Microbiological and Chemical Studies in the Seas of Hiuchi and Bingo—II

The distribution of inorganic nitrogen compounds and the metabolic rates of these compounds by microorganisms as a whole were investigated in the Seas of Hiuchi and Bingo. The results obtained are as follows:

1. Of inorganic nitrogen compounds, the contents in sea water, those in bottom muds, the uptake or liberation rates of microorganisms as a whole in sea water, and the liberation rates from bottom muds to sea water are 0.2～4.0 μg at. N/l, 3～60 μg at.N/100 g, 0.01～0.5 μg at.N//lhr, and 0.3～1.9 μg at.N/100 cm²/hr, respectively, and these contents or rates of ammonia usually are the largest of these inorganic nitrogen compounds.
2. From the above-mentioned results and the others, it is suggested that the nitrogen in the seas circulates mainly in sea water itself and the course of nitrogen cycle, which passes through bottom muds, is not so important, and further that, of the cycle of inorganic nitrogen compounds, the main course is the course which ammonia is liberated from organic nitrogen compounds and it is immediately uptaked by microorganisms, and the course which it is oxidized to nitrate and the others are not so important.

     

Cobalt content in the shallow sea sediments

Cobalt contained in the sediments from Maizuru Bay and Wakasa Bay was determined by the atomic absorption method. Cobalt content in the surface layer of the bottom sediments averaged 15.2 and 6.7g/g dry matter in Maizuru Bay and in Wakasa Bay, respectively. The vertical distribution of cobalt was almost uniform in the column of bottom sediments. Geographically, the cobalt content in sediments tended to be inverse proportion to the distance from the coast in Wakasa Bay. Considering the distribution of cobalt, it is reasonably concluded that cobalt is not a limiting factor to the production of vitamin B₁₂ by microorganisms in these regions.     

Distribution,behavior and fate of PCBs in the marine environment

I am extremely grateful and honored for being awarded the Okada Prize (1985) for my study. The present article reviews my research on the distribution, behavior and fate of PCBs in the marine environment. The outline of this study is summarized as follows:

1. Polychlorinated biphenyls (PCBs) were detectable in the wide range of environmental media and biota of the Seto-Inland Sea, Japan, in which much high concentrations were found in sediment and biological samples due to their hydrophobic, lipophilic and less biodegradable properties as well as their extensive production and use in estuarine and coastal regions.
2. PCBs extend the boundaries of their distribution all over the global environment, being evidenced by their occurrence in open ocean atmosphere, hydrosphere and biosphere, even in Antarctica. The global contamination of PCBs is much more prominent in northern hemisphere than in southern hemisphere.
3. The sinking rate of PCBs from surface to deeper layers in open ocean water column is relatively slower in tropical waters than in high latitude ones. This implies the possible prolonged contamination of persistent synthetic organic chemicals in the tropical marine environment.
4. The bioaccumulation processes in marine ecosystems can be explained by the physicochemical and biochemical properties of PCBs and the metabolic capacity of organisms. In higher animals, additional factors such as parturition and lactation are also related to this process.
5. Total PCB load in global environment was estimated to be about 370 thousand tons. Of this, most amounts were in coastal sediment and open ocean water. Presently, about 780 thousand tons of PCBs are still in use mainly in electrical equipments. In order to reduce the PCB levels in marine environment, pertinent measures to prevent the further discharge and safe disposal of PCBs are required.

     

Marine environmental studies on outbreaks of red tides in neritic waters

The cause of red tides appearing in neritic waters in Japan have been discussed by several workers in relation to the development of eutrophication. The author has been engaged in marine environmental studies on outbreaks of red tides, mainly, in the Seto Inland Sea since 1964 using a combination of the following approaches:

1. surveys of the red tides that have occurred,
2. elucidation of the oceanographical and biological characters of the water areas where red tides occur,
3. isolation of the red tide organisms for physiological studies of their growth,
4. chemical and biological assays of the growth promoting factors, and
5. estimation of the effects of pollutants on the growth of the red tide organisms.

