FLUX by FIN:FLUX by FIN: Fish mediated carbon and nutrient flux between northeastern Gulf of Mexico seagrass beds and offshore reef fish communities.Fish mediated carbon and nutrient flux between northeastern Gulf of Mexico seagrass beds and offshore reef fish communities.

James Nelson, Chris Koenig, Felicia Coleman and Jeff ChantonFlorida State University Department of Oceanography, Biological Sciences Dept. and FSU Coastal and Marine Laboratory

AbstractAbstract  Each winter millions of pounds of fish migrate from their summer home in the seagrass beds of the Florida Big Bend to over winter and spawn nearly 100 miles away on offshore reefs. Understanding the role this fish mediated nutrient flux plays in sustaining fisheries production is vital to proper management of this extremely valuable northern Gulf of Mexico resource. To determine the viability of using stable isotope analysis to track diet shifts in wild gag grouper (Mycteroperca microlepis) populations, we conducted a diet shift experiment on four gag held in the laboratory. Each month biopsies of the muscle, liver, and gonad tissue were taken and the 13C values determined. Fish were initially fed a diet of mackerel and then shifted to a diet of pinfish. The results indicate that we are able to trace the pinfish diet as it was incorporated into the tissues. The carbon turnover rates varied widely among the three tissues with muscle being the slowest with a mean turnover rate of 0.005 ‰ day-1, gonad tissue was intermediate with a turnover rate of 0.01 ‰ day-1 and liver was the fastest with a turnover rate of 0.014 ‰ day-1. Although it is generally believed that metabolism is insignificant in tissue turnover rates for ectotherms, we found that adult gag tissue turnover is driven primarily by metabolic turnover and not growth. Based upon the results of this study evidence exists that physiological changes during the life cycle of gag may enhance our ability to detect these changes in diet. Preliminary data from offshore specimens suggest that gag gonad tissue is composed of material attained from a lower trophic level than that of muscle tissue. Although preliminary this is an indication that seagrass derived prey are entering the offshore food web at a critical time in the gag reproductive cycle. Despite the great numbers of studies that speculate about the importance of this type egress or “outwelling” to adjacent ecosystems, this is one of the first to attempt demonstrate or quantify it.

Turnover DataTurnover Data

Then and NowThen and Now

Left; A day long fishing trip circa 1960 landing 3,800 lbs in the N.E. Gulf. Right; An “Awesome” day long fishing trip in 2008 yielding 300 lbs in the same area as the photo to the left. Should our hypothesis and preliminary data be correct, it would add a new facet to the way we think of inshore habitats. Long thought of as a nursery ground these areas could very well be supplying offshore habitats with a large proportion of the nutrients required to sustain the yields we depend on. Such a finding would have major management implication for our area and similar marsh habitats throughout the world.

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Does Fin Flux Stack Up?Does Fin Flux Stack Up?

LEFT; These plots show the results of the least squares non-linear regression to determine the amount of muscle turnover due to metabolism. The dotted line indicates turnover dictated entirely by observed growth (C=1) and the solid line indicate the best-fit line determined by least squares regression using the metabolic turnover equation. All of the values calculated for C were significant at the 0.05 level when fitted using a least squares regression.

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RIGHT; The red line approximates the first day of December. During this time of year gag are preparing to migrate and spawn. Although only based on a few individuals the data appears to show that the fat stores of the liver are utilized in the gonad in preparation for spawning. If this is the case then our ability to detect a pulse of seagrass derived carbon may be enhanced by the physiological changes undertaken by gag prior to spawning.

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Evidence of Flux by Fin?Evidence of Flux by Fin?

ABOVE; This plot shows a preliminary stable isotope analysis of the food web in the Northeastern Gulf of Mexico based on the samples we have collected thus far as part of the NOAA/FSU collaboration under NGI. The benthic feeders consist of red porgies and blue angel fish. The water column feeders consist of vermillion snapper, tomtates, sand perch, banks seabass, and inshore lizard fish. The inshore Seagrass residents consist of pinfish, pigfish, and spot. The gag muscle and gonad values shown were taken during gag spawning season (Feb). This preliminary data appears to support our hypothesis that gag switch to feeding significantly on inshore derived prey. The gonad tissue is significantly depleted in 15N relative to muscle tissue which reflects the lower trophic position of the seagrass derived prey items.

Gag 1 Female 83 cmGag 1 Female 83 cm

Gag 4 Female 80 cmGag 4 Female 80 cm

Gag 2 Male 101 cmGag 2 Male 101 cm

Gag 3 Female 71 cmGag 3 Female 71 cmGag 1 LiverGag 1 Liver

Gag 1 GonadGag 1 Gonad

ObjectivesObjectives1. Determine the isotopic turnover in the tissues of live gag. DONE

2. Use the turnover rates to determine strength of seagrass carbon pulse.

3. Determine the impact of seagrass derived carbon and nutrients on gag grouper reproductive productivity

MethodsMethodsExperimental Methods:1. Live gag were captured in the summer brought back to marine lab.2. The gag were fed a diet of pelagic bait fish (mackerel) for 8 weeks.3. The gag were switched to a pinfish diet.4. Each tissue was Re-sampled every month.

Surgical Methods:1. Fish were anesthetized using MS-222.2. Fish were placed in a cradle with a anesthetic solution of seawater running

over their gills.3. Biopsies of the liver, gonad, muscle were then taken.4. The surgeries were repeated each month.

The “Forgotten Coast” ParadoxThe “Forgotten Coast” ParadoxThe northern coast of the Gulf of Mexico is one of the most diverse and pristine coastal regions in the United States. It is characterized by towering sand dunes on sugar white beaches, wide ranging salt marsh habitats home to rare assemblages of flora and fauna, and the largest continuous expanse of seagrass habitat left in the western hemisphere. Besides its natural beauty the region is also extremely biologically productive, supporting many major recreational and commercial fisheries.

Recreational fishing alone generates over $5.2 billion annually for the state of Florida. This combination of natural beauty and sporting opportunity have turned the region into a hotbed of coastal development earning it the real estate nickname “Forgotten Coast”. However, the very thing that attracted people to the region may be destroyed by those who have come to enjoy it.

Understanding how these systems function is critical to ensure that as development continues, proper techniques are used to maintain the productivity of the region. So people will be able to continue to enjoy the ecosystem services that drew them to this unique area in the first place.

Nitrogen SourcesNitrogen Sources

Apalachicola River1.73*1010 g N yr-1

Atmospheric Deposition N.E. GOM 5.45*1010 g N yr-1

Pinfish from Big Bend 4.08*108 N yr-1

Trophic steps required to become available to gag

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Tropic transfer efficiency of Nitrogen = 0.28

Apalachicola River 1.35*109–3.78*108 g N yr-1

Atmospheric Deposition N.E. GOM1.19*109-3.34*108 g N yr-1

Pinfish from Big Bend4.08*108 N yr-1

Based on our estimates a single species of fish (Pinfish) flux ~14-36 % of the total nitrogen available to grouper annually in the N.E. Gulf of Mexico. Since the pinfish flux is directly available as a prey item and is not lost to bacterial respiration or sedimentation we hypothesize that this flux contributes significantly to the high fishery yields in the area.