Presentation on theme: "Centre for Shellfish research Introduction, impact and management of the Pacific oyster Crassostrea gigas in Dutch coastal waters Aad Smaal, Karin Troost."— Presentation transcript:
Centre for Shellfish research Introduction, impact and management of the Pacific oyster Crassostrea gigas in Dutch coastal waters Aad Smaal, Karin Troost & Jeroen Wijsman Institute for Marine Resources and Ecosystem Studies
Flat Oyster (Ostrea edulis) culture since 1870 Problems with overstocking (1890), shell disease (1930), severe winters (1963) and Bonamia (1980) Introduction Pacific Oyster (Crassostrea gigas) in 1964 to restore oyster culture Pacific oyster culture:1550 ha bottomplots meanwhile proliferation: by (unexpected) reproduction in warm summers and larval dispersal INTRODUCTION C. gigas in the OOSTERSCHELDE
musselplots oysterplots Oosterschelde and Wadden Sea are main areas for shellfish bottom culture WAD OS
1980: 15 ha 1990: 210 ha 2002: 640 ha 2005: 800 ha OYSTER PROLIFERATION ON TIDAL FLATS: reconstruction on the basis of aerial photographs and ground truth
Centre for Shellfish research TOWARDS AN OYSTERSCHELDE ? OYSTER STOCK OOSTERSCHELDE hamln kg kg/m2 oysterbed totalaliveflesh (ww) TIDAL FLATS GULLIES700???? ROCKY SHORES100????
Centre for Shellfish research FURTHER PROLIFERATION 20 days
Centre for Shellfish research Biomass Surface N obs *10^6 kg Ha 2002:0.1 n.d n.d : : OYSTERS WADDEN SEA 2005
North Sea Texel Sylt Eastern Wadden Sea Western Wadden Sea The Netherlands Germany Colonization of the German Wadden Sea - Sylt Oyster culture: Proliferation from Dutch Wadden Sea 1998
Centre for Shellfish research BEFOREAFTER PACIFIC OYSTER INVASION : characteristics epifauna, reef builder, resistant, filter feeder
OTHER DOMINANT FILTER FEEDERS Cockle Native infauna, dynamic, resilient Mussel Native epifauna, forms bed structures, slow recovery, resistant
OTHER INVASIVE SHELLFISH SPECIES Slipper limpet 1930 Drilling mussel 1896Soft clam 1250 ? Razor clam 1978 Mainly infauna, No reef building
Centre for Shellfish research HYPOTHESIS Exotic species that are able to build resistant structures may change ecosystems more dramatically than resilient species As the oyster is typically a resistant species (eco-engineer) the introduction may induce a regime shift See: Smaal et al, IN: The Comparative Roles of Suspension-Feeders in Ecosystems, Dame RF Olenin S (Eds.) Kluwer Academic Publishers, Dordrecht.
Centre for Shellfish research IMPACT CONSEQUENCES - Food role in the- Shellfish culture - Recruitment ecosystem- Nature conservation - Space- Recreation
FOOD: competition Biomass Filtration capacity (5 – 25 l/h) Competition with other filter feeders: decrease of mussel growth Meat content of marketed mussels Oyster 32% Mussel 44 % Cockle 24 % days Carrying capacity problem:
RECRUITMENT: - gregarious settlement of oysters: positive feedback - filtration of (mussel) larvae: competition PhD project Karin Troost oysterbedcontrol nr of larvae
SPACE: - Oysters settle on mussel and cockle beds - Oysters settle in subtidal areas including mussel culture plots - Oysters take over rocky shore fauna on average > 60 % coverage - Oysters form new habitat (reefs) on tidal flats
Centre for Shellfish research ECOSYSTEM ROLE OF OYSTER BEDS suspension feeding capacity: HIGH recruitment capacity: HIGH habitat type: epifauna or infauna: EPIFAUNA eco-engineering potential = substrate formation: POSITIVE FEEDBACKS = reef building: YES ability to form structures: HIGH RESISTANCE
Centre for Shellfish research REGIME SHIFT ? If oyster become dominant than changes in - species composition - food availability for waders - local geomorphology - habitat complexity - resilience - regime shift CONSEQUENSES ?
CONSEQUENSES for SHELLFISH CULTURE: - increased competition = production capacity change NATURE CONSERVATION: - less food for birds = carrying capacity change RECREATION: - health risk = multi-user conflict
WHAT TO DO? step 1 - Biomass reduction step 2 - Maintenance step 3 – Exploitation 2006: Experimental fishery 2 * 25 ha BACI oysters, sed, birds, mf 10 mln kg = m3 100 shiploads
Centre for Shellfish research If you cant beat them, eat them