The red tide organisms surveyed wereEutreptiella sp. (Euglenophyceae),Dictyocha fibura (Chrysophyceae),Chattonella marina, C. antiqua, Fibrocapsa japonica, Heterosigma akashiwo (Chloromonadophyceae),Prorocentrum minimum, P. triestinum, Gymnodinium mikimotoi, G. nelsoni, Gymnodinium type '65,Noctiluca miliaris, Protogonyaulax catenella, Gonyaulax polygramma, Peridinium quinquecorne (Dinophyceae) andMesodinium rubrum (Ciliata). Most of these species were isolated and cultured for physiological studies. Algal growth potential in sea water was assayed in Hiuchi Nada and Beppu Bay. Growth promoting activity was found in sea water about 2km off shore from the industrial zone which locates along the coast of Beppu Bay. The effects of industrial wastes were examined forEutreptiella sp.,Heterosigma akashiwo andProrocentrum triestinum. Sulfite pulp waste caused marked promotion of growth in these organisms. The growth promoting activity of the waste was elucidated by chelation of the waste with iron. After the oil spill which occurred at Mizushima Bay in 1974, a heavy red tide ofNoctiluca miliaris appeared, followed byProrocentrum minimum. Polycyclic and polar fractions in heavy oil separated by chromatography were suspected to be the growth promoting substances. Natural growth promoting chemicals, uracil and thymine, were found in interstitial water of bottom mud of Beppu Bay in concentrations of 58–120, and 28–83?g per 100 g dry mud, respectively. The mechanism of fish kills caused by red tides was another subject of study.     

Trichodesmium in the East China Sea

A study is made on the surface distribution ofTrichodesmium thiebautii Gomont in the East China Sea during the years 1961–1967.

1. This alga is very scarce or absent in the period from January to March, and begins to increase in May and June, reaching the maximum population density from July to September, and again decreases in October and November.
2. In summerT. thiebautii is predominantly distributed in the area along the Kuroshio current with high densities of 10²–10³ filaments/l, occasionally exceeding 10³ filaments/l. This alga is estimated to occupy the major part or almost all the parts of chlorophylla in situ contained in the surface water of this season.
3. The occurrence ofT. thiebautii off the southern coasts of Central Japan seems to be caused rather by the multiplication in its own habitat than by the transportation by the Kuroshio current from the East China Sea.

     

Oil pollution in the Izu Islands waters

The oil pollution in the Izu Islands waters are observed as follows:

1. Globules and lumps of oil were collected 2.56 g on the average in wet weight by each taw(174 m³) of a larval net at 389 stations, up to the maximum collection of more than 500 g.
2. On the investigation of the Oshima—Torishima line (J1–J10), globules and lumps of oil were collected more at the south of the Kuroshio Current than at the north.
3. In the coastal region (T1–T19) of Japan, many globules and lumps of oil were collected when a cold water mass was located at the west side of the Izu Islands, from south to east side of where the Kuroshio Current took a roundabout and closed near to the Bōsō peninsula (Aug. 1971, Jun. 1972, Aug. 1972), or when the Kuroshio Current took a roundabout the cold water mass which extended as far as Oshima from the coast of the Bōsō peninsula (Sept. 1971).

     

Influence of bottom topography on an upwelling current: Generation of long trapped filaments

We investigate the influence of bottom topography on the formation and trapping of long upwelling filaments using a 2-layer shallow water model on the f-plane. A wind forced along-shore current, associated with coastal upwelling along a vertical wall, encounters a promontory of finite width and length, perpendicular to the coast.In the lower layer, topographic eddies form, which are shown to drive the formation of a filament on the front. Indeed, as the upwelling current and front develop along the coast, the along shore flow crosses the promontory, re-arranging the potential vorticity structure and generating intense vortical structures: water columns with high potential vorticity initially localized upon the promontory are advected into the deep ocean, forming cyclonic eddies, while water columns from the deep ocean with low potential vorticity climb on the topography forming a trapped anticyclonic circulation. These topographic eddies interact with the upper layer upwelling front and form an elongated, trapped and narrow filament.Sensitivity tests are then carried out and it is shown that:

