A checklist of recent freshwater Japanese endemic diatom taxa was compiled. 427 recent freshwater diatom taxa have been described from Japan. 122 taxa are reported only from Japan and should be endemic. 29 taxa were reported from both Japan and other East Asian countries. 204 taxa have never been used since their first description and are regarded as ‘Practically Non-existent Species (PNS)’ and omitted from the analysis.
The stings of box jellyfishes can be fatal, so knowing the fauna of a certain area is important to save lives. Five described and two still-undescribed species of Cubozoa have been reported from Thailand: Chironex indrasaksajiae, Chironex sp., Chiropsella sp., Chiropsoides buitendijki, Copula sivickisi, Morbakka fenneri, and Tripedalia cystophora. We made detailed observations of the morphology of two of the species newly recorded in Thailand: Alatina morandinii and Tripedalia binata. The molecular phylogeny of these species is also discussed. Additional investigations are needed to understand the diversity of Cubozoa in Thailand.
The optimal spatial resolution for analysis of the spatial distribution of organisms is determined by the scale of their ecological processes (e.g., mobility of target species). This study examined the spatial extent of habitats of five megafaunal species with different levels of mobility [(1) the shrimp, Nematocarcinus sp. (benthic, comparatively low mobility); (2) the galatheid crab, Shinkaia crosnieri (benthic, low mobility); (3) the lithodid crab, Paralomis sp. (benthic, high mobility); (4) the snailfish, Liparidae sp. (demersal, high mobility); and (5) the deep-sea spiny eel, Notacanthidae sp. (demersal, high mobility)], which are associated with a deep-sea hydrothermal field in the Okinawa Trough. We obtained species presence–absence and abiotic environmental data (water temperature, proportional coverage of soft-sediment area, water depth, and five bathymetric parameters) from observation records by deep-sea submersibles and conducted a spatial analysis using three types of statistical models and a multi-model ensemble forecasting method. We prepared 10 data sets of the environmental variables by changing the spatial resolution from finer 0.00005° (ca. 5.3 m) to coarser 0.0005° (ca. 52.5 m). Accuracy of the models for the benthic species with comparatively low mobility was higher than that for the benthic and demersal species with high mobility and enhanced with decreasing grid-cell size (finer resolutions) of environmental data. By contrast, the accuracy of the models for the latter group varied more gently with the changing spatial resolution. The results showed that the proposed method is potentially useful to map the local-scale spatial distribution of the target species, sedentary benthic animals in particular, and that considering an appropriate spatial resolution in predicting the species distributions is important. These findings will help to enable management and subsequent conservation of deep-sea ecosystems.
Scrippsiella trochoidea produces a calcareous walled cyst with spines during its life history. It has been recently reported that the calcareous wall can be decalcified under acidified conditions in coastal areas linked to hypoxia caused by bacterial activities. In this study, in order to determine whether the calcareous cysts can be a biological tool for indicating an in situ hypoxic environment, the morphology of S. trochoidea cysts in the surface sediments of Ise Bay, Japan, was examined in relation to dissolved oxygen concentrations in the bottom water. The surface sediments were collected from the inner to outer parts of the bay in May 2014 and June 2018. The living cysts of S. trochoidea were counted separately into two morphotypes: cyst with calcareous wall (calcareous walled-type cyst) and without the wall (naked-type cyst). The proportions (%) of naked-type cyst abundance in the total living cyst population showed an increasing tendency in the hypoxic environment of the inner and central parts of Ise Bay, but not in the normoxic environment at the mouth. This result supports the supposition that the naked-type cyst of S. trochoidea can be used as a biological indicator for the assessment of hypoxia in coastal areas.
It is known that suction, namely, the tension of moisture in sediments, governs the distribution of the sandy beach amphipod Haustorioides japonicus, which occurs on the intertidal zones of open sandy beaches. Against this background, field studies were conducted to investigate whether there is a universal linkage between the suction and the distributions of three Haustorioides species, H. japonicus, H. munsterhjelmi, and H. koreanus, and to clarify the relationship between the distribution of these three species on shores and the variation in suction associated with the tide-induced variation in groundwater level. The study sites were as follows: Maze and Gokahama beaches, located on the coast of the Sea of Japan in Honshu, Japan and Tsuyazaki beach on the coast of the Genkai Sea in Kyushu, Japan for H. japonicus; Shari beach in Hokkaido, Japan for H. munsterhjelmi; and Samyang beach on Jeju Island, South Korea for H. koreanus. The field sites had different tidal ranges, from 0.2 to 2.81 m. The obtained results showed that the suction governed the variations of the habitat geophysical environments (degree of saturation, sediment compaction, water content, and sediment hardness) of surficial sediments in sandy beaches, and the distributions of the three Haustorioides species are associated with particular suctions, irrespective of the differences among the three Haustorioides species, the differences in tidal ranges, and the variations in tidal level. In addition, the tidal migrations of H. japonicus and H. munsterhjelmi were caused by shifts in their suitable zones for burrowing.
