l)5 The Biotic Ingredients of the Wadden Sea
245
Significance o/the ingredient/or the Wadden Sea
The single-cell algae of microphytobenthos and phytoplankton are the most important primary producers of the Wadden Sea. They are a food source of meio- and
macrobenthos. The high rate of primary production is a characteristic property of
the Wadden Sea.
Another important role of the microphytobenthos is that they reduce the erodibility of the sediment surface (Holland et al. 1974). This "stabilization" of the
sediment is presumably an important requirement for the larval settlement of many
macrobenthic species (cf. Chap. 5.3).
Stability properties: persistence and resilience
The primary production of microphytobenthos and phytoplankton might be regarded as persistent if in the definition of persistence we allow for a wide range of
variation of the rate of primary production. Primary production does not, however,
seem to be constant because in some parts of the Wadden Sea a marked increase of
primary production has been observed during the past decades, presumably due to
an increased input of nutrients to the Wadden Sea (Asmus et al. 1998).
The overall abundance and species composition of phytoplankton within a certain year is as variable as the variables which mainly determine abundance and
species composition, temperature and nutrient concentration (see Chap. 5.1). In
addition, rare episodic events may occur which increase variability, e.g., the
blooms of Coscinodiscus cOflcinnus and Phaeocystis pouchetii after an ice winter
(Chap. 5.1 and 7). Both of these species are adapted to temperatures lower than
those typical of the Wadden Sea and thus had a temporary competitive advantage
during the long-lasting low temperatures in spring 1996, which led to a bloom of
these species in the East Frisian Wadden Sea - at the expense of "normal" species
which did not bloom here as usual.
The presence of benthic diatoms in the sediment is resilient to disturbances
(e.g., storms, drift ice, algal mats; Chaps. 6 and 7) and in turn extremely persistent.
Nevertheless, the phenology of the abundance of benthic diatoms showed marked
differences in different years, which are mainly due to variations of the abiotic
conditions and of grazing pressure (Reise 1992).
Stability mechanisms
The mechanisms responsible for the stability properties of the microalgae in the
Wadden Sea are similar to those of the bacteria: high potential population growth
rates and high species diversity. In addition, the abiotic conditions which are required for high primary production (e.g., better light conditions in the intertidal
during low tides, dynamic water body, availability of nutrients and remineralization) are persistent and resilient. However, benthic diatoms themselves contribute
to the stability properties of the abiotic ingredient "oxic layer" by the production of
oxygen.
Two mechanisms are responsible for the resilience of benthic algae to local
disturbances: Firstly, disturbed areas are recolonized from undisturbed areas via
the tidal currents (cf. Chap. 6). Grubb & Hopkins (1986) call this mechanism "re-
245
Significance o/the ingredient/or the Wadden Sea
The single-cell algae of microphytobenthos and phytoplankton are the most important primary producers of the Wadden Sea. They are a food source of meio- and
macrobenthos. The high rate of primary production is a characteristic property of
the Wadden Sea.
Another important role of the microphytobenthos is that they reduce the erodibility of the sediment surface (Holland et al. 1974). This "stabilization" of the
sediment is presumably an important requirement for the larval settlement of many
macrobenthic species (cf. Chap. 5.3).
Stability properties: persistence and resilience
The primary production of microphytobenthos and phytoplankton might be regarded as persistent if in the definition of persistence we allow for a wide range of
variation of the rate of primary production. Primary production does not, however,
seem to be constant because in some parts of the Wadden Sea a marked increase of
primary production has been observed during the past decades, presumably due to
an increased input of nutrients to the Wadden Sea (Asmus et al. 1998).
The overall abundance and species composition of phytoplankton within a certain year is as variable as the variables which mainly determine abundance and
species composition, temperature and nutrient concentration (see Chap. 5.1). In
addition, rare episodic events may occur which increase variability, e.g., the
blooms of Coscinodiscus cOflcinnus and Phaeocystis pouchetii after an ice winter
(Chap. 5.1 and 7). Both of these species are adapted to temperatures lower than
those typical of the Wadden Sea and thus had a temporary competitive advantage
during the long-lasting low temperatures in spring 1996, which led to a bloom of
these species in the East Frisian Wadden Sea - at the expense of "normal" species
which did not bloom here as usual.
The presence of benthic diatoms in the sediment is resilient to disturbances
(e.g., storms, drift ice, algal mats; Chaps. 6 and 7) and in turn extremely persistent.
Nevertheless, the phenology of the abundance of benthic diatoms showed marked
differences in different years, which are mainly due to variations of the abiotic
conditions and of grazing pressure (Reise 1992).
Stability mechanisms
The mechanisms responsible for the stability properties of the microalgae in the
Wadden Sea are similar to those of the bacteria: high potential population growth
rates and high species diversity. In addition, the abiotic conditions which are required for high primary production (e.g., better light conditions in the intertidal
during low tides, dynamic water body, availability of nutrients and remineralization) are persistent and resilient. However, benthic diatoms themselves contribute
to the stability properties of the abiotic ingredient "oxic layer" by the production of
oxygen.
Two mechanisms are responsible for the resilience of benthic algae to local
disturbances: Firstly, disturbed areas are recolonized from undisturbed areas via
the tidal currents (cf. Chap. 6). Grubb & Hopkins (1986) call this mechanism "re-