BSEP116B Biodiversity in the Baltic Sea - Helcom

Box 1.2. Regime shifts in the Baltic Sea as detected by an Integrated Ecosystem Assessment
The ICES/HELCOM Working Group on Integrated Assessments
of the Baltic Sea (WGIAB) has conducted Integrated Ecosystem
Assessments (IEAs) on a number of offshore and one coastal
sub-region of the Baltic Sea (see table) (ICES 2008a). IEAs are
multivariate analyses of time series of the physical, chemical
and biological environment as well as socio-economic factors.
The analyses were targeted to assess the impact of climate,
fisheries, and eutrophication on the different sub-regions.
All seven sub-regions investigated displayed pronounced
structural changes, i.e., regime shifts, during the past two
to three decades. The major period of restructuring in the
Baltic sub-regions was at the end of the 1980s. The Sound,
central Baltic Sea, Gulf of Riga, Gulf of Finland, and Bothnian
Bay also underwent structural change during the mid-1990s,
probably related to the major inflow in 1993.
For the central Baltic Sea, two relatively stable periods were
detected in 1974–1987 and 1994–2006. The first period
was characterized by comparatively high cod and
herring spawner biomass and recruitment, and high
abundances of the copepod Pseudocalanus acuspes,
whereas in the later period the system was spratdominated
with high abundances of Acartia spp. and
Temora longicornis. Between the two shifts, there was
a transition period of highly variable climatic and hydrographic
conditions and no major inflow events, resulting
in low salinity and high temperature values.
The main drivers of the observed ecosystem changes
vary between sub-regions, but they all include the
increasing temperature and decreasing salinity influenced
by large-scale atmospheric processes. In addition
to temperature and salinity, fishing pressure was
identified as an important driver for the central Baltic
Sea and Bothnian Sea as well as nutrients for the
highly eutrophied Gulf of Finland.
Regime shifts (RS 1 to RS 4) in the different sub-basins of the Baltic Sea in several time periods.
System Period covered RS 1 RS 2 RS 3 RS 4
The Sound 1979–2005 1987/88 1995/96
Central Baltic Sea 1974–2006 1987/88 1994/95
Gulf of Riga 1974–2006 1988/89 1997/98
Gulf of Finland 1979–2007 1988/89 1995/96 2002/03
Bothnian Sea 1979–2006 1982/83 1988/89
Bothnian Bay 1979–2006 1987/88 1993/94
Kvädöfjärden, Northern Baltic Proper 1971–2006 1976/77 1987/88 2004/05
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There is ample evidence for a positive relationship
between the number of species and ecosystem
productivity and stability over time as well as for
the capacity of an ecosystem to recover after
disturbances (Naeem & Li 1997, Worm et al.
2006). Changes in the environment that result in
decreased biodiversity are therefore considered
to make systems less resilient and more prone to
undergo regime shifts. In an ecosystem such as
the Baltic Sea that is characterized by low species,
genetic, and functional diversity, protection of
biodiversity is thus central to ensuring ecosystem
resilience.
1.5 Protection of
biodiversity—Global and
European targets
Protection of biodiversity is an integral part of
the ecosystem approach to the management
of human activities. The 1992 United Nations
Convention on Biological Diversity has provided
the basis and concepts for much of the work on
biodiversity protection. At the UN World Summit
on Sustainable Development in 2002, the governments
committed themselves to significantly
reducing the rate of biodiversity loss by 2010.
Halting the loss of biodiversity by 2010 is also a