Distribution of Fresh-water Sponges and Bryozoa in Lake Biwa

Abstract

The distribution of fresh-water sponges and bryozoa of Lake Biwa were investigated from August 1963 to January 1965. Along the lake shore of the lake, the specimens were collected on the surfaces of reeds, aquatic plants, and some wooden piers at about 1-2 m depth (Fig. 1).
As shown in Figs. 2 and 3, six species sponges and four species bryozoa were obtained. The species of the sponges are in order of abundance: Spongilla lacustris (LINNÉ) > Spongilla semispongilla (ANNANDALE) > Heteromeyenia baileyi var. petri (LAUTERBORN) > Spongilla clementis ANNANDALE, Ephydatia mülleri (LIEBERKÜHN), and Ephydatia mülleri var. japonica (HILGENDORF). Those of the bryozoa are Plumatella emarginata ALLMAN> Pectinatella gelatinosa OKA> Lophopodella carteri (HYATT)> Fredericella sultana (BLUMENBACH). It was noticeable that both Sp. lacustris and Pl. emarginata were distributed more widely than the other species in the lake.
On the whole, it seems that both sponges and bryozoa are found more in the eastern shore than in the western shore and more in the north basin than in the south basin of the lake. In the south basin, Sp. lacustris was abundant, but Sp. clementis was not found. Pl. emarginata predominated in the north basin as well as the east shore. Pec. gelatinosa was more abundant in the south basin than the north basin.
The vertical distribution of sponges and bryozoa on the reed-stems are shown in Fig. 4. Generally speaking, they are more abundant on reeds growing at the sandy bottom than on those at the muddy bottom.