BSEP116B Biodiversity in the Baltic Sea - Helcom

iomass can be used to assess environmental conditions
and disturbance events.
Limnocalanus macrurus
In the context of the Baltic Sea Action Plan (BSAP),
benthic invertebrate communities relate to the ecological
objectives of the BSAP that aim for ‘Thriving
and balanced communities of plants and animals’
and ‘Viable populations of species’ in order to
secure a favourable conservation status of Baltic
Sea biodiversity. Specifically, these objectives relate
to restoring and maintaining seafloor integrity at a
level that safeguards the functions of ecosystems.
The relevant BSAP targets include that by 2021 (a)
a ‘natural’ range in the distribution and abundance
of habitat-forming species should be obtained,
(b) degradation should be halted and recovery of
marine biotopes/habitats ensured, and (c) a natural
abundance and diversity of all elements of the
marine food web should be secured.
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determine the abundance and composition of the
zooplankton make it difficult to recommend specific
actions. Nevertheless, a reduction of eutrophication
and implementation of sustainable fisheries
practices are important measures that will safeguard
the future diversity of this organism group.
Zooplankton are currently not a core variable in the
HELCOM COMBINE monitoring programme. Based
on the important role of zooplankton in the Baltic
Sea food web and their usefulness as an indicator
for pelagic ecosystem conditions, it is recommended
that zooplankton be included as a core
variable in this monitoring.
3.4 Benthic invertebrate
communities
Soft-sediment macrofaunal communities are
central elements of Baltic Sea ecosystems and
provide important ecosystem functions and services.
These functions include, for example, the provision
of food for higher trophic levels and through
the processing, reworking and irrigation of the
sediments, benthic macrofauna enhance oxygen
penetration and biogeochemical degradation of
organic matter in the sediments. Most macrobenthic
animals are relatively long-lived (several years)
and thus integrate changes and fluctuations in the
environment over a longer period of time. Hence,
variations in species composition, abundance and
3.4.1 Status and trends
The distribution and diversity of brackish-water
macrobenthic communities in the Baltic Sea are
constrained by the distinctive salinity and oxygen
gradients present (Segerstråle 1957, Rumohr
et al. 1996, Laine 2003). Owing to the overall low
salinity, benthic communities in the Baltic Sea are
substantially less diverse than in fully marine environments
and comprise a mix of species of marine,
brackish–water, and limnic origin (Remane 1934,
Bonsdorff 2006). The characteristic salinity range
in most of the Baltic Sea coincides with the species
diversity minimum for aquatic habitats as described
by Remane (1934), i.e., where the distributions of
marine and limnic species meet.
The latitudinal distribution of marine macrozoobenthos
in the Baltic Sea is limited by the gradient
of decreasing salinity towards the north. The
decreasing salinity reduces macrozoobenthic
diversity, affecting both the structure and function
of benthic communities (Elmgren 1989, Ruhmohr
et al. 1996, Bonsdorff & Pearson 1999). In addition,
the distribution of benthic communities is
driven by strong vertical gradients. Generally,
the more species-rich and abundant communities
in shallow-water habitats (with higher habitat
diversity) differ from the deep-water communities,
which are dominated by only a few species
(Andersin et al. 1978). The Baltic Proper has a more
or less permanent halocline at 60–80 m, whereas