176
6 Rccolol11zatlOn of Tidal Flat, After Disturbance
have resulted in a scheme where an early successional stage dominated by opportunistic species and r-strategists is followed by further stages with mainly kselected species (Grassle & Grassle 1974; McCall 1977; Pearson & Rosenberg
1978; Rhoads et al. 1978). This classic succession model was further elaborated by
investigations on the colonization mode of larvae, postlarvae or adults (Dauer &
Simon 1976; Santos & Simon 1980; Smith & Brumsickle 1989; Savidge & Taghon 1988; Frid 1989), the dependence on the size of the disturbance (Probert 1984;
Thrush et al. 1996) as well as the timing of the disturbance (Simon & Dauer 1977;
Zajac & Whitlatch 1982 a; Bonsdorff & Osterman 1985). However, this scheme
was not found to be valid for all soft-sediment communities, as in some cases a
recolonization occurred that was more dependent on the area and time instead of
following clear successional stages (Zajac & Whitlatch 1982 b). This is especially
the case when the benthic community is composed of opportunistic, stress-tolerant
species and is naturally in a state resembling an early successional stage of the
above mentioned scheme (Zajac & Whitlatch 1982 b; Gamenick et al. 1996).
In the ecosystem research project ELA W A T, the recolonization experiments
were carried out under the central topic of the reaction of benthic organisms to
disturbances and the search for possible stability properties of the Wadden Sea
ecosystem (Chap. 2). This chapter summarizes unpublished results of experiments
carried out by Tecklenborg, Keuker-Ri.idiger, Blome and Langner. Their experiments targeted the question how timing, kind and intensity of a disturbance may
affect a benthic community. The recolonization of small infauna and microphytobenthos were recorded. The mode of recolonization and relevant geochemical
parameters were assessed in collaboration with other sub-projects. The experiments were carried out in the main study area of ELA W A T in a sandflat on the
Groninger Plate (Fig. 3.1.4), where the community was characterized by the lugworm Arenicola marina and the sand mason Lanice conchilega.
As a disturbance, the plots were defaunated to simulate the cover of tidal flats
by extensive mats of filamentous green algae. Such events had occurred in the
Wadden Sea in the 1980s, depriving the sediment underneath the algal layer of
oxygen and finally causing the death of benthic organisms (Reise et al. 1994). The
"black spots" occurring in the East Frisian Wadden Sea can be interpreted as a
long-lasting effect of this event (Hopner & Michaelis 1994).
The ice winter 1995/96 was taken as an occasion to study the regeneration of
the tidal tlat community after this natural disturbance and to compare the recolonization pattern with the results of the recolonization experiments of the preceding
years. In contrast to the more localized effects of the disturbance experiments, the
ice winter affected the entire region (Beukema et al. 1993, Chap. 7). While the
defaunation reduced all benthic organisms in the experimental plots, the ice winter
selectively killed the cold sensitive species (Beukema 1979, 1989; Chaps. 5, 7).
Thus regeneration of benthic communities can be different for the experimental
and natural disturbances investigated here.
6 Rccolol11zatlOn of Tidal Flat, After Disturbance
have resulted in a scheme where an early successional stage dominated by opportunistic species and r-strategists is followed by further stages with mainly kselected species (Grassle & Grassle 1974; McCall 1977; Pearson & Rosenberg
1978; Rhoads et al. 1978). This classic succession model was further elaborated by
investigations on the colonization mode of larvae, postlarvae or adults (Dauer &
Simon 1976; Santos & Simon 1980; Smith & Brumsickle 1989; Savidge & Taghon 1988; Frid 1989), the dependence on the size of the disturbance (Probert 1984;
Thrush et al. 1996) as well as the timing of the disturbance (Simon & Dauer 1977;
Zajac & Whitlatch 1982 a; Bonsdorff & Osterman 1985). However, this scheme
was not found to be valid for all soft-sediment communities, as in some cases a
recolonization occurred that was more dependent on the area and time instead of
following clear successional stages (Zajac & Whitlatch 1982 b). This is especially
the case when the benthic community is composed of opportunistic, stress-tolerant
species and is naturally in a state resembling an early successional stage of the
above mentioned scheme (Zajac & Whitlatch 1982 b; Gamenick et al. 1996).
In the ecosystem research project ELA W A T, the recolonization experiments
were carried out under the central topic of the reaction of benthic organisms to
disturbances and the search for possible stability properties of the Wadden Sea
ecosystem (Chap. 2). This chapter summarizes unpublished results of experiments
carried out by Tecklenborg, Keuker-Ri.idiger, Blome and Langner. Their experiments targeted the question how timing, kind and intensity of a disturbance may
affect a benthic community. The recolonization of small infauna and microphytobenthos were recorded. The mode of recolonization and relevant geochemical
parameters were assessed in collaboration with other sub-projects. The experiments were carried out in the main study area of ELA W A T in a sandflat on the
Groninger Plate (Fig. 3.1.4), where the community was characterized by the lugworm Arenicola marina and the sand mason Lanice conchilega.
As a disturbance, the plots were defaunated to simulate the cover of tidal flats
by extensive mats of filamentous green algae. Such events had occurred in the
Wadden Sea in the 1980s, depriving the sediment underneath the algal layer of
oxygen and finally causing the death of benthic organisms (Reise et al. 1994). The
"black spots" occurring in the East Frisian Wadden Sea can be interpreted as a
long-lasting effect of this event (Hopner & Michaelis 1994).
The ice winter 1995/96 was taken as an occasion to study the regeneration of
the tidal tlat community after this natural disturbance and to compare the recolonization pattern with the results of the recolonization experiments of the preceding
years. In contrast to the more localized effects of the disturbance experiments, the
ice winter affected the entire region (Beukema et al. 1993, Chap. 7). While the
defaunation reduced all benthic organisms in the experimental plots, the ice winter
selectively killed the cold sensitive species (Beukema 1979, 1989; Chaps. 5, 7).
Thus regeneration of benthic communities can be different for the experimental
and natural disturbances investigated here.