The species composition and population numbers of zooplankton and attached animals in littoral vegetation zone in Lake Biwa were investigated during spring and summer of 1966 and 1967.
The plankters were collected with 0.5 liter cylindrical water sampler, and attached animals with vinyl-sack.
In the Yamanoshita Bay where the investigation was carried out intensively, littoral vegetation developed was as follows : In the marginal zone there were emerged plants
(Phragmites, Zizania and
Carex), among which patches of sub-merged plants were observed. In the outer part, submerged plants, such as
Elodea, Potamogeton, etc., developed widely.
Much more numbers of species of zooplankton were found in the littoral zone than in the offshore area. In the former, abundant species were
Chydorus sphaericus and
Alona guttata, whereas
Daphnia longispina and
Conochilus unicornis in the latter.
Between the littoral stations there was no remarkable difference in the total density of zooplankton, but the species composition was remarkably different each other : i.e.,
Eodiaptomus japonicus and
Bosminopsis deitersi were numerous in open littotal area, whereas
Chydorus sphaericus, Mesocyclops leuckarti, Euchlanis dilatata and
Philodina roseola were numerous in vegetational belt.
Zooplankters living in vegetational belt were divided into two types by their modes of life as follows : completely free-swimming species and species which sometimes attached on aquatic plants and swam freely in other times.
In the latter type of species, much more number of individuals remained attached and only few individuals swam freely at least in the daytime. For instance, attached number of
Chydorus sphaericus was 60-120 times higher than the swimming one per unit water column.
The total population number of attached animals changed according to the vegetation type. Attached animals usually occurred more abundantly in
Potamogeton belt than in
Elodea belt, and much less in
Phragmites belt than in the former two submerged plants area.
It was observed that the changes in number of free-swimming animals at small open space between
Potamogeton leaves were strictly parallel with that of attached ones on the submerged plant. In such area, attached animals will be supply-base for the planktonic ones.
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