• •baroclinic instability of the front does not play a major role on the formation of long trapped filaments;
• •increasing the duration of the wind forcing increases the upwelling current and limits the offshore growth of the filament;
• •modifying the promontory characteristics (width, length, height and slopes) has strong impact on the filament evolution, sometimes leading to a multipolarisation of the potential vorticity anomaly structure which results in much more complicated patterns in the upper layer (numerous shorter and less coherent filaments). This shows that only specific promontory shapes can lead to the formation of well defined filaments;
• •adding bottom friction introduces a slight generation of potential vorticity in the bottom layer over the promontory, but does not significantly alter significantly the formation of the filament along the outcropped front in the present configuration;
• •modifying the stratification characteristics, in particular the density jump between the layers, has only a weak influence on the dynamics of topographic eddies and on filament formation;
• •the influence of capes is also modest in our simulations, showing that topography plays the major role in the formation of long and trapped upwelling filaments.

     

Abyssal current along the northern periphery of Shikoku Basin

Abyssal currents along the northern periphery of the Shikoku Basin south of Japan were measured by current meters moored off Cape Daio-zaki, Cape Shiono-misaki and Cape Ashizuri-misaki and on the eastern foot of the northernmost part of the Kyushu-Palau Ridge. Total length of observation off Cape Shiono-misaki was about five years including the periods of the Kuroshio large meander and no meander. Analyses of current data show:

1. Mean currents with a magnitude of 5–10 cm sec^?1 were observed during the whole observation period at all of current meters which were set 400 m above the sea bottom that was deeper than 4,500 m. The mean current for each current meter was parallel to the local bottom contour arond each station and was toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left.
2. At each station located above the shelf toe off Cape Daio-zaki and off Cape Shiono-misaki and on the foot of the Kyushu-Palau Ridge, the mean current increases with depth (a bottomward intensification of the mean current), and the vertical extent of the mean current is estimated to be about 2,000 m above the sea bottom.
3. At a station located at 2,600 m depth on the continental slope off Cape Shiono-misaki, no bottom-ward intensification of currents was observed.

These results strongly suggest that a steady abyssal flow exists in the depths deeper than about 3,000 m along the northern and northwestern peripheries of the Shikoku Basin. Existence of the abyssal circulation system is also suggested, at least, in the north of the Shikoku Basin.     

Distribution of pelagic blue-green algae in the North Pacific Ocean

The distribution of pelagic blue-green algae, especially ofTrichodesmium thiebautii, was investigated on the basis of the collection of theHakuhō Maru Cruise KH-69-4 along 155°W (50°N-15°S) in the North Pacific Ocean from September to November 1969.

1. Five species were identified:Trichodesmium thiebautii (most predominant),T. erythraeum, Oscillatoria sp.,Katagnymene spiralis andRichelia intracellularis.
2. T. thiebautii was most abundant in the western North Pacific central water and abundant next to it in the equatorial water, but it did not occur in the subarctic water.
3. T. thiebautii was ubiquitously distributed in the lower layer of 100–200 m in the equatorial water, though not in a large quantity.
4. T. thiebautii inhabited only the water warmer than 20°C. In its main habitat, nitrate and nitrite were almost zero, but ammonia and phosphate were present. There was not found any correlation between its occurrence and the salinity.
5. Blue-green algae were generally thinly populated in the water rich in diatoms.

