<strong>Bathymetric distribution of aquatic Oligochaeta in Lake Kizaki, Central Japan</strong>

Abstract

Bathymetric distribution of aquatic oligochaetes was studied at 8 stations with different depths (mean depth 16.7 ± 9.4 m, min. 5.3 m, max. 29.4 m) in July 2012 in mesotrophic Lake Kizaki, Nagano Prefecture, Central Japan. The average density was 10424 ± 5346 individuals m -2 . Oligochaetes were numerically dominant at all sampling stations. High density, sometimes more than 10000 individuals m -2 , was recorded at 3 stations (St. 4, 5, and 6) deeper than 18 m.Maximum density was 20561 ± 13864 individuals m -2 at Station 4 (depth 29.4 m, ignition loss of sediment 13.5%, bottom water temperature 8.1 °C and DO of bottom water 0.12 mg l -1 ). We identified a total of 5 genera and 7 species belonging to three subfamilies: i.e., 1 species of Naidinae, 2 species of Rhyacodrilinae and 4 species of Tubificinae. Dominant species (in order of abundance) were Tubifex tubifex (Müller, 1774) (8550 ± 6317 individuals m -2 ; 82.0%) andLimnodrilus spp. (L. hoffmeisteri Claparède, 1862 and L. claparedeianus Ratzel, 1868) (1710 ± 1383 individuals m -2 ; 16.4%). Tubifex and Limnodrilus were obtained from every station, and the density of T. tubifex tended to be higher as the depth became greater, while Limnodrilus spp. was also widely distributed, but with a peak value at a depth of 5.3 m in the shallowest station. From the submerged plant zone, Ophidonais serpentina (Müller, 1773) was collected. An earlier study by Hirabayashi & Hayashi (1994) showed that in 1985 the average density of aquatic oligochaetes was 435 ± 428 individuals m -2 , oligochaetes dominated in only four locations and were distributed over the whole lake approximately equally. Comparisons of our data with the earlier studies have shown that oligochaete density has increased greatly according to Hirabayashi & Hayashi (1994). We suggest that a decrease in dissolved oxygen concentration of bottom water was due to an increase in organic matter content of the sediment. As a result, T. tubifex could expand their habitats in the profundal zone.

A comparison of results from previous and present investigations of benthic macroinvertebrates in the small and shallow Lake Shoji, Fuji Five Lakes, Japan

“…Ariizumi et al (1997) and Yamanashi Prefecture (2005) reported that the water became anoxic at the depth of 6 m. We also observed in our study that the bottom water became anoxic in September when deeper than 6 m. In other words, the anoxic layer and anaerobic layer have thickened since the 1930s and 1970s. Hirabayashi et al (2007) reported that the density of oligochaetes increased greatly in Lake Kizaki due to an increase of organic matter in the bottom sediments, and that bacterial activity was high while DO greatly decreased in deep regions. In our study in September 2011, we could not collect chironomid larvae, except for P. akamusi, in the deeper regions (>10 m) (Table 2).…”

<strong>Profundal oligochaete faunas (Annelida, Clitellata) in Japanese lakes</strong>

“…Faunal records of lake profundal oligochaetes in Japanese lakes have been accumulated since 1980s in accordance with an increase in faunistic and ecological studies of lake zoobenthos (Ito 1978;Ito and Uno 1980;Ito et al 2002Ito et al , 2005Fukuhara et al 1987;Yasuda and Okino 1987;Ohtaka 1994Ohtaka , 1995Ohtaka , 2001aOhtaka , b, 2004Ohtaka , 2006Ohtaka , 2009aOhtaka and Kikuchi 1997;Ohtaka and Ito 2002;Ohtaka and Iwakuma 1993;Ohtaka and Martin 2011;Nishino 1995, 1999;Ohtaka et al 1988Ohtaka et al , 2006Ohtaka et al , 2010Nishino et al 1999;Fend and Ohtaka 2004;Hirabayashi et al 2007Hirabayashi et al , 2012Martin and Ohtaka 2008). Comparing these records, species composition of profundal oligochaetes in Japanese lakes can be basically explained by the scheme of Timm (2012), but faunal differences among respective lakes and the factors determining the species composition have not been well understood yet.…”

Macrozoobenthic Community Structure in the Kemayungan-Linduk Waters, Banten Bay

“…A positive correlation between Clitellata density and depth possibly related to a decrease in dissolved oxygen level of bottom water was due to an increase in the organic matter content of the sediment [33]. Accordance [34], water depth may be related to food availability which plays a pivotal role in structuring the benthic community such as Echinoderm.…”