Energy Flow in Benthic Assemblages: Portugal and North Sea Tidal Basins
243
modes during equal time fractions. Hence, secondary production has been
split that way. Omnivorous potential has been calculated as the percentage of
the production of species in common for two feeding types.
11.4 Production
11.4.1 Primary Production
The quantity and quality of the primary production turn out to be quite
different in both systems (Table 11.2).
Salt Marshes. In the Ria Formosa lagoon, salt marshes are the dominant
primary producers, due to its areal extent and its high production rate per
area (about 60 % of the entire primary production). This figure, however, only
holds when the extrapolation of the production rate of the Spartina zone to
other salt marsh habitats is valid. There are good reasons in favour [see e. g.
Bouchard and Lefeuvre (1996) for an Atriplex portulacoides salt marsh at
Mont Sant Michel, France]. S. maritima covers about 8km 2 corresponding to
one-third of the salt marsh area.
In the Sylt -R0m0 Bay salt marsh vegetation contributes only to a very
limited degree to the primary production. It mainly grows above mean high
tide level (Puccinellia maritima, Festuca rubra, Armeria maritima); only the
pioneer stages of Salicornia stricta and Spartina anglica extend their range
30 cm below mean high tidal level. Therefore, most of the 10 km 2 of these salt
marshes are inundated only during storm floods; this is equivalent to 250 to
20 tidal cycles or 125-10 days per year depending on the accretion level.
Seagrass Beds. The principal seagrass species is Zostera noltii in both
intertidal areas. Z. marina is rare in both systems. In the Ria Formosa, it is
almost entirely restricted to the subtidal region, whereas in the Sylt -R0m0 Bay
it occurs only intertidally, while the subtidal population has disappeared since
1932 (Asmus and Asmus 2000). Cymodocea nodosa is, next to Z. noltii, the
principal subtidal species in the Ria Formosa. The subtidal benthic primary
production figure is based on a contribution of 5 km 2 subtidal seagrass beds
with the same primary production as Z. noltii in the intertidal zone. C. nodosa
is lacking in the Sylt-R0m0 Bay due to the biogeographical range of this
warm-temperate to subtropical species (Den Hartog 1970).
In the production estimate for the Sylt-R0m0 Bay microphytobenthos and
epiphyte production is also included. This explains why production per area
is nearly twice as high as in the Ria Formosa. In terms of seagrass above-
243
modes during equal time fractions. Hence, secondary production has been
split that way. Omnivorous potential has been calculated as the percentage of
the production of species in common for two feeding types.
11.4 Production
11.4.1 Primary Production
The quantity and quality of the primary production turn out to be quite
different in both systems (Table 11.2).
Salt Marshes. In the Ria Formosa lagoon, salt marshes are the dominant
primary producers, due to its areal extent and its high production rate per
area (about 60 % of the entire primary production). This figure, however, only
holds when the extrapolation of the production rate of the Spartina zone to
other salt marsh habitats is valid. There are good reasons in favour [see e. g.
Bouchard and Lefeuvre (1996) for an Atriplex portulacoides salt marsh at
Mont Sant Michel, France]. S. maritima covers about 8km 2 corresponding to
one-third of the salt marsh area.
In the Sylt -R0m0 Bay salt marsh vegetation contributes only to a very
limited degree to the primary production. It mainly grows above mean high
tide level (Puccinellia maritima, Festuca rubra, Armeria maritima); only the
pioneer stages of Salicornia stricta and Spartina anglica extend their range
30 cm below mean high tidal level. Therefore, most of the 10 km 2 of these salt
marshes are inundated only during storm floods; this is equivalent to 250 to
20 tidal cycles or 125-10 days per year depending on the accretion level.
Seagrass Beds. The principal seagrass species is Zostera noltii in both
intertidal areas. Z. marina is rare in both systems. In the Ria Formosa, it is
almost entirely restricted to the subtidal region, whereas in the Sylt -R0m0 Bay
it occurs only intertidally, while the subtidal population has disappeared since
1932 (Asmus and Asmus 2000). Cymodocea nodosa is, next to Z. noltii, the
principal subtidal species in the Ria Formosa. The subtidal benthic primary
production figure is based on a contribution of 5 km 2 subtidal seagrass beds
with the same primary production as Z. noltii in the intertidal zone. C. nodosa
is lacking in the Sylt-R0m0 Bay due to the biogeographical range of this
warm-temperate to subtropical species (Den Hartog 1970).
In the production estimate for the Sylt-R0m0 Bay microphytobenthos and
epiphyte production is also included. This explains why production per area
is nearly twice as high as in the Ria Formosa. In terms of seagrass above-