194
7 Effects of the Icc WlI1tcr 1 (J95/%
recolonization of the intertidal by cold sensitive species lie subtidally, future studies on recruitment after ice winters should include both the intertidal and subtidal
benthic systems.
7.1
I ntrod uction
In the three years of investigation meteorological parameters varied strongly, resulting in a pronounced variability of seasonal processes in the Spiekeroog backbarrier system (Chap. 3.5). Especially in the winter 1995/96 extreme conditions
were observed, including a cold period of about three months with ice cover for
48 days in the East Frisian Wadden Sea. Because the effects of disturbances were
of major interest to ELA W A T (Chap. 2), this cold period was an opportunity to
study its effects on the chemical and biological processes in the Wadden Sea. The
direct effects of the ice winter as well as the following regeneration were observed
until September 1996. The results give an indication of mechanisms taking place
after large-scale climatic perturbations in the Wadden Sea ecosystem.
7.2
The "Disturbing" Effects of the Ice Winter 1995/96
The effects of a cold winter vary with the duration of the ice cover, the air temperature and the location within the intertidal. Ice-scour mainly affects exposed
parts of the intertidal such as fringes of tidal channels or mussel beds. The cooccurring long term periods of easterly winds result in a prolonged emergence of
areas close to the high water level (HWL), which are subsequently exposed to the
extreme temperature regime of the air. Accordingly, the effects on the biota may
be ordered as follows.
7.2.1
Mechanical Effects
Already at the end of December 1995 an ice layer of several cm up to over one
meter thickness had developed on the sandflats of the Groninger Plate. At this
time, the surface temperatures of the sediment reached about _2° C; the mean temperature over the three cold months (middle of December 1995 until the middle of
March 1996) was -0.5° C.
By movements of the ice back and forth with the tides epibenthic structures
such as Laniel' conchi/ega tuhes and mussel beds (Mytilus edulis) disappeared
from the studied tidal tlats Groninger Plate and Swinnplate (Figs. 3.1.3. and 3.1.4).
The biogenic mud layer on the Swinnplate was removed by the ice as well as by
the loss of the Mytilus cover (Chap. 3.4). Ice-scour was also responsible for the
appearance of mud in formerly pure sandy areas of the Swinnplate and Groninger
Plate and already in spring Heteromastus filiformis inhabited these areas
(Chap. 3.5).
7 Effects of the Icc WlI1tcr 1 (J95/%
recolonization of the intertidal by cold sensitive species lie subtidally, future studies on recruitment after ice winters should include both the intertidal and subtidal
benthic systems.
7.1
I ntrod uction
In the three years of investigation meteorological parameters varied strongly, resulting in a pronounced variability of seasonal processes in the Spiekeroog backbarrier system (Chap. 3.5). Especially in the winter 1995/96 extreme conditions
were observed, including a cold period of about three months with ice cover for
48 days in the East Frisian Wadden Sea. Because the effects of disturbances were
of major interest to ELA W A T (Chap. 2), this cold period was an opportunity to
study its effects on the chemical and biological processes in the Wadden Sea. The
direct effects of the ice winter as well as the following regeneration were observed
until September 1996. The results give an indication of mechanisms taking place
after large-scale climatic perturbations in the Wadden Sea ecosystem.
7.2
The "Disturbing" Effects of the Ice Winter 1995/96
The effects of a cold winter vary with the duration of the ice cover, the air temperature and the location within the intertidal. Ice-scour mainly affects exposed
parts of the intertidal such as fringes of tidal channels or mussel beds. The cooccurring long term periods of easterly winds result in a prolonged emergence of
areas close to the high water level (HWL), which are subsequently exposed to the
extreme temperature regime of the air. Accordingly, the effects on the biota may
be ordered as follows.
7.2.1
Mechanical Effects
Already at the end of December 1995 an ice layer of several cm up to over one
meter thickness had developed on the sandflats of the Groninger Plate. At this
time, the surface temperatures of the sediment reached about _2° C; the mean temperature over the three cold months (middle of December 1995 until the middle of
March 1996) was -0.5° C.
By movements of the ice back and forth with the tides epibenthic structures
such as Laniel' conchi/ega tuhes and mussel beds (Mytilus edulis) disappeared
from the studied tidal tlats Groninger Plate and Swinnplate (Figs. 3.1.3. and 3.1.4).
The biogenic mud layer on the Swinnplate was removed by the ice as well as by
the loss of the Mytilus cover (Chap. 3.4). Ice-scour was also responsible for the
appearance of mud in formerly pure sandy areas of the Swinnplate and Groninger
Plate and already in spring Heteromastus filiformis inhabited these areas
(Chap. 3.5).