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In the Arctic Ocean, the life cycles of interzonal omnivorous copepods have been studied, whereas little information is available on the life cycles of mesopelagic carnivorous species. Here, the life cycles of two mesopelagic carnivorous copepods (Paraeuchaeta glacialis and Heterorhabdus norvegicus) are described from vertically stratified samples collected at an annual ice-station (SHEBA) in the western Arctic Ocean during 1996-1997. Reproduction estimated to occur between January and March for both species. Vertical distributions and population growth varied between the species. Early copepodite stages and adult males of P. glacialis were distributed in deeper layers, whereas late copepodite stages and adult females were observed in shallower layers. The skewed sex ratio towards females was observed for adults, which may be related to the cease feeding and short longevity for adult males. In contrast, all the H. norvegicus life stages were distributed in the mesopelagic layer. Clear peaks of the young stages and their sequence suggest that H. norvegicus may complete its life cycle within 1 year. A specialized feeding mode (incorporating a venomous injection spine and large beak) could be a key trait facilitating the achievement of rapid growth in H. norvegicus in the food-limited mesopelagic layer.

In the Arctic Ocean, the life cycles of interzonal omnivorous copepods have been studied, whereas little information is available on the life cycles of mesopelagic carnivorous species. Here, the life cycles of two mesopelagic carnivorous copepods (Paraeuchaeta glacialis and Heterorhabdus norvegicus) are described from vertically stratified samples collected at an annual ice-station (SHEBA) in the western Arctic Ocean during 1996-1997. Reproduction estimated to occur between January and March for both species. Vertical distributions and population growth varied between the species. Early copepodite stages and adult males of P. glacialis were distributed in deeper layers, whereas late copepodite stages and adult females were observed in shallower layers. The skewed sex ratio towards females was observed for adults, which may be related to the cease feeding and short longevity for adult males. In contrast, all the H. norvegicus life stages were distributed in the mesopelagic layer. Clear peaks of the young stages and their sequence suggest that H. norvegicus may complete its life cycle within 1 year. A specialized feeding mode (incorporating a venomous injection spine and large beak) could be a key trait facilitating the achievement of rapid growth in H. norvegicus in the food-limited mesopelagic layer.

The southern part of the Okhotsk Sea off Hokkaido has rich fishery resources supported by high primary production. The phytoplankton community has been described by several studies based on size-fractionated chlorophyll a concentration and primary production; however, the details of the species composition of nano- and micro-protist communities have not been well investigated. We evaluated the spatial distribution and relationship with hydrography of nano- and micro-protist communities in the southern region of the Okhotsk Sea off Hokkaido during the summer of 2019. Forty-two species of diatoms from 19 genera, dinoflagellates from 7 genera, tintinnid ciliates, oligotrich ciliates, and 1 genus of silicoflagellates were identified. Their spatial distribution showed distinct differences among the taxa. Cluster analysis based on the protist cell density identified six groups with geographically well-distinguished distributions. Diatom-dominant communities were distributed in the Cold Water Belt and Soya warm current along the coastal area of Hokkaido. Nanoflagellate-dominated communities were distributed in the offshore area. Some harmful species of diatoms (Pseudonitzschia pseudodelicatissima) and dinoflagellates (Alexandrium spp.) were dominant in the Cold Water Belt off Wakkanai. We suggest that the upwelling of cold water could increase the abundance of harmful species, with immanent negative impacts on marine ecosystems or fishery resources. In summary, the species composition and abundance of the summer protist community was strongly related to different water masses in the southern part of the Okhotsk Sea off Hokkaido.

An increasing body of work has shown the potential impacts of subglacial discharge from marine-terminating glaciers on the marine environment around Greenland. Upwelling of nutrients associated with rising buoyant plumes near the front of marine-terminating glaciers plays a key role in maintaining the high productivity of connected fjords. The response of protist communities to subglacial discharges into fjords nevertheless remains poorly understood. Here we show data of water properties, nutrients, and protist communities during two summers in 2018 and 2019 in a Greenlandic fjord system fed by marine-terminating glaciers. This study included the period of intense summer melting of the Greenland Ice Sheet in 2019. The data revealed high nutrient concentrations in 2019 that were attributed to intensified upwelling of nutrients and dissolved iron into the subsurface layer. The source of the iron and the nutrients was subglacial discharge and deep fjord water, respectively. Intense glacial discharges in 2019 mitigated nitrate and phosphate limitations of phytoplankton in the fjord and resulted in an increase of chlorophyll a in the subsurface layer and growth of large diatoms. Heterotrophic protists such as dinoflagellates, tintinnids, and nanoflagellates were more abundant in the summer of 2019. We concluded that nutrient upwelling by subglacial discharges was the major driver of the structure of lower trophic levels in fjord ecosystems. We hypothesize that the more intense melting of glaciers and related increase in subglacial discharge will enhance nutrient upwelling, and increased summer productivity in fjords until the glaciers retreat and terminate on land.

A remarkable early sea-ice reduction event was observed in the northern Bering Sea during 2018. In turn, this unusual hydrographic phenomenon affected several marine trophic levels, resulting in delayed phytoplankton blooms, phytoplankton community changes, and a northward shift of fish stocks. However, the response of the zooplankton community remains uncharacterized. Therefore, our study sought to investigate the zooplankton community shifts in the northern Bering Sea during the summers of 2017 and 2018 and evaluate the effects of early sea-ice melt events on the zooplankton community, population structure of large copepods, and copepod production. Five zooplankton communities were identified based on cluster analysis. Further, annual changes in the zooplankton community were identified in the Chirikov Basin. In 2017, the zooplankton community included abundant Pacific copepods transported by the Anadyr water. In 2018, however, the zooplankton community was dominated by small copepods and younger stages of large copepods (Calanus glacialis/marshallae and Metridia pacifica), which was likely caused by reproduction delays resulting from the early sea-ice reduction event. These environmental abnormalities increased copepod production; however, this higher zooplankton productivity did not efficiently reach the higher trophic levels. Taken together, our findings demonstrated that zooplankton community structure and production are highly sensitive to the environmental changes associated with early sea-ice reduction (e.g., warm temperatures and food availability).

