Odawa Bay Research Articles

Growth and Maturation of Sargassum ringgoldianum in Odawa Bay, Miura Peninsula, Kanagawa Prefecture

Growth and Maturation of Sargassum ringgoldianum in Odawa Bay, Miura Peninsula, Kanagawa Prefecture

High 210Po atmospheric deposition flux in the subtropical coastal area of Japan

Bulk atmospheric deposition fluxes of 210Po and 210Pb were measured at three coastal regions of Japan, the Pacific Ocean coastal area of the Japanese mainland (Odawa Bay), the Chinese continental side of Japanese coastal area (Tsuyazaki), and an isolated island near Okinawa (Akajima). Wet and dry fallout collectors were continuously deployed from September 1997 through August 1998 for periods of 3 to 31 days depending on the frequency of precipitation events. Annual 210Pb deposition fluxes at Odawa Bay (35°N 139°E), Tsuyazaki (33°N 130°E) and Akajima (26°N 127°E) were 73.3 ± 8.0, 197 ± 35 and 78.5 ± 8.0 Bq m −2 y −1, respectively. Higher 210Pb deposition was observed at the Chinese continental side of Japanese coast than at the Pacific Ocean coastal site. The high 210Pb atmospheric flux at the Chinese continental side coast was thought to be attributable to 222Rn-rich air-mass transport from the Chinese continent during the winter monsoon. In contrast, the annual 210Po deposition fluxes at the three study sites were 13.0 ± 2.3 (Odawa Bay), 21.9 ± 4.4 (Tsuyazaki) and 58.4 ± 7.7 (Akajima) Bq m −2 y −1, respectively, indicating unusual high 210Po deposition at Akajima during winter. Anomalous unsupported 210Po input was observed during summer 1997, suggesting unknown source of 210Po at this area.

Early life history characteristics and genetic homogeneity of Conger myriaster leptocephali along the east coast of central Japan

To study the population structure of the Japanese conger eel, Conger myriaster, we investigated the age, total length, developmental stage and mitochondrial (mt) DNA genetic variation among the leptocephali collected from three different locations along the east coast of central Japan. A total of 79 individuals was collected at the same period of time in March 1998 from Iwaki (northern site), Odawa Bay (middle site) and Ise Bay (southern site). Results from morphological measurements and otolith age determination indicated that the mean total length of leptocephali from Iwaki was about 10 mm shorter than those from Odawa Bay and Ise Bay, the average age of the samples from Ise Bay was about 50 days older than those of the sample from Iwaki and Odawa Bay, and the leptocephali in metamorphic stage appeared only in Ise Bay samples. The otolith data also suggested the existence of at least two spawning seasons in 1997. These regional differences suggested that the early life history characteristics of the Japanese conger eel might differ between geographically different areas along the east coast of central Japan. Phylogenetic analysis based on mtDNA sequence data indicated no significant genetic differentiation between samples collected from different locations, implying intensive gene flow between geographically distant areas.

Effect of seasonal changes on the carbohydrate levels of eelgrass Zostera marina at Odawa Bay

Effect of seasonal changes on the carbohydrate levels of eelgrass Zostera marina at Odawa Bay

三浦半島南部西岸，小田和湾周辺から得られた｀１４´Ｃ年代資料

三浦半島南部西岸，小田和湾周辺から得られた｀１４´Ｃ年代資料

Estimates of Denitrification and Nitrification in Coastal and Estuarine Sediments

Denitrification and nitrification in sediments of Tama Estuary and Odawa Bay, Japan, were investigated by the combined use of a continuous-flow sediment-water system and a N tracer technique. At Odawa Bay, the nitrification rate was comparable to the nitrate reduction rate, and 70% of the N(2) evolved originated from nitrogenous oxides (nitrate and nitrite) which were produced by the action of nitrifying bacteria in the sediments. At Tama Estuary, the nitrate reduction rate was 11 to 17 times higher than the nitrification rate, and nitrogenous oxides derived from ammonium accounted for only 6 to 9% of the N(2) evolution by denitrification.

Growth and maturation of the small filefish Rudarius ercodes in Odawa Bay.

Juveniles less than 20mm total length (TL) were collected by hand beam trawl from July through October. Small-sized fish 30 to 50mm TL began to be recruited to the catch by boat seine from August through September. Although they showed annual fluctuation of pattern in the length frequency distribution, small-sized fish grew up to large-sized fish from 50 to 70mm TL in spring through summer of the next year. A negative relationship between population density and growth in weight was observed. The spawning season is estimated to extend from May through September judging from the seasonal change of a gonadsomatic index. Some small-sized fish recruitd in summer also had well developed gonads. The rate of group maturity for females at around the end of August or time of recruitment showed annual variation, and was lower in 1977 when population density was higher than in other years.

