Arctodiaptomus dorsalis is an invasive calanoid copepod from America, and is now found in 23 out of 32 lakes and rivers in the Philippines. Live specimens of A. dorsalis were collected from Lake Taal and cultured in the laboratory. The specimens were reared under three different temperatures (25°C, 30°C, and 35°C) with the same food and light conditions, i.e. ~105 cells mL−1 of Chlamydomonas reinhardtii and 12L:12D at ~60 lx, respectively. Post-embryonic development times from hatching to adult decreased from 31.5 d to 18.3 d as the temperature increased, while those during naupliar stages were quite similar, i.e. 4.4, 2.8 and 2.3 d at 25, 30 and 35°C, respectively. The naupliar durations were substantially shorter than the copepodid stages. Clutch sizes were almost the same, 8.7–9.2 eggs clutch−1, among all temperatures tested, while hatching success decreased from 85.9% at 25°C to 24.2% at 35°C. Overall survival rates from hatching to adult decreased as well from 67% at 25°C to 23% at 35°C. This is the first successful attempt to culture A. dorsalis collected from a freshwater lake in the Philippines.
This study examines the effects of the sea urchin Diadema setosum on algal composition, coverage and biomass on barren ground. In cage experiments, the effects of D. setosum density were examined at 5 levels over the range of 0–8 ind. m−2. Algal coverage and number of species, densities and lengths of Sargassum spp. on experimental blocks in each cage were measured monthly. In the cage without D. setosum, algal coverage and biomass were higher than in cages with D. setosum. For D. setosum density of 1 ind. m−2 and higher, decreased algal coverage and decreased biomass and density of Sargassum spp. were observed. D. setosum at a density higher than 2 ind. m−2 had a negative effect on algal species numbers. Consequently, algae could grow when the D. setosum density was fewer than 2 ind. m−2. This study revealed that grazing by D. setosum has a great effect on the seaweed bed ecosystems along the coast of central Japan.
The concentration of mycosporine-like amino acids (MAAs) of phytoplankton and the attenuation coefficients of ultraviolet radiation (UVR) were determined in coastal surface waters in Sagami Bay during the period from 2004 to 2012 to examine the seasonal cycle. Four major MAAs, including mycosporine-glycine, palythine, shinorine, and porphyra-334, were detected throughout the year. Mycosporine-glycine was the most dominant type, reaching more than 100 nM, whereas porphyra-334 was the least dominant type, barely reaching 20 nM. The total concentration of the four MAAs was high in the high water temperature (WT) months (February–July) and low in the low WT months (August–January). The seasonal cycle was repeatedly sustained for six years. The attenuation of ultraviolet radiation at two wavelengths, 320 and 340 nm, also followed a similar seasonal cycle: high in the warm period and low in the cool period. The attenuation of UVR at two wavelengths (kd and kd) was linearly correlated with the concentration of MAAs (p<0.01). Solar energy was the environmental driving force responsible for the seasonal cycles of MAAs, which were further enhanced by increased biomass and nutrient availability. Individual groups in the phytoplankton community might share roles to protect the entire community from UVR in the marine ecosystem by producing various MAAs.
The Paracalanus parvus species complex is one of the most dominant and ecologically important copepod groups in the waters around Japan. However, the overall taxonomic classification of the species complex has not been sufficiently defined to date. In this study, both genetic and morphological analyses were performed on specimens of the P. parvus species complex collected along the “O-line”, a monitoring line located at 138°E, south of Japan. Among the individuals collected, P. nanus specimens were clearly distinguishable morphologically, whereas other specimens could be classified into three reproductively isolated species. These distinctions are based on genetic analyses of the mitochondrial cytochrome oxidase subunit I (mtCOI) and nuclear large subunit (nLSU) ribosomal RNA. By comparing the genetic and morphological data with findings from previous studies, these three species were identified as P. tropicus, P. indicus, and an as-yet undescribed species (Paracalanus sp. (NWP)). The latter possesses a humped forehead and was found to be a dominant species within the surveyed continental slope area. As a distinguishing characteristic, the humped forehead was not consistently useful as it was prominent in only about half of the individuals collected. Morphological discrimination between this species and P. indicus was only made possible by comparing the relative length of exopod segment 3 on swimming leg 4. Despite morphological similarities among member species, ecological studies on the P. parvus species complex conducted around Japan may mostly concern the undescribed species, Paracalanus sp. (NWP), considering that P. indicus was found only in warmer waters in this study.
Methane-oxidizing bacteria (MOB) are regarded as key players in aquatic ecosystems, which can mitigate greenhouse gas emissions to the atmosphere. Among phylogenetically diverse MOB, those of the phylum Proteobacteria have been regarded as major methane oxidizers in environments, and they are classified into two major groups, type I and type II. Another group of MOB, ‘Candidatus Methylomirabilis oxyfera’ and its close relatives have also been detected in various environments, but their predominance over proteobacterial MOB has hardly ever been reported. Feitsui Reservoir (FTR) is a subtropical reservoir situated in Taiwan, where the predominance of ‘M. oxyfera’-like phylotypes in a planktonic MOB community was first reported. In this study, planktonic MOB of three types (‘M. oxyfera’-like, type I and type II) were quantified with catalyzed reporter deposition-fluorescence in situ hybridization, to reveal seasonal variation and vertical distribution in the FTR. The MOB were enumerated for 161 samples obtained from 8 water depths on 23 sampling days over 16 months. The results obtained in this study will provide valuable basic data for a better understanding of MOB communities in the environment, giving insights into the global methane budget.
A non-metric multi-dimensional scaling (nMDS) analysis based on 10 quantitative morphological characteristics showed significant morphological differences among snipefishes of the genus Macroramphosus from the northwestern Pacific including the East China Sea and the southern Pacific, northern Atlantic, and southern Atlantic oceans. Individuals of theses four sea areas were significantly different from each other for at least one characteristic. Considering these results along with those of previous molecular analyses, Macroramphosus is suggested to have speciated or genetically diverged among sea areas.