Environmental Engineering Reference
In-Depth Information
Fig. 17
One way to interpret the minimum dimension measurements (
red line
) for selected organism
types:
A
mussel larvae,
B
-
D
gastropod larvae,
E
young oyster,
F
Foraminifera (phytoplankton),
top
shows individual from the side and bottom the same individual from the top,
G
Foraminifera
and
H
decapod larvae. All organisms shown here are well above 50
ʼ
m in minimum dimension
(Photos
A
-
G
Stephan Gollasch,
H
Matej David)
Fig. 18
On board test of a fl ow camera
Another issue are colony forming species. A question arose in which size category
a colony falls when the single cell is below 50
ʼ
m in minimum dimension but the
colony is above 50
m in minimum dimension. A team of experts, i.e. the ICES/
IOC/IMO Working Group on Ballast and Other Ship Vectors, believes that in those
cases the individual specimen size should be measured. This group fi nding, which
was also accepted by IMO, is based upon the D-2 standard as it refers to organisms
and not to colonies. Further, viability assessments should address the smallest unit
able to reproduce which is the individual and not the colony. Based on these conclu-
sion the size of the individuals should be measured and not the colony. For an expe-
rienced analyst this is not a problem, but machine counts may result here again in a
wrong size categorisation of organisms.
ʼ
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