9.6 Conclusions
255
Sea (e.g., between tides, tlow regime, sedimentation and morphology). For the
biotic ingredients, the following mechanisms at the individual or population level
are responsible for stability mechanisms:
• high diversity (taxonomic or functional)
• high reproduction
• high mobility
• phenotypic plasticity
• tlexible feeding behaviour
• physiological tolerance
It was shown that organisms of the microfauna, meiofauna and macrofauna are
able to react to disturbances by both "resilience in-situ" and "resilience by migration" (Chaps. 6 and 7).
Using the "4-box-model" (Holling's terminology, 1986), this list of stability
mechanisms suggests that the Wadden Sea of today is permanently in the "exploitation phase". According to Holling, complex systems first have an exploitation
phase and then proceed to a "conservation phase" which is characterized by the
dominance of K-strategists, sessile species and biogenic structures, which effectively buffer environmental tluctuations. A typical example of this transition is the
succession of tree species, which ends in a local climax community where the
canopy trees provide the biogenic structure buffering environmental tluctuations.
The original Wadden Sea of 1000 or more years ago may have been in a conservation phase, but long-lasting and permanent human impact (loss of habitats and
large, long-living species) has changed the system and still continues to do so
(Wolff 1993 and pers. comm.).
The mobility and tlexibility in life cycles of the organisms of the Wadden Sea
has also been reported for other soft-bottom communities and in general for ecosystems with a natural variability of driving forces and is regarded as the precondition for their resilience (Chap. 6; Costanza et al. 1993; DeAngelis & White
1994).
Conditions for regeneration after disturbances
Virtually all ingredients of the Wadden Sea have stability properties which are
directly or indirectly linked to the tides or to the existence of the tidal flats. The
tides determine morphology, flow regime and sedimentation which, in turn, determine almost all processes which are decisive for life in the Wadden Sea (e.g.,
settlement, dispersal). If anthropogenic impacts affect this tide-driven web of processes, important stability mechanisms may break down. For example, areas which
may serve as sources of recolonization as well as the unrestricted transport of dispersal stages are crucial for the resilience of benthic organisms to disturbances
(Chaps. 5.3 and 6). If anthropogenic impact leads to a loss of habitat heterogeneity
and the tlow regime, regeneration after disturbances may be impeded. In order for
the natural stability mechanisms to fully unfurl their potential, the natural, tidedriven abiotic framework must continue to exist. To enable the stability mechanisms of the organisms to work, care must be taken that the abiotic processes
which enable these mechanisms in the first place are a primary focus of conservation.
255
Sea (e.g., between tides, tlow regime, sedimentation and morphology). For the
biotic ingredients, the following mechanisms at the individual or population level
are responsible for stability mechanisms:
• high diversity (taxonomic or functional)
• high reproduction
• high mobility
• phenotypic plasticity
• tlexible feeding behaviour
• physiological tolerance
It was shown that organisms of the microfauna, meiofauna and macrofauna are
able to react to disturbances by both "resilience in-situ" and "resilience by migration" (Chaps. 6 and 7).
Using the "4-box-model" (Holling's terminology, 1986), this list of stability
mechanisms suggests that the Wadden Sea of today is permanently in the "exploitation phase". According to Holling, complex systems first have an exploitation
phase and then proceed to a "conservation phase" which is characterized by the
dominance of K-strategists, sessile species and biogenic structures, which effectively buffer environmental tluctuations. A typical example of this transition is the
succession of tree species, which ends in a local climax community where the
canopy trees provide the biogenic structure buffering environmental tluctuations.
The original Wadden Sea of 1000 or more years ago may have been in a conservation phase, but long-lasting and permanent human impact (loss of habitats and
large, long-living species) has changed the system and still continues to do so
(Wolff 1993 and pers. comm.).
The mobility and tlexibility in life cycles of the organisms of the Wadden Sea
has also been reported for other soft-bottom communities and in general for ecosystems with a natural variability of driving forces and is regarded as the precondition for their resilience (Chap. 6; Costanza et al. 1993; DeAngelis & White
1994).
Conditions for regeneration after disturbances
Virtually all ingredients of the Wadden Sea have stability properties which are
directly or indirectly linked to the tides or to the existence of the tidal flats. The
tides determine morphology, flow regime and sedimentation which, in turn, determine almost all processes which are decisive for life in the Wadden Sea (e.g.,
settlement, dispersal). If anthropogenic impacts affect this tide-driven web of processes, important stability mechanisms may break down. For example, areas which
may serve as sources of recolonization as well as the unrestricted transport of dispersal stages are crucial for the resilience of benthic organisms to disturbances
(Chaps. 5.3 and 6). If anthropogenic impact leads to a loss of habitat heterogeneity
and the tlow regime, regeneration after disturbances may be impeded. In order for
the natural stability mechanisms to fully unfurl their potential, the natural, tidedriven abiotic framework must continue to exist. To enable the stability mechanisms of the organisms to work, care must be taken that the abiotic processes
which enable these mechanisms in the first place are a primary focus of conservation.