Zooplankton of the open Baltic: Extended Atlas - IOW

3.5. Biomass determination
Information about numbers of organisms in a certain volume of water
does not provide knowledge about their body mass which is essential for the
analyses of trophic webs, energy balance calculations and zooplankton
productivity estimation. The calculation of biomass is a way to overcome this
problem if suitable individual biomass factors or proper morphometric
approaches are applied (for reviews see: Table 4.12 in Postel et al., 2000;
Telesh & Heerkloss, 2002, 2004). Such biomass determination is zooplankton
specific, in contrast to quantifying the biovolume or other sum biomass
parameters of the entire sample by volumetric or other procedures (for details
see Postel et al., 2000). The advantage of determining zooplankton biomass
using the conversion factors or length/mass correlations is in clear results that
can not be falsified by phytoplankton and detritus.
For zooplankton monitoring purposes in the Baltic Sea area, biomass
factors were recommended according to Hernroth (1985). This compilation
includes individual wet mass of six copepod and three cladoceran taxa basing
on volume calculations by morphometric approaches, for example, of
Chojnacki and Jankowski (1982), Chojnacki (1983), and Chojnacki (1986)
and the successive conversion to wet mass. The compilation was
supplemented by literature data for rotifers, chaetognaths, appendicularians
and some copepods. Seasonal and regional differences were considered;
therefore the amount of data was sufficient. Coarse conversion factors were
used to reach comparability. Rough factors may produce significant errors
when multiplied by large individual numbers. Therefore, factors and length to
mass ratios based on direct measurements should be preferably used. There
are some of those available from the Northern Baltic Sea (Kankaala &
Johansson, 1986; Kankaala, 1987; Tanskanen, 1994); they are based on the
kryo-conservation technique (Latja & Salonen, 1978; Salonen, 1979).
Currently, the Monitoring and Assessment Group of the Helsinki
Commission (HELCOM MONAS) is going to include length to carbon ratios
and individual carbon factors for the major mesozooplankton species as a
standard procedure in the Manual for Marine Monitoring
(http://www.helcom.fi/groups/monas/CombineManual/AnnexesC/en_GB/ann
ex7/) basing on the rapid kryo-conservation technique (c.f. Postel et al.,
2007).
32