On the decrease of Sabellaria reefs in the North Sea

Bundesanstalt für Gewässerkunde
Koblenz - Berlin
On the decrease of Sabellaria reefs in the North Sea
- the role of anthropogenic impacts THE PROBLEM
7°
8°
9°
In historic times extensive reefs mainly of the tube-building
1926
55°
1925
Sabellaria - historical records
DENMARK
polychaete Sabellaria spinulosa occurred frequently in the sublittoral of the German Wadden Sea.
1932
sublittoral
1938
7°
55°
living reef (Sabellaria spinulosa)
1932
The natural succession in sabellarian reefs is characterized by
1925
1939
1926
1939
1925
1925
1925
1925
dead reef
phases of (1) rapid growth after origin and (2) by stagnation followed by (3) destruction.
eulittoral
living reef (Sabellaria spinulosa)
9°
DENMARK
sublittoral
1925
living reef (Sabellaria spinulosa)
living reef (Sabellaria alveolata)
8°
Sabellaria - recent records
1925
1991
1991
year of record
1993
1939
year of last record
Husum
Middle of the 1920
Husum
th
a netto decrease of sabellarian reefs at the
German North Sea coast started, but the reasons were unknown.
Eider
Eider
NORTH SEA
German Bight
NORTH SEA
German Bight
1921
1938
WHY?
1937
1919
54°
1926
1870th
1980
th
1921
1910th
Cuxhaven
1976
1921
1984
Bremerhaven
1980th
Bremerhaven
1996
1991-1996
Weser
Emden
POSTER presented on 33th European Marine Biology Symposium, 7. - 11. Sep 1998, Wilhelmshaven, Germany
1996
Jade 1995
Wilhelmshaven
Weser
1952
THE
NETHERLANDS
1991-1995
recently only three living reefs have remained, two in the Jade,
the third southerly from the island Sylt.
Wilhelmshaven
Elbe
Cuxhaven
Among the occurrence of dead reefs (lumps of empty tubes)
1984
Jade
54°
Elbe
Brake
GERMANY
Ems
The poster summarises information on the effects of anthropogenic impacts on sabellarian reefs. Finally a first action
plan is presented to activate reef development.
Emden
THE
NETHERLANDS
Brake
GERMANY
Ems
ANTHROPOGENIC IMPACTS
7°
55°
8°
9°
Shrimp trawl fishery
7°
DENMARK
55°
8°
recent intensity
Ostrea edulis
high
9°
1986
Oyster beds
1991
7°
DENMARK
55°
9°
DENMARK
Main aspects
1993
main areas of occurrence
1924
medium
8°
Coastal engineering
1927
Embanking (1000-1899 AD)
extermination of natural beds
Embanking (1900-1995 AD)
1995
none
Embanking (1400-1963 AD)
Crassostrea gigas
no data available
culture area, since 1986
Causeway
wild population
Source: Stock et al. (1996): Ökosystemforschung Wattenmeer - Synthesebericht.
1991
Husum
Deepening (Dredging & dumping)
NCZ = nautical charts zero
SD = ship draught
year of first record
1927
Husum
Eider
beginning of construction
Husum
Eider
NORTH SEA
German Bight
Eider
NORTH SEA
German Bight
NORTH SEA
German Bight
1938
54°
54°
1820 on NCZ -3,8 m
1936 on NCZ -10 m
1957 on NCZ -11 m
1964 on NCZ -12 m
1974 on NCZ -13,5 m
54°
1924
Elbe
Cuxhaven
Elbe
Cuxhaven
1850
Jade
Jade
Bremerhaven
Wilhelmshaven
Weser
Emden
Brake
Bremerhaven
Wilhelmshaven
1967 on NCZ -8,5 m
1980 on NCZ -11 m
Weser
Emden
THE
NETHERLANDS
1891 on NCZ -7,3 m
1921 on NCZ -10 m
1969 on NCZ -12 m
1998 on NCZ -14 m
Jade
Bremerhaven
Wilhelmshaven
Weser
GERMANY
Ems
THE
NETHERLANDS
Emden
Brake
GERMANY
Ems
1985 on NCZ -5,7 m
1992 on NCZ -6,3 m
THE
NETHERLANDS
Ems
! The main operation area of the shrimp fishery in the Wadden
Sea is alongside the slopes of the tidal channels.
! Total landings of the shrimp fishery have fluctuated but have
not increased since the 1920th.
! The size of the fleet has declined but on the other side fishing
gear has become larger and more efficient.
