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

Abstract

In order to clarify the current status of the benthic community of Lake Shoji, and to examine the difference with the last quantitative data of the lake by Miyadi (1932) and Kitagawa (1973), the distribution of benthic macroinvertebrates in this lake was studied. Also, a comparison of the benthic fauna and density was made between the present and previous studies, with a discussion concerning the succession of benthic macroinvertebrates in relation to changes in the lake bottom environment. On March 1, 2010, and September 7, 2011, bathymetrical sampling surveys were carried out using a standard Ekman-Birge grab at each of the 7 locations in Lake Shoji. The average densities of the benthic communities for all the stations were 4,107 inds. m-2 , comprised principally of oligochaetes 50.2%, chironomids 48.6%, and chaoborid 1.2% in March 2010, whereas in September 2011 the average density was 1,185 inds. m-2 , and mostly comprised of oligochaetes 86.6% and chironomids 13.4%. On the other hand, the average biomasses (wet weight) of these benthic macroinvertebrates in March 2010 were composed of 33.3% oligochaetes, 62.8% chironomid larvae, and 3.9% chaoborid larvae, as opposed to 48.8% oligochaetes and 51.2% chironomid larvae, respectively, in September 2011. Propsilocerus akamusi (Tokunaga, 1938) and Procladius sp. of chironomid larvae were the dominant species, making up 10.0% and 17.6%, respectively, of the total chironomid fauna in density, and 83.2% and 9.2% in biomass in March 2010. The mean density of P. akamusi was about 2.5 times higher than that reported by Kitagawa in the 1970s. In recent years, the number of P. akamusi larvae has tended to increase; they are widely distributed, and the anoxic-layer and anaerobic-layer are thickening, especially during summer to late fall in Lake Shoji, suggesting that the lake is in the process of eutrophication.

Role of Chironomus plumosus (Diptera, Chironomidae) Population in the Central Zone of the Shallow Lake Trasimeno (Italy)

“…The comparison of the benthic survey of the central zone of the lake (current study) with the results of the survey conducted in the littoral zone [9] for the period 2018-2021 detects a macrobenthic community composed of Chironomidae larvae and Naidid Oligochaeta with, also in this case, similar proportions (Chironomidae: 35.54 vs. 40.72%; Naididae: 56.39 vs. 61.99%) (Table S5). This distribution of benthic macrofauna is frequently found in literature studies carried out on shallow lakes, considering both the littoral and the central areas [42,43]. Regarding the chironomid community, the littoral area showed much greater biodiversity, with the presence of 18 chironomid taxa vs. 5 in the central zone (Table 2).…”

Change of macrobenthic communities in the 1930s, 1970s and 2015 in the mesotrophic Lake Nojiri, Central Japan

“…We previously investigated species composition, density, biomass and distribution pattern of benthic fauna in a wide range of mesotrophic/eutrophic lakes: Lake Shoji (shallow eutrophic; Hirabayashi et al, 2012), Lake Kawaguchi (shallow mesotrophic-eutrophic; Hirabayashi et al, 2008), Lake Yamanaka (shallow mesotrophic; Hirabayashi et al, 2004), Lake Kizaki (deep mesotrophiceutrophic; Hirabayashi et al, 1994) and Lake Suwa (shallow hypertrophic; Hirabayashi et al, 2003). In comparison with data of the 1930s (Miyadi, 1931(Miyadi, , 1932 and 1970s (Kitagawa, 1973a(Kitagawa, , 1973b, the present lake bottom environment has greatly changed in these lakes, i.e., an anoxic layer develops during the summer in the deeper regions, as a result of which oligochaetes became dominant taxa, especially T. tubifex.…”