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Mysids play an essential role as the dominant prey species for coastal fishes. In Japan, the mysid Neomysis awatschensis (Brandt, 1851) is commonly distributed in estuarine and shallow coastal waters with high productivity due to supply of nutrients from the watershed. The present study investigates the distribution and life history of the mysid N. awatschensis in relation to biotic and abiotic factors by monthly sampling from March 2014 to July 2015 at stations along the Yura River estuary, the central Sea of Japan. The Yura River physical conditions change seasonally and are affected by its discharge. Salt-wedge-intrusions were frequently observed and found up to 18 km from the river mouth from April to December 2014 when river discharge was low, whereas in 2015 intrusions were less pronounced, possibly due to river mouth clogging. Clear seasonality was observed in mysid density, showing highest densities (up to 202 inds/m2) in spring and early summer in contrast with lowest densities ( Those results suggest that reproduction is partially suppressed by variable and oligotrophic conditions in the Yura River estuary. Combined with the flexibility to seasonal changes in temperature and food availability, the great tolerance to acute salinity fluctuations allows N. awatschensis to maintain its population in the estuary.

To investigate the potential environmental effects of pond farming for Apostichopus japonicas in Yellow River estuary, we examined discrepancies of distance-based typical pollution indicators (TOC, TN, NO 3 − , NH 4 + , NO 2 − and PO 4 3− ) and biochemical tracers (δ 13 C and δ 15 N) in water column and sediment, as well as dietary characteristics of dominant macrobenthos between farming and non-farming areas. The results revealed that studied variables in water column showed no uniform spatial differences. Meanwhile, those in sediment displayed similar decrease tendencies from farming pond to the adjacent tidal flat, which was considered to represent the environmental effects of farming. Biochemical tracers (δ 13 C and δ 15 N) in both water column and sediment confirmed the origin of organic matters from the aquaculture waste. The detectable dispersion distance of aquaculture waste was restricted to an area within 50 m distance as determined by most variables in sediment (TOC, TN, NO 3 − and NH 4 + ), particularly by C:N ratio and δ 13 C with which origins of the wastes were traced. Bayesian mixing models indicated that in the farming area BMA had a larger contribution, while POM (marine) showed a smaller contribution to the diets of Helice tridens and Macrophthalmus abbreviates compared to those in the non-farming area. The overall results showed that pond farming for Apostichopus japonicus in the Yellow River estuary altered the local environment to a certain extent. For methodological consideration, sediment biogeochemical characteristics as a historical recorder much more effectively reflected aquaculture waste accumulation, and stable isotope approaches are efficient in tracing the origin and extent of various allogenous sources.

Sansha Bay, facing the East China Sea, is characterised by high fish production (Pseudosciaena crocea, 91,000 t yr–1) and the polyculture of seaweeds (Saccharina japonica and Gracilaria lemaneiformis) and abalone (Haliotis discus hannai). To investigate the environmental effects of fish farming on sediments, surface (0–1 cm) sediments were collected from 41 stations grouped into four areas: fish, seaweed, and abalone farms and reference area. The physical and chemical parameters of these sediments were analysed. Nitrogen and phosphorus loadings from trash fish as feed were estimated to be 12,000 and 2,400 t yr–1, respectively, accounting for 90% and 86% of the total anthropogenic loading in Sansha Bay. However, no significant differences were observed in stable C and N isotope ratios, carbon-to-nitrogen ratio, total organic carbon, total nitrogen, total phosphorus, acid volatile sulfide, water content, and silt–clay fraction among the four areas (Kruskal–Wallis test, P > 0.05). Principal component and cluster analyses supported this conclusion, indicating that fish farming has no significant effect on the sediment. The amount of N removed by the cultured seaweed was estimated to be 288 t yr–1, accounting for only 2% of the N loaded from fish farming. The results suggested that the dispersion of fish farm-derived wastes were primarily facilitated by the topographic and hydrodynamic characteristics of Sansha Bay, such as its large depth (∼90 m), strong currents (1.4–1.9 m s–1), large tidal amplitude (5.4 m), and rapid exchange (