     

A submersible study in the western Blanco fracture Zone,N.E. Pacific: Structure and evolution during the last 1.6 Ma

During July and August 1991, the French-American Blanconaute dive program used the French submersibleNautile to investigate the West Blanco Depression (WBD), a deep, elongate trough located at the intersection of the Blanco Transform Fault Zone with the southern Juan de Fuca Ridge (JdFR). Twenty dives were carried out along the north wall of the WBD, which exposes the upper oceanic crust over a 65 km distance, from the JdFR axis (to the west) to the oblique trace of an ancient propagator (to the east, crustal age around 2 Ma). Thirteen of these dives were precisely located within a 13 × 7 km zone of the north wall, covered by a high-resolution sonar mapping operation during the Blancotrough cruise in 1987. This series of geological traverses, plus 4 dives across the south wall of the WBD (one dive) and the adjacent Parks Plateau (3 dives), collected 242 rock samples. We report here the main results of the dive program and preliminary laboratory studies:

1. Transform-related tectonic activity has recently abandoned the southern margin of Parks Plateau, and is presently located inside the WBD area, mainly along its northern wall. The tectonic features observed are compatible with a right-lateral strike-slip system, with a NE-SW extensional component.
2. Three main lithological units are exposed along the north wall of the WBD. From top to bottom, they are: (1) a Volcanic Unit, forming a steep upper cliff, made of massive and pillow flows and basaltic dikes, with an estimated average thickness of 800 m; (2) a less steep Transition Zone, about 150 to 400 m thick, largely masked by rubble but exposing both diabase outcrops and pillow flows; and (3) a massive Diabase Unit, exposed over 700–800 m, with a dike complex structure visible from place to place, and cut by a net of hydrothermal veins. Deep crustal rocks such as gabbros were not observed.
3. Spectacular mass-wasting features are visible all along the north wall of the WBD. About 60% of the face of the wall is masked by talus cones, rubble, rock avalanche deposits and slide blocks. Three main landslides, of approximately one km³ in volume each, were tentatively identified. One of them was mapped in detail and consists of an approximately 300 m thick (0.85 km³), coherent slide block detached from a zone where intense hydrothermal alteration and faulting have obviously weakened the bedrock, that is in places entirely altered to blue clays.
4. The basaltic lavas of the WBD north wall show a remarkable evolution with time, from east to west. Around the tip of the ancient propagator, they are restricted to primitive, olivine-rich picritic basalts. Proceeding westward, they exhibit a wide range of differentiation, including highly fractionated, FeTi-rich ferrobasalts at about 35–45 km from the JdFR axis. When approaching the JdFR axis, the FeTi enrichment decreases gradually, and the ferrobasalts evolve towards slightly differentiated MORB-type basalts, typical of the southern JdFR. This magmatic evolution marks the transition from the end of a propagating rift regime to a steady-state accretion regime.
5. The WBD north wall also permits the study of weathering and hydrothermal alteration processes and their evolution in space and time. Vertically, the alteration products evolve from oceanic weathering and zeolite facies (Volcanic Unit) to the greenschist facies (Transition Zone and Diabase Unit). Horizontally, the evolution with time is mainly a general hydration of the crust that is, however, very irregularly distributed.
6. Several vertical magnetic traverses along the north wall of the WBD, using a bottom magnetometer attached to the basket of the submersible, have shown a sharp 5000 to 7000 nT positive anomaly at about 3500 m depth. This anomaly corresponds exactly to the first appearance of extrusive pillow-lava outcrops, and confirms the dramatic decrease in magnetic anomaly amplitude below that depth, detected during the Blancotrough cruise in 1987. The vertical magnetic profiles thus appear to have imaged the base of the magnetic source layer.

     

Characteristics of deep currents off Cape Shiono-misaki before and after formation of the large meander of the Kuroshio in 1981

Deep currents measured by moored current meters over the shelf-slope off Cape Shiono-misaki, Kii Peninsula during the period from 28 April, 1981 to 4 May, 1982 are analyzed to determine characteristics of the deep current before and after the large meander of the Kuroshio formed. The observed deep currents show some different characteristics between the periods before and after the formation of the large meander of the Kuroshio,i.e.:

1. The mean current direction over the shelf slope changed to westward after the meander was formed, though it was eastward at two offshore stations before the meander was formed.
2. The eddy kinetic energy, \(ke((\overline {u'^2 } + \overline {\upsilon '^2 } )/2)\) became large at all stations after the meander formed.
3. It appears that there were current variations in the period band shorter than 10 days which propagated offshore before the meander formed but inshore after the meander formed.
4. After the meander formed, the current variations with a period of O(25 days) were amplified at two of the three stations. The current variations in this period band showed high coherence among the three stations.

