Standing stocks and production rates of phytoplankton and planktonic copepods in the Inland Sea of Japan

Standing stocks and production rates of phytoplankton and planktonic copepods were investigated at 15 stations in the Inland Sea of Japan during four cruises in October–November 1979, January, April and June 1980. The overall mean of phytoplankton biomass was relatively constant during the study period, ranging from 2.3 mg chl.a m^–3 in April to 3.6 mg chl.a m^–3 in October–November. Primary production was low in January (mean: 90 mg C m^–2 d^–1), but higher than 375 mg C m^–2 d^–1 on the other occasions. Integrated annual primary production was 122 g C m^–2 yr^–1. In terms of carbon weight,Paracalanus parvus was the most important copepod species. The variation of the mean copepod biomass (range: 7.6 mg C m^–3 in April to 20.2 mg C m^–3 in June) was smaller than that of copepod production, which was estimated by the Ikeda-Motoda's physiological method. Copepod producion was low in cold seasons (0.6 and 0.9 mg C m^–3 d^–1 in January and April, respectively), and increased, following the elevation of primary production, to 4.9 mg C m^–3 d^–1 in June. Annual copepod production was 33.7 g C m^–2 yr^–1, of which herbivore (secondary) production was 26.4 g C m^–2 yr^–1 (21.7% of primary production). The ratios of pelagic planktivorous fish catch and total fish catch to the primary production were 0.82 and 1.8%, respectively, indicating very high efficiency in exploiting fishery resources in the Inland Sea of Japan.     

Phosphorus content of zooplankton from the Inland Sea of Japan

Measurements of phosphorus content were made for eleven species of copepods, two species of mysids, shrimps (including mysis stage) and chaetognaths, and one species ofNoctiluca, cirriped (naupliar stage) and crab (zoeal stage) from the Inland Sea of Japan. The body phosphorus content (P, inµg) is highly correlated to prosome length (L, inµm) for copepods, which is expressed as logP=2.90 ×logL–9.34. Mean phosphorus content expressed as percent of dry weight is 1.30% for copepods, 1.39% for mysids, 0.63% for a decapod shrimpAcetes japonicus, and 0.80% for chaetognaths.Noctiluca contains phosphorus of only 0.36%. The comparatively higher phosphorus content of suspension-feeding copepods may be related to the constant supply of phosphorus-rich phytoplankton in this region.     

Length-weight relationships of important zooplankton from the Inland Sea of Japan

Measurements of dry weight, carbon- and nitrogen contents together with the body length of important zooplankton from the Inland Sea of Japan were made using freshly caught specimens. The values of the former three parameters were found to be highly correlated to length, and species specific regression equations were calculated for 10 species of Copepoda (Calanus sinicus, Euchaeta plana, E. concinna, Centropages abdominalis, Sinocalanus tenellus, Acartia clausi, A. tsuensis, Tortanus forcipatus, Oithona brevicornis andO. similis), 3 species of Cladocera (Podon leuckarti, P. polyphemoides andPenilia avirostris), 1 species of each of Mysidacea (Neomysis japonica), and Natantia (Acetes japonicus), and two forms of Chaetognatha (Sagitta crassa andS. crassa f.naikaiensis).     

Heavy metals and accumulation rates of sediments in Osaka Bay,the Seto Inland Sea,Japan