The faecal pellets egested by zooplankton are essential as they influence the vertical material flux in oceans. As mesozooplankton are dominant within the plankton community in the southern Okhotsk Sea during early summer, the vertical material flux via mesozooplankton is expected to be substantial. However, quantitative information on their faecal pellets is currently lacking. In this study, we evaluated the taxonomic accounts of the entire plankton community, including microplankton, mesozooplankton, and macrozooplankton, in the 0-1000 m water column. The ingestion and egestion rates of the zooplankton were also estimated. We used a fine-mesh (63 mu m) plankton net along with an imaging technique (with ZooScan) to quantify the amount of in-situ faecal pellets. Furthermore, on-board experiments were conducted to estimate the faecal pellet egestion by the dominant zooplankton species. Cosmopolitan diatom species were found to dominate the microplankton biomass, whereas the large-sized calanoid copepod Metridia okhotensis, which performs nocturnal ascent diel vertical migration, dominated the mesozooplankton biomass. Two euphausiid species with different body sizes, namely the small-sized Thysanoessa inermis and the large-sized Euphausia pacifica, were found to be dominant among the macrozooplankton. The highest density and mass of faecal pellets (1888 pellets m(-3), 2.96 mg C m(-3)) was observed in the 0-100 m layer during the daytime. Throughout the layer, the volumes of the faecal pellets peaked at 0.010-0.015 mm(3), which corresponded with the size of the pellets egested by M. okhotensis in the on-board laboratory experiments. The large-sized faecal pellets (> 0.2 mm(3)), which were inferred to be egested by euphausiids, were only observed during the night-time. Based on the on-board experiments, the faecal pellets egested by all the meso- and macrozooplankton species contained phytoplankton cells that possessed a fluo-rescent ability. Furthermore, cyanobacter

Aetideidae is a calanoid copepod family dominant in the mesopelagic layer of the Arctic Ocean for which little ecological information is available because species identification, especially of early copepodite stages, is difficult. In this study, we developed a species identification flow for the whole copepodite stages of five sympatric aetideid copepods (Chiridius obtusifrons, Gaetanus tenuispinus, G. brevispinus, Aetideopsis multiserrata, and A. rostrata). Vertical distributions and seasonal population structures of these species were evaluated using a year-round sample time-series collected at the drifting ice station (SHEBA) in the western Arctic Ocean. Combinations of morphological characteristics (prosome length, cephalosome, and prosome widths) were used to identify the early copepodite stages to species. Aetideopsis rostrata was distributed in deep waters (1,032-1,065 m) throughout the year. The other species all were found at 600-700 m during the midnight sun. However, during the polar night, the vertical distributions of each species were distinct, resulting from ascent, descent, or depth maintenance, indicating seasonal vertical migration which may function to reduce inter-specific competition during the polar night when food resources are scarce. Reproduction timing varied among four aetideid copepods: C.obtusifrons and G. tenuispinus showed polar night ascent and reproduction at the end of the polar night, whereas G. brevispinus and A. multiserrata showed descent or depth maintenance during the polar night and reproduction at the beginning of the polar night. There was not sufficient data to examine reproduction timing of A. rostrata. Common for all aetideid species, delta N-15 values of the adult females indicate more carnivorous feeding modes during the polar night than those in the midnight sun. Such vertical distribution and timing of reproduction variation among these five aetideid copepods may function to reduce species competition in the mesopel

Fourteen isoforms of the monocarboxylate transporter (MCT) have been reported. Among the MCT isoforms, MCT1, MCT2, and MCT4 play a role in l-lactate/proton cotransport and are involved in the balance of intracellular energy and pH. Therefore, MCT1, MCT2, and MCT4 are associated with energy metabolism processes in normal and pathological cells. In the present study, we evaluated the expression of MCT1, MCT2, and MCT4 and the contribution of these three MCT isoforms to l-lactate uptake in hepatocellular carcinoma (HCC) cells. In HepG2 and Huh-7 cells, l-lactate transport was pH-dependent, which is characteristic of MCT1, MCT2, and MCT4. Furthermore, l-lactate uptake was selectively inhibited by MCT1 and MCT4 inhibitors in HepG2 and Huh-7 cells. Kinetic analysis of HepG2 cells demonstrated that l-lactate uptake was biphasic. Although the knockdown of MCT1 and MCT4 in the HepG2 cells decreased the uptake of l-lactate, the knockdown of MCT2 had no effect on the uptake of l-lactate. Consequently, we concluded that both MCT1 and MCT4 were involved in the transport of l-lactate in HepG2 and Huh-7 cells at pH 6.0. In contrast, PXB-cells, freshly isolated hepatocytes from humanized mouse livers, showed lower MCT4 expression and l-lactate uptake at pH 6.0 compared to that in HCC cell lines. In conclusion, MCT4, which contributes to l-lactate transport in HCC cells, is significantly different in HCC compared to normal hepatocytes, and has potential as a target for HCC treatment.

The faecal pellets egested by zooplankton are essential as they influence the vertical material flux in oceans. As mesozooplankton are dominant within the plankton community in the southern Okhotsk Sea during early summer, the vertical material flux via mesozooplankton is expected to be substantial. However, quantitative information on their faecal pellets is currently lacking. In this study, we evaluated the taxonomic accounts of the entire plankton community, including microplankton, mesozooplankton, and macrozooplankton, in the 0-1000 m water column. The ingestion and egestion rates of the zooplankton were also estimated. We used a fine-mesh (63 mu m) plankton net along with an imaging technique (with ZooScan) to quantify the amount of in-situ faecal pellets. Furthermore, on-board experiments were conducted to estimate the faecal pellet egestion by the dominant zooplankton species. Cosmopolitan diatom species were found to dominate the microplankton biomass, whereas the large-sized calanoid copepod Metridia okhotensis, which performs nocturnal ascent diel vertical migration, dominated the mesozooplankton biomass. Two euphausiid species with different body sizes, namely the small-sized Thysanoessa inermis and the large-sized Euphausia pacifica, were found to be dominant among the macrozooplankton. The highest density and mass of faecal pellets (1888 pellets m(-3), 2.96 mg C m(-3)) was observed in the 0-100 m layer during the daytime. Throughout the layer, the volumes of the faecal pellets peaked at 0.010-0.015 mm(3), which corresponded with the size of the pellets egested by M. okhotensis in the on-board laboratory experiments. The large-sized faecal pellets (> 0.2 mm(3)), which were inferred to be egested by euphausiids, were only observed during the night-time. Based on the on-board experiments, the faecal pellets egested by all the meso- and macrozooplankton species contained phytoplankton cells that possessed a fluo-rescent ability. Furthermore, cyanobacter

