Foreword
Birds play a prominent
role as bioindicators: They are
conspicuous, one of the best studied groups of
organisms, relatively easy to observe and in the focus
of public interest and care. As top predators, raptors
and seabirds accumulate persistent chemicals,
which affect their physiology, reproduction and
even survival. This can cause population declines,
which have frequently been an indicator of
environmental change.
This value of birds was
also recognized for the Wadden Sea
by the Trilateral Monitoring and Assessment Group
(TMAG 1997), which has an outstanding importance
for the life cycle of millions of
bird individuals each year. Consequently, among the
parameters of the Trilateral Monitoring and Assessment
Program (TMAP) selected to assess the ecological
state of the Wadden Sea, five refer to birds:
“Numbers and Distribution of Breeding Birds”,
“Monitoring of Migratory Birds”, “Beached Bird
Surveys (BBS)” and “Contaminants in Bird Eggs”
are implemented; the fifth parameter “Breeding
Success” was proposed, tested successfully in
a pilot study (Thyen et al. 1998), but to date
has still not been implemented trilaterally.
With respect to chemical
pollution in the Wadden Sea,
coastal birds have proven to be an excellent monitoring
system. Bird eggs are a favorable matrix
as they indicate the local pollution, and in the
long-term they reveal temporal trends in the contamination
of the reproductive females and by
that in the environments. Therefore, on the German
Wadden Sea coast, monitoring with bird eggs
has been carried out since 1981. In two TMAP reports
(Becker et al. 1998, Becker et al. 2001), the
successful implementation of the parameter and
its value to assess the current ecological state of
the Wadden Sea ecosystem with respect to contamination
was presented in detail. The first
report in this volume 18 is an update of
the recent contamination status of birds in the Wadden
Sea. The focus is on geographical variation of
contamination from the Netherlands to Denmark,
and on the temporal trends for three periods,
1998–2003, 1991–2003 and 1981–2003. For
the first time, temporal trends of Chlordane levels
are presented, which have been analyzed since
1998.
The Wadden Sea burden by
pollutants slowly moves towards
meeting the Targets of the Wadden
Sea Plan: Concomitant with thedecreasing levels with time, also the
strong intersite and inter-specific
differences present during the
1980s have been reduced. On the other hand, the
results show stagnation or rather increases of pollution
of Wadden Sea biota, including birds, and
some local problems of recent anthropogenic discharges
of micropollutants (e.g. at the western Wadden
Sea, Ems estuary and Jade), even of contaminants prohibited
long time ago such as Chlordanes. The
results reveal that the Elbe estuary and
the inner German Bight are still the hot spot of
chemical contamination in the Wadden Sea. Birds
are vulnerable to the effects of chemicals, and
the second report in this volume presents results
of a specific investigation from the mid
1990s, which combined the parameters “Contaminants in
Bird Eggs“ and “Breeding Success” at
selected sites to facilitate data assessment and give
us a better understanding about the influence of
pollutants on bird populations. The effects of
environmental chemicals on reproductive success
and mass growth of four common larid species
were investigated, Common Tern (Sterna hirundo),
Herring Gull (Larus argentatus), Common Gull
(Larus cannus), and Black-headed Gull (Larus
ridibundus), breeding at highly (Elbe) and low
polluted areas (Jade). In general, the contaminants levels
were not clearly associated with parameters of
reproduction, with the exception of hatching
success in Common Gulls breeding at the
Elbe Estuary which was probably impaired by HCB,
DDE and HCH. The report comes to the conclusion that
during the 1990s bird reproduction in
general was not at risk by toxic substances on the
Wadden Sea coasts.
The presentation of both
reports in this volume of Wadden
Sea Ecosystem No. 18 aims to show
that the combination of different TMAP parameters provides
deeper insight into the dynamics and
effects of chemical contamination of breeding
birds in the Wadden Sea. Just the use of birds
in their function as both accumulative and sensitive
indicators of chemical contamination, demonstrates
their full value as an early warning system
to monitor the ecological state of the Wadden
Sea with respect to chemical pollution. We
hope that this issue will support the final implementation of
the parameter “Breeding Success” at
selected sites of the Wadden Sea.
Peter H. Becker and
Jacqueline Muñoz Cifuentes
top
of page
|
