Interim report of the HELCOM CORESET project

4.18. Biomass of microphageous mesozooplankton
1. Working team: Zooplankton (ZEN)
Author: Elena Gorokhova and Lutz Postel
Acknowledged persons: Maiju Lehtiniemi
1. Working team: Zooplankton (ZEN)
2. Name of candidate indicator:
Biomass of microphagous mesozooplankton
3. Unit of the candidate indicator
mg/m 3
4. Description of proposed indicator
Biomass is calculated using abundance of microphagous feeders present in mesozooplankton community
and their individual weights. Alternatively (or in addition), contribution of microphagous biomass to
total mesozooplankton biomass can be used.
The indicator refl ects composition of zooplankton community and availability of small-sized phytoplankton
and bacterioplankton, the increase in the latter is commonly observed with increasing eutrophication.
It also negatively related to food availability for zooplanktivorous fi sh.
5. Functional group or habitat type:
Zooplankton/plankton
6. Policy relevance
MSFD Descriptor 1 (Biodiversity), Criteria 1.6.2. Relative abundance and or biomass.
BSAP Ecological Objective: Viable population of species, Target: By 2021 all
elements of the marine food webs, to the extent that they are known, occur at natural and robust abundance
and diversity.
7. Use of the indicator in previous assessments
None
8. Link to anthropogenic pressures
Directly impacted by (1) fi sheries (through predation), (2) changes in thermal regime and salinity, (3)
introduction of synthetic compounds and (4) invasive species (via predation)
Indirectly impacted by (1) eutrophication (through changes in food abundance and size spectra), and (2)
commercial fi sheries (through changes in pelagic food webs),
9. Pressure(s) that the indicator refl ect
Eutrophication increases abundance and productivity of small-sized phytoplankton and bacterioplankton,
which stimulates production and standing stocks of microphagous species. In addition, increased
biomass of microphagous species implies decreased food quality and availability for fi sh.
10. Spatial considerations
The index is strictly area-specifi c, possibly limited to the areas generally dominated by crustacean zooplankton,
such as open sea areas in the Baltic proper, western Gulf of Finland and southern Baltic.
11. Temporal considerations
Averaged over growth season. In areas where seasonal monitoring data are available, the assessment
could be done on a seasonal basis.
12. Current monitoring
National monitoring programmes, HELCOM (reported variable).
13. Proposed or perceived target setting approach with a short justifi cation.
The applicability and targets should be tested and validated for specifi c areas. The long term data or
data from relatively pristine areas must be provided by national labs to serve for target setting. A discussion
regarding development of common target setting approach is needed.
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