Data from tidal stations showed that sea level variations with a period of O(30 days) were also amplified along the south coast of Japan after the meander was formed. But sea level variations were not coherent with current variations in this period band.     

Chemical environment for red tides due toChattonella antiqua in the seto inland sea,Japan

Severe red tides due toChattonella antiqua occur sporadically during summer in the Seto Inland Sea, Japan, and cause significant damage to the fishing industry. In order to assess the chemical environment with respect to the outbreak ofC. antiqua, environmental factors that affect the growth ofC. antiqua were monitored around the Ie-shima Islands, the Seto Inland Sea, in the summer of 1986. In addition, a growth bioassay of the seawater usingC. antiqua was conducted under a semicontinuous culture system. Although temperature, salinity and light intensity were optimum for the growth ofC. antiqua, red tides by this species did not occur. Concentrations of NH ₄ ⁺ , NO ₃ ^? and PO ₄ ^3? were low (<0.4, <0.2, <0.06 µM, respectively) above the thermocline (8–12 m) and high below it (0.6–2, 4–8, 0.4–0.8 µM, respectively). Vitamin B₁₂ concentrations did not change significantly between the surface (0 m) and below the thermocline (25 m) in the level of 2–4 ng·l^?1. The growth bioassay revealed that in the surface waters, concentrations of N- as well as P- nutrients were too low to support a rapid growth ofC. antiqua. At the depth of 25 m, neither N, P nor B₁₂ limited the growth rate. In order to obtain more quantitative information on the growth rate as a function of the concentrations of N- and P- nutrients,C. antiqua was grown in a semicontinuous culture system by changing nutrient concentrations systematically. The observed growth rate (μ) can be approximated as follows: $$\mu = \mu _{\max } .\frac{{S_N }}{{K_g ^N + S_N }}.\frac{{S_{PO4} }}{{K_g ^P + S_{PO4} }},$$ whereS _N is the concentration of NO ₃ ^? plus NH ₄ ⁺ (0–6 µM),S _PO, the concentration of PO ₄ ^3? (0–0.6 µM), μ_max (0.97 d^?1) the maximal growth rate,K ₀ ^N (1.0 µM) andK ₀ ^P (0.11 µM) the half saturation constants for NO ₃ ^? and PO ₄ ^3? , respectively. Using the above equation with nutrient concentrations measured, the rate at which seawater supports the growth ofC. antiqua can be estimated and this can be used for the assessment of chemical environments with respect to the outbreak ofC. antiqua.     

On the mean sea levels at various locations along the coasts of Japan

The yearly variations of mean sea levels at various locations along the coasts of Japan have been investigated, based upon the data of observation taken at 55 tide-gauge stations from 1953 to 1970, and some discussions have been made on the relationships between those variations and meteorological and oceanographical conditions, etc. The results obtained are as follows:

1. In cases covering 90% of all the tide-gauge stations, the magnitude of the annual mean rate of variation of ground level is less than 10 mm/year, and the mean value of the magnitude for all the stations is ?3.17 mm/year, while that exclusive of Osaka is ?1.7 mm/year.
2. The effect of atmospheric pressure variation on the height of annual mean sea level is of the order of several centimeters in view from both time and place.
3. In view of the characteristic types of variations, the coasts of Japan may be divided into five regions of similar mean sea level deviations. And in the yearly variations of mean sea levels, there can be seen a kind of variation which corresponds to the variation of oceanographical conditions such as abnormal fall of seawater temperature.
4. The mean sea level deviations at various locations along the coasts of Japan, referred to the standard sea level “T.P.” are different for different places. Namely, (1) on the coast of the Japan Sea, the west coast of Kyushu, the coast of Sanriku and the coast of Hokkaido, the mean sea level is higher than on the Pacific coasts from Southern Kyushu to Southern Honshu. (2) Along the coast of the Seto-Inland Sea, the mean sea level is generally higher.