Aetideidae is a calanoid copepod family dominant in the mesopelagic layer of the Arctic Ocean for which little ecological information is available because species identification, especially of early copepodite stages, is difficult. In this study, we developed a species identification flow for the whole copepodite stages of five sympatric aetideid copepods (Chiridius obtusifrons, Gaetanus tenuispinus, G. brevispinus, Aetideopsis multiserrata, and A. rostrata). Vertical distributions and seasonal population structures of these species were evaluated using a year-round sample time-series collected at the drifting ice station (SHEBA) in the western Arctic Ocean. Combinations of morphological characteristics (prosome length, cephalosome, and prosome widths) were used to identify the early copepodite stages to species. Aetideopsis rostrata was distributed in deep waters (1,032-1,065 m) throughout the year. The other species all were found at 600-700 m during the midnight sun. However, during the polar night, the vertical distributions of each species were distinct, resulting from ascent, descent, or depth maintenance, indicating seasonal vertical migration which may function to reduce inter-specific competition during the polar night when food resources are scarce. Reproduction timing varied among four aetideid copepods: C.obtusifrons and G. tenuispinus showed polar night ascent and reproduction at the end of the polar night, whereas G. brevispinus and A. multiserrata showed descent or depth maintenance during the polar night and reproduction at the beginning of the polar night. There was not sufficient data to examine reproduction timing of A. rostrata. Common for all aetideid species, delta N-15 values of the adult females indicate more carnivorous feeding modes during the polar night than those in the midnight sun. Such vertical distribution and timing of reproduction variation among these five aetideid copepods may function to reduce species competition in the mesopel

An increasing body of work has shown the potential impacts of subglacial discharge from marine-terminating glaciers on the marine environment around Greenland. Upwelling of nutrients associated with rising buoyant plumes near the front of marine-terminating glaciers plays a key role in maintaining the high productivity of connected fjords. The response of protist communities to subglacial discharges into fjords nevertheless remains poorly understood. Here we show data of water properties, nutrients, and protist communities during two summers in 2018 and 2019 in a Greenlandic fjord system fed by marine-terminating glaciers. This study included the period of intense summer melting of the Greenland Ice Sheet in 2019. The data revealed high nutrient concentrations in 2019 that were attributed to intensified upwelling of nutrients and dissolved iron into the subsurface layer. The source of the iron and the nutrients was subglacial discharge and deep fjord water, respectively. Intense glacial discharges in 2019 mitigated nitrate and phosphate limitations of phytoplankton in the fjord and resulted in an increase of chlorophyll a in the subsurface layer and growth of large diatoms. Heterotrophic protists such as dinoflagellates, tintinnids, and nanoflagellates were more abundant in the summer of 2019. We concluded that nutrient upwelling by subglacial discharges was the major driver of the structure of lower trophic levels in fjord ecosystems. We hypothesize that the more intense melting of glaciers and related increase in subglacial discharge will enhance nutrient upwelling, and increased summer productivity in fjords until the glaciers retreat and terminate on land.

To evaluate seasonal changes in a protist community (diatoms, dinoflagellates and ciliates) and their production in the southern Okhotsk Sea, water sampling was conducted approximately once a week from July 2016 to July 2017 at Mombetsu Port. Diatoms were the predominant category of the three taxa throughout the study period. The abundances of all taxa were high from March to September and were low from October to February. Four groups (A-D) were identified by cluster analysis according to abundance. Group A, of which Thalassiosira spp. were dominant, occurred in March. Group B showed the highest abundance (7.7 x 10(4) cells L-1), with Chaetoceros spp. and Pseudo-nitzschia spp. being dominant. In group C, Odontella spp. and pennate diatoms were dominant and occurred from November to February. Group D was mainly observed in late October, and pennate diatoms were dominant. Seasonal changes in the predominant species of diatoms were explicitly observed, and these changes were associated with water mass exchanges. For dinoflagellates, abundance was highest in July 2016, and biomass and production were highest in September. Large fluctuations in the ciliate biomass in July 2016 might have been induced by the high growth rate, which reflects the high chlorophyll a concentration and water temperature and a decrease in predation pressure. The estimated primary production was lower than that reported in previous studies, which could reflect differences in the depth of the research areas and the methods used for estimating production. In the coastal area of the southern Okhotsk Sea, where production is high, not only the species composition but also the protist community varied clearly with season because of variations in the water mass. (C) 2021 Elsevier B.V. All rights reserved.

Pelagic polychaetes are distributed from the sea surface to greater depths of the oceans worldwide, but little information is available regarding their ecology. This study investigated the vertical distribution of abundance, biomass and community structure of pelagic polychaetes at a single station in the western subarctic Pacific based on day-night vertical stratified samples collected from a 0 to 1000 m water column during four seasons covering 1 year. The polychaete abundance and biomass ranged from 0 to 757 ind. 1000 M-3 and 0-6.1 mg WW m(-3), respectively. Ten pelagic polychaete species belonging to nine genera and six families were identified. From cluster analysis based on abundance, the polychaete community was divided into five communities. Each community occurred at different depth layers. Two surface groups seen at 0-200 m were dominated by two carnivorous species: Tomopteris septentrionalis and Typhloscolex muelleri. The deepest group, dominated by the particle feeder Pelagobia longicirrata, was seen at 500-1000 m. Two transition groups occurred in the intermediate depths. These vertical distributions of the pelagic polychaete communities were common throughout the season and day. Water mass, food availability and the oxygen minimum layer are put forth as environmental factors that affect the pelagic polychaete community.