The metal load into sediments and the change in the sedimentary environment of Osaka Bay in the Seto Inland Sea have been studied through geochemical analysis of core sediments, using both Pb-210 dating and a selective chemical leaching technique. Analytical results from a 6-m core of sediment show that copper and zinc pollution started in the late 1800's and the present enrichment ratios of copper and zinc, relative to background levels (20 mg kg^–1 for Cu and 94 mg kg^–1 for Zn), are 2.8 and 4.1, respectively. The present anthropogenic copper and zinc loads into Osaka Bay sediments, are 47 and 368 ton yr^–1, while natural copper and zinc loads are 40 and 186 ton yr^–1, respectively. Osaka Bay sediment at the present day is considered to be seriously polluted by zinc, now. The vertical profiles of copper and zinc in four successively separated fractions (10% acetic acid soluble fraction: F-HAC, 0.1M hydrochloric acid-soluble fraction: F-HCl, hydrogen peroxide-soluble fraction: F-H₂O₂ and hydrofluoric acid-soluble fraction: F-HF) from the core sediments indicate that enrichments of copper and zinc in the upper layer of the sediment are dependent on increases in the metal contents of the F-HAC, F-HCl and F-H₂O₂ fractions. Copper in F-HAC, and zinc in F-HAC and F-HCl, seem to be of anthropogenic origin.Results of sequential studies of the whole Seto Inland Sea can be summarized as follows: At the present time, the sedimentary loads of copper and zinc over the whole Seto Inland Sea area are 630 and 3,500 ton yr^–1, respectively, while the natural and anthropogenic loads are 320 and 310 ton yr^–1 for copper and 1,800 and 1,700 ton yr^–1 for zinc, respectively.     

Relations between fecal pellet volume and body size for major zooplankters of the Inland Sea of Japan

Measurements of fecal pellet volume together with body length/body carbon weight were made for major zooplankters of the Inland Sea of Japan. The pellet volume was highly correlated with animal body size for copepods (10 species combined), a mysid (Neomysis japonica), a larvacean (Oikopleura dioica) and a pelagic shrimp (Acetes japonicus), and a specific equation was given for each group. A single equation could describe the composite relationship between pellet volume (PV, m³) and body carbon weight (C, g) for copepods andN. japonica: logPV=0.85logC+4.56. Balanid nauplii,O. dioica and a doliolidDolioletta gegenbauri produced pellets larger, butA. japonicus produced pellets smaller, than those by copepods andN. japonica of equivalent body carbon weight. In general, larger zooplankters produce larger fecal pellets. Hence, the size composition of the zooplankton community is an important parameter for the variation in the vertical flux of material via fecal pellets.     

Standing stocks and production rates of phytoplankton and abundance of bacteria in the Seto Inland Sea, Japan

Standing stocks and production rates of phytoplankton and abundance of bacteria were investigated at 39 stations in the Seto Inland Sea, Japan during four crulses in October 1993, January, April and June 1994. Primary productivity was measured by the¹³C tracer method. Photosynthetic rate varied from 0.41 to 32.1 μgC/1/h with an average value of 4.67 μgC/l/h. Annual primary production was estimated to be 218 gC/m²/year. Annual primary production in this study was 1.8 times as high as the values which were previously reported at same area. The reason for the disagreement between our primary production value and previous values is not thought to be due to the difference of methods used for measuring primary production or the different Chl.a concentrations but to the method of estimating the primary production in the euphotic zone from thein vitro measurements. The distribution of bacterial cells in surface seawater was examined during the same cruises. Bacterial cell density ranged from 0.32 to 3.4×10⁶ cells/ml. The density was relatively high in the eutrophic regions of Hiroshima Bay and Osaka Bay In addition, a high density of bacteria was also observed in an area within Suo Nada where Chl.a was relatively low. The disparity between Chla and bacterial density in Suo Nada suggests that bacterial abundance can be controlled by the availability of substrates other than phytoplankton exudate.     

中沙大环礁四种大型海藻的光生理特征比较及其对升温的响应

生活于珊瑚礁区的大型海藻可以与珊瑚一起为礁栖生物提供食物和栖息地, 它们在维护珊瑚礁生态系统生物多样性中起着极为重要的作用。本论文比较研究了生活于我国南海中沙大环礁区4种优势海藻的生化组分、光合特征及其对海水升温的生理响应,其中厚膜藻(Grateloupia ellipitica)和粉枝藻(Liagora samaensis)为红藻, 钙扇藻(Udotea flabellum)和仙掌藻(Halimeda discoidea)为绿藻。结果显示, 与绿藻相比, 红藻藻体叶绿素(Chl a)和类胡萝卜素含量更低且含有藻胆素, 红藻的光补偿点(E_C)和呼吸速率(R_d)均显著低于绿藻。海水升温提高了4种海藻的光能利用效率(α)、E_C、R_d和日净光合固碳量; 同时, 升温还降低红藻的饱和光强(E_K)、提高绿藻的最大光合放氧速率(P_max)。结果还显示, 海水升温在光强较低时提高红藻的光合放氧速率, 光强较高时则降低其放氧速率; 升温也提高绿藻的光合放氧速率, 但光强变化对升温效应的影响不显著。基于4种海藻的光生理特征以及升温效应的种间差异性可见, 短时间升温(~4℃)有利于中沙大环礁区海藻的光合作用; 与绿藻相比, 该升温效应更有利于红藻。     