Sandy beach habitats are mainly controlled by the physical environmental factors. This study investigated the effects of winter storms on populations of sandy beach infaunal peracarids. Two contrasting areas on the Japan Sea coast were selected: exposed sandy beaches in Niigata and protected sandy beaches in Sado. Regional differences in the mortality rate of two species of peracarids, Haustorioides japonicus and Excirolana chiltoni, were examined over two years, focusing on periods of high storm intensity (fall and winter) when sandy beach habitats are frequently disturbed. The results demonstrated that: (1) the mortality rate on the exposed beaches (Niigata) was significantly higher than that on the protected beaches (Sado); (2) the mortality rate in 2009–2010 was significantly higher than that in 2008–2009; and (3) the mortality rates were not significantly different between the two species. Sediment grain size, sorting coefficient, and beach slope were not different between the two study areas. Dominant waves during the stormy seasons were from the northwest, to which the beaches in Niigata were directly exposed. Moreover, mean wave height was higher in 2009–2010 than in 2008–2009. Therefore, the variations in wave disturbances were herein considered to be the major cause of the mortality variations in the two species. According to the predicted scenarios of climate changes, wave intensification will likely increase in the future, therefore increasing the mortality and the potential risk of local extinctions of these sandy beach infaunal animals.
Freshwater mollusks often show high intraspecific variability in shell morphology, which may cause incongruences between molecular phylogeny and morphology-based species taxonomy. However, it remains unclear how morphological variations in freshwater snails are associated with different habitats such as rivers, ponds, and lakes. In the present study, we investigated the morphological variation in the shells of the viviparid freshwater snail Sinotaia quadrata in the Kahoku Lagoon in Japan, which was converted from a brackish to a freshwater lagoon 60 years ago. This newly established freshwater habitat is particularly well-suited for studies on how morphology is associated with environments. We found clear differences in shell morphologies between the S. quadrata populations sampled inside and outside of the lagoon. The S. quadrata sampled in the lagoon had thicker and more elongated shells with wider apertures than those sampled outside of the lagoon. No relationship was found between shell morphology and the distance between sampling sites. This suggests that the divergence in shell morphology occurred over a fairly short time period by rapid adaptation or phenotypic plasticity. Although it is unclear whether these differences are caused by phenotypic plasticity or adaptation, the present findings suggest that the shell morphologies of freshwater snails easily change under the influence of the environment. The high flexibility in shell morphology should be carefully considered when managing or studying freshwater mollusks.
In intertidal sediments, bacteria attach to sand grains in mixed-species biofilms and inhabit the surrounding porewater as free-living communities. The large densities, high species diversity, and complex spatial distribution of sediment-attached bacteria implicate inter-specific competition as a likely force in structuring sediment communities. Both sediment-attached and free-living bacteria secrete antibiotics as a common means of competition. To establish the frequency of antibiotic production, bacteria isolated from intertidal sediments and porewater were screened using a disc-diffusion assay. Among sediment-attached bacteria, 39% displayed the ability to produce antibiotics, whereas significantly fewer of the porewater-associated bacteria (23.5%) produced inhibitory compounds. Denaturing gradient gel electrophoresis (DGGE) was used to identify a selection of isolated antibiotic-producing bacteria within whole-community environmental samples. Through sequencing a region of the 16S rRNA gene, the relative abundances of 4 antibiotic producers were established to be between 4.3–9.4% of the DGGE community profile. The high frequency of antibiotic-producing bacteria in sediments, and their significant quantitative contribution to the community composition, suggest that antibiosis likely plays a significant role in structuring benthic microbial communities.
Velella velella widely occurs in the tropical and temperate oceans of the world and the number of mass strandings of colonies is increasing. Although its historical presence in the south-western Indian Ocean is known, recent observations are limited to Tanzania, Mauritius and South Africa. This is the first record of V. velella from Madagascar and the Mozambique Channel since 1964. Given the perceived increase in gelatinous zooplankton abundance, the lack of recent reports from this area highlights the need to monitor its presence to help coastal communities face the negative consequences of potential blooms.