Purpose Patients with preexisting autoimmune disease (PAD) are often excluded from clinical trials assessing immune checkpoint inhibitors (ICIs). Therefore, the safety of ICI therapy in patients with PAD remains unclear. Herein, we evaluated the incidence of immune-related adverse events (irAEs) in patients with PAD when compared with non-PAD patients. Methods We searched MEDLINE/PubMed, Web of Science, and Google Scholar for eligible studies from inception to January 2021. Observational studies reporting the incidence of irAEs in patients with and without PAD were included. We then performed a meta-analysis of eligible studies using forest plots. The primary endpoint of this study was the incidence rate of irAEs between patients with and without PAD. Results We identified three prospective and three retrospective studies involving 206 patients with PAD and 3078 patients without PAD. In the meta-analysis, 128 patients with PAD (62.1%) experienced irAEs, which occurred in 51.9% of non-PAD patients, resulting in an odds ratio (OR) of 2.14 (95% confidence interval [CI] 1.58–2.89). In the subgroup analysis, the incidence of irAEs was significantly higher in patients with PAD (OR = 2.19, 95% CI [1.55–3.08]). Furthermore, no significant heterogeneity or publication bias was detected, indicating that our meta-analysis could be generalized to clinical settings. Conclusion This meta-analysis demonstrated that PAD was a risk factor for irAE incidence. These results suggest that monitoring the occurrence of irAEs in patients with PAD is required to manage irAEs appropriately.

To evaluate seasonal changes in a protist community (diatoms, dinoflagellates and ciliates) and their production in the southern Okhotsk Sea, water sampling was conducted approximately once a week from July 2016 to July 2017 at Mombetsu Port. Diatoms were the predominant category of the three taxa throughout the study period. The abundances of all taxa were high from March to September and were low from October to February. Four groups (A-D) were identified by cluster analysis according to abundance. Group A, of which Thalassiosira spp. were dominant, occurred in March. Group B showed the highest abundance (7.7 x 10(4) cells L-1), with Chaetoceros spp. and Pseudo-nitzschia spp. being dominant. In group C, Odontella spp. and pennate diatoms were dominant and occurred from November to February. Group D was mainly observed in late October, and pennate diatoms were dominant. Seasonal changes in the predominant species of diatoms were explicitly observed, and these changes were associated with water mass exchanges. For dinoflagellates, abundance was highest in July 2016, and biomass and production were highest in September. Large fluctuations in the ciliate biomass in July 2016 might have been induced by the high growth rate, which reflects the high chlorophyll a concentration and water temperature and a decrease in predation pressure. The estimated primary production was lower than that reported in previous studies, which could reflect differences in the depth of the research areas and the methods used for estimating production. In the coastal area of the southern Okhotsk Sea, where production is high, not only the species composition but also the protist community varied clearly with season because of variations in the water mass. (C) 2021 Elsevier B.V. All rights reserved.

To evaluate the effects of meltwater discharge from marine-terminating glaciers on a fjord protist community in northwestern Greenland during summer, we investigated the distribution, abundance and biomass of the protist community and their relationships with hydrographic parameters. In the standing stock of protists, dinoflagellates (46.4%) and oligotrich ciliates (39.5%) were dominant throughout the study region. With respect to vertical distribution, oligotrich ciliates were abundant in the surface layer, mainly due to suitable food conditions (abundance of diatom and nanoflagellates). Near glaciers, relatively high chlorophyll a (chl a) concentrations were found in the subsurface layers associated with the low-temperature, high-turbidity and slightly high nutrient levels, indicating that the nutrient inputs from the upwelling glacial meltwater plume increased primary production. Large-sized Protoperidium spp. were found only at stations near glaciers where nutrients were abundant, and heterotrophic dinoflagellates showed strong relationships with nanoflagellates. These findings suggest that the upwelling associated with subglacial meltwater discharge can stimulate nanoflagellate production, resulting in increases in ciliate and heterotrophic dinoflagellate production.

The community structure and life cycle of dominant chaetognath species were studied in a 0-1000-m water column in the Oyashio region, western subarctic Pacific, six times during the year from March 2003 to February 2004. The abundance of chaetognaths ranged from 3235 to 6691 inds. m(-2). Throughout the study period, ten chaetognath species belonging to nine genera were identified. Among the chaetognaths, Eukrohnia hamata accounted for 39-62% of the abundance, followed by E. hamata/Eukrohnia bathypelagica juveniles, Parasagitta elegans, and E. bathypelagica. The species diversity (H') of chaetognaths varied between 1.12 and 1.50. For E. hamata, individuals had a body length ranging from 2.3-23.8 mm. The abundance of juveniles fluctuated from 22.0-48.3% and was higher in June 2003. Based on cohort analysis, recruitment of E. hamata juveniles occurred from spring to summer, and they reached a body length of 8 mm in one year. The overwintered population showed rapid growth from June to October, when they reached 15 mm in body length. Eukrohnia hamata showed little growth in winter and reproduced the subsequent spring. Thus, a two-year life cycle of E. hamata is proposed for the population in the Oyashio region. For comparable information about the life cycle of E. hamata, an eight to ten-month generation length was reported for the population in the eastern subarctic Pacific. These regional differences in the generation length of E. hamata are attributed to differences in habitat temperature, with much higher temperatures in the eastern (3.8-6.0 degrees C) than the western (2.3-2.9 degrees C) subarctic Pacific.

Scaphocalanus magnus is a large copepod species with a worldwide distribution. Information on the ecology of this species is scarce. In this study, S. magnus was collected using vertically stratified net sampling from an ice station in the western Arctic Ocean over a year. The vertical distribution differed between periods of polar night and midnight sun, with core depth distributions of 264–381 m for the polar night and 518–745 m for the midnight sun. The shallower distribution during the polar night may have resulted from the animals moving upwards to find sufficient food during the less productive season. The abundance of early copepodite stages showed clear seasonality. The C2 and C3 stages were abundant June–August and August–September, respectively. After C4, seasonality in abundance was not clear. For C4 and C5, body sizes and masses were greater for males than for females while the opposite was the case for C6. Adult males do not feed and thus have shorter life spans than females, skewing the adult sex ratio towards females. For these mesopelagic particle feeding copepods, a long residence time at C6F suggests that in a varying food environment, it is possible to wait to initiate reproduction until favourable food conditions occur.

