254
<) StahIiIly Properties !I1 the Waddcll Sca
The resilience of the biotic ingredients is mostly considered in the case of spatially localized disturbances: resilience in the performance of bacteria and benthic
algae in disturbed areas, as well as resilience in the distribution pattern of macrobenthic species and in the species composition of benthic communities.
The mechanisms which are responsible for the stability properties are similar to
those of the abiotic ingredients. All these mechanisms enable resistance or resilience and thus persistence.
9.6
Conclusions
In this chapter, we have tried to assess the stability properties of the abiotic and
biotic ingredients of the Wadden Sea which were studied by ELA WA T. Stability
properties are emergent properties which can only be perceived on a certain level
of description and have no direct meaning at lower levels of description. Our enumeration showed that the ingredients exhibit certain stability properties on certain
spatial and temporal scales. However, it is impossible for practical and principle
reasons to attribute stability properties for the entire Wadden Sea. The practical
reasons for this are that, firstly, ELA WAT could only study a subset of ingredients
over too short a time span (Chap. 10), and secondly, the significance of interactions between ingredients and species was not sufficiently studied. The principle
reasons are, besides those listed by Grimm et al. (1992) and Grimm (1996), that
the identification of emergent properties at the level of the ecosystem depends on
the identification of the ecosystem itself (cf. Wiegleb & Brbring 1996; lax et al.
1998) - a task which has not yet been fully performed for the Wadden Sea.
In the following we will summarize our findings concerning the scale dependence of stability properties and the conditions required to enable regeneration after
disturbances.
Scale dependence of stability properties
For both abiotic and biotic ingredients, our enumeration showed that on small
spatial and temporal scales the variables of interest show little constancy or high
variability. Constancy, and in the case of disturbances, resilience only shows up at
larger scales. On even larger scales (many decades and more) and for the entire
Wadden Sea or large parts thereof, persistence would prevail under natural conditions. However, historical records and long-term studies seem to indicate slow
changes among both abiotic ingredients (e.g., morphology) and of biotic ingredients (species composition, primary production, biomass, bird abundance).
For many ingredients it proved difficult to identify reference dynamics. It
turned out that certain states, e.g. certain snapshots of the Wadden Sea, are unsuitable as a reference. Instead, the state of the Wadden Sea is its dynamics!
Survey of stability mechanisms
Stability mechanisms of abiotic ingredients are often coupled to supra-regional
processes (e.g., climate) or are due to negative feedback loops within the Wadden
<) StahIiIly Properties !I1 the Waddcll Sca
The resilience of the biotic ingredients is mostly considered in the case of spatially localized disturbances: resilience in the performance of bacteria and benthic
algae in disturbed areas, as well as resilience in the distribution pattern of macrobenthic species and in the species composition of benthic communities.
The mechanisms which are responsible for the stability properties are similar to
those of the abiotic ingredients. All these mechanisms enable resistance or resilience and thus persistence.
9.6
Conclusions
In this chapter, we have tried to assess the stability properties of the abiotic and
biotic ingredients of the Wadden Sea which were studied by ELA WA T. Stability
properties are emergent properties which can only be perceived on a certain level
of description and have no direct meaning at lower levels of description. Our enumeration showed that the ingredients exhibit certain stability properties on certain
spatial and temporal scales. However, it is impossible for practical and principle
reasons to attribute stability properties for the entire Wadden Sea. The practical
reasons for this are that, firstly, ELA WAT could only study a subset of ingredients
over too short a time span (Chap. 10), and secondly, the significance of interactions between ingredients and species was not sufficiently studied. The principle
reasons are, besides those listed by Grimm et al. (1992) and Grimm (1996), that
the identification of emergent properties at the level of the ecosystem depends on
the identification of the ecosystem itself (cf. Wiegleb & Brbring 1996; lax et al.
1998) - a task which has not yet been fully performed for the Wadden Sea.
In the following we will summarize our findings concerning the scale dependence of stability properties and the conditions required to enable regeneration after
disturbances.
Scale dependence of stability properties
For both abiotic and biotic ingredients, our enumeration showed that on small
spatial and temporal scales the variables of interest show little constancy or high
variability. Constancy, and in the case of disturbances, resilience only shows up at
larger scales. On even larger scales (many decades and more) and for the entire
Wadden Sea or large parts thereof, persistence would prevail under natural conditions. However, historical records and long-term studies seem to indicate slow
changes among both abiotic ingredients (e.g., morphology) and of biotic ingredients (species composition, primary production, biomass, bird abundance).
For many ingredients it proved difficult to identify reference dynamics. It
turned out that certain states, e.g. certain snapshots of the Wadden Sea, are unsuitable as a reference. Instead, the state of the Wadden Sea is its dynamics!
Survey of stability mechanisms
Stability mechanisms of abiotic ingredients are often coupled to supra-regional
processes (e.g., climate) or are due to negative feedback loops within the Wadden