1. Benthic calcification in the Dutch North Sea area Frederic Gazeau NIOO-CEME Work in progress…… Maspalomas 5/12/2006

2. Calcification ► Ca 2+ + 2HCO 3 - ↔ CaCO 3 + CO 2 + H 2 O ► Process realized by organisms such as corals, calcifying macroalgae, foraminifera, echinoderms, pteropods, coccolithophorids, molluscs…. ► Increased atmospheric pCO 2 may threatened these organisms  BUT most studies focused on corals, macroalgae and planktonic calcifiers ► Recent experiment showed preliminary evidences that molluscs calcification will be reduced under higher atmospheric CO 2 in the range of IPCC expectations for 2100 ► Very few estimates of benthic calcification in temperate ecosystems over large areas (last to date: Smith, 1972 over the Southern California shelf)

3. Datasets ► 2 datasets used  Netherlands Institute for Fisheries Research  National Institute for Coastal and Marine Management / RIKZ ► > 130,000 records, 2,500 sampling stations, area of > 60,000 km 2 ► Data of densities and fresh weights from 1990 to 2004 ► Calcimass (g CaCO 3 m -2 ) calculated from fresh weight vs. shell weight relationships ► Gross calcification = calcimass x turnover (yr -1 ) ► Turnover data for major species provided by Joana Cardoso (NIOZ) Only intertidal areas sampled in the Westerschelde, Oosterschelde and Wadden Sea

4.  Species counts  Westerschelde : 5  Oosterschelde: 7  Wadden Sea: 8  Coastal zone: 38  Cockles are very important in intertidal areas  In the 0-20m area  Spisula subtruncata  Ensis Biodiversity What are the major species? Westerschelde Oosterschelde Wadden Sea Coastal zone 0-20 m

5. Biodiversity depths > 20m  213 species!!!!!  Clear dominance of Echinoids  Work in progress

6. Fresh weight / Shell weight

7. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Turnover (P/B in yr ) Cerastoderma edule Mytilus edulis Crassostrea gigas Macoma balthica Spisula subtruncata Ensis 1 year 2 years≥3 years 1 year 2 years≥3 years 1 year 2 years≥3 years Turnover = Growth rate  Data from Joana Cardoso (NIOZ)  All data based on SHELL growth

8. Oosterschelde ► No large temporal variations ► Cockles are the main producers ► BUT:  Oysters were not well sampled ► Kater (2003): ► >300 g CaCO 3 m -2 yr -1  Important aquaculture site in the Netherlands (oysters and mussels) ► Based on production values provided by the Dutch Fish Product Board  Mussels: 100 g m -2 yr -1  Oysters: > 500 g m -2 yr -1

9. Westerschelde estuary ► No aquaculture ► Cockles are the main producers ► Very low calcimass and calcification rates

10. Wadden Sea ► Large variations:  5-155 g CaCO 3 m -2 yr -1 ► Wild mussels are the main producers ► Also an important site for aquaculture  But large ecosystem (2700 km 2 )  Mussel culture covers 15% of the surface area of the Dutch Wadden Sea ► 8 g CaCO 3 m -2 yr -1

11. Coastal zone (0-20 m) ► Very large variations ► Values between 1 and 28 CaCO 3 m -2 yr -1

12. Gross calcification g CaCO 3 m -2 yr -1 Cerastoderma edule24 Mytilus edulis11 Crassostrea gigas*328 Culture Mytilus edulis100 Culture Crassostrea gigas550 Sub-Total~1000 Cerastoderma edule8 Macoma balthica1 Sub-Total9 Cerastoderma edule21 Macoma balthica1 Mytilus edulis 43 Culture Mytilus edulis 8 Sub-Total 73 Spisula subtruncata4 Ensis 6 Sub-Total10 15 mmol CO 2 m -2 d -1 Oosterschelde Westerschelde Wadden Sea Coastal zone 0-20 m 0.2 mmol CO 2 m -2 d -1 1.2 mmol CO 2 m -2 d -1 0.3 mmol CO 2 m -2 d -1 Derived CO 2 fluxes (ψ = CO 2 /CaCO 3 of 0.6) * Derived from Kater (2003) Coastal zone > 20 m Work in progress……. Close to coral reefs estimates Low values

13. Preliminary conclusions ► Aquaculture is very important and represents a main source of carbonate production ► CO 2 production by gross calcification ► CO 2 production by shell burning ► Oosterschelde close to coral reef production (Milliman: 1500 g CaCO 3 m -2 yr -1 ) ► Small values for the coastal zone, Westerschelde estuary and Wadden Sea ► A low total Dutch North Sea benthic calcification rate is expected ► < Milliman’s estimate for shelves (20-100) ► << Smith’s estimate for the Southern California shelf (400)

14. Future work ► Gross calcification in the >20m area ► Shell removal by fisheries (known) ► Estimates of shell removal by birds (known) ► Data on shell weight in sediments (known)  Together with sedimentation rates estimates ► Estimate of net accumulation rates and net CO 2 fluxes