The intensity and frequency of harmful algal blooms (HABs) have increased, posing a threat to human seafood resources due to massive kills of cultured fish and toxin contamination of bivalves. In recent years, bacteria that inhibit the growth of HAB species were found to be densely populated on the biofilms of some macroalgal species, indicating the possible biological control of HABs by the artificial introduction of macroalgal beds. In this study, an artificially created Ulva pertusa bed using mobile floating cages and a natural macroalgal bed were studied to elucidate the distribution of algal growth-limiting bacteria (GLB). The density of GLB affecting fish-killing raphidophyteChattonella antiqua, and two harmful dinoflagellates, were detected between 10^6 and 10^7 CFU g^-1 wet weight on the biofilm of artificially introduced U. pertusa and 10 to 10^2 CFU mL^-1 from adjacent seawater; however, GLB found from natural macroalgal species targeted all tested HAB species (five species), ranging between 10^5 and 10^6 CFU g^-1 wet weight in density. These findings provide new ecological insights of GLB at macroalgal beds, and concurrently demonstrate the possible biological control of HABs by artificially introduced Ulva beds.

In recent years, the northern Bering Sea has experienced changes in the timing of sea-ice retreat and in hydrographic conditions during the summer. The influence of these environmental changes on the diatom community has not been examined. In this study, we investigated the spatial changes in the diatom community of the northern Bering Sea during the summers of 2017 and 2018, and evaluated the effects of environmental variability on these communities. We found that the diatom cell density and diversity varied with water masses. A cluster analysis based on cell density revealed that the diatom communities were separated into four groups, and that the distributions of three of these groups were different spatially between 2017 and 2018. In the Bering Strait and the Chirikov Basin regions, the diatom communities differed between 2017 and 2018. In 2017, these diatom communities were dominated by cold-water species such as Chaetoceros gelidus and Chaetoceros spp. (subgenus Hyalochaetae), while in 2018, the community was dominated by cosmopolitan species such as Thalassionema nitzschioides and Chaetoceros spp. (subgenus Phaeoceros). NMDS and multiple regression analysis indicated that the timing of the sea-ice retreat was the most important contributor to the differences in the diatom community. In contrast, there was no year-to-year difference south of St. Lawrence Island, possibly because nutrients were depleted and phytoplankton types other than diatoms were dominant.

We examined the abundance and horizontal and vertical distributions of epipelagic ctenophores and scyphomedusae in the northern Bering Sea using an underwater video camera during July of 2017 and 2018. The effects of environmental and biological parameters on the distribution of these species were evaluated by generalized additive modelling (GAM). In 2017, the dominant ctenophore, Bolinopsis infundibulum, was mainly distributed in the north and west of St. Lawrence Island (SLI), and their vertical distribution varied with the region but not by the time of day. We found that B. infundibulum was distributed in the upper pycnocline north of SLI, but below the pycnocline west of SLI. Biological interactions with other gelatinous zooplankton may explain these regional differences in vertical distribution; GAM analysis revealed a negative interaction between B. infundibulum and the large scyphomedusa, Chrysaora melanaster, which occurred in the upper layer in the west of SLI. B. infundibulum may avoid that layer to reduce feeding competition. For the ctenophore, Beroe sp., vertical and horizontal distributions were similar to those of B. infundibulum, and GAM analysis also revealed a positive interaction for both species. As B. infundibulum is an important prey of Beroe sp., a prey-predator interaction may result from their similar horizontal and vertical distributions. Standing stocks of epipelagic ctenophores and scyphomedusae in 2018 were low compared to those in 2017, by a factor of 1/20 (C. melanaster) and1/90 (Beroe sp.). This might be due to annual differences in water mass in this region, in that the thermal conditions characterized by a high abundance of the dominant B. infundibulum in 2017 (<2 and >8 degrees C) were absent in 2018. As this drastic decrease in standing stock in 2018 was apparent for both ctenophores and scyphomedusae, food availability was hypothesized to be poor that year.

Zooplankton community structure in the northern Bering Sea may change significantly over relatively short periods due to the inflow of different water masses and the seasonal release of meroplankton, although details of these changes are still unclear. We studied the zooplankton community in the northern Bering Sea from June to September of 2017 and examined seasonal changes in the community structure and stage structure of the dominant species. Zooplankton abundance ranged from 41,000 to 928,000 ind. m(-2), with the greatest abundances near 174 degrees W during July. Copepods were the dominant taxa, comprising 10-98% of zooplankton abundance, with benthic larvae such as bivalves dominant at some stations during July and August. Cluster analysis of abundances divided the station/zooplankton communities into seven groups. West of 172 degrees W, clear seasonal changes were not observed, because the Bering Chukchi Winter Water persisted in the deep layer and sampling was only conducted in this region in July and August. In contrast, the community structures east of 172 degrees W differed every month due to water masses changes, meroplankton release, and copepod production associated with the phytoplankton bloom. Despite the changes of water mass, development for the dominant large copepods (Calanus glacialis/marshallae, Eucalanus bungii and Metridia pacifica) was revealed from their population stage structures. Seasonal shifts in species within Neocalanus and appendicularians were driven by water mass exchanges. This study demonstrates that zooplankton community in the northern Bering Sea varies substantially on a monthly time scale. Therefore, to evaluate the impact of climate change on zooplankton, it is important to consider both the seasonal period and the dominant water masses present.

Zooplankton community structure in the northern Bering Sea may change significantly over relatively short periods due to the inflow of different water masses and the seasonal release of meroplankton, although details of these changes are still unclear. We studied the zooplankton community in the northern Bering Sea from June to September of 2017 and examined seasonal changes in the community structure and stage structure of the dominant species. Zooplankton abundance ranged from 41,000 to 928,000 ind. m(-2), with the greatest abundances near 174 degrees W during July. Copepods were the dominant taxa, comprising 10-98% of zooplankton abundance, with benthic larvae such as bivalves dominant at some stations during July and August. Cluster analysis of abundances divided the station/zooplankton communities into seven groups. West of 172 degrees W, clear seasonal changes were not observed, because the Bering Chukchi Winter Water persisted in the deep layer and sampling was only conducted in this region in July and August. In contrast, the community structures east of 172 degrees W differed every month due to water masses changes, meroplankton release, and copepod production associated with the phytoplankton bloom. Despite the changes of water mass, development for the dominant large copepods (Calanus glacialis/marshallae, Eucalanus bungii and Metridia pacifica) was revealed from their population stage structures. Seasonal shifts in species within Neocalanus and appendicularians were driven by water mass exchanges. This study demonstrates that zooplankton community in the northern Bering Sea varies substantially on a monthly time scale. Therefore, to evaluate the impact of climate change on zooplankton, it is important to consider both the seasonal period and the dominant water masses present.