Geographical and seasonal variations in abundance,biomass and estimated production rates of microzooplankton in the Inland Sea of Japan

We measured abundance and biomass of 3 major groups of microzooplankton, i.e. tintinnids, naked ciliates and copepod nauplii, at 21 stations in the Inland Sea of Japan in October 1993, January, April and June 1994. The average abundance of the microzooplankton over the entire Inland Sea of Japan ranged from 2.39×10⁵ indiv. m^–3 in January to 4.00×10⁵ indiv. m^–3 in April. Ciliated protozoans, i.e. tintinnids plus naked ciliates, numerically dominated the microzooplankton. The average biomass of the microzooplankton was exceedingly high in October (8.62 mg C m^–3) compared to that in the other months (2.06, 2.79 and 2.68 mg C m^–3 in January, April and June, respectively). The ciliated protozoans also dominated in terms of biomass except in October, when copepod nauplii were more important. Estimated production rate of the microzooplankton was highest in October (average: 6.02 mg C m^–3d^–1) and followed in order by June, April and January (1.94, 1.14 and 0.54 mg C m^–3d^–1, respectively). Due to higher specific growth rate, the production rate by the ciliated protozoans far exceeded that by the copepod nauplii. The trophic importance of the microzooplankton in the pelagic ecosystem of the Inland Sea of Japan was assessed by estimating carbon flow through the microzooplankton community.     

Measurements of carbon dioxide in the Seto Inland Sea of Japan

The carbon dioxide in seawater (pCO₂) was measured in the Seto Inland Sea of Japan using newly developed equilibrator instrument designed to be free from the correction for addition or extraction of the carbon dioxide from carrier gas. The temperature dependence of pCO₂ was about 4.5%pCO₂/°C for a single seawater sample which was processed as free from biological activity and change in total carbon dioxide content during an experiment. The decrease in pCO₂ during daylight hours due to the photosynthetic fixation was about 30% of the daily mean of pCO₂ during warm months and about 15% during cold months. The effect of carbon dioxide exchange between air and seawater on pCO₂ was about 0.6 ppm in August and about 0.1 ppm in March. This is negligible small compared with the daily oscillation of carbon dioxide in seawater.     

Seasonal variation of water temperature in the Seto Inland Sea

The seasonal variation of water temperature in the Seto Inland Sea, Japan is examined using data analysis and numerical experiments and is shown to be controlled by heat exchange through the sea surface and horizontal heat dispersion from the Pacific Ocean. The average water temperature goes down from the Pacific Ocean to the center of the Seto Inland Sea indicating that 4.0 to 6.0×10¹⁵ cal day^?1 (1.6 to 2.5×10¹⁶ joule day^?1) of heat is transported from the Pacific Ocean to the Seto Inland Sea and is lost through the sea surface. The amplitude of seasonal variation of water temperature is large at the center of the Seto Inland Sea and the maximum water temperature is reached first at Bisan Straits and last at Iyo-Nada.     

Sedimentation rates and heavy metal pollution of sediments in the Seto Inland Sea

