244
M. Sprung et al.
ground production, however, estimates are lower (260 g C m- 2 a-I) when compared with Ria Formosa sites (350 g C m- 2 a-I).
Green Algae. These are regular elements in intertidal areas of the inner Ria
Formosa during winter. However, they may persist all year round at some
spots that are subject to anthropogenic pollution, above all by domestic
waste-water input (AnibaI1998). In the Wadden Sea, they have occasionally
been quite common particularly during summer months in certain years
(Reise and Siebert 1994; Asmus et al. 1998). Their contribution to the production of the whole system is very difficult to estimate. In the Ria Formosa
lagoon it is, with 36 g C m- 2 a-I, the main source of primary production of the
mud flats (AnibaI1998). For the whole Wadden Sea, green algal production
was assessed to be 15 g C m- 2 per year, when a maximum coverage of 5-10 %
of the intertidal area is assumed (Reise et al. 1993). Hence, it has been assumed
to be insignificant in comparison with other sources.
Microphytobenthos. This is the principal source of primary production on
the sand flats of the Ria Formosa lagoon and on seagrass beds, mud flats and
sand flats of the Sylt -R0m0 Bay. In the intertidal zone of the Sylt -R0m0 Bay,
microphytobenthos attains 83 % of the primary production. The contribution
for the Ria Formosa sites turned out to be much lower, for sand flats onethird, for mud flats, whose production is dominated by green algae, less than
one-tenth of the Sylt-R0m0 Bay.
Phytoplankton. Its importance increases with inundation time and water
depth. For the Ria Formosa lagoon, estimates are subject to strong local and
temporal variation.
These variations are the result of the concomitant action of nutrient availability, water turbidity and action of suspension feeders. The filtering activity
of suspension feeders per unit area may not be extreme. Mendon<;:a (1992)
registered in the lower intertidal zone a benthic filtering activity in field
chambers of 23.11 m- 2 h- I (median in a seagrass bed) and 36.11 m- 2 h-I
(median on a sand flat). However, taking into account the current speed and
water depth, it can be calculated that at this particular site about 10 % of the
water column will be cleared during a spring tidal cycle and 37 % during a
neap tidal cycle by the action of suspension feeders.
An annual average of 100 g C m- 2 has been assumed as most realistic for
phytoplankton production. This estimate is based on an average of 45 g C m- 2
recorded during an annual cycle in 199011991 for intertidal sites, and on 14C
incubations by Falcao et al. (1991) in 1985/6 which varied between 0.780.7jlg C I-I h-I.Assuming a water depth of 1 m as representative for the whole
lagoon would imply that phytoplankton contributes roughly 11 % to total
primary production.
M. Sprung et al.
ground production, however, estimates are lower (260 g C m- 2 a-I) when compared with Ria Formosa sites (350 g C m- 2 a-I).
Green Algae. These are regular elements in intertidal areas of the inner Ria
Formosa during winter. However, they may persist all year round at some
spots that are subject to anthropogenic pollution, above all by domestic
waste-water input (AnibaI1998). In the Wadden Sea, they have occasionally
been quite common particularly during summer months in certain years
(Reise and Siebert 1994; Asmus et al. 1998). Their contribution to the production of the whole system is very difficult to estimate. In the Ria Formosa
lagoon it is, with 36 g C m- 2 a-I, the main source of primary production of the
mud flats (AnibaI1998). For the whole Wadden Sea, green algal production
was assessed to be 15 g C m- 2 per year, when a maximum coverage of 5-10 %
of the intertidal area is assumed (Reise et al. 1993). Hence, it has been assumed
to be insignificant in comparison with other sources.
Microphytobenthos. This is the principal source of primary production on
the sand flats of the Ria Formosa lagoon and on seagrass beds, mud flats and
sand flats of the Sylt -R0m0 Bay. In the intertidal zone of the Sylt -R0m0 Bay,
microphytobenthos attains 83 % of the primary production. The contribution
for the Ria Formosa sites turned out to be much lower, for sand flats onethird, for mud flats, whose production is dominated by green algae, less than
one-tenth of the Sylt-R0m0 Bay.
Phytoplankton. Its importance increases with inundation time and water
depth. For the Ria Formosa lagoon, estimates are subject to strong local and
temporal variation.
These variations are the result of the concomitant action of nutrient availability, water turbidity and action of suspension feeders. The filtering activity
of suspension feeders per unit area may not be extreme. Mendon<;:a (1992)
registered in the lower intertidal zone a benthic filtering activity in field
chambers of 23.11 m- 2 h- I (median in a seagrass bed) and 36.11 m- 2 h-I
(median on a sand flat). However, taking into account the current speed and
water depth, it can be calculated that at this particular site about 10 % of the
water column will be cleared during a spring tidal cycle and 37 % during a
neap tidal cycle by the action of suspension feeders.
An annual average of 100 g C m- 2 has been assumed as most realistic for
phytoplankton production. This estimate is based on an average of 45 g C m- 2
recorded during an annual cycle in 199011991 for intertidal sites, and on 14C
incubations by Falcao et al. (1991) in 1985/6 which varied between 0.780.7jlg C I-I h-I.Assuming a water depth of 1 m as representative for the whole
lagoon would imply that phytoplankton contributes roughly 11 % to total
primary production.