In recent years, the northern Bering Sea has experienced changes in the timing of sea-ice retreat and in hydrographic conditions during the summer. The influence of these environmental changes on the diatom community has not been examined. In this study, we investigated the spatial changes in the diatom community of the northern Bering Sea during the summers of 2017 and 2018, and evaluated the effects of environmental variability on these communities. We found that the diatom cell density and diversity varied with water masses. A cluster analysis based on cell density revealed that the diatom communities were separated into four groups, and that the distributions of three of these groups were different spatially between 2017 and 2018. In the Bering Strait and the Chirikov Basin regions, the diatom communities differed between 2017 and 2018. In 2017, these diatom communities were dominated by cold-water species such as Chaetoceros gelidus and Chaetoceros spp. (subgenus Hyalochaetae), while in 2018, the community was dominated by cosmopolitan species such as Thalassionema nitzschioides and Chaetoceros spp. (subgenus Phaeoceros). NMDS and multiple regression analysis indicated that the timing of the sea-ice retreat was the most important contributor to the differences in the diatom community. In contrast, there was no year-to-year difference south of St. Lawrence Island, possibly because nutrients were depleted and phytoplankton types other than diatoms were dominant.

We examined the abundance and horizontal and vertical distributions of epipelagic ctenophores and scyphomedusae in the northern Bering Sea using an underwater video camera during July of 2017 and 2018. The effects of environmental and biological parameters on the distribution of these species were evaluated by generalized additive modelling (GAM). In 2017, the dominant ctenophore, Bolinopsis infundibulum, was mainly distributed in the north and west of St. Lawrence Island (SLI), and their vertical distribution varied with the region but not by the time of day. We found that B. infundibulum was distributed in the upper pycnocline north of SLI, but below the pycnocline west of SLI. Biological interactions with other gelatinous zooplankton may explain these regional differences in vertical distribution; GAM analysis revealed a negative interaction between B. infundibulum and the large scyphomedusa, Chrysaora melanaster, which occurred in the upper layer in the west of SLI. B. infundibulum may avoid that layer to reduce feeding competition. For the ctenophore, Beroe sp., vertical and horizontal distributions were similar to those of B. infundibulum, and GAM analysis also revealed a positive interaction for both species. As B. infundibulum is an important prey of Beroe sp., a prey-predator interaction may result from their similar horizontal and vertical distributions. Standing stocks of epipelagic ctenophores and scyphomedusae in 2018 were low compared to those in 2017, by a factor of 1/20 (C. melanaster) and1/90 (Beroe sp.). This might be due to annual differences in water mass in this region, in that the thermal conditions characterized by a high abundance of the dominant B. infundibulum in 2017 (<2 and >8 degrees C) were absent in 2018. As this drastic decrease in standing stock in 2018 was apparent for both ctenophores and scyphomedusae, food availability was hypothesized to be poor that year.

In recent years, marine ecosystems have changed due to the drastic sea ice reduction in the Arctic Ocean, but the relationship between copepod phenology and environmental drivers is unclear. To reveal the relationship, seasonal changes in the flux (abundance of swimmers), population structure, lipid accumulation and gonad maturation of four dominant copepods (Calanus hyperboreus, Metridia longa, Paraeuchaeta glacialis and Heterorhabdus norvegicus) were studied using a sediment trap deployed at a depth of 222 m in the Pacific-Arctic sector from October 2010 to September 2013. C. hyperboreus, mostly comprising copepodid stage 6 females (C6F), exhibited several peaks in flux in spring and autumn. C. hyperboreus C6Fs were dominated by lipid-rich specimens year-round, and gonad development was observed in these samples from February to April. The M. longa flux showed no clear seasonality. Gonad maturation of M. longa C6Fs occurred from February to September. P. glacialis flux exhibited two peaks in autumn of 2011 and 2012. In contrast to the former two species, lipid-rich, mature P. glacialis C6Fs occurred year-round. H. norvegicus copepodid stage 6 males (C6Ms) also occurred throughout the year, likely because H. norvegicus has functional feeding appendages, even in C6Ms. From generalized additive models, C. hyperboreus, M. longa and P. glacialis showed relationships with daytime length and/or sea ice concentrations, but the relationship patterns were different. These findings suggest that the response (e.g., vertical migration) to the environmental parameters could vary with species and the drastic sea ice reductions may affect the copepod phenology in the Pacific-Arctic sector.

In Greenland, tidewater glaciers discharge turbid subglacial freshwater into fjords, forming plumes near the calving fronts. To evaluate the effects of this discharge on the zooplankton community in the fjords, we collected sea surface zooplankton samples in Bowdoin Fjord in north-western Greenland during the summer of 2016 and made microscopic, OPC and ZooScan analyses. Within the three quantitative methods, ZooScan has advantages that can evaluate various parameters (e.g., abundance, biomass, size and taxonomic information) simultaneously and has the ability to eliminate abiotic particles, such as silt and sediment, which are abundant in samples. Based on taxonomic biomass data, the zooplankton community is clustered into three groups, which varied spatially: inner, middle and outer fjord groups. Jellyfish dominated the outer fjord group, and barnacle cypris larvae dominated the middle fjord group. For the inner fjord group, large-sized Calanus spp. and chaetognaths were abundant. Since these species are characterized with oceanic taxa, they would intrude through the deep fjord water and subsequently be upwelled through entrainment of glacially modified plume water. From the NBSS analysis on zooplankton size spectra, the steep slope of NBSS in the middle fjord community suggests that the high productivity was caused by the addition of meroplanktonic cypris larvae.

