Cenozoic history of the tropical marine biodiversity hotspot.

The region with the highest marine biodiversity on our planet is known as the Coral Triangle or Indo-Australian Archipelago (IAA)1,2. Its enormous biodiversity has long attracted the interest of biologists; however, the detailed evolutionary history of the IAA biodiversity hotspot remains poorly understood3. Here we present a high-resolution reconstruction of the Cenozoic diversity history of the IAA by inferring speciation-extinction dynamics using a comprehensive fossil dataset. We found that the IAA has exhibited a unidirectional diversification trend since about 25 million years ago, following a roughly logistic increase until a diversity plateau beginning about 2.6 million years ago. The growth of diversity was primarily controlled by diversity dependency and habitat size, and also facilitated by the alleviation of thermal stress after 13.9 million years ago. Distinct net diversification peaks were recorded at about 25, 20, 16, 12 and 5 million years ago, which were probably related to major tectonic events in addition to climate transitions. Key biogeographic processes had far-reaching effects on the IAA diversity as shown by the long-term waning of the Tethyan descendants versus the waxing of cosmopolitan and IAA taxa. Finally, it seems that the absence of major extinctions and the Cenozoic cooling have been essential in making the IAA the richest marine biodiversity hotspot on Earth.

Geochemical distribution of heavy metal elements and potential ecological risk assessment of Matsushima Bay sediments during 2012-2016.

Heavy metal pollution of marine sediments has attracted a great deal of attention because of its persistence, bioaccumulation, and toxicity. To evaluate the effects of mega-tsunami, anthropogenic activities, and redox conditions on heavy metal accumulation in coastal areas, sediments from Matsushima Bay, Miyagi Prefecture, Japan, were sampled to test variations in heavy metal spatial distribution on the bay floor during 4 years following the 2011 Tohoku Earthquake tsunami. Cluster analysis and principal component analysis were performed to assess the influencing factors and potential sources of heavy metal enrichment in the sediments of the bay. Additionally, the sediment enrichment levels of heavy metals were assessed on the basis of the enrichment factor (EF). The results of multivariate statistical analyses showed that the Ti, Fe, V, Pb, and Zn contents in Matsushima Bay sediments, which were transported mainly from Sendai Bay, depended on the mud content. The value of EF < 2 for Fe, V, Pb, and Zn indicated that these elements were not enriched. The value of EF > 7 for Cu suggested that the contamination levels in western Matsushima Bay were moderate to severe in every sampling year from 2012 to 2016 by anthropogenic activities. From the values of EF > 5 for U and Mo during 2012 and 2014, the severe enrichment of both elements in these periods may be explained by contamination with 2011 tsunami deposits; the improvement in 2015-2016 suggests that there was recovery of the tsunami-affected sediment composition to its original state. The values of EF > 3 for Mn and As indicated moderate to severe contamination with these heavy metals in the bay mouth area during 2015. This was likely explained by more oxic bottom conditions in the mouth of Matsushima Bay during that year.

Ecological shifts due to anthropogenic activities in the coastal seas of the Seto Inland Sea, Japan, since the 20th century.

Multiproxy analyses were conducted using sediment cores in a low-polluted coastal site (Hiuchi-nada) in the Seto Inland Sea (SIS), Japan. Heavy metal and organic pollution peaked in the 1960s and the bottom environments have ameliorated since the 1980s due to several environmental regulations. First ecological shifts in meiobenthic ostracodes and diatoms occurred in the 1960s due to the initiation of eutrophication. Then, a second ecological shift occurred in the 1980s due to the amelioration of the water and the bottom quality. A compilation of similar analytical results in the coastal seas of the SIS reveals three types of ecological and environmental history since the 20th century. The environmental improvement since the 1980s affects the ecosystems, in particular, in a low-polluted bay. However, ecological compositions are different from those prior to the 1960s, suggesting that the ecosystem was not recovered but changed into the next stage in the SIS.

Anthropogenic impacts on meiobenthic Ostracoda (Crustacea) in the moderately polluted Kasado Bay, Seto Inland Sea, Japan, over the past 70 years.

Two sediment cores were obtained from Kasado Bay, a moderate-polluted enclosed bay in Japan, to examine anthropogenic impacts on Ostracoda over the past ca. 70 years. We analyzed ostracode abundance and diversity, grain size, and CHN, and used (210)Pb and (137)Cs as the dating method. The present study showed that cross-plot comparisons of ostracode abundance and each environmental factor, based on sediment core data, could be used to identify ostracode species as indicators for anthropogenic influences. Ostracode abundance reflected mainly the changes that had occurred in total organic carbon content in sediments related to eutrophication, but heavy metal concentration did not directly influence several ostracode abundance in the bay. Environmental deterioration because of eutrophication started in the 1960s. The regulations regarding the chemical oxygen demand in waters introduced in the 1980s probably influence ostracode abundance for certain species in this period. Currently, Kasado Bay is not experiencing severe degradation.

The influences of various anthropogenic sources of deterioration on meiobenthos (Ostracoda) over the last 100 years in Suo-Nada in the Seto Inland Sea, southwest Japan.

This study focuses on the relationships of water and sediment quality with meiobenthos (Ostracoda) over the past 100 years, using a sediment core obtained from Suo-Nada in the Seto Inland Sea, Japan. We compared high-resolution ostracode results with geochemical and sedimentological data obtained from the study core as well as with rich environmental monitoring data that are available. R-mode cluster analysis revealed two bioassociations (BC, KA). Until the 1960 s, assemblages continued to show high diversity. They changed in approximately 1970, when excessive nutrients and organic matter began to be supplied, and most species decreased in number. All species of bioassociation BC were dominant again by the mid-1990 s; however, those of bioassociation KA containing infaunal species did not increase and have been absent or rare since the 1970s because organic pollution of sediments has continued to date. This study provided robust baseline for ostracode-based long-term environmental monitoring in East Asia.