214
80
GREVELINGEN
• seagrass Zostera marina
60
• macro-algae
40
20
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60
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1987
VEERSE MEER
AM J J
1987
1988
1989
JASONOJ
1988
1889
P.R. Nienhuis
Fig. 7.12. Percentage coverage of Zostera marina and macro algae in vertical projection on the sediment in permanent sample plots in Veerse Meer lagoon (below) and
Grevelingen lagoon (above). Size of sample plots is 15 x 15 m 2 , water depth at both
localities is 1.25 m. (Nienhuis 1989)
In eutrophic waters, such as Veerse Meer, macroalgae became more
prominent. Here, seagrasses cover only 3% of the surface area of the
lagoon while macro algae - mainly Ulva - cover 20%. The lagoon is
dominated by Ulva species during summer, producing roughly
500 gCm- 2 year- 1 at a maximum in shallow areas. The averaged contribution to the annual carbon budget ofVeerse Meer is 120gCm- 2 year-I,
which is 27% of the lagoon's budget (Fig. 7.11). The high nitrogen load of
Veerse Meer not only resuls in a high producttion of phytoplankton, but
also in mass growth of Ulva in shallow areas.