Denitrification, Nitrate Reduction, and Oxygen Consumption in Coastal and Estuarine Sediments

Denitrification and consumption of oxygen and nitrate in sediments from Tama Estuary, Odawa Bay, and Tokyo Bay were measured in an experimental sediment-water system. Filtered seawater containing [N]nitrate flowed continuously over undisturbed sediments, and the concentrations of O(2), nitrate, and nitrite in the influent and effluent and of N(2) in the effluent were monitored. Under steady-state conditions, the rate of nitrate consumption was the same order of magnitude as the rate of oxygen consumption in Tama Estuary sediments, whereas the former rate was one order of magnitude lower than the latter rate in Odawa Bay and Tokyo Bay sediments. Denitrification accounted for 27 to 57% of the nitrate consumption.

Relations between distribution and mode of life of asteroid populations in odawa bay

In a small cove, Odawa Bay, at the Pacific coast of central Japan, the modes of life of starfishes collected by a small Danish seine were surveyed. On Astropeeten scoparius, A. polyacanthus and Luidia quinaria of five species of starfish collected, theri foods were examined by gut contents analysis. Food of both species of Astropecten was resemble with each other, but it was different with it of L. quinaria which feeds mainly on ophiurans. Distributions of asteroids in the bay were revealed; A. scoparius and Asterias amurensis were found in bay-head area having muddy sediment, A. polyacanthus is found in the same area on rocks or pbbles, and L. quinaria in extensive areas with soft bottom over the bay. The breeding seasons of starfishes were estimated that both species of Astropecten were May-June, L. quinaria around August, A. amurensis February-April, and A. pectinifera April-May. From the results above, it would be considered that the five asteroids having the modes of life resemble each others coexist in Odawa Bay shifting mutually their food habit, habitat, breeding season and so on.

Population fluctuation of three species of embiotocid fishes in the Zostera marina belt of Odawa Bay.

1) Population fluctuation of embiotocid fishes in Odawa Bay, Kanagawa Prefecture, was examined on the basis of data on catch per haul by the tow net (Gorota-ami) from 1974 to 1977. 2) The Zostera belt of Odawa Bay was divided into four areas and abundance indices for each species within each area and for the total area of the Zostera belt were calculated. 3) The range of estimates (between years) for the total mortality coefficient (Z), calculated from the estimated daily decrease in the natural logarithmic value of an abundance index of the 0+age population, is estimated at 0.010-0.028 in D. viridis, 0.009-0.033 in D. temmincki and 0.021-0.048 in N. ransonneti. 4) The reliability of the calculation of the abundance index is discussed in connection with various factors which may have effect on the estimate of Z.

Inter-specific relations surrounding the three species of embiotocid fishes in the Zostera marina belt of Odawa Bay.

Inter-specific relations concerning three species of embiotocid fishes, Ditrema viridis, Ditrema temmincki and Neoditrema ransonneti, in the Zostera belt of Odawa Bay are discussed in the present paper. From the seasonal changes in fish fauna appearing in the Zostera belt, the utilization of the Zostera belt as a habitat of fishes was examined. D. viridis and d. temmincki are members of year-round residents and N. ransonneti is one of the seasonal residents. The O+ age group of D. viridis and D. temmincki have high probability to come into contact with other year-round residents, especially Rudarius ercodes, which occur frequently in the cath and are predominant in the Zostera belt. These fishes tend to reduce competition for the same food resources by6 means of different seasonal population fluctuation or segregation of microhabitat. The O+ age of N. ransonneti mainly use the Zostera belt as a spawning or nursery ground.

Seasonal change in the standing crop of eelgrass Zostera marina L.) in Odawa Bay, Central Japan

The standing crop of eelgrass populations in Odawa Bay, central Japan, showed a unimodal seasonal variation with a peak during April–May (155 to 242 g dry weight m−2) and a trough in December (14–31 g m−2). A similar trend was observed with respect to leaf area index. The daylight hours appeared to be mainly responsible for this variation. The population densities ranged from 171 to 501 shoots m−2 in spring and from 59 to 213 in winter. The spring populations consisted of vegetative and flowering shoots, but in the other seasons only vegetative shoots were found. Three different canopy structures of eelgrass were identified and which were clearly distinguishable in the diagram of biomass. The texture of bottom sediments was apparently responsible for the differentiaton of these canopy structures.

