2 ELA W AT: Goals and Conceptual Framework
7
As ELA W A T thus entered uncharted territory it is not surprising that the conceptual framework developed during the course of the project. This process is
documented in the synthesis of the project presented here, along with the actual
results of the synthesis. Although resilience stood in the foreground at the beginning of ELA WAT (as retlected in the title of the project with "Elastizitat" being
German for resilience), it became increasingly obvious that studying resilience
would not be an end in itself but a diagnostic tool to investigate basic processes in
the Wadden Sea and to integrate the results of the sub-projects. Thus, stability
properties were not taken as a mechanistic model imposed on the Wadden Sea
ecosystem (cf. Reise 1994) in which all parts interact like cogs and lead to deterministic, predictable behaviour of the entire system (such as a "balance of nature").
The elements of the conceptual framework of ELWAT are described below.
Subsequently, the task for the synthesis of ELA WAT and, in turn, the structure of
this book are explained.
What do we mean by the Wadden Sea "ecosystem"?
ELA W AT focused on the original ecosystem definition by Tansley (1935), which
reads in a modern version by Likens (1992) as follows: An ecosystem is "a spatially explicit unit of the Earth that includes all of the organisms, along with all
components of the abiotic environment within its boundaries" (see also lax 1994a;
lax et al. 1993). Following this definition, the Wadden Sea can be defined as an
ecosystem whose spatially explicit unit is given by the tidal area. As the Wadden
Sea is a transition zone between land and sea, like any other tidally dominated
shallow sea or estuary, the outer margins - the high- and low water line - are open
borders to adjacent terrestrial and marine systems (Costanza et al. 1993). The
organisms living in this tidal area are adapted to the living conditions changing
with each tidal cycle. Yet the habitat of many organisms extends beyond the tidal
area (Reise 1985): pelagic larvae of intertidal benthic organisms, for example,
occur in North Sea waters. The Wadden Sea is also a major nursery ground for
fish and crustaceans of the North Sea. Migratory birds, who rest in the Wadden
Sea on their migration between tropical wintering grounds and arctic breeding
grounds, have the largest habitat range of Wadden Sea visitors. Thus the Wadden
Sea is just a temporary home for many organisms.
Disturbances and disturbance regime: definitions
The stability property "resilience" (see below) can only be assessed in relation to
disturbance-induced changes. Thus, ELA WAT focused on the investigation of
mainly natural, small-scale and short-term disturbances. Following lax et al.
(1993), the definition of disturbance by Pickett & White (1985) was used in
ELA W A T, whereby "a disturbance is any relatively discrete event in time that
disrupts ecosystem, community, or population structure and changes resources,
substrate availability, or the physical environment". This definition combines
cause and effect. However, forming an objective judgement on disturbance effects
is often not easy.
7
As ELA W A T thus entered uncharted territory it is not surprising that the conceptual framework developed during the course of the project. This process is
documented in the synthesis of the project presented here, along with the actual
results of the synthesis. Although resilience stood in the foreground at the beginning of ELA WAT (as retlected in the title of the project with "Elastizitat" being
German for resilience), it became increasingly obvious that studying resilience
would not be an end in itself but a diagnostic tool to investigate basic processes in
the Wadden Sea and to integrate the results of the sub-projects. Thus, stability
properties were not taken as a mechanistic model imposed on the Wadden Sea
ecosystem (cf. Reise 1994) in which all parts interact like cogs and lead to deterministic, predictable behaviour of the entire system (such as a "balance of nature").
The elements of the conceptual framework of ELWAT are described below.
Subsequently, the task for the synthesis of ELA WAT and, in turn, the structure of
this book are explained.
What do we mean by the Wadden Sea "ecosystem"?
ELA W AT focused on the original ecosystem definition by Tansley (1935), which
reads in a modern version by Likens (1992) as follows: An ecosystem is "a spatially explicit unit of the Earth that includes all of the organisms, along with all
components of the abiotic environment within its boundaries" (see also lax 1994a;
lax et al. 1993). Following this definition, the Wadden Sea can be defined as an
ecosystem whose spatially explicit unit is given by the tidal area. As the Wadden
Sea is a transition zone between land and sea, like any other tidally dominated
shallow sea or estuary, the outer margins - the high- and low water line - are open
borders to adjacent terrestrial and marine systems (Costanza et al. 1993). The
organisms living in this tidal area are adapted to the living conditions changing
with each tidal cycle. Yet the habitat of many organisms extends beyond the tidal
area (Reise 1985): pelagic larvae of intertidal benthic organisms, for example,
occur in North Sea waters. The Wadden Sea is also a major nursery ground for
fish and crustaceans of the North Sea. Migratory birds, who rest in the Wadden
Sea on their migration between tropical wintering grounds and arctic breeding
grounds, have the largest habitat range of Wadden Sea visitors. Thus the Wadden
Sea is just a temporary home for many organisms.
Disturbances and disturbance regime: definitions
The stability property "resilience" (see below) can only be assessed in relation to
disturbance-induced changes. Thus, ELA WAT focused on the investigation of
mainly natural, small-scale and short-term disturbances. Following lax et al.
(1993), the definition of disturbance by Pickett & White (1985) was used in
ELA W A T, whereby "a disturbance is any relatively discrete event in time that
disrupts ecosystem, community, or population structure and changes resources,
substrate availability, or the physical environment". This definition combines
cause and effect. However, forming an objective judgement on disturbance effects
is often not easy.