In oceans worldwide, chaetognaths are the second most dominant zooplankton taxa and have vital transfer roles between herbivores and higher trophic organisms. Despite the chaetognath's importance, little is known regarding their ecology in the Chukchi Sea, where recent ice reduction is prominent in the Arctic Ocean. We made comparisons of the chaetognath abundance, biomass, community structure (total length and gonadal maturation) and feeding impacts between the years 1991 and 2007. Within the chaetognath community, Parasagitta elegans was the abundant species, and Eukrohnia hamata only occurred in the southern region in 2007. Yearly differences were detected in chaetognath abundance, biomass, total length and gonadal maturation. All of these parameters were greater and more advanced in 1991 than in 2007. The most prominent yearly differences were in the horizontal distributions of chaetognaths, primarily in the northern region in 1991 and the southern region in 2007. The southern chaetognath populations observed in 2007 were considered to be transported by the Pacific water through the Bering Strait. Because of the differences in the original populations between the Chukchi Sea in 1991 and the Bering Sea in 2007, differences in these two years may be due to regional differences. As the Arctic warms, the horizontal distribution pattern, similar with 2007 in this study, will be more pronounced.

In the Bering Sea shelf, annual changes in the sea ice extent are large. In this study, we compare the viable diatom resting stages in sediments during the summer of 2017 when the sea ice retreat was late and 2018 when the sea ice retreat was early. South of St. Lawrence Island, the germinating cell number was 10-100 times greater in 2018 than it was in 2017. The taxonomic composition also showed large annual differences: Fragilariopsis/Fossula spp., which are ice algae species, were abundant in 2017, but Thalassiosira spp. dominated in 2018. Satellite observations confirmed that sea ice diminished before the ice-edge bloom in 2018, but sea ice remained until the ice-edge bloom in 2017. This study shows that the community composition of viable diatom resting stages is largely affected by the timing of the sea ice retreat.

To evaluate the temporal changes in zooplankton size spectra, optical plankton counter (OPC) measurements were made of high-frequency time-series zooplankton samples collected at approximately 3.5-day intervals in Mombetsu Harbour, which is located in the southern Okhotsk Sea, from January to December 2011. Based on biomasses of 47 equivalent spherical diameter (ESD) size classes binned at 0.1 mm intervals across 0.35-5 mm, the Bray-Curtis similarity index separated the zooplankton community into six groups (A-F). The occurrence of each group was separated seasonally. Thus, groups A and B were observed during the ice-covered season and summer season, respectively. During March and June, groups C-F were observed. Their occurrence varied in the short term in relation to the exchange of water masses. Groups A and C, which were observed from January to April, showed flatter normalized biomass size spectra (NBSS) slopes ( -0.85 to -1.1), which indicate low productivity. In contrast, the other groups showed steeper slopes (-1.31 to -1.52) from May to December, with high productivity. Throughout the year, the frequency of highly productive groups occurred at a high level (95.2%). Although the seasonal variability in zooplankton size and productivity in Mombetsu Harbour was mainly governed by water mass exchanges, the productivity was continuously high throughout nearly all of the one-year study period. (C) 2018 Published by Elsevier B.V.

In the Bering Sea, warming and reduction of summer sea-ice cover are driving species ranges towards the Arctic. Tanner crab, Chionoecetes bairdi, is a commercially important species in the SE Bering Sea with a northerly range margin in 62 degrees N. In this paper, using plankton samples collected in the Pacific sub-Arctic/Arctic sector during summer, we report for the first time the presence of larval stages (zoea II) of C. bairdi far from its northern limit of the distribution, in the south of St. Lawrence Island during 1991, and even crossing the Bering Strait into the Chukchi Sea during 1992. We suggest that the long planktonic phase (3-5 months), in combination with the oceanographic circulation, may facilitate eventual long-distance transport.

Seasonal changes in zooplankton swimmer (ZS) abundance, biomass and community structure were evaluated based on samples collected by moored sediment traps at a depth of 200 m in the subarctic (SA) and subtropical (ST) western North Pacific. Based on these samples, we made comparisons on two topics: 1) latitudinal (subarctic vs. subtropical) changes in ZS abundance, biomass and community and 2) quantitative differences between the ZS and particle organic carbon (POC) fluxes based on data from moored or drifting sediment traps. The results showed that the ZS flux was greater in the SA (annual mean: 311 ind. m−2 day−1 or 258 mg C m−2 day−1) than in the ST (135 ind. m−2 day−1 or 38 mg C m−2 day−1). The peak ZS flux was observed from July–August in the SA and from April–May in the ST. The dominant taxa were Copepoda and Chaetognatha in the SA and Ostracoda and Mollusca in the ST. These latitudinal differences are likely related to the dominance of large-sized Copepoda in the SA, regional differences in the timing of the spring phytoplankton bloom, and the magnitude and size structure of primary producers. The percent composition of ZS to the total C flux (= ZS+POC flux) varied by region: 85–95% in the SA and 47–75% in the ST. These differences between the ZS composition and the total C flux are most likely caused by the dominance of large-sized Copepoda (Neocalanus spp. and Eucalanus bungii) in the SA.

While length-weight (L-W) regressions for warm-water zooplankton taxa from the waters neighbouring Japan already exist, they are still missing for comparable cold-water species. In this study, the L-W regressions of 41 species belonging to 12 taxa that are dominant in the Oyashio region were reported. The body length and volume of zooplankton were measured with an image-analysis system, and the effects of lipid accumulation in Copepoda on their mass and chemical composition were quantified. The L-W regressions had a high coefficient of determination (mean r2 = 0.886). For the chemical composition, the water composition ranged from 69.8 to 95.2% wet mass (WM), carbon (C) composition from 3.8 to 60.8% dry mass (DM) and nitrogen (N) composition from 1.0 to 10.1% DM. Taxon-specific differences in the chemical composition were marked for the gelatinous taxa (Appendicularia, Cnidaria, Salpida), which also had high water and low C composition. Because C is an index of lipids, high water compositions together with low lipid compositions are considered to be characteristics of the gelatinous taxa. The most significant effects of lipid accumulation in the Copepoda are changes in DM and C. Within the same developmental stage, the DM and C compositions of the full lipid-containing specimens showed 495% and 741% increases, respectively, over those of the low lipid-containing specimens. These differences exceeded the changes after moulting (78.1%) for general copepod species. Thus, lipid accumulation should be evaluated for the accurate mass estimation of boreal Copepoda by image analysis.