Sedimentation rates in ten sediment cores from Hiroshima Bay in the Seto Inland Sea of Japan were determined with the |2210|0Pb technique, and heavy metals were analyzed. The sedimentation rates vary from 0.18 to 0.33 g cm|2-2|0 yr|2-1|0. The highest sedimentation rates were observed in the northern part of the bay at the mouth of Ota River, while lower sedimentation rates not more than 0.20 g cm⁻² yr⁻¹ were observed at stations close to narrow water-ways, or where water depth was shallow. The contents of copper and zinc in the sediment cores began to increase around 1930 as a result of increased human activity, and have remained almost unchanged since 1970 possibly because of regulation of pollutant discharge. The natural background values of copper and zinc in the sediment of this bay range from 16 to 27 mgkg⁻¹ and 70 to 105 mg kg⁻¹, respectively. The total amounts of anthropogenic copper and zinc deposited in the sediments since about 1930 are estimated to be 0.5–2.7 ton km⁻² and 2.2–14.5 ton km⁻², respectively. At the present-day, the anthropogenic loads of copper and zinc to the sediments of the whole bay are 26 ton yr⁻¹ and 183 ton yr⁻¹, and these values constitute 39% and 48% of the total sedimentary loads at the present-day, respectively.     

Sedimentation rates and heavy metal pollution of sediments in the Seto Inland Sea

In the Suo-Nada area of the Seto Inland Sea, Japan, sedimentation rates and the sedimentary record of anthropogenic metal loads were determined by combining the Pb-210 dating technique with heavy metal analysis of the sediments. The sedimentation rates vary from 0.11 to 0.27 g cm^–2 yr^–1. Lower sedimentation rates were observed in the eastern part of the basin which is characterized by a bottom with sand and gravel, and fast tidal currents.Anthropogenic and natural loads of copper and zinc into the sediments are 34 and 326, and 65 and 375 ton yr^–1, respectively. The anthropogenic loads are fairly low compared with those of the other main areas of sediment accumulation in the Seto Inland Sea. The highest level of zinc and copper pollution was observed in the western part of the basin because of waste discharge from an old and big ironworks outside basin since the early 1900's.     

Sedimentation rates and heavy metal pollution of sediments in the Seto Inland Sea

In the Hiuchi-Nada area of the Seto Inland Sea, Japan, sedimentation rates were determined with the Pb-210 technique, and heavy metals in sediments were also analyzed. Sediments were collected in twelve short sediment cores and a long sediment core, using 1-m and 6-m gravity corers.The sedimentation rates vary from 0.14 to 0.31 g cm^–2yr^–1. The highest sedimentation rate was observed in the central part of the area, while lower sedimentation rates were observed in the eastern part.In Hiuchi-Nada, a remarkable increase in copper and zinc contents is noticeable as early as the 1800's. Over the past 240 years a copper smelter at the south-western side of this area has been causing serious pollution of the sediment. Now, anthropogenic copper and zinc loads into the sediment are 123 and 376 ton yr^–1 compared to natural copper and zinc loads of 82 and 401 ton yr^–1, respectively. The highest level of copper and zinc pollution was observed in the 1960's, when the relative enrichments above background values (copper; 19 and zinc; 93 mg kg^–1) were 5.5 and 2.8, respectively.     

Preliminary report on radionuclide concentrations in the bottom waters at the entrance of Wakasa Bay with special reference to the Japan Sea Proper Water

Marked fluctuation of concentrations of⁹⁰Sr and¹³⁷Cs was observed in the bottom waters at the entrance of Wakasa Bay during 1987–1992, and the cause was investigated. The concentrations of⁹⁰Sr and¹³⁷Cs in the bottom waters were significantly low when the upper level of the Japan Sea Proper Water (JSPW) was high and covered the sampling depth, but high when the upper level of the JSPW was low. The cause of the fluctuation observed in the bottom waters is, therefore, suggested to be the vertical fluctuation of the upper level of the JSPW on the shelf slope, which has been little described before.     

Structure and species diversity of the zooplankton community of the Inland Sea of Japan

Seasonal fluctuations in composition and abundance of zooplankton of the Inland Sea of Japan were investigated in 1979–1980. Some of the areas in the environment were found to be eutrophic and sharp temperature variations occurred with seasons. In this scenario, zooplankton populations peaked in autumn. Copepods were the dominant component and six species of this group formed about 88% of the total zooplankton counts. Species groups are categorized based on distributional characteristics. Zooplankton composition was more or less homogeneous in each season within the area studied and a few oceanic species which occurred had only limited influence on community structure. Species diversity was low and competition among species was weak. The results indicated a poor quality biotope probably resulting from a deterioration of water quality and an environment which favours r-selection.     

