6.4 Recolonization Following the Ice Winter
185
zation in all treatments with high individual numbers, has probably settled in the
experimental plots as both larvae and postlarvae (compare Chap. 5.5). In 1995, its
abundances in the experimental plots exceeded those from control plots by 2-3
fold. But at that time P. elegans was very abundant throughout the study area of
the Groninger Plate, which, together with a high spatial variability of the benthos,
requires careful interpretation.
6.4.
Recolonization Following the Ice Winter 1995/96
M icrophytohenthos
The individual abundances and species number of benthic diatoms were not affected by the ice winter (Keuker-Rildiger, Ramm, unpub!.). Even immediately
after the winter, mean abundances of 75 000-110 000 indo cm 2 were recorded,
which was comparable to values recorded in the previous summer. In spring 1996,
species number and abundances were a little lower than values from the same time
of 1995. The composition of the diatom assemblage according to the abundances
of their life modes followed the same seasonal development as in previous years,
with mobile diatoms prevailing in the spring period and a higher proportion of
sessile and colony-forming diatoms residing during the summer period. As a consequence of the ice winter, three species (Coscinodiscus concinnus, Achnanthes sp., Nitzschia sp.) were recorded in the backbarrier system of Spiekeroog,
which had not been found here before. In the summer months, cyanobacteria were
frequently found in the sediment.
Nematodes
Some nematodes and other meiofauna organisms were found alive in the ice and
thus survived the winter (Blome, unpub!.). But in February 1996 the lowest
nematode abundances of the entire study period were recorded (160 indo 2 cm·\
The individual density doubled monthly and reached values of 1145 indo 2 cm 2 in
June, which was higher than abundances recorded in previous years. For single
species, the time of year with their highest abundances had shifted. Two scavenging nematode species (Oncholaimellus calvadosicus and Viscosia rustica) dominated the assemblage in winter. The species number of nematodes recorded in
1996 was about the same as in preceding years.
Macrofauna
Immediately after the ice winter only 4 species 200 cm' were recorded (Tecklenborg, unpub!.). With increasing colonization of the tidal flats, this value increased
to 10-12 species 200 cm' by June. This value was comparable to the control
situation of the spring experiment of 1994.
The abundances of the small macrofauna were very low after the ice winter
(about 52 indo 38.5 cm
2
in spring). They increased only with the recruitment in
early June. In the following two months, the abundances of juveniles exceeded
185
zation in all treatments with high individual numbers, has probably settled in the
experimental plots as both larvae and postlarvae (compare Chap. 5.5). In 1995, its
abundances in the experimental plots exceeded those from control plots by 2-3
fold. But at that time P. elegans was very abundant throughout the study area of
the Groninger Plate, which, together with a high spatial variability of the benthos,
requires careful interpretation.
6.4.
Recolonization Following the Ice Winter 1995/96
M icrophytohenthos
The individual abundances and species number of benthic diatoms were not affected by the ice winter (Keuker-Rildiger, Ramm, unpub!.). Even immediately
after the winter, mean abundances of 75 000-110 000 indo cm 2 were recorded,
which was comparable to values recorded in the previous summer. In spring 1996,
species number and abundances were a little lower than values from the same time
of 1995. The composition of the diatom assemblage according to the abundances
of their life modes followed the same seasonal development as in previous years,
with mobile diatoms prevailing in the spring period and a higher proportion of
sessile and colony-forming diatoms residing during the summer period. As a consequence of the ice winter, three species (Coscinodiscus concinnus, Achnanthes sp., Nitzschia sp.) were recorded in the backbarrier system of Spiekeroog,
which had not been found here before. In the summer months, cyanobacteria were
frequently found in the sediment.
Nematodes
Some nematodes and other meiofauna organisms were found alive in the ice and
thus survived the winter (Blome, unpub!.). But in February 1996 the lowest
nematode abundances of the entire study period were recorded (160 indo 2 cm·\
The individual density doubled monthly and reached values of 1145 indo 2 cm 2 in
June, which was higher than abundances recorded in previous years. For single
species, the time of year with their highest abundances had shifted. Two scavenging nematode species (Oncholaimellus calvadosicus and Viscosia rustica) dominated the assemblage in winter. The species number of nematodes recorded in
1996 was about the same as in preceding years.
Macrofauna
Immediately after the ice winter only 4 species 200 cm' were recorded (Tecklenborg, unpub!.). With increasing colonization of the tidal flats, this value increased
to 10-12 species 200 cm' by June. This value was comparable to the control
situation of the spring experiment of 1994.
The abundances of the small macrofauna were very low after the ice winter
(about 52 indo 38.5 cm
2
in spring). They increased only with the recruitment in
early June. In the following two months, the abundances of juveniles exceeded