OrExport of Secondary Production in
Ecosystems
ECOSYSTEM SUBSIDY EXAMPLES
Salmon returning from the sea
Migrations of birds and large mammals
River movement of detritus
*But very few studies have attempted to quantify the impact of the subsidy in the recipient ecosystem.
BECAUSE MOST OF THE PRODUCTIVITY
AND ENERGY IS IN PLANTS & VERY
LITTLE IS IN ANIMALS,
ANIMALS CAN’T BE IMPORTANT IN STRUCTURING ECOSYSTEMS.
RIGHT?
Kitchell et al. 1979BioScience 29: 28 -34
Transformation TranslocationTWO ROLES OF ANIMALS
WHY MIGHT TRANSLOCATION BE CONSUMERS IMPORTANT? • Mobility and behavior of animals can cause
substantial and rapid redistribution of nutrients.
• They can readily cross physical mixing boundaries, such as temperature or salinity stratification.
• They often make migrations that cross ecosystem boundaries.
• They are TASTY bits that enter foodwebs
EGGS
LARVAE
JUVENILE
ADULT
ESTUARY
0-age year class
1, 2, 3 age year class
OCEAN
ECOSYSTEM BOUNDARY
MENHADEN
MASS BALANCEThe mass of how many larvae entering the estuary equals
the mass of one juvenile leaving the estuary?
Entering Leaving
NET EXPORT IS A FUNCTION OF:
TIMING OF MIGRATIONWhen do they cross the ecosystem boundary compared to growth and mortality?
GROWTH RATEIncrease in size of individual
TIME
MORTALITY RATEHow many are there?
TIME (OR SIZE)
ENTERING
LEAVING
ENTERING LEAVINGTiming February October
Length (mm) 22 90
Dry Weight (g) 0.02 4.4
Nitrogen (ppt) 120 117
Phosp. (ppt) 26 30
GROWTH AND TIMING
MASS BALANCE
Net Flux = exit-enter
(# juv. exit) x (mass one juv. )*(ConcJuv) - (# larvae enter) x (mass one larvae)*(ConcLarvae)
0 = (1 juvenile) x (mass)*(CJ) - (? larvae) x (mass)*(CL)
Break even number is the number of larvae entering that exactly balance one juvenile leaving = Net flux of zero
? Larvae = (1 juvenile) x (mass)x (CJ) / (mass)*(CL)
Net Flux = Zero
/Breakeven # = ( ) ( )x (% NJ) x (% NJ)
ENTERING
LEAVING
Areal net flux
(g /m2/ yr)
Menhaden Detritus (water-borne)
Carbon 23 150
Nitrogen 3 4
Phosphorus 1 1
Areal net flux(g /m2/ yr)
Menhaden Detritus(water-borne)
Carbon 23 150
Nitrogen 3 4
Phosphorus 1 1
EXPORT FROM ESTUARIES TO OFFSHORE ECOSYSTEM
Seagrass
Offshore Reefs
Big Bend Seagrass
3000 km2 of seagrass
High primary production
Exports:Lots and Lots of Pinfish
Leave and most do not return
Northeastern Gulf of Mexico
Lower primary production
High fishery yields
An Ecosystem Subsidy
1. The fall egress of seagrass dwelling fishes to offshore reefs constitutes a major food source for reef communities.
2. This migration contributes directly the reproductive productivity of spring spawning groupers.
THE HYPOTHESIS
SECONDARY PRODUCTION
SEAGRASS Shallow/Deep Reefs GAG
d13C 25 % (S.E. 0.63)d 34S 18.5 % (S.E. 0.01)
Benthic Feeders Piscivores
1. Seagrass habitat derived organic matter reaches shallow water reefs and is consumed by resident species and gag grouper
2. Flux by fin provides ~20 % of the biomass on shallow water reefs and in gag muscle tissue.
3. Gag are likely making a pre-spawning migration to shallow water to feed intensively on the seagrass species.
CONCLUSIONS
DOES FIN FLUX STACK UPPinfish AbundanceNitrogen is the limiting nutrient
in the Gulf of Mexico. This fish flux could represent a large movement of nitrogen to the Gulf.
Lucky for me Chris Stallings of the FSUMCL decided to figure out how many fish are in the Big Bend.
Each year 1.5 Billion pinfish leave the seagrass beds of the Big Bend
By using a length weight curve we can estimate the total amount of organic nitrogen contained in the pinfish flux.
2009 2010
MAJOR NITROGEN SOURCES
Trichodesmium
Apalachicola River
Atmosphere
Nitrogen Sources
Apalachicola River1.7*1010 g N yr-1
Atmospheric Deposition5.4*1010 g N yr-1
Big Bend Pinfish6.5*108 N yr-1
Trophic steps required to become available to gag3-4 3-4 0
Tropic transfer efficiency of Nitrogen = 0.28
Apalachicola River 1.3*109–3.8*108 g N yr-1
Atmospheric Deposition1.2*109-3.3*108 g N yr-1
Big Bend Pinfish6.5*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.
Nitrogen Sources
Apalachicola River1.7*1010 g N yr-1
Atmospheric Deposition5.4*1010 g N yr-1
Big Bend Pinfish6.5*108 N yr-1
Trophic steps required to become available to gag3-4 3-4 0
Tropic transfer efficiency of Nitrogen = 0.28
Apalachicola River 1.3*109–3.8*108 g N yr-1
Atmospheric Deposition1.2*109-3.3*108 g N yr-1
Big Bend Pinfish6.5*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.
SO WHAT DOES IT ALL MEANIn our system seagrass habitat and the productive inshore environment provide a significant source of organic matter to the offshore environment via the movement of fishes.
This link is critical to the reproduction of a highly valuable fisheries species in the northern Gulf.
These fishes also carry organic toxins such as MeHg and thus provide a link between near shore pollution and contamination of food fishes (e.g. grouper and tuna).
Globally this phenomenon is likely very common in temperate coast regions where season changes in temperature make near shore waters too cold to inhabit.
Stable isotopes provide a powerful tool than can be used to quantify the impacts of ecosystem subsidies.
The TIDE projectTrophic cascades and Interacting control processes in a
Detritus-based aquatic Ecosystem
The TIDE project is a National Science Foundation Integrated Research Challenges in Environmental Biology (IRC-EB) funded study investigating the long-term fate of coastal marshes in the Plum Island watershed. Specifically this project will look at the interactive effects of nutrient enrichment and the removal of top level consumers in several small tidal creeks of the Rowley river.
Consequences in Ecosystems
Johnson & Short 2012
Pair-wise RegressionR2=0.99, p= 0.004
Trophic BottleneckObserved an increase (4x) in the abundance of inedible long lived snails in fertilized creek.
Mummichog experience high mortality over the winter.
Increased direct or indirect competition for food between the long lived snail and the short lived mummichog.
Control Conditions
Eutrophic Condition Short Term
Effects on Fisheries Species?
Eutrophic Condition Long Term
ConclusionsEutrophication initially increased production of mummichog but some tipping point was reached and now production is decreasing
Possible mechanisms are habitat degradation or a trophic bottleneck. We are working to examine these new questions.
Mummichog may provide an important trophic subsidy to striped bass.
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