Temporal changes of ostracode assemblages and anthropogenic pollution during the last 100 years, in sediment cores from Hiroshima Bay, Japan

Abstract

Temporal changes of ostracodes during the last 100 years observed in three sediment cores from Hiroshima Bay, the Seto Inland Sea, Japan, provide valuable information about influences on ostracodes caused by anthropogenic pollution. This is the first detailed report of historical records of the relationship between ostracodes and pollution established from core samples drilled in the polluted inner bay. At least 38 ostracode species were identified from 40 samples. Based on biofacies, the density of ostracodes and the faunal structure, it is elucidated that industrialization combined with the effects of the second world war caused a decrease in the density and a increase in the equitability of ostracodes, and that anthropogenic pollution caused a simplification of ostracode assemblages in Hiroshima Bay. The response of two particular ostracode species to anthropogenic pollution is also demonstrated. Callistocythere alata was sensitive and Bicornucythere bisanensis has a strong resistance for anthorogenic pollution in ostracode species. Thus, the relative frequencies of these two ostracodes can be used as an indication of such pollution. We discuss the limitations of using recent ostracode assemblages in the analysis of the palaeoenvironment, resulting from the changes induced by anthropogenic pollution during the last 100 years.

Historical records of coastal eutrophication-induced hypoxia

“…Rather surprisingly, these 100-200-yr sediment records revealed no major changes in ostracod diversity at any of the four stations in Osaka Bay. Yasuhara et al (2003) reported similar patterns in Hiroshima Bay. Ostracod abundances decreased from the 1940s in the inner bay while the relative abundance of B. bisanensis increased and diversity remained relatively stable over the 100-yr record.…”

“…Over shorter time scales, oscillations in the diversity of the two taxa show some correspondence, although the match is not precise. As mentioned above, ostracod abundance in Osaka Bay began to decline at the innermost, hypoxia-influenced station (OBY) around 1910-1920 while diversity remained stable (Yasuhara et al, 2007). In the same core, foraminiferans increased in abundance from ∼1920 to ∼1965 before undergoing a relatively modest decrease (Tsujimoto et al, 2006b), while diversity decreased substantially after ∼1920.…”

“…In area column B = Baltic; D = Denmark; F = Finland; N = Norway; S = Spain; Fla = Florida; Mx = Mexico. See Brush (2001), Cronin and Vann (2003), Kemp et al (2000) and Rabalais et al (2007) Andrén et al (1999); 7) Barmawidjaja et al (1995); 8) Blackwelder et al (1996); 9) Bratton et al (2003) ; 10) Brunner (2006); 11) Cearreta et al (2000); 12) Chen et al (2001); 13) Chmura et al (2004); 14) Clarke et al (2003); 15) Clarke et al (2006); 16) Colman and Bratton (2003); 17) Cooper (1995); 18) Brush (1991, 1993); 19) Cornwell et al (1996); 20) Cronin and Vann (2003) Thomas et al (2000Thomas et al ( , 2004; 55) Toyoda and Kitazato (1995); 56) Tsujimoto et al (2006a); 57) Tsujimoto et al (2008); 58) Turner and Rabalais (1994); 59) Turner et al (2004); 60) Turner et al (2006); 61) Voss and Struck (1997); 62) Willard et al (2003); 63) Yasuhara et al (2003); 64) Yasuhara and Yamazaki (2005); 65) Yasuhara et al (2007); 66) Zheng et al (2003); 67) Zimmerman and Canuel (2000); 68) Zimmerman and Canuel (2001); 69) Zimmerman and Canuel (2002) …”

“…Cronin and Vann (2003) consider the increased intensity of seasonal anoxia to be the most likely explanation for this recent faunal shift. Yasuhara et al (2007) described changes in ostracod abundance, diversity and faunal composition in four cores taken along a transect from the innermost part of Osaka Bay (Japan) near the mouth of the Yodo River, to the centre of the Bay. The total abundance of ostracods decreased from 1910-1920 at the innermost station (OBY) and from ∼1960 at the next (inner) station (OS3) along the transect.…”

Modern benthic ostracodes from Lutzow-Holm Bay, East Antarctica: paleoceanographic, paleobiogeographic, and evolutionary significance

“…Seventeen percent (1171 out of 6767 total specimens) were living. Ostracode biotopes were determined by Q-mode cluster analysis based on Horn's overlap index (Horn 1966) and the unweighted pair group method with arithmetic mean (UPGMA: Sneath and Sokal 1973), which have been successfully applied for ostracode faunal analysis (e.g., Yasuhara et al 2003;Irizuki et al 2004;Yasuhara et al 2004), using PAST ver. 1.38b (http://folk.uio.no/ohammer/past/; Hammer et al 2001).…”