The North Sea Coasts
205
primary production of about 100 gCm- 2 year -1, in the Dutch Wadden
sea. The primary production per average m 2 by littoral seagrass (Zostera
marina, Z. noltii) and by macroscopic algae (mainly Ulva spp. and
Enteromorpha spp.) is probably negligibly low, but act]lal biomass and
production data for these macrophytes are too limited for sound generalizations. Before the outbreak of the "wasting disease" of the seagrass in
1932, the vast sublittoral Zostera beds (15000 ha) in the Dutch Western
Wadden Sea contributed considerably to primary production in this part
of the Wadden Sea, probably about 20-40 gCm- 2 year -1 (Van den Hoek
et al. 1979).
In the records of the nineteenth century, the total area occupied by
Zostera in the Dutch western Wadden Sea and the Zuiderzee was
estimated at 6500 ha, and by Van Goor (1921) at 15000 ha (Den Hartog
and Polderman 1975). Position and size of the sublittoral Zostera marina
beds underwent long-term fluctuations in the period 1869-1930. The
mapping of 1930 shows roughly a doubling of the area occupied by
Zostera marina, compared with 1969. Z. marina also occurred in the
former Zuiderzee, where it even grew in water with salinities lower than
6%0. Z. marina penetrated into eulittoral sand and mudflats as a form
with narrow leaves, where it was accompanied by Zostera noltii. The
latter species penetrated into the Zuiderzee as far as the 10%0 isohaline
(Den Hartog 1970). Z. noltii at present occurs on eulittoral flats in the
Wadden Sea from about mean high water neap downwards and Z.
marina from about mean low water neap downwards. Where Z. marina
grows in higher eulittoral positions it tends to occupy shallow depressions in the flats where water is retained during ebb; in such places Z.
noltii occupies small elevations. Eulittoral Zostera-stands are found on
nearshore flats and on tidal watersheds. The historic contribution (up to
1932) of sublittoral Z. marina to the production of organic matter in the
Wadden Sea can be only very roughly approximated, because neither
exact biomass nor primary production measurements from that period
are available (Van den Hoek et al. 1979).
Upto 1930, there was quite an important local seagrass industry along
the southwestern coasts of the Dutch Wadden Sea. Washed up seagrass
was collected, and the beds which were sufficiently shallow during ebb,
were harvested with scythes. The seagrass was used as packing material
and for stuffing cushions and mattresses. In the Dutch Eastern Wadden
Sea, and in the German Wadden Sea such an industry did not exist,
apparently because extensive sublittoral Zostera meadows were lacking.
However, in the German Northern Wadden Sea an important sublittoral
Z. marina stand has been described for the coast of the isle of Sylt
(Nienburg 1927; Wohlenberg 1935,1937). It is likely that relatively high
205
primary production of about 100 gCm- 2 year -1, in the Dutch Wadden
sea. The primary production per average m 2 by littoral seagrass (Zostera
marina, Z. noltii) and by macroscopic algae (mainly Ulva spp. and
Enteromorpha spp.) is probably negligibly low, but act]lal biomass and
production data for these macrophytes are too limited for sound generalizations. Before the outbreak of the "wasting disease" of the seagrass in
1932, the vast sublittoral Zostera beds (15000 ha) in the Dutch Western
Wadden Sea contributed considerably to primary production in this part
of the Wadden Sea, probably about 20-40 gCm- 2 year -1 (Van den Hoek
et al. 1979).
In the records of the nineteenth century, the total area occupied by
Zostera in the Dutch western Wadden Sea and the Zuiderzee was
estimated at 6500 ha, and by Van Goor (1921) at 15000 ha (Den Hartog
and Polderman 1975). Position and size of the sublittoral Zostera marina
beds underwent long-term fluctuations in the period 1869-1930. The
mapping of 1930 shows roughly a doubling of the area occupied by
Zostera marina, compared with 1969. Z. marina also occurred in the
former Zuiderzee, where it even grew in water with salinities lower than
6%0. Z. marina penetrated into eulittoral sand and mudflats as a form
with narrow leaves, where it was accompanied by Zostera noltii. The
latter species penetrated into the Zuiderzee as far as the 10%0 isohaline
(Den Hartog 1970). Z. noltii at present occurs on eulittoral flats in the
Wadden Sea from about mean high water neap downwards and Z.
marina from about mean low water neap downwards. Where Z. marina
grows in higher eulittoral positions it tends to occupy shallow depressions in the flats where water is retained during ebb; in such places Z.
noltii occupies small elevations. Eulittoral Zostera-stands are found on
nearshore flats and on tidal watersheds. The historic contribution (up to
1932) of sublittoral Z. marina to the production of organic matter in the
Wadden Sea can be only very roughly approximated, because neither
exact biomass nor primary production measurements from that period
are available (Van den Hoek et al. 1979).
Upto 1930, there was quite an important local seagrass industry along
the southwestern coasts of the Dutch Wadden Sea. Washed up seagrass
was collected, and the beds which were sufficiently shallow during ebb,
were harvested with scythes. The seagrass was used as packing material
and for stuffing cushions and mattresses. In the Dutch Eastern Wadden
Sea, and in the German Wadden Sea such an industry did not exist,
apparently because extensive sublittoral Zostera meadows were lacking.
However, in the German Northern Wadden Sea an important sublittoral
Z. marina stand has been described for the coast of the isle of Sylt
(Nienburg 1927; Wohlenberg 1935,1937). It is likely that relatively high