The Chinese white shrimp Penaeus chinensis is one of the most economically important crustacean species in China with respects to both capture and aquaculture. Stable carbon and nitrogen isotope ratios ( δ 13C and δ 15N) was analyzed to reveal its potential dietary characteristics, in particular contributions of primary producers as food sources, as well as isotopic niche width and potential food competitions with materials from Haizhou Bay in Yellow Sea, a state-level germplasm source conservation and stock recovery area. The results confirmed that bivalves served as an important diet of P.chinensis and the prawn incorporated a mixture of benthic microalgae and marine phytoplankton as food sources, while terrestrial organic matter supposed to be made minimum contributions. Benthic microalgae overwhelmingly dominated in the dietary proportion (mode), and accounted for 90% of the food sources in comparison with the contribution of 10% of marine phytoplankton. Penaeus chinensis was closest to Charybdis japonica and Dorippe japonica in isotopic compositions. Trophic niche widths were similar in P.chinensis and D. japonica, and they were larger than that of C.japonica, as determined by the sizes of SEAb (Bayesian standard ellipse areas). The overlaps of standard ellipse areas of P.chinensis with C. japonica and D. japonica were 98.5% and 86.5% respectively, indicating intense competition for food between P.chinensis and the other two species. In the views of food availability and competition, biomasses of benthic microalgae, bivalves and C.japonica and D.japonica may regulate the population of P.chinensis in Haizhou Bay.

In order to examine the efficiency of co-culturing fish with the Japanese common sea cucumber Apostichopus japonicus , field cultivation experiments were conducted in Gokasho Bay, central Japan. I cultured A. japonicus juveniles below a fish cage and at a control station for 238 days, monitored the wet weight, and analyzed its stable carbon and nitrogen isotopes (δ 13 C, δ 15 N) together with potential food sources, and found that (1) juveniles cultured below fish cages exhibited high survivorship (96%) and significantly higher specific growth rate (1.9%) than those at the control site (1.2%), and (2) the juveniles had significantly reduced δ 13 C values (mean ± SD = − 19.1 ± 0.3‰ vs. −17.5 ± 0.4‰ at the control station), suggesting the incorporation of C 3 plant material in fish feed through fish feces and settling organic matter. All sea cucumbers which were further cultured for additional 307 days below fish cages grew to the marketable size (range and mean wet weight = 142–181 g, 160 g, n = 9). In order to evaluate the effect of density on growth, 6 culture vessels, in which 1, 5, 10, 15, 20 and 25 juveniles of A. japonicus were stocked, were maintained below the fish cage over 118 days. The results showed that the final mean weight of A. japonicus decreased from 6.68 g to 0.94 g as the density increased with a large variation of weight at the end of the experiment (coefficient of variation = 52.1–62.2%), suggesting that there was competition between individuals for a limited food supply and there were intraspecific effects on the growth. This study shows the possibility of integrated multi-trophic aquaculture in which A. japonicus is cultured in the water column below fish cages, because the survival and growth of the sea cucumbers were enhanced due to the ability to avoid predator interactions and adverse environmental conditions as well as nutritional feed supply from the fish cage.

We investigated the fluctuations of carbon and nitrogen stable isotope ratios in benthic consumers and their potential food sources to determine the spatial and temporal variations in the utilization of available organic matter, indicating the origin and pathways of energy from Yura Estuary to Tango Sea, Japan. Field samplings were conducted from the upper estuary to offshore with sampling frequency of twice per season from April (spring) 2006 to February (winter) 2007. The δ13C signatures of the upper and lower estuary benthos showed depleted and in wide range (−28.9‰ to −13.5‰) compared to the enriched and within narrow range signatures of marine benthos (−20.6‰ to −14.0‰) in all seasons. On the contrary, the δ15N signatures of benthic communities showed decreasing trend seaward and summer values were different from the other seasons. Using the dual isotope and multisource mixing models, we estimated the relative contributions of potential food sources to the benthos diet. River POM played an important source of energy for the estuarine benthos, especially in winter when river discharge was high. Marine POM served as an important alternative food for the estuarine benthos from spring to autumn when seawater intruded the bottom estuary. Benthic microalgae were the major food source at the shallow coast throughout the year, while marine POM fueled the deep coast and offshore benthic food webs. Spatial and temporal feeding variations in estuarine benthic communities were driven by the hydrology of the estuary, whereas primary production and transport of food source dictated diet variations of marine benthic communities. The elucidation of the dynamic energy subsidy among aquatic systems highlights the importance of the land–sea transition zones that is crucial for benthic secondary productions.