A total of 100 mesozooplankton samples collected with NORPAC nets from a 0 to 150-m depth at latitudinal stations (35-44 degrees N) along 155 degrees E each May from 2002 through 2011 were analyzed. The mesozooplankton abundance at each station varied from 39 to 1106 ind. m(-3). The mesozooplankton biomass was consistently higher (80-100 mg DM m(-3)) in the transition domain (40-42 degrees N) than the biomass in the other domains. An empirical metabolic rate-based carbon budget model indicated that production of mesozooplankton suspension feeders was highest (120-175 mg C m(-2) d(-1)) in the transition domain. A comparison between the production of the mesozooplankton suspension feeders and the food requirement of mesozooplankton carnivores indicated that the latter was well fulfilled by the former in the subarctic and transition domains. However, the food requirement of the mesozooplankton carnivores was near equal to or exceeded the production of mesozooplankton suspension feeders in the subtropical domain. As an annual event, the feeding migration of epipelagic fish to the transition and subarctic domains in summer may be interpreted by their utilization of the excess secondary production (production of mesozooplankton suspension feeders). (C) 2015 Elsevier Ltd. All rights reserved.

The short-tailed shearwater (Ardenna tenuirostris) is one of the abundant marine top predators in the Pacific; this seabird spends its non-breeding period in the northern North Pacific during May-October and many visit the southern Chukchi Sea in August-September. We examined potential factors affecting this seasonal pattern of distribution by counting short-tailed shearwaters from boats. Their main prey, krill, was sampled by net tows in the southeastern Bering Sea/Aleutian Islands and in the Bering Strait/southern Chukchi Sea. Short-tailed shearwaters were mainly distributed in the southeastern Bering Sea/Aleutian Islands (60 +/- 473 birds km(-2)) in July 2013, and in the Bering Strait/southern Chukchi Sea (19 +/- 91 birds km(-2)) in September 2012. In the Bering Strait/southern Chukchi Sea, krill size was greater in September 2012 (9.6 +/- 5.0 mm in total length) than in July 2013 (1.9 +/- 1.2 mm). Within the Bering Strait/southern Chukchi Sea in September 2012, short-tailed shearwaters occurred more frequently in cells (50 +/- 50 km) where large-sized krill were more abundant. These findings, and information previously collected in other studies, suggest that the seasonal northward movement of short-tailed shearwaters might be associated with the seasonal increase in krill size in the Bering Strait/southern Chukchi Sea. We could not, however, rule out the possibility that large interannual variation in krill abundance might influence the seasonal distribution of shearwaters. This study highlights the importance of krill, which is advected from the Pacific, as an important prey of top predators in the Arctic marine ecosystem.

A doliolid species belonging to the genus Paradoliopsis was photographed by an Autonomous Visual Plankton Recorder (AVPR) off the eastern seaboard of Japan in October 2014 at 493–512 m depth. Two Paradoliopsis gonozooids were also captured on the video record of the ROV Crambon at 372–373 m depth during the same cruise. This is the first record of this genus from the Pacific Ocean, and although it resembles the sole described species in this genus, P. harbisoni Godeaux, 1996, some aspects of its morphology suggest it may be an as-yet-undescribed species.

Within the calanoid copepods, the bioluminescent species comprise 5-59% of the abundance and 10-15% of the biomass in the world's oceans. Most of the luminous species belong to the superfamily Augaptiloidea. The composition of bioluminescent species within the calanoid copepods shows latitudinal patterns; 5-25% of total calanoid copepods are found in high-latitude oceans, while 34-59% are in low-latitude oceans, reflecting a prey-predator relationship. Bioluminescent species of calanoid copepods are able to produce the light-emitting substrate coelenterazine. It is then transferred to higher predators through the food chain, and might be used for bioluminescence in other luminous organisms. A notable feature of copepod bioluminescence is the secreted-type, and its major function may be as an antipredatory response or a defensive behavior. Identification of more than 20 luciferase genes from calanoid copepods has revealed the highly conserved sequences of those genes. This leads us to the speculation that the genes for luciferase within the group of calanoid copepods have evolved independently of comparable genes outside of this group. We discuss here the ecological and biological functions of copepod bioluminescence, the significant diversity in luminous intensity, which might be evolutionarily relevant to their motility and habitat depth, and the promising future directions of bioluminescence studies.

The advection of warm Pacific water and the reduction in sea ice in the western Arctic Ocean may influence the abundance and distribution of copepods, a key component of food webs. To quantify the factors affecting the abundance of copepods in the northern Bering and Chukchi seas, we constructed habitat models explaining the spatial patterns of large and small Arctic and Pacific copepods separately. Copepods were sampled using NORPAC (North Pacific Standard) nets. The structures of water masses indexed by principle component analysis scores, satellite-derived timing of sea ice retreat, bottom depth and chlorophyll a concentration were integrated into generalized additive models as explanatory variables. The adequate models for all copepods exhibited clear continuous relationships between the abundance of copepods and the indexed water masses. Large Arctic copepods were abundant at stations where the bottom layer was saline; however they were scarce at stations where warm fresh water formed the upper layer. Small Arctic copepods were abundant at stations where the upper layer was warm and saline and the bottom layer was cold and highly saline. In contrast, Pacific copepods were abundant at stations where the Pacific-origin water mass was predominant (i.e. a warm, saline upper layer and saline and a highly saline bottom layer). All copepod groups showed a positive relationship with early sea ice retreat. Early sea ice retreat has been reported to initiate spring blooms in open water, allowing copepods to utilize more food while maintaining their high activity in warm water without sea ice and cold water. This finding indicates that early sea ice retreat has positive effects on the abundance of all copepod groups in the northern Bering and Chukchi seas, suggesting a change from a pelagic–benthic-type ecosystem to a pelagic–pelagic type.

Recent studies indicate an increase in atmospheric turbulence in the Chukchi Sea due