The North Sea Coasts
213
green algae} and seagrasses contribute significantly to the carbon budget.
In Grevelingen the rooted seagrass Zostera marina covered 20% of the
surface area of the lagoon and had a net production of 150 gCm- 2
yeac 1 • Eelgrass contributes only 14% to the annual carbon budget, while
phytoplankton provides 60% (Fig. 7.11). Recently the population of Zostera marina in Grevelingen drastically decreased: from an area of 4000 ha
in 1986 to 300 ha in 1993. Water quality did not change during that
period. The water is still very clear and rather poor in nutrients. Spatial
competition between seagrasses and macro algae is out. of the question.
Macroalgae playa subordinate role in Grevelingen lagoon (cf. Fig.7.12).
There is much speculation on the causes of the recent seagrass decline in
the Grevelingen lagoon. Obviously, the decrease cannot be attributed to
eutrophication phenomena. One of the stronger hypotheses connects
nitrogen limitation in the environment to the retention of the generative
reproduction in Zostera marina (Van Lent and Verschuure 1994) and
hence to the decline of the entire population.
Ems-Dollard
160 gC m- 2 i 1
Veerse Meer
450 9 C m-2y-1
SG
ITIJ] phytoplankton
IlETI microphytobenthos
Wadden Sea
310 9 C ni 2 y-1
Oosterschelde
240gC ni2;1
•
seagrasses
•
macro-algae soft
Grevelingen
320 9 C m-2y-1
Westerschelde
275 gC m-2j1
IIIIIIIIIII salt -marsh plants
D macro-algae hard
or combination
MAS.
MAH
Fig. 7.11. Preliminary average annual carbon budget of primary producers in Dutch
estuaries. SG Seagrass; MAS macroalgae on soft substrates; MAH macro algae on hard
substrates; SMP salt-marsh plants. (Nienhuis 1992)
213
green algae} and seagrasses contribute significantly to the carbon budget.
In Grevelingen the rooted seagrass Zostera marina covered 20% of the
surface area of the lagoon and had a net production of 150 gCm- 2
yeac 1 • Eelgrass contributes only 14% to the annual carbon budget, while
phytoplankton provides 60% (Fig. 7.11). Recently the population of Zostera marina in Grevelingen drastically decreased: from an area of 4000 ha
in 1986 to 300 ha in 1993. Water quality did not change during that
period. The water is still very clear and rather poor in nutrients. Spatial
competition between seagrasses and macro algae is out. of the question.
Macroalgae playa subordinate role in Grevelingen lagoon (cf. Fig.7.12).
There is much speculation on the causes of the recent seagrass decline in
the Grevelingen lagoon. Obviously, the decrease cannot be attributed to
eutrophication phenomena. One of the stronger hypotheses connects
nitrogen limitation in the environment to the retention of the generative
reproduction in Zostera marina (Van Lent and Verschuure 1994) and
hence to the decline of the entire population.
Ems-Dollard
160 gC m- 2 i 1
Veerse Meer
450 9 C m-2y-1
SG
ITIJ] phytoplankton
IlETI microphytobenthos
Wadden Sea
310 9 C ni 2 y-1
Oosterschelde
240gC ni2;1
•
seagrasses
•
macro-algae soft
Grevelingen
320 9 C m-2y-1
Westerschelde
275 gC m-2j1
IIIIIIIIIII salt -marsh plants
D macro-algae hard
or combination
MAS.
MAH
Fig. 7.11. Preliminary average annual carbon budget of primary producers in Dutch
estuaries. SG Seagrass; MAS macroalgae on soft substrates; MAH macro algae on hard
substrates; SMP salt-marsh plants. (Nienhuis 1992)