In order to examine the efficiency of Ulva spp. (Chlorophyta) as a bioindicator and biofilter for dissolved inorganic nitrogen discharged from coastal fish farms, field surveys and field cultivation experiments were conducted in Gokasho Bay, central Japan. Naturally occurring green algae Ulva spp. were collected in and around a fish farm in February, May and July, and their δ 15 N and tissue N contents were analyzed. Values of these parameters obtained in May and July decreased with the distance from the fish cages, suggesting that Ulva spp. occurring in close vicinity to the fish farm assimilated the fish-excreted N. To evaluate this uptake, we cultured round cut pieces of thalli of Ulva ohnoi in transparent chambers beside a fish cage and at a control station for 2 weeks in May, July and September. The specific growth rate and N fixation rate of the thalli cultivated beside the fish cage showed 12.8–23.6% and 4.2–13.9 mg N g DW − 1 day − 1 , respectively, which were significantly higher than those at the control station and found to be among the highest levels known for seaweed biofilters. The high growth rates during the warm season and easy cultivation indicate the suitability of Ulva ohnoi as a biofilter.

We examined the feeding niche of four species of molluscs by analysis of their stable isotope signatures and cellulase activities to determine if they could utilize terrestrial organic matter. The molluscs and potential food sources were collected from the upper, middle and lower estuary of the Yura River from spring 2007 to winter 2008. All species showed positive cellulase activity which highlighted their potential to digest terrestrial organic matter. Consumption and assimilation of terrestrial organic matter by estuarine molluscs however varied spatially and temporally, reflecting species-specific differences in feeding niche and in response to variations in food availability in the estuary. Thus, terrestrial primary production in the catchment area supports secondary production of molluscs in the Yura River estuary.

We investigated the distribution of δ13C and δ15N of organic matter among benthic communities from the upper estuary of Yura River to offshore of Tango Sea, Japan, to determine spatial variation in utilization of organic matter by benthic communities. The δ13C values of benthic animals ranged from −27 to −15‰ in the upper estuary, −21 to −15‰ in the lower estuary, −20 to −16‰ in the shallow coast (5–10 m depths), −18 to −16‰ in the deep coast (30–60 m depths) and −19 to −15‰ in offshore (100–150 m depths) stations. Adapting the dual isotope values to mixing models, we estimated the relative contributions of potential food sources to the benthos diet. Phytoplankton and macroalgae that intruded the estuary in summer were utilized as alternative food aside from the terrestrial-origin organic matter assimilated by the estuarine benthic consumers. Resuspended benthic microalgae were important source of energy in the shallow coastal stations, while abundant supply of phytodetritus fueled the deep coastal and offshore benthic food webs. Spatial difference in the diet of benthic communities depends largely on the shifts in the primary carbon source. Thus, benthic communities are important link of autochthonous/allochthonous production and secondary production in the continuous river–estuary–marine system.

To evaluate the relative importance of possible food sources, including riverine particulate organic matter, reeds, benthic microalgae, seaweeds, cultured laver (Porphyra) and coastal phytoplankton, for commercial bivalves and co-occurring benthic animals, 73 macrofaunal species were collected from intertidal and subtidal soft bottoms in the inner part of Ariake Sound, Kyushu, southern Japan, and their isotopic compositions were analyzed. The results revealed that (1) both intertidal and subtidal food webs were constituted of 3 trophic levels, (2) suspension-feeding bivalves utilize a mixture of benthic microalgae and coastal phytoplankton, and omnivores and carnivores incorporate benthic microalgae and phytoplankton through their intermediate prey, and (3) 3 bivalves (Scapharca kagoshimensis, Modiolus metcalfei and Atrina lischkeana) inhabiting both intertidal and subtidal bottoms showed similar seasonal fluctuations, suggesting no difference in the diet composition among the species and between the 2 habitats. We conclude that a large biomass of benthic microalgae which was approximately equal to that of phytoplankton and the strong tidal currents that would resuspend benthic microalgae and transport them to subtidal bottom areas account for the benthic microalgal and phytoplankton based trophic structure in the inner part of Ariake Sound.

