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P.H. Nienhuis
macroalgae. The eulittoral and sublittoral vegetation of macrophytes
changed significantly after World War II, owing to increased
eutrophication. Zostera marina communities disappeared or reduced
substantially and were replaced by green algal accumulations (Ulva
spp.) in shallow habitats.
4. In the German Wadden Sea a decrease in seagrass distribution and
abundance was observed during and after the wasting disease in
1931-1933, but to a lesser extent than in the Dutch Wadden Sea. Some
eulittoral populations of Zostera marina re-established themselves,
but all sublittoral populations disappeared, owing to increased
turbidity and eutrophication.
5. There was an increase in green macro algal mats (mainly
Enteromorpha prolifera) from 1978 onwards. After 1989, the increase
becomes alarming, especially between the outlets of the river Ems,
Weser and Elbe. Quantitative evidence to substantiate this algal
"increase", however, is scarce.
6. In the Dutch Wadden Sea sublittoral seagrasses (Zostera marina) have
become extinct after the "wasting disease" in 1932-1933. In the 1970s
eulittoral Z. marina and Z. noltii stands also gradually declined.
Increased eutrophication, turbidity and bottom trawling by fisherman
are mentioned as responsible factors.
7. Communities in the Dutch Wadden Sea did not show a shift from
seagrass-dominance to green-algal dominance (cf. German Wadden
Sea). Local accumulations of macro algae (Enteromorpha and Ulva)
frequently occur and are seemingly increasing but these vegetations
are not considered as a management problem.
8. The 300 km of exposed sandy beaches along the west coast of the
Netherlands and Belgium do not suffer from undesired accumulations
of green algae.
9. The estuaries and lagoons in the SW Netherlands show a diversified
picture: Grevelingen lagoon is a stagnant mesotrophic watermass,
where Zostera marina is the (potential) dominant and green macroalgae are virtually absent. Veerse Meer lagoon is a stagnant eutrophic
lake, where Ulva spp. dominates and creates nuisance to water
managers. Oosterschelde is a mesotrophic clear tidal estuary where
green algae are subordinate. Westerschelde is a turbid, eutrophic tidal
estuary, where turbidity is presumably limiting macro algae mass
development.
P.H. Nienhuis
macroalgae. The eulittoral and sublittoral vegetation of macrophytes
changed significantly after World War II, owing to increased
eutrophication. Zostera marina communities disappeared or reduced
substantially and were replaced by green algal accumulations (Ulva
spp.) in shallow habitats.
4. In the German Wadden Sea a decrease in seagrass distribution and
abundance was observed during and after the wasting disease in
1931-1933, but to a lesser extent than in the Dutch Wadden Sea. Some
eulittoral populations of Zostera marina re-established themselves,
but all sublittoral populations disappeared, owing to increased
turbidity and eutrophication.
5. There was an increase in green macro algal mats (mainly
Enteromorpha prolifera) from 1978 onwards. After 1989, the increase
becomes alarming, especially between the outlets of the river Ems,
Weser and Elbe. Quantitative evidence to substantiate this algal
"increase", however, is scarce.
6. In the Dutch Wadden Sea sublittoral seagrasses (Zostera marina) have
become extinct after the "wasting disease" in 1932-1933. In the 1970s
eulittoral Z. marina and Z. noltii stands also gradually declined.
Increased eutrophication, turbidity and bottom trawling by fisherman
are mentioned as responsible factors.
7. Communities in the Dutch Wadden Sea did not show a shift from
seagrass-dominance to green-algal dominance (cf. German Wadden
Sea). Local accumulations of macro algae (Enteromorpha and Ulva)
frequently occur and are seemingly increasing but these vegetations
are not considered as a management problem.
8. The 300 km of exposed sandy beaches along the west coast of the
Netherlands and Belgium do not suffer from undesired accumulations
of green algae.
9. The estuaries and lagoons in the SW Netherlands show a diversified
picture: Grevelingen lagoon is a stagnant mesotrophic watermass,
where Zostera marina is the (potential) dominant and green macroalgae are virtually absent. Veerse Meer lagoon is a stagnant eutrophic
lake, where Ulva spp. dominates and creates nuisance to water
managers. Oosterschelde is a mesotrophic clear tidal estuary where
green algae are subordinate. Westerschelde is a turbid, eutrophic tidal
estuary, where turbidity is presumably limiting macro algae mass
development.