3.4
Zooplankton Biomass and its Relation to Particulate
Matter in the Upper 200 m of the Arabian Sea during
the NE Monsoon
]. LENZ
In investigating food relationships in the sea and the rate of metabolism from the
lower to the higher levels in the food web, basic information may be gained from
studying the biomass of the main groups of organisms which build up this system of
energy transfer in the ocean. Biomass measurements of zooplankton catches, which in
most cases are a mixture of herbivores, carnivores and omnivores, mainly cover the
second and third links in the common food chain. Regarded in this way, zooplankton
biomass studies are important for gaining an insight into the fish production of the oceans.
I. Determination of the Zooplankton Biomass
Although the measurement itself if a fairly simple procedure, there are at present
many methodological problems in the determination of the zooplankton biomass; this
greatly complicates all attempts for a worldwide comparison of the values obtained.
These problems arise from the general difficulty of separating small zooplankton from
large phytoplankton organisms, from the varying catching abilities and mesh sizes of
the nets used, and from the different methods used to measure the biomass, such as
the determination of settling volume, displacement volume, wet weight, dry weight,
dry weight of organic matter and carbon content. The 3 last have the advantage of
being independent of the very variable water content in plankton animals, which in
addition varies with the concentration of the preservative and preservation time.
They therefore appear more suitable for productivity studies than the other 3, as the
figures obtained are usually more reliable and facilitate comparisons with similar data
recorded in standing stock studies such as those for particulate matter. On the other
hand, they have the disadvantage of spoiling the sample for further systematic studies.
The biomass of the quantitative zooplankton samples taken by the Indian Ocean
Standard Net (IOSN) from the upper 200 m layer during the "Meteor" expedition to
the Arabian Sea in 1964/65 (Fig. 1 in BABENERD et ai., 1973, this volume) was determined
from formalin-preserved samples. A quarter of each sample was analysed for dry weight
and organic matter. From the latter, the carbon content of the sample may be estimated
by assuming a factor of 0.6 (CUSHING et ai., 1958). Altogether 91 samples, including
12 double hauls, were analysed in this way. The data collected have been published by
KREYetal. (1971).
Zooplankton Biomass and its Relation to Particulate
Matter in the Upper 200 m of the Arabian Sea during
the NE Monsoon
]. LENZ
In investigating food relationships in the sea and the rate of metabolism from the
lower to the higher levels in the food web, basic information may be gained from
studying the biomass of the main groups of organisms which build up this system of
energy transfer in the ocean. Biomass measurements of zooplankton catches, which in
most cases are a mixture of herbivores, carnivores and omnivores, mainly cover the
second and third links in the common food chain. Regarded in this way, zooplankton
biomass studies are important for gaining an insight into the fish production of the oceans.
I. Determination of the Zooplankton Biomass
Although the measurement itself if a fairly simple procedure, there are at present
many methodological problems in the determination of the zooplankton biomass; this
greatly complicates all attempts for a worldwide comparison of the values obtained.
These problems arise from the general difficulty of separating small zooplankton from
large phytoplankton organisms, from the varying catching abilities and mesh sizes of
the nets used, and from the different methods used to measure the biomass, such as
the determination of settling volume, displacement volume, wet weight, dry weight,
dry weight of organic matter and carbon content. The 3 last have the advantage of
being independent of the very variable water content in plankton animals, which in
addition varies with the concentration of the preservative and preservation time.
They therefore appear more suitable for productivity studies than the other 3, as the
figures obtained are usually more reliable and facilitate comparisons with similar data
recorded in standing stock studies such as those for particulate matter. On the other
hand, they have the disadvantage of spoiling the sample for further systematic studies.
The biomass of the quantitative zooplankton samples taken by the Indian Ocean
Standard Net (IOSN) from the upper 200 m layer during the "Meteor" expedition to
the Arabian Sea in 1964/65 (Fig. 1 in BABENERD et ai., 1973, this volume) was determined
from formalin-preserved samples. A quarter of each sample was analysed for dry weight
and organic matter. From the latter, the carbon content of the sample may be estimated
by assuming a factor of 0.6 (CUSHING et ai., 1958). Altogether 91 samples, including
12 double hauls, were analysed in this way. The data collected have been published by
KREYetal. (1971).