For improving the economic and environmental sustainability of fish farming, it is necessary to optimize feeding regimes. From this viewpoint, we monitored the growth and mortality of red sea bream (Pagrus major), C and N fluxes and sediment chemistry at 2 commercial fish cages; cage 1 (conventional satiation feeding) and cage 2 (restricted feeding: same feeding frequency but 18% reduction in the feed amount) for 276 days. The similar specific growth rates (0.43% in cage 1 and 0.39% in cage 2) but different feed conversion efficiencies (0.54 in cage 1 and 0.62 in cage 2) and mortality (> 2-times higher in cage 1) between the 2 cages, indicate overfeeding in cage 1 culture. Elemental and stable isotopic analyses of sediment trap materials enabled the quantification of waste feed- and fecal matter-derived organic matter (OM) separately. The results shows that (1) aquaculture-derived OM comprised most of the fish-farm settling OM, excluding the period from January to April, when natural OM often accounted for a half of the bulk OM, (2) there was a difference in the seasonal trend between the fluxes of waste feed and fecal matter, and (3) there were no differences in the percentage compositions and fluxes of waste feed and fecal matter between the 2 cages. The isotopic analysis showed that the waste feed-derived OM in the sediment below cage 2 was 24% less than that below cage 1, suggesting effect of restricted feeding. Determining the relative amount of waste feed and fecal matter in settling and sedimentary OM is an effective method to evaluate the optimum feeding regime.

We report the properties of paramagnetic defects in SiCN films which are used as copper diffusion barriers. Electron spin resonance (ESR) signals with a g value of 2.003 and the Δ H PP of 1.1–1.2 mT were observed for as-grown and UV-illuminated SiCN films. These characteristics of the observed ESR signals are very similar to those of the K 0 center in N-rich silicon nitrides. We also show that a substantial increase in the leakage current occurs by exposing the SiCN films to UV illumination. We suggest that the paramagnetic defects generated by the UV illumination are responsible for this current increase.

Three species of the callianassid genus Nihonotrypaea occur intertidally in the Ariake Sound estuarine system, southern Japan; they consist of two sandflat species (N. japonica; N. harmandi) and one boulder-beach species (N. petalura). Nihonotrypaea harmandi and N. petalura are distributed along the coastline in the relatively oligotrophic sea area extending from the outermost part of the sound to the open sea, while N. japonica occurs in the more eutrophic area situated at the middle part of the sound. The trophic conditions of the two areas affect the abundance of phytoplankton in the water column relative to that of benthic microalgae in the sediment. The carbon and nitrogen stable isotope compositions of N. japonica and its potential food sources have been analysed in an earlier study, specifying phytoplankton as the exclusive food source. Potential food sources for N. harmandi and N. petalura were analysed to make interspecific comparisons of the assimilated diets in relation to the shrimp habitat characteristics. Food sources of the shrimps were assessed based on the diet-tissue isotopic fractionation of N. harmandi and N. japonica (δ 13 C=2.0‰, δ 15 N=4.0‰), which had been determined by an earlier laboratory feeding experiment. Of several potential food sources for N. harmandi and N. petalura, riverine organic matter, sewage effluents, live/detrital terrestrial plants, and seagrass were not food sources. For N. petalura, live seaweed, in particular Sargassum spp., growing on boulders and cobbles during the seaweed high-growth season, and seaweed-derived detritus buried in the sediment and live Enteromorpha compressa during the seaweed low-growth season were the most likely food sources. For N. harmandi, phytoplankton (or fresh phytoplankton-derived detritus) and benthic microalgae constituted the most likely food sources. The δ 13 C value of the estimated diet for N. harmandi was higher than that for N. japonica by 0.6‰, while the δ 15 N value for N. harmandi was lower by 2.6‰. The food sources for the

