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Copyright Brandon Cole

Stable isotopes as natural markers to assess trophodynamics and habitat connectivity in tropical snappers
Back-reef habitats (i.e. mangroves, seagrass beds, patch reefs) represent critical nurseries for many important fishery species in the tropics, and as coastal ecosystems are continually subjected to habitat loss, degradation, and over-fishing, identifying the most productive nearshore nurseries within these systems is becoming increasingly urgent. The aims of the current study are to (a) evaluate the effectiveness of otolith stable isotopes (δ13C, δ18O) as natural markers of nursery origin for juvenile snappers (Lutjanidae) within the Belize back-reef lagoon and (b) characterize regional, cross-shelf, and seasonal variability in primary production and food web dynamics for these juvenile snappers using stable isotopes 13C, δ15N) in tissues. Preliminary results indicate that isotopic signatures in otoliths may be useful in determining relative contribution rates of juvenile snappers produced at inshore and offshore nurseries within the back-reef, and dietary analyses suggest that the sources of primary productivity available to juvenile snappers inhabiting back-reef habitats may vary considerably by shelf position as well as season.





Early life ecology of dolphinfishes in the northern Gulf of Mexico

Dolphinfishes support commercial and recreational fisheries throughout their global range, however, our understanding of their ecology and habitat use during early life is limited. The aim of this study is to evaluate the role of the northern Gulf of Mexico (nGOM) as essential habitat of dolphinfishes and to identify conditions that characterize productive nursery areas for these species. Larvae were collected using neuston nets during summer ichthyoplankton surveys in the nGOM from 2007-2010. Generalized Additive Models (GAMs) were used to assess spatial and temporal variations in abundance across the Loop Current and its associated eddy systems, and nutritional condition, reflecting food availability, will be analyzed through RNA:DNA ratios. Results show that larvae of both species were abundant and broadly distributed across our sampling area, suggesting that this region may be important spawning or nursery habitat of these species. Additionally, models indicate that that the abundance of common dolphinfish is influenced by oceanographic conditions related to mesoscale features in the Gulf.

Funding: McDaniel Charitable Foundation, LSU, LDWF

 
 
Ecology of fishes associated with Sargassum
Relatively little information exists on the structure and dynamics of pelagic ecosystems, despite the fact that these systems contribute substantially to total primary production, biogeochemical cycling, and global fishery yields. Sargassum (brown floating algae) is the primary structural habitat feature for juvenile invertebrates and fishes in surface waters of the Atlantic Ocean and Gulf of Mexico, however the ecological function of these habitats is poorly understood. We are using several complimentary approaches to better understand trophic and community structure as well as population dynamics of Sargassum associated fishes. Surveys of Sargassum communities are conducted using larval purse seines to determine species composition as well as juvenile distribution and abundance of important fishery species (e.g. greater amberjack). Otolith based aging techniques are then used to examine relationships of age and growth of Sargassum-associated finfish. To assess food web structure, we are using stable isotopes and fatty acids as natural biomarkers to determine source(s) of organic matter and trophic relationships of associated consumers. These markers are then used to trace pathways of energy flow through the food web from autotrophs to apex predators providing valuable information on the trophic structure of pelagic shelf ecosystems.


 
Early-life ecology of snapper
Snapper support large recreational and commercial fisheries in the Gulf of Mexico of considerable economic value. Recent stock assessments have estimated red snapper to be overfished, and thus the ability to identify potentially important nursery habitats during vulnerable juvenile stages is vital to recovering the stock and improving management strategies. The aims of this study are to determine patterns of habitat use by newly settled individuals and assess the quality of different natural banks and habitats used during early life. Digital side-scan sonar and multi-beam bathymetric data are used to define habitat type (mud, shell) and vertical relief at several different banks on the inner-continental shelf of Texas. Otolith based aging is used to determine age at settlement as well as hatch date. Results from this study indicate that both shell and mud habitats associated with inner-shelf banks serve as settlement habitat of red snapper and have the potential to serve as nursery habitat of this species.

Funding: NOAA MARFIN


Dr. Jay R. Rooker Department of Marine Biology
Texas A&M University @ Galveston
1001 Texas Clipper Rd, Galveston, Texas 77554
rookerj@tamug.edu 409-740-4744
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