As for the leading causes of the above deviations, we may safely enumerate the following ones, viz. (a) the effect of the deflecting force of the earth's rotation on currents, and (b) the effect of variation of seawater density. However, as regards the relative importance of these two effects, no decisive conclusion can yet be given for the present.     

Hydrographic structure in association with deep boundary current in the north of the Shikoku Basin

High quality CTD data were collected in the north of the Shikoku Basin where an abyssal boundary current has been observed through direct current measurements. Analyses of hydrographic data showed:

1. Colder and saltier water (heavier water) compared to surrounding waters is found above the continental shelf-toe and the eastern flank of the Kyushu-Palau Ridge where the existence of the abyssal boundary current has been expected. The heavier water has a horizontal extent of about 50 km.
2. The heavier water has the vertical scale of 2000 m from the sea bottom, and is associated with a thermal wind shear which enhances a component of the flow toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left in the abyss. The assumed “level of no motion” at about 2500 m depth gives the geostrophically estimated current in a good agreement with the directly measured current.

A volume transport associated with the colder and higher salinity water is estimated to be about 2 Sv off Cape Shiono-misaki which may include a recirculation above the Nankai Trough. This is about twice of the transport estimated in the interior of the Shikoku Basin through a vorticity balance between the stretching term and latitudinal variation of the planetary vorticity.     

Interactions between oceanic and gravity tides,as analysed from world-wide earth tide observations and ocean models

The problem of interactions between earth tides and oceanic tides is rather complex as it involves effects of newtonian attraction, loading and associated change of earth potential, tangential pressure and friction on the moving ocean floor which are not always easy to evaluate, principally for coastal or island stations. This paper takes advantage of two facts:

1. By the end of 1983 the International Center of Earth Tides has collected and evaluated a considerable amount of data from 223 stations including those of the Trans World Profiles developed by the same group of authors (102 stations). This ensures, for the first time, a World wide distribution including the tropical areas and the southern hemisphere.
2. In 1978–80, new oceanic cotidal maps of high quality, established by E.W. Schwiderski, became available.

We have calculated, for the eight principal tidal waves, the correlations between the observed gravity variations and those resulting from a calculation based upon the Schwiderski maps. This correlation is highly significant. At the level of accuracy of the best transportable gravimeters the agreement is perfect except at a few places where effects of lateral heterogeneities in the mantle can perhaps be suspected. These cotidal maps can therefore be safely used as working standards for other geodetic and geophysical applications.     

深圳湾、大鹏湾海水和底泥中维生素B_1,B_(12)测定结果及初 步分析

于1989－1991年对深圳湾、大鹏湾海水及底记的维生素B1和B12含量进行了测定。结果表明，两湾海水中维生素B1和B12含量绝大多数在10ng／L以下；在底泥中的含量最高也仅36×10－9，不会诱导赤潮发生。     

Distribution and seasonal variation of vitamin B12, thiamine and biotin in the sea

The distributions and seasonal variations of vitamin B₁₂, thiamine and biotin were investigated in waters of the North Pacific Ocean, the East China Sea, and the bays and inlets along the Pacific coast of Japan, by use of microbiological assay methods. A marine diatom Cyclotella nana clone 3H for vitamin B₁₂, and marine yeast Cryptococcus albidus for thiamine, and a marine bacterium Achromobacter sp. strain yH-51 for biotin were used as assay organisms. In the surface water of Sagami Bay, monthly changes in the amounts of the three dissolved vitamins followed closely that of chlorophyll a, being highest in July and lowest during late autumn and winter. The geographical and vertical distributions of thiamine and biotin in the sea generally showed similar patterns to that of chlorophyll a, whereas vitamin B₁₂ did not always follow the trend. Amounts of particulate thiamine and biotin corresponded to about 1 % of that of the dissolved form in the surface water of the North Pacific Ocean. In the coastal waters, however, they were at times found to be 144.0 % and 53.9 % respectively.     