The stable carbon and nitrogen isotope ratios of the sedimentary organic matter (SOM) collected from 41 stations in and around a coastal fish farm in Japan were measured to quantify aquaculture-derived organic matter in the sediment. SOM in the fish-farm area (within 30 m from the edge of cages) is characterized by its reduced δ 13 C (mean Δδ 13 C=−0.4‰) and enriched δ 15 N (mean Δδ 15 N=+0.9‰) values, which reflect the deposition of C3-plant-derived and fish-derived elements, respectively. Compositions of waste feed (WF) and fecal matter (FM) in SOM at each station was determined based on the isotopic compositions of feed (δ 13 C= −20.2‰, δ 15 N=9.7‰), fish feces (δ 13 C=−24.3‰, δ 15 N=6.3‰) and marine organic matter in the sediment (δ 13 C=−19.9‰, δ 15 N=5.5‰). The sediment in the fish-farm area was characterized by high WF and FM ratios in SOM (28.8% and 11.9%). As the distance from the fish cages increased, aquaculture-derived organic matter decreased exponentially. The spatial extent of waste dispersal extended to an area up to 300 m, whereas dissolved oxygen of the bottom water and acid volatile sulfides in the sediment were affected even at stations 600 m away from the fish farm. There was a significant negative relationship between the aquaculture-derived nitrogen content in the sediment and the mean current velocity, suggesting that areas (water depth=ca. 18 m)

Current flow under fish-farm cages was investigated in eight net-pen fish farms in Gokasho Bay and Owase Bay, Pacific coast of central Japan, to assess the assimilative capacity of the water body. Time-averaged current velocities during neap- and spring-tide periods were determined using plaster balls and a concomitant current meter set 1 m above the seabed. An index of suitable location for fish farms (ISL), which is given by DV2, where D is the water depth (m) and V is the mean current velocity (m/s), is proposed. Field data on biotic and abiotic factors that have been obtained from the same stations were used to validate ISL. Values of biotic and abiotic factors changed along a gradient of ISL versus annual fish production. As ISL values decreased and fish-production levels increased, values of dissolved oxygen of the bottom water decreased, values of sediment total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD) and acid-volatile sulfide (AVS) increased, and values of biomass, density and number of species of the macrobenthos decreased. Three zones of fish-farm environments, i.e., healthy, cautionary and critical zones, which had been defined on the basis of the macrofauna and chemical factors, were also arranged in a gradient of ISL and fish production. The healthy zone was located at areas having large ISL values, whereas the critical zone was located at areas having small ISL values and a high level of fish production. As fish-production levels increased, the cautionary zone shifted to areas having larger ISL values. These findings suggest that bathymetry and water flow control waste dispersal and loading, and ISL is an effective indicator of the assimilative capacity. Plaster balls can be used as a pragmatic tool in determining time-averaged current velocities.

Environmental deterioration around fish farms has been widespread in Japanese coastal areas. In order to prevent self-induced deterioration of the surrounding environment, the “Law to Ensure Sustainable Aquaculture Production” was enacted in 1999. Criteria based on three indicators, i.e., (1) dissolved oxygen content of water in fish cages, (2) acid volatile sulfide content (AVS-S) in the sediment and (3) the occurrence of macrofauna under the fish cages were determined to promote the “Aquaculture Ground Improvement Program” by applying this Law. The second criterion (AVS-S) is based on the assimilative capacity of the sediments to organic wastes from a fish farm. For applying this criterion to each farm, the maximum phase in the process of biological remineralization must be detected for a farm site when the benthic oxygen uptake (BOU) rates shows maximum. The peak of BOU, however, could not be determined during a survey in Gokasho Bay, suggesting a need for reexamination regarding the practical application of this criterion. In order to obtain data for refining the third criterion (macrofauna), a quantitative survey was conducted at 22 fish farms (red sea bream and yellowtail) along the Kumano-nada coast, central Japan. The biomass of the macrobenthos peaked in sediments containing 1.2 mg/g of total nitrogen, where the majority of aerobic mineralization of the loaded organic matter is supposed to occur. In summer, animals were scarcely found in sediments with AVS-S>1.7 mg/g, suggesting that this is a critical condition for the fish farm environment. An index embayment degree (ED), which represents the topographic conditions of a farm site, is proposed to discriminate artificial factors arising from fish farming activities from the natural factors related to the topography. Community parameters of the macrobenthos and environmental factors were significantly correlated with ED ( P

