Oyster production - Restore America's Estuaries

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Oyster production - Restore America's Estuaries

Dutch delta area- Stormflood 1953- Highly populated area- Economic hotspot- Below sea level*


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Storm flood February 1, 1953: + 4 m HW 1835 victimsMain cause: dikes were too low for the flood; lack of maintenance


RESPONSE: DELTA PROJECT, start 1957primary approach: = closing off the estuaries from the sea= except for the shipping routes= creation of freshwater lakes (agriculture)- New waterwayEntrance to Rotterdam- Haringvliet- Grevelingen- Oosterschelde- Veerse Gat- WesterscheldeEntrance to Antwerp


DELTA: before and afterOriginal plan: freshwater lakesChanges in priorities with time:agriculture


1974: protest against closure of the Oosterschelde• Increased environmental awareness• Freshwater = pollution• Loss of shellfish culture• Socio-political climate (>sixties)Alternative solution: storm surge barrier= protection against flooding= maintenance of tidal system


OOSTERSCHELDE project: large scale coastal engineering


THE OOSTERSCHELDE : a changing ecosystemtotal surface(km2)PRE POST ∆%452 351 -22tidal flats (km2) 183 118 -36salt marshes 17 6 -65(km2)mean tidal range 3.7 3.25 -12(m)mean tidal volume 1230 880 -28(km3)residence time (d) 5-50 10-100 +50total volume(km3)freshwater load(m3/s)3050 2750 -1070 25 -64


OOSTERSCHELDE project: IMPACTS• Before (80-84) – after (86-90) studies• Hydrodynamics, geomorphology,ecology, shellfish culture, models• Reported in > 40 papers• Main outcomes:= reduced tidal volume- long term loss of intertidal habitats= from an estuary to a tidal bay:- reduced river inflow- lower nutrients, higher salinityfishery & aquaculture ?


OOSTERSCHELDE : FISHFyke catches based data 1979 – 1988; 70 speciesDominant species:- Flounder- Eel- Eelpout- Plaice- Sculpin- Pout- Herring- Sole- Dab- Whiting


OOSTERSCHELDE : change in fyke catch frequencyBefore – aftercomparison := changes partlyrelated to the project= occur at wider scale= influenced by yearclass strength= no overall impact


Oosterschelde: bottom culture mussels and oystersMus s elplots2200 haOysterplots: 1550 ha


Mussel and Oyster productionmln kg freshmln kg2001601208040051Mussel production57636975818793oyster production32.521.510.5052 57 62 67 72 77 82 87 92 979905CrassostreaOstreawadzlMussel productionfrom Wadden Seaand Oosterschelde:80 mln kg / yrCulture cycle starts inWadden Sea; OS isused for growoutOyster production1 – 3 mln kg / yearFlat oyster: BonamiaPacific oyster instead


Impact on Mussel and Oyster productionMussel culture :adaptation to newconditionsmn kg freshl6040200mussel production OS80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95Oyster culture :Introduction Bonamia3Oyster productionand Pacific oysterNo barrier effect :maintenance ofmln kgf fresh2.521.510.50flat oysterpacific oysterproductivity80818283848586878889909192939495Barrier constructionperiod: 1985-1986


Mussels: primary production as driving force%3530252015105078 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97YearsWestCentralgC.m -2600 .year -1 YearsWest500Central400300200100080 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98- Flesh content has maintained- PP has maintained- Correlation flesh - PP- Standing stock of musselsmanaged by the farmers :stableFlesh (%)30R² = 0.58652791248789829084962181808318200 250 300 350 400 450 500 550 600Primary production (gC.m -2 .year -1 )Central


Feedback through filtrationparadox:Nutrient loads Primary production~ equalHypothesis:Filtration andnutrient regenerationby the mussels stimulateprimary production


Oosterschelde a case study• Maintenance of primary production• Residence time >• Water transparency >• Nutrient loads


CONCLUSIONS SHELLFISH OOSTERSCHELDE:• Production has maintained• Lower nutrient loads and increased residence time made theecosystem more self-sustaining• Shellfish filtration and nutrient regeneration stimulatedphytoplankton turnover and maintained primary production• This is due to feedback by filter feeders• ...and the farmers, as the farmers are managing the stocks• example of the role of aquaculture in ecosystem management


= aquaculture structures for shore protectionPROTECTION AND PRODUCTIONNovel approach.... As a response to climate change :how to couple coastal defense withsustainable economic functions:production- Building coastal infrastructure is costly- Economic use gives returns continuous improvement- Sustainability includespreservation of natural valuesPPPprotection preservationAquaculture options = oysters as eco-engineers= land-based aquaculture


Historic land reclamation: subsidence and seapageWithout reclamation:salt marshes:natural sedimentationWith reclamation:land thrinks below sealevel := increasing vulnerability= increasing seapageNew land useDelta without present situation red = seapage areasreclamationwithout dikes


LAND- BASED AQUACULTURE• New agribussiness• Prevent subsidence• Exploits seapageSeasalter UKPilot plant forIntegrated cultureRagworm - soleAlgae - shellfishMarennes-OleronOyster clairesCockle farm


FITS IN BROADER VISION: Increase dynamics, increaseresilience, restore estuarine characteristics


....based on lessons from the Delta ProjectFreshwater lakes:eutrophication; blue-green algae;no mixing of river runoffSaline lakes: stratification;oxygen depletion, eutrophicationTidal bay: tidal flat erosionand habitat lossRestore dynamics


OOSTERSCHELDE barrier : critical evaluation pointsPro’s• Safety for the mid-term future: depends of sea level rise• Maintenance of tidal functions: productivity, mixing• Maintenance of seafood production (shellfish culture)Con’s• tidal volume reduction by 28 % : sand hunger, habitat loss• freshwater reduction by 64 % : no gradients, low nutrients• costs : initial 4*10^9 USD, maintenance 25 * 10^6 USD/yr.... so for the Ike Dike: integrate in coastal zone management


Thank you

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