Distribution and biomass of eelgrass (Zostera marina L.) and other seagrasses in Odawa Bay, Central Japan

In Odawa Bay, central Japan, three species of seagrass occur, Zostera marina L., Z. japonica Aschers. et Graebner and Halophila ovalis Hook. f., of which the eelgrass, Z. marina, forms dense and wide beds in shallow littoral areas. The ecological distribution of these seagrasses was studied by diving observations from which it was determined that depth distribution was closely related to transparency of water and/or degree of insolation. The area of Odawa Bay covered with the eelgrass and the total eelgrass biomass in May 1977 were estimated to be ca. 68.2 ha, and ca. 101.2 tons dry weight.

小田和湾アマモ場におけるアミメハギの個体数動変

Seasonal and annual population fluctuations of Rudarius ercodes in the Zostera bed in Odawa Bay were studied. A recruitment group of small sized fish occurred every summer and grew into large sized fish by spring of the following year. The number of catch per haul of each recruitment group was used as an index of relative population density. From the seasonal changes of this index, three peaks were observed in September-October, May-June, and August-September at the head of the bay and in October-November, April-May, and August-October at the mouth of the bay. In winter only a few individuals stayed at the monuth and none at the head of the bay, although they were distributed in both areas in other seasons. From the change of the number per haul of three recruitment groups at each peak, it was found that the great annual population fluctuation at the first peak decreased gradually and the population level approached about 100 individuals per haul at the third peak. These facts suggest the possiblilty of movement in and out of the bay and some process of population regulation.

小田和湾の藻場におけるウミタナゴ類3種の生長および再生産

1) The seasonal growth pattern and the reproductive processes of embiotocid fishes around Odawa Bay, Kanagawa Prefecture, are examined on the basis of measuring age, body length and weight, fat weight, gonad weight, and the size and number of young in brood. 2) Two regression straight lines fit the data of relations between body length and body weight for females and two or three regression lines may be applied to the data of relations between total body length and body weight for embryos at the stage of gestation in the ovary of female mother of three species of embiotocid fishes. 3) The value of the coefficient of variation is shown to continue to rise up until the individuals reach about 70mm in fork length, then gradually decreased as the individuals grew older. 4) The growing season is seen to occur roughly from May to September and the non-growing season from October to February of the next year. In D. viridis and D. temmincki, the males are 2 or 3mm bigger in mean body length than the females during the growing season of the first year but during the growing season of second year, the females are bigger than the males. 5) A time lag of about six months between males and females of D. viridis and D. temmincki is seen in the reproductive cycle and the fat contained have a close relation to sexual maturation. 6) Embryos are born at the stage of juvenile or young after about 3 months gestation in the ovaries of females. In 1+year old mother, D. viridis has generally 12-13 young, N. ransonneti has 10-11 young and D. temmincki has 8-9 young. The size of young born is the biggest in D. temmincki and the smallest in N. ransonneti.

小田和湾の藻場におけるウミタナゴ類3種の摂餌生態

1) The diet and feeding ecology of embiotocid fishes around Odawa Bay, Kanagawa Prefecture, are examined on the basis of qualitative and quantative analyses of the gut contents. 2) The main food items of the 0+age group is gammarid amphipods in D. viridis, gammarids and caprellid amphipods in D. temmincki and copepods in N. ransonneti. 3) The amount of food intake per body weight is shown to be 2-3% in D. viridis, 2-5% in D. temmincki and 1-4% in N. ransonneti. 4) The seasonal change of the food items utilized by the 0+age group of D. viridis and D. temmincki correspond fairly well to that of relative abundance of phytal animals in the Zostera belt. 5) The 1+age group of D. viridis and D. temmincki utilize a wider variety of types and larger sized food items which are not always predominant in the Zostera belt. 6) The food items of N. ransonneti show no seasonality and N. ransonneti does not seem to depend on phytal animals in the Zostera belt as food resources.

小田和湾の藻場におけるウミタナゴ類3種の生息場所および分布

小田和湾の藻場におけるウミタナゴ類3種の生息場所および分布

Simultaneous determinations of nitrification and nitrate reduction in coastal sediments by a 15N dilution technique.

Nitrification, the oxidation of ammonia to nitrite and nitrate, and nitrate reduction by bacteria in coastal sediments of Mangoku-Ura and Odawa Bay were simultaneously determined by a 15N dilution technique. In muddy sediments of Mangoku-Ura, nitrate reduction proceeded at a rate of 10(-2) to 10 X 10(-2) microgram-atoms of N/g per h. Nitrification was far less intensive. Denitrification, or N2 production from nitrate, accounted for about 30% of the nitrate reduction. A simultaneous occurrence of nitrification and nitrate reduction with a similar rate of 10(-2) microgram-atoms of N/g per h was demonstrated in sandy sediment collected from a Zostera bed of Odawa Bay.