The acute toxicities of formaldehyde to one- and two-year-old pearl oysters, Pinctada fucata martensii, were determined under a semi-static condition at 20 and 25°C. The median lethal concentration (LC50) lowered progressively as the duration of exposure increased. The toxicity curves became almost asymptotic with the time axis by 96 h. The 96 h-LC50 was 7.7 mg/l at 20°C and 5.3 mg/l at 25°C for the one-year-old pearl oyster. It was 10.2 mg/l at 20°C and 6.4 mg/l at 25°C for the two-year-old pearl oyster. Variations of the dissolved oxygen concentration and the formaldehyde concentration in the test solutions imply that pearl oyster can defend themselves from toxic effects of formaldehyde by reducing their respiration rate. Furthermore, pearl oysters are capable of lowering the formaldehyde concentration in surrounding water, thus defending themselves.

Spatial and temporal distribution of larvae of Paraprionospio sp. (form A), an indicator of organic pollution in Japanese coastal waters, was investigated from May 1982 to November 1982 in Kumihama Bay, an area where oxygen-deficient water develops from late spring through autumn. This species has a less opportunistic life history represented by a seasonal peak in recruitment (September–October 1982). Simultaneously with the deoxygenation in May, larvae appeared in the bottom layer and were subsequently found through November almost exclusively in water layers with oxygen levels below 1 mg l −1 . Larvae displayed no changes in vertical distribution in a 24-h study conducted in August 1980. These observations indicate that larvae have the ability to tolerate anoxic or hypoxic water throughout their entire development. It is hypothesized that the adaptation of larvae to hypoxic water may explain the high abundances of Paraprionospio sp. (form A) in organically polluted sediments.

In order to obtain data relevant to increasing the numbers of prey organisms for shorebirds, the population of benthic animals and the environment were surveyed from 1982 to 1989 in three areas (Marsh A, Marsh B and Lagoon) of Wild Bird Park, which was laid out on reclaimed land in Osaka Port. In Marsh A, formed by standing rainwater, marine benthic organisms intruded as seawater was introduced. In Marsh B, created by the pumping in of seawater, intertidal gammarids disappeared and chironomid larvae dominated as freshwater gradually replaced the seawater. In the Lagoon, connected to the sea by ducts, a large biomass and high species diversity were found but large, intertidal animals were scarce. A comparison with the results of surveys made on the tidal flat at the mouth of Onosato River suggests that natural features should be introduced into Wild Bird Park for the future development of an intertidal assemblage.

The life history and population structure of Paraprionospio sp. (form A), an indicator of organic pollution in Japanese coastal waters, were studied in Kumihama Bay over a 19-month period. Breeding of Paraprionospio sp. (form A) occurred at a low level throughout the year, but there were two peaks, namely, in spring and in late summer through autumn. However, intense recruitment was restricted to a short period between October and November, when recovery of levels of dissolved oxygen in the bottom water began. After 3 to 4 months worms began to develop their germ cells, and then they became indistinguishable from the adult population. The life span of individuals is estimated to be 1 yr or longer. This species has no brood protection, a large brood size with a maximum of 43 000 oocytes · individual which is positively correlated to body size, and a long planktonic-larval stage that lasts for nearly 2 months. These features suggest that this species is not opportunistic but belongs to a group of species that is able to respond to large-scale disturbances and can take advantage of the timing of oxygen recovery.

Laboratory experiments and a field study were conducted to investigate the effects of temperature on feeding activity and growth rate of the spionid polychaete Paraprionospio sp. (form A). Worms were maintained at various constant temperatures which ranged from 7 to 25°C. 100% mortality occurred at 7° C. This sensitivity to low temperatures may inhibit the spread of this species to the northern part of Japan. Paraprionospio sp. feed on surface deposits and excrete rod-like fecal pellets around the opening of their tubes. Feeding activity, which was determined from the weight of fecal pellets, was accelerated as temperature increased. The total amount of feces eliminated by a worm during the 1st yr of life is estimated to range between 2.7 and 14.0 g. Growth, measured by addition of setigers during 30 days, was barely apparent at 11°C. However, at higher temperatures, growth rates increased significantly. Growth curves, which were derived from the results of the laboratory experiments and incorporated seasonal fluctuation of temperature, agree well with similar data derived from the field study.