Utilizing environmental DNA and imaging to study the deep-sea fish community of Takuyo-Daigo Seamount.

The increase in interest of mining at seamounts means there is a critical need to establish baseline inventories through environmental survey, with the aim of promoting the conservation and stewardship of these remote habitats. To efficiently evaluate fish biodiversity around a seamount, we compared environmental DNA (eDNA) methods using seawater and sponge samples against methods using imagery obtained with a remotely operated vehicle (ROV) and a free-fall deep-sea camera lander called the Edokko Mark I on the Takuyo-Daigo Seamount (153.0°E, 23.5°N) in the northwestern Pacific Ocean. We detected a total of 18 fish families by these methods. The fish fauna detected on the seamount included many families commonly found in deep-sea areas and were similar to the fish fauna of other seamounts located at similar latitudes in the northwestern Pacific. Significant differences in the patterns of detection of fish families between the eDNA and imaging methods is attributed to the differing powers of detection of some fish groups between methods (related to primer compatibility and fish size). For deep-sea fish, the difference in fish composition at the family level between seawater and sponge eDNA methods was not significant, but the difference between Edokko Mark I and ROV methods was significant; the latter difference is likely due to whether or not bait is used to attract fish. Although the eDNA workflow implemented here requires improvements, the use of eDNA and imaging methods in combination provided better insight into the biodiversity of deep-sea fishes in the deep-sea around a seamount, where our knowledge of the fish fauna has been extremely limited. Our recovery of eDNA from seawater and sponge samples around the seamount demonstrates the potential of these methods for facilitating environmental baseline surveys and impact assessments of mining activities to obtain results not previously possible with the use of visual methods only.

Preliminary study on the acute effects of hydrogen sulfide on Amphipoda (Lysianassoidea; Pseudorchomene sp. and Anonyx sp.) collected from deep-sea floors in the Sea of Japan.

To study the environmental impact of the assessment technologies for the development of shallow methane hydrate zones in the Sea of Japan, deep-sea amphipods (Pseudorchomene sp. and Anonyx sp.) were collected from a depth of approximately 1000 m and were tested for H2S toxicity. At 0.57 mg L-1 H2S, all specimens of Pseudorchomene sp. were dead after 96 h, whereas all individuals survived at 0.18 mg L-1. Moreover, Anonyx sp. had a survival rate of 17 % after 96 h at 0.24 mg L-1. A similar toxicity test was conducted with the coastal amphipod Merita sp., a detritivore, and all individuals died within 24 h at 0.15 mg L-1. These results suggested that compared with coastal detritivorous amphipods, deep-sea detritivorous amphipods, which also live near biomats with sediment H2S concentrations exceeding 10 mg L-1, showed a higher tolerance to H2S.

Calcification rates of a massive and a branching coral species were unrelated to diversity of endosymbiotic dinoflagellates.

BACKGROUND: To explore the possibility that endosymbiotic dinoflagellates (Symbiodiniaceae) are associated with coral calcification rates, we investigated the diversity of symbiotic algae in coral colonies with different calcification rates within massive and branching corals (Porites australiensis and Acropora digitifera). METHODS AND RESULTS: Genotyping symbiotic algae from colonies with different calcification rates revealed that all the colonies of both species harbored mainly Cladocopium (previously clade C of Symbiodinium). The Cladocopium symbionts in P. australiensis were mainly composed of C15 and C15bn, and those in A. digitifera of C50a and C50c. We did not detect clear relationships between symbiont compositions and calcification rates within the two coral species. CONCLUSIONS: Our results suggest that different coral calcification rates within species may be attributed to genetic factors of coral hosts themselves and/or within symbiont genotypes.

Non-bleached colonies of massive Porites may attract fishes for selective grazing during mass bleaching events.

In this study we investigated the variation in grazing scar densities between bleached and non-bleached colonies of massive Porites species in Sekisei Lagoon (Okinawa, southwestern Japan) during a mass bleaching event in 2016. The grazing scar densities and bleaching susceptibility varied among neighboring colonies of massive Porites spp. However, non-bleached colonies had significantly more surface scars than bleached colonies. One explanation for these variations is that corallivorous fishes may selectively graze on non-bleached, thermally tolerant colonies. This is the first report of a relationship between grazing scars and the bleaching status of massive Porites spp. colonies during a mass bleaching event.

THE ROLE OF ZINC FINGER PROTEIN IN RNAi INTERFERENCE IN A UNICELLULAR GREEN ALGA CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE).

In our previous study, we generated a strain of 19-P (1030) in which artificial RNA interference (RNAi) was induced by transcribing a hairpin RNA of ~780-bp stem. We utilized this RNAi-induced strain to uncover RNAi-related genes. Random insertional mutagenesis was performed to generate tag-mutants that show a RNAi deficient phenotype. The 92-12C is one such tag-mutant, which bears a 14-kb deletion in chromosome 1. Complementation of 92-12C revealed that a protein gene, including a Cys-Cys-Cys-His-type zinc finger motif and an ankyrin repeat motif, is essential for effective RNAi in Chlamydomonas reinhardtii (Dangeard). BLAST analysis revealed that the zinc finger protein is homologous to an mRNA splicing-related protein of other species. Therefore, one of the probable scenarios is that mRNA coding for RNAi-related proteins cannot be properly spliced, which causes RNAi deficiency in the 92-12C tag-mutant.