Resting stage cells of six diatom species, Actinoptychus senarius, Biddulphia alternans, Lithodesmium variabile, Odontella longicruris, O. mobiliensis, and Detonula pumila were newly identified from bottom sediments of Ago Bay, central Japan. The resting stage cells of A. senarius, B. alternans and L. variabile are very similar in morphology to their vegetative cells; hence, these resting stage cells are “resting cells”. The resting stage cells of O. longicruris and O. mobiliensis closely resemble the vegetative cells in morphology, therefore, they are regarded as resting cells. However, they have some morphological differences compared with the vegetative cells, indicating a possibility of them being resting spores. The resting stage cells of D. pumila are quite different in morphology from the vegetative cells; therefore, these are “resting spores”. The morphology of the resting spore of D. pumila is circular in valve view. In girdle view, each valve shows the same shape, slightly vaulted, and has a distinct mantle. As a common feature of the resting stage cells of the six species, the plastids show a darker color than those of vegetative cells, and are positioned unevenly in the cells.
Rates of oxygen consumption (R) and ammonia excretion (E) of a total of 22 species of zooplankton and hyperbenthos, which weighed 0.0012 to 26.7 mg dry mass (DM), from inshore and slope waters of the Great Barrier Reef were determined at in situ temperatures (23 to 30°C). Rs ranged from 0.0048 to 118.3 μL O2 ind.−1 h−1 and Es from 0.00051 to 15.9 μg NH4-N ind.−1 h−1. Stepwise regression analyses in which the differences in body mass are taken into account revealed that zooplankton and hyperbenthos exhibited comparable R, but the latter showed lower E than the former. As a result, the atomic ratio of R to E (O : N) of hyperbenthos (geometric mean: 53.1) was greater than that (16.4) of zooplankton. No appreciable differences were evident in C and N composition of the bodies between zooplankton-hyperbenthos; total carbon (C) ranged from 18.0 to 47.2% of DM and total nitrogen (N) from 2.4 to 12.7% of DM, with C : N ratios of 3.1–7.5. Judging from C and N composition, protein was the major component of body organic matter of both zooplankton and hyperbenthos. In terms of N-specific R and N, the present zooplankton data are comparable to those published on tropical zooplankton and small fishes with similar body N. Compared with zooplankton, lower specific Es and higher O : N ratios of hyperbenthos were interpreted to reflect their partial or entire dependence on diets characterized by lower N composition (detritus).
Diatom dynamics in the ocean represents one of the most interesting research themes for marine ecologists. Recent studies have shown the significance of viruses as potential sources of mortality for diatom populations, as well as the more traditional environmental factors. Here, we report the isolation and characterization of a new single-stranded DNA (ssDNA) virus (Csp05DNAV) that causes lysis in Chaetoceros sp. TG07-C28, isolated from the surface water of Ago Bay, Japan. The virus was isolated from the sediments in Ago Bay, and its infection was both lytic and species-specific. The latent period was estimated to be <24 h. The virion is 32–34 nm in diameter, and accumulates in the nucleus of host cells. Csp05DNAV has a closed circular ssDNA genome, which includes a partially double-stranded region. Partial sequence analysis revealed that the open reading frame of this virus genome was similar to the putative replicase-related proteins of previously reported diatom viruses that harbor a ssDNA genome; specifically, CsalDNAV, CdebDNAV, ClorDNAV, and CtenDNAV. Based on the genome structure, Csp05DNAV is considered to belong to the genus Bacilladnavirus. As both the host and virus were isolated from Ago Bay, the host-virus system probably is ecologically important in the bay. This finding provides basic information towards elucidating diatom dynamics in coastal waters.
Argis lar and A. hozawai are commercially important deep-sea crangonid shrimps of closely similar morphology. A previous study described three morphological characters to distinguish A. lar and A. hozawai was based on comparison of specimens of different size, raising the possibility that these characters are features of intraspecific differences related to body size. In the present study, mitochondrial DNA fragments encoding the cytochrome oxidase subunit I (COI) gene were sequenced in order to reassess the morphological criteria purported to separate A. lar and A. hozawai, based on specimens collected under a synchronous and sympatric sampling design. Two distinct clades were detected (p-distance 7.72%) supported by high bootstrap values, which completely correspond to A. lar and A. hozawai identified by morphological characters. Accordingly, A. lar and A. hozawai should be treated as two distinct species for appropriate fisheries management.