Elbe
Cuxhaven
1958 on NCZ -12 m
1964 on NCZ -13 m
1967 on NCZ -15 m
1969 on NCZ -17 m
1971 on NCZ -18,5 m
1998
Brake
1887 on SD 5 m
1913 on SD 7 m
1925 on SD 8 m
1953 on SD 8,7 m
1972 on NCZ -9 m
GERMANY
! In former times the native oyster Ostrea edulis was of widespread occurrence in the Wadden Sea alongside the tidal channels from low tide level down to about -6 m.
! The most serious and permanent destruction of habita /biotops
in the Wadden Sea is caused by measures of coastal protection
including land reclamation.
! Overexploitation exterminated these populations.
! However most areas along the German North Sea coast have
been embanked before 1900.
! The sites of former oyster beds are now occupied mainly by
blue mussel beds.
! Regular culturing of the Pacific oyster Crassostrea gigas
began in 1986 at the island Sylt.
! Since 1991 wild population of Crassostrea gigas were observed in the Wadden Sea with increasing abundances.
! In the 20th century several causeways were constructed which
have significant influences on the hydrological system in the
surrounding Wadden Sea.
! During the last 100 years the estuaries were repeatedly
deepened. This caused a permanent dredging and dumping of
sediments in the estuaries up to now.
CONCLUSION
Many biotic and abiotic factors act simultaneously in an unpredictable way on sabellarian reefs interfered with anthropogenic effects.
An intensive analysis showed that the decrease of sublittoral sabellarian reefs in the German Wadden Sea is ultimately caused by human
interference:
>
Shrimp trawl fishery:
>
Oyster fishery:
Shrimp fisheries with bottom trawls are carried out in the main distribution area of sabellarian reefs.
It is to suggest that mechanically destruction of reefs by gears as well as extinction of reefs by net catch were a
main cause of the decline. It is to assume that recently shrimp fisheries prevented reef development.
Oyster beds, in some areas an important natural hard substrate for Sabellaria, declined by overexploitation.
It is to suggest that the extinction of oysters has negative consequences on the number of reefs, but complete
disappearance of reefs is unlikely. However it is take notice that since several years the pacific oyster spread
into the WaddenSea as well as the european oyster has by first individuals reappeared.
>
Coastal engineering:
Building of dikes and dams as well as deepening have caused changes in hydrological conditions.
It is to suggest that these activities have effects on single reefs, but complete disappearance of reefs is unlikely.
First action plan
C
C
To activate sabellarian reef development the establishment of undisturbed sublittoral areas along the slopes of selected tidal channels
will be a first suitable action.
A monitoring should be done primarily in areas where sabellarian reefs recently occur to get more information about population
dynamics of Sabellaria in the Wadden Sea.
Federal Institute of Hydrology
Kaiserin-Augusta-Anlagen 15-17
D - 56068 Koblenz
GERMANY
Main Data Sources
Buhs, F. & K. Reise (1997): Epibenthic fauna dredged from tidal channels in
the Wadden Sea of Schleswig-Holstein: spatial patterns and a long-term
decline.- Helgoländer Meeresunters. 51: 343-359.
Linke, O. (1951): Neue Beobachtungen über Sandkorallen-Riffe in der
Nordsee. - Natur und Volk 81: 77-84.
Nehring, S. (1999): Oyster beds and Sabellaria reefs. In: De Jong, F., Bakker,
J.F., van Berkel, C.J.M., Dankers, N.M.J.A., Dahl, K., Gätje, C. Marencic,
H. & Potel, P. (Eds.), Wadden Sea Quality Status Report. Common
Wadden Sea Secretariat Wilhelmshaven, Wadden Sea Ecosystem No. 9:
146-147.
Reise, K (1982): Long-term changes in the macrobenthic invertebrate fauna
of the Wadden Sea: are polychaetes about to take over?- Neth. J. Sea
Res. 16: 29-36.
Riesen, W. & K. Reise (1982): Macrobenthos of the subtidal Wadden Sea:
revisited after 55 years.- Helgoländer Meeresunters. 35: 409-423.
Schuster, O. (1952): Die Vareler Rinne im Jadebusen.- Abh. senckenberg.
naturf. Ges. 486: 1-38.
Vorberg, R (1995): On the decrease of sabellarian reefs along the German
North Sea coast.- Publ. Serv. géol. Lux. 29: 87-93.
Vorberg, R. (1997): Auswirkungen der Garnelenfischerei auf den
Meeresboden und die Bodenfauna des Wattenmeeres.- Schriftenreihe
naturwissenschaftliche Forschungsergebnisse Bd. 54, Verlag Dr.
Kovac Hamburg: 1-191.
Stefan Nehring
Department Animal Ecology