Jin-Yong Ha

A usage of CO2 hydrate: convenient method to increase CO2 concentration in culturing algae.

The addition of CO2 to algal culture systems can increase algal biomass effectively. Generally, gas bubbling is used to increase CO2 levels in culture systems; however, it is difficult to quantitatively operate to control the concentration using this method. In this study, we tested the usability of CO2 hydrate for phytoplankton culture. Specifically, green algae Pseudokirchneriella subcapitata were cultured in COMBO medium that contained dissolved CO2 hydrate, after which its effects were evaluated. The experiment was conducted according to a general bioassay procedure (OECD TG201). CO2 promoted algae growth effectively (about 2-fold relative to the control), and the decrease in pH due to dissolution of the CO2 in water recovered soon because of photosynthesis. Since the CO2 hydrate method can control a CO2 concentration easily and quantitatively, it is expected to be useful in future applications.

The Predation Impact of Larval Pseudorasbora parva (Cyprinidae) on Zooplankton: a Mesocosm Experiment

ABSTRACT The impact of larvae of the fish Pseudorasbora parva on a zooplankton community was studied by adding the fish to tanks housing a zooplankton community established with resting eggs from the bottom sediment of a lake. The fish strongly depressed the populations of most planktonic cladoceran and rotifer species but not the abundances of copepod nauplii or the periphytic rotifers Monostyla spp. and Lecane spp. Gut content analyses showed that the fish larvae strongly selected for the periphytic rotifer Lecane spp.

Diversification of mitochondrial genome of Daphnia galeata (Cladocera, Crustacea): Comparison with phylogenetic consideration of the complete sequences of clones isolated from five lakes in Japan

To characterize genetic diversity and gene flow among Daphnia galeata populations, the complete nucleotide (nt) sequences of the mitochondrial (mt) DNAs of D. galeata clones isolated from five lakes in Japan (Lakes Shirakaba, Suwa, Kizaki, Kasumigaura, and Biwa) were determined. Comparison of non-synonymous (amino acid altering) substitution rates with synonymous substitution rates of D. galeata mt protein-coding genes demonstrated that ATPase8 and COI genes were the most and least susceptible, respectively, to the evolutional forces selecting the aa substitutions. Several non-synonymous substitutions were found in ATPase8 and ATPase6 even in the comparison that no synonymous substitution was found. Comparison of the total number of nt variations among the mt DNAs suggested the phylogenetic relationship ((((Shirakaba/Suwa, Kizaki), Kasumigaura), Biwa), D. pulex). Maximum-likelihood analysis using the total nt sequences of mt protein-coding genes confirmed this relationship with bootstrap values higher than 98%. All the mtDNAs of the analyzed Japanese D. galeata clones contained a control region of essentially the same structure that is distinct from those of the previously reported European Daphnia species of the D. longispina complex. The two control regions of different structures spread among mtDNAs of the Japanese and European Daphnia species, respectively, probably after the divergence of the Japanese D. galeata under different selection pressures associated with their habitats.

Long-term zooplankton community records (1996–2017) for Lake Suwa (Japan)

The impact of eutrophication on aquatic ecosystems remains an important topic in aquatic ecology; however, recent successes in water quality restoration in highly eutrophicated water bodies present new research potential regarding re-oligotrophication. Successfully reducing nutrient loading from sewage treatment through restoration activities, induces large changes in phytoplankton composition and biomass, particularly replacement of cyanobacterial dominance. In Lake Suwa, a shallow eutrophic lake in central Japan, recovery has occurred due to water quality restoration efforts since the 1970s. The improvement of lake trophic state from hypertrophic to mesotrophic is accompanied by various changes, such as rapid decreases in biomass of phytoplankton, benthic invertebrates and planktivorous pond smelt, and increases in biomass of aquatic vegetation, mainly floating leaved plants. During re-oligotrophication, zooplankton are important because they are major secondary producers in lake ecosystems. In Lake Suwa, the Research and Education Center for Inland Water Environment, Shinshu University has collected bi-weekly zooplankton samples and analyzed species composition since 1996, when the lake was in a hypertrophic state with serious Microcystis blooms. Lake Suwa is one representative lake for re-oligotrophication in a shallow eutrophic system, and our zooplankton dataset can be used to understand the changes in ecosystem structure and function.