investigating natural variability in early life history traits and the consequences of that variability to recruitment (Sponaugle et al. 2006), early juvenile growth, and survival of a common reef fish, Thalassoma bifasciatum, in the Florida Keys (Sponaugle et al. 2006, Sponaugle & Grorud-Colvert 2006, Grorud-Colvert & Sponaugle 2010). Experimental studies have been used to further tease apart critical ecological processes occurring during the transition between the larval and juvenile stages (Grorud-Colvert & Sponaugle 2006). Tauna Rankin recently used a long-term recruitment record, light trap collections, field manipulations, and otolith and molecular analyses to examine aspects of population replenishment in another model species, the bicolor damselfish, Stegastes partitus (Rankin 2010, Rankin & Sponaugle 2011; Rankin & Sponaugle in review). Kayelyn Simmons, a summer intern from Hampton University, also used otolith analyses to examine regional differences in juvenile S. partitus growth (Simmons et al. ASLO poster). Evan D'Alessandro expanded this work beyond our model reef fish taxa to commercially important snappers (Lutjanidae) and barracuda (Sphyraena barracuda) (D'Alessandro 2010, D'Alessandro et al. 2010, D'Alessandro & Sponaugle 2011, D'Alessandro et al. in review ).
Much of our above work has used hindcasted otolith growth records of juveniles (i.e. successful settlers), but we have also examined larval growth directly by comparing otolith growth rates of larvae collected at different distances across the Straits of Florida. Sponaugle et al. (2009) found that larval Thalassoma bifasciatum grow more rapidly along the western portion of the Straits and have fuller guts than more offshore larvae. D'Alessandro et al. (2010) found a similar spatial pattern of larval growth in several snapper species. Recent ichthyoplankton collections are being used by Katie Shulzitski to examine the relationship between larval growth and their position inside and outside of mesoscale eddies [see http://yyy.rsmas.miami.edu/groups/reef-fish-ecology/lab%20member.htm#katie]. Martha Hauff is comparing larval growth and condition indices and examining how these vary with distance from shore along the Florida Keys [see http://www.rsmas.miami.edu/groups/larval-fish/Students_staff.cfm ]. Several undergraduates have used otolith analysis to examine spatial and temporal patterns in growth of larval clupeids (Jared Robbins, UM Honors Thesis) and selective mortality of larval T. bifasciatum (Jennifer Boulay, UM Honors Thesis).
Billfishes:
As part of a collaborative National Science Foundation -sponsored study of the transport, growth, and fate of billfish larvae in the highly dynamic Florida Straits [see http://www.rsmas.miami.edu/groups/larval-fish/Ongoing.cfm for details], we investigated whether growth of larval sailfish and blue marlin varies spatially. There were few patterns in overall growth for either species, but recent growth of blue marlin larvae was directly related to the composition of their prey (Sponaugle et al. 2010). Larval age and growth data were also incorporated into a fisheries-independent method of quantifying spatial and temporal patterns of abundance and spawning of these highly migratory species (Richardson et al. 2009).
FISH BEHAVIOR
Larval reef fish behavior:
An essential component of larval reef fish transport and survival is their capacity for active behavior. Klaus Huebert completed a series of experiments to examine the behavioral capabilities of larvae as they near settlement. Initial experiments conducted at sea used wild-caught larvae demonstrated that pressure influences vertical positioning (Huebert 2008). SCUBA divers also tracked larvae in situ seaward of Florida Keys reefs to measure active orientation behavior of late-stage larvae (Huebert & Sponaugle 2009). These experimental data were augmented by the analysis of vertical positioning of natural populations of larvae caught during a series of targeted 48-hr cruises (Huebert et al. 2010, and in revision ).
Juvenile reef fish behavior:
We have been interested in how recruitment and early juvenile survival are influenced by variation in the local abundance of predators, as occurs in predator-rich marine protected areas. Kirsten Grorud-Colvert conducted a series of mesocosm and laboratory experiments to quantify the influence of predation on trait selection in young reef fishes using the bluehead wrasse, Thalassoma bifsciatum, as a model species (Grorud-Colvert & Sponaugle 2006; Grorud-Colvert 2006). Tauna Rankin conducted in situ experiments with the bicolor damselfish, Stegastes partitus, to examine the mechanisms underlying observed patterns in otolith growth and trait-mediated survival (Rankin & Sponaugle in review ).
INVERTEBRATES
While clearly not a primary research focus in my lab, the larval supply and recruitment of marine invertebrates is also of broad interest. Projects have ranged from extensive nightly time-series of larval supply of brachyuran crabs to Barbados (Reyns & Sponaugle 1999) to a shorter time series investigation of patterns of stomatopod larval supply (undergraduate Honors Thesis of Paige Roberts). We continue to retain all plankton and light trap samples with the optimistic expectation that time and resources will eventually enable the analysis of these data for invertebrates.
****Disclaimer****
Several projects listed on this page are based upon work supported by the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in that material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.