Carbon dioxide in surface seawaters of the Seto Inland Sea,Japan

Observations were made of time variations of carbon dioxide in seawater, pCO₂, and in the atmosphere, PCO₂, in the Seto Inland Sea of Japan. The pCO₂ data showed well defined diurnal variation; high values at nighttime and low values during daylight hours. The pCO₂ correlated negatively with dissolved oxygen. These results denote that the diurnal variation of pCO₂ is associated with effects of photoplankton's activity in seawater. The pCO₂ measured in the Seto Inland Sea showed higher values than the PCO₂ during June to November, denoting transport of carbon dioxide from the sea surface to the atmosphere, and lower values during December to May, denoting transport of carbon dioxide from the atmosphere to the sea surface. The exchange rates of carbon dioxide were calculated using working formula given by Andriéet al. (1986). The results showed that the Seto Inland Sea gained carbon dioxide of 1.0 m-mol m^–2 d^–1 from the atmosphere in March and lost 1.7 m-mol m^–2 d^–1 to the atmosphere in August.     

Trophic structure of the Barents Sea fish assemblage with special reference to the cod stock recoverability

The species composition and trophic structure of the Barents Sea fish assemblage is analysed based on data from research survey trawls and diet analyses of various species. Atlantic cod was the dominant fish species encountered, accounting for more than 55% by abundance or biomass. Only five fish species (long rough dab, thorny skate, Greenland halibut, deepwater redfish and saithe) were sufficiently abundant to be considered as possible food competitors with cod in the Barents Sea. However, possible trophic competition is not high, due to low spatial and temporal overlap between cod and these other species. Analyses of fish assemblages and trophic structures of the Barents Sea and other areas (North Sea, Western Greenland, Newfoundland-Labrador shelf) suggest that Barents Sea cod is the only cod stock for which the ability to recover may not be restricted by trophic relations among fishes, due to a lack of other abundant predatory species and low potential for competition caused by spatial-temporal changes.     

Wax and wane of Chattonella (Raphidophyceae) bloom with special reference to competition between Skeletonema (Bacillariophyceae) in the Ariake Sea, Japan

The raphidophyte Chattonella and the bacillariophyte Skeletonema are representative bloom-causing organisms in the Ariake Sea, Japan. Changes in their abundance were monitored to clarify the role of river discharge in the red tides caused by these organisms in the innermost area of the sea. In late June 2010, heavy rain occurred and subsequently river discharge increased. A Chattonella bloom occurred after heavy rain on July 5, although Chattonella abundance was very low (<1?cell?ml^?1) before the heavy rain (June 29). Maximum cell density reached 4.2?×?10³?cells?ml^?1 at the surface. Thus, the bloom developed as the river plume extended in the estuary. During the course of extension of the river plume, the Chattonella population rapidly developed using the nutrients supplied by the river. Just after the Chattonella bloom, heavy rain occurred again and a very large quantity of river water flowed into the estuary. Consequently, the salinity of the surface decreased to 5 in the study area on July 16. Chattonella did not migrate to the surface probably because of the overlying low-salinity water; Chattonella formed a thin layer (20–50?cm in thickness) at the depth where salinity was 10. However, a Skeletonema population developed at the surface. On July 20, Skeletonema density at the surface exceeded 10⁵?cells?ml^?1. With the decline of the Skeletonema abundance due to the nutrient limitation, Chattonella again formed bloom probably using deep-nutrient pool by their vertical migration behavior. The present study clearly demonstrates that the Chattonella can form dense bloom after the heavy rain. The seed population awaiting the river discharge is probably essential to the rapid development of Chattonella in the estuary.     

Open Ocean Originated Phosphorus and Nitrogen in the Seto Inland Sea,Japan

The ratios of phosphorus and nitrogen originating from land and the open ocean in the Seto Inland Sea, which is the largest semi-enclosed coastal sea in Japan, have been estimated from data on total phosphorus and nitrogen loads and observed concentrations of total phosphorus and nitrogen. The ratios of land-origin and open-ocean-origin total phosphorus and nitrogen in the Seto Inland Sea are 0.28:0.72 and 0.19:0.81, respectively.