New record of occurrence ofSergia lncens (Hansen) (crustacea,sergestidae) off Tung-kang,Taiwan, with special reference to phylogeny and distribution of the species

The commercially important sergestid shrimp,Sergia lucens (Hansen), has long been considered an endemic species of Japan because it had been found only in Suruga Bay and neighbouring waters. Recently, however, a considerable amount of a similar shrimp was caught by trawl nets off Tung-kang, southwestern Taiwan. This shrimp is distributed at depths of 100–300 m on the continental slope, around a deep submarine canyon adjacent to the mouth of the Kao-ping River. A morphological comparison with specimens from Suruga Bay reveals that the shrimp is identical toS. lucens. However, a slight difference in the patterns of water-soluble proteins was observed in a thin layer isoelectrophoretic examination. A difference was also observed in the spawning season of the two populations, indicating sexual and geographic isolation. Considering the distribution and phylogeny of the family Sergestidae, based on a possible evolutionary development from a benthic neritic organism to a pelagic oceanic one along the generaSicyonella-Sergestes-Sergia, it is assumed thatS. lucens entered a lower epipelagic habitat in the coastal waters from the warm oceanic mesopelagic habitat of the original stock. A hypothesis is proposed that speciation ofS. lucens from the original stock occurred when it was trapped in a semi-enclosed inlet (the paleo-East China Sea Gulf) that existed at the present Okinawa Trough during the late Pliocene to early Pleistocene. The inlet was deep, but had a neritic environment due to drainage from ancient large river systems, including the paleo-Yangtze River. The species expanded its distribution to the neighbouring waters during the warm interglacial period. However, a rapid rise in sea level after 14,000 years significantly changed the environmental conditions in the distributional area and the species could not expand into a neritic environment, which was too shallow for survival. Accordingly,S. lucens populations remained only in Suruga Bay and Tung-kang waters, where the environment has remained stable for the last 17,000 years or more. The two areas have the following common characteristics:

1. A large amount of fresh water is discharged into the deep submarine canyon adjacent to the river mouth.
2. The northeastern part is surrounded by land so that a direct inflow of boreal water into the environment is blocked.
3. Warm Kuroshio extension water intrudes and mixes with water from the rivers, and for Suruga Bay there is a current system that keeps distribution of the eggs and larvae restricted to the local habitats.

Taiwan annually exported some tens of metric tons of the driedS. lucens to Japan for the last few years, but the standing stock of Tung-kang waters is probably not as large as that in Suruga Bay.     

Wave impacts on structures with rectangular geometries: Part 2 decks,baffles and seawalls with impermeable or porous surfaces

This paper considers wave impacts on baffles, on baffles or decks adjacent to a vertical wall, and on porous seawalls and/or sea beds. For seawalls and vertical baffles, impacts can occur in steep waves, whilst a deck can be struck from below by a rising wave crest either in open sea or in a tank with standing waves (sloshing). A simple analytical model for the pressure impulse, P, due to a wave of idealized geometry and dynamics is developed and applied to the following geometries with impermeable surfaces:

• •horizontal wave impact onto a vertical wall with a deck at the waterline,
• •vertical wave impact under a deck in the same configuration (equivalent to vertical water impact of a horizontal plate),
• •horizontal wave impact onto a surface-piercing vertical baffle in open sea,
• •as for 3. but with the baffle in front of a wall,
• •as for 4. but with a deck extending from the vertical wall to the baffle,
• •bottom-mounted baffle in front of a wall with impact occurring on the wall.

We also consider cases that complement part 1 of this paper to include the effect on impacts on a seawall with a porous sea bed and/or sea wall with/without a berm. Finally we reconsider case 3) above but with a porous baffle.The method uses eigenfunction expansions in each of the rectangular regions that satisfy some of the impermeable or porous surface conditions, and a simplified free-surface condition. Their unknown coefficients are determined from the impact boundary condition, impermeable or porous boundary conditions and by matching the solutions, in any two neighbouring rectangles, along their common boundary. Although the fluid motion is treated rather crudely, the method yields the pressure impulse throughout the entire region. Impulses, I, and moment impulses, M, on all or parts of the structure are also presented.