Changes in the vertical distribution of dissolved CH, were monitored during the autumnal lake overturn period in mesotrophic Lake Nojiri, Japan (4.4 km* in area and 9.4 X 10' m3 in vol). A survey in 1992 revealed that the surface CH, concentration was highest in December, when the lake overturned. During the following two winters (1993-1994 and 1994-1995) we carried out detailed sampling during the autumnal overturn period. As a result of lake overturn in mid-December, CH, that had accumulated in the hypolimnion during the stratification period mixed rapidly throughout the water column. Increased CH, in the epilimnion quickly disappeared after the overturn as a result of the rising of CH, oxidation activity throughout the water column. The in situ-specific CH, oxidation rate peaked at 0.274, 0.235, and 1.01 d-' at 0.5, 20, and 36 m, respectively, during the overturn, and then declined the following month. During this period, the diffusive flux of methane across the air-water interface increased but was not the dominant sink (avg rate of 4.5 kg lake-' d-l); instead, methane oxidation in the water column was the dominant CH, sink (avg rate of 67.8 kg lake-' d-l), removing -94% of the CH, during the overturn period. A significant methane flux from the bottom sediments throughout the overturn period was confirmed but decreased gradually as the overturn proceeded. The production of organic carbon as a result of CH, oxidation in the water column by methanotrophs was comparable in extent to that generated by primary production at that time.

Long-term seasonal variations in water-column methane oxidation were studied in the eutrophic, shallow Lake Kasumigaura, Japan. The entire water column was oxic throughout the year. Measurements were taken monthly from July 1991 to March 1996. The oxidation rates were derived from time-course dissolved methane concentration measurements during the bottle incubation at in situ temperature. The existence of methane oxidation activity in the oxic lake water was confirmed. Methane oxidation was distinctly seasonal, with low activity from January to April and high activity from August to November. Maximum methane oxidation was observed in late summer or early autumn, when the turnover time of dissolved methane was usually shorter than half a day. Methane oxidation activity does not depend on water temperature, dissolved methane concentration, dissolved oxygen, or dissolved inorganic nitrogen. The annual average methane consumption rate was 12.3 5 15.5 mg CH, m 2 d I. Methane oxidation was the dominant methane sink. consuming an annual average of 74% of dissolved methane in the water column of Lake Kasumigaura.

No abstract

To clarify the phylogenetic position of Vestimentifera (tube worms), 346-bp fragments of the elongation factor-1 alpha (EF-1 alpha) gene (939-1286 according to the numbering of the human gene) of a vestimentiferan, Lamellibrachia sp., a sternaspid polychaete, Sternaspis scutata, an earthworm, Pheretima sp., and a gastropod, Alviniconcha hessleri, were sequenced. From the amino acid sequences of these EF-1 alpha, and those of two other vertebrates and two arthropods, phylogenetic relationships were deduced by the maximum likelihood (ML) method, by which the phylogenetic tree can be inferred without assuming constancy of the molecular evolutionary rate. For the ML tree and all of seven alternative trees, whose log-likelihoods could not be discriminated from that of the ML tree by the criterion of the standard error, the vestimentiferan, the polychaete, and the oligochaete formed a clade, excluding the arthropods and the gastropod as outgroups. This result is convincing evidence that Vestimentifera are protostomes that are closely related to Annelida. The ML tree suggests that Vestimentifera are more closely related to Polychaeta than to Oligochaeta, though the data were not sufficient to discriminate these three groups at a significant level. From recent evidence such as morphological characteristics and molecular information, it may safely be said that vestimentiferans should be included in the Annelida provided this phylum contains polychaetes and oligochaetes.

No abstract

A novel method for analyzing halobacterial pigments was developed, in which retinal was liberated from halobacterial rhodopsins as retinal oxime by hydroxylamine, ethyl beta-apo-8'-carotenoate was introduced as an internal standard, and the pigments including bacterioruberin and beta-carotene were analyzed by HPLC at the same time. With this method, we revealed that light enhances the biosynthesis of bacterioruberin and the conversion of beta-carotene to retinal, but does not affect beta-carotene biosynthesis in Halobacterium salinarum strain Oyon Moussa-16. Low oxygen tension given in the light brought a slight increase in retinal accumulation, although its biosynthesis from beta-carotene is an oxygenation reaction. This paradox could be explained by the increase in beta-carotene biosynthesis.

No abstract

The decomposition of organic material deposited in a small bay has been investigated. With a marine species of Pseudomonas as an assay organism, material deposited during summer and during winter were both actively decomposed. However, differences in the two types of sediment were apparent from the quantities of nutrients and carbohydrate available to the assay organism, as well as to the antibiotic activity of the two sediments. From calculations on the in situ nutrient and carbon budget for the sediment in the same area, it was determined that nitrogen was regenerated most rapidly, followed by phosphorus and carbon. The rate of sediment decomposition, determined as the ratio of the input of material to the steady‐state level in the sediment, is suggested as a basis for the biological comparison of nearshore marine sediments.