Y.5 The Biotic Ingredients of the Wadden Sea
253
demographic consequences, for example by resulting in a decline of certain bird
species.
Stability mechanisms
Little can be inferred from the studies under ELA W AT about the mechanisms
responsible for the relative constancy of bird abundance because these mechanisms
mainly function outside the Wadden Sea. It seems clear, however, that the constantly high abundance of food resources in the Wadden Sea is an important factor
in the predictability of the overall abundance of the migratory birds. Wadden Sea
"petrol station" is very reliable from the point of view of the migratory birds.
Resistance to ice winters relies on mechanisms at the individual level. Flexibility with respect to their prey properties or prey species enables the birds to even
survive extreme weather conditions. Moreover, their migratory behaviour is flexible. Birds leave the Wadden Sea earlier than usual under bad weather conditions.
Extreme scenarios
In the view of birds which use the macrozoobenthos as food, evidently a Wadden
Sea without macrozoobenthos would be disastrous. From the point of view of the
other fauna, especially the macrozoobenthos, the total disappearance of the birds
would probably have less dramatic consequences. Because of the rather small
proportion of available biomass consumed by birds, it can be assumed that birds do
not control the dynamics of the benthic species but merely influence them numerically. However, there is too little empirical evidence and theoretical insight into
the mode of interaction between birds and their prey in the Wadden Sea to be sure
about this point.
9.5.5
Summary: Biotic Ingredients of the Wadden Sea
The assessment of stability properties of the biotic ingredients of the Wadden Sea
follows a similar pattern as for the abiotic ingredients (9.4.4): on a short time scale
(from a few days to a year) and small areas - low constancy (or high unpredictability); on an intermediate time scale (a few years to several decades) and larger
areas - constancy (or low variability), with resilience in the case of disturbances;
and on a long time scale (many decades and longer) and the entire Wadden Sea -
persistence. It must be emphasized, however, that in the long term abiotic boundary conditions may continue to change slowly but surely as a result of anthropogenic influences. Several species were exterminated in the Wadden Sea by overexploitation. Furthermore, the loss of species reported for the past was often linked to
the loss of key habitats such as oyster reefs, Sabellaria reefs, or salt marshes
(Reise 1992, 1991). The ongoing loss of mudflats may have similar consequences
III the future.
As with meteorological conditions, there are no reference "states" for biotic
components: there are no "normal" years. At best, reference dynamics can be
identified, i.e. typical elements of the phenology, and typical ranges of abundances
for certain species.
253
demographic consequences, for example by resulting in a decline of certain bird
species.
Stability mechanisms
Little can be inferred from the studies under ELA W AT about the mechanisms
responsible for the relative constancy of bird abundance because these mechanisms
mainly function outside the Wadden Sea. It seems clear, however, that the constantly high abundance of food resources in the Wadden Sea is an important factor
in the predictability of the overall abundance of the migratory birds. Wadden Sea
"petrol station" is very reliable from the point of view of the migratory birds.
Resistance to ice winters relies on mechanisms at the individual level. Flexibility with respect to their prey properties or prey species enables the birds to even
survive extreme weather conditions. Moreover, their migratory behaviour is flexible. Birds leave the Wadden Sea earlier than usual under bad weather conditions.
Extreme scenarios
In the view of birds which use the macrozoobenthos as food, evidently a Wadden
Sea without macrozoobenthos would be disastrous. From the point of view of the
other fauna, especially the macrozoobenthos, the total disappearance of the birds
would probably have less dramatic consequences. Because of the rather small
proportion of available biomass consumed by birds, it can be assumed that birds do
not control the dynamics of the benthic species but merely influence them numerically. However, there is too little empirical evidence and theoretical insight into
the mode of interaction between birds and their prey in the Wadden Sea to be sure
about this point.
9.5.5
Summary: Biotic Ingredients of the Wadden Sea
The assessment of stability properties of the biotic ingredients of the Wadden Sea
follows a similar pattern as for the abiotic ingredients (9.4.4): on a short time scale
(from a few days to a year) and small areas - low constancy (or high unpredictability); on an intermediate time scale (a few years to several decades) and larger
areas - constancy (or low variability), with resilience in the case of disturbances;
and on a long time scale (many decades and longer) and the entire Wadden Sea -
persistence. It must be emphasized, however, that in the long term abiotic boundary conditions may continue to change slowly but surely as a result of anthropogenic influences. Several species were exterminated in the Wadden Sea by overexploitation. Furthermore, the loss of species reported for the past was often linked to
the loss of key habitats such as oyster reefs, Sabellaria reefs, or salt marshes
(Reise 1992, 1991). The ongoing loss of mudflats may have similar consequences
III the future.
As with meteorological conditions, there are no reference "states" for biotic
components: there are no "normal" years. At best, reference dynamics can be
identified, i.e. typical elements of the phenology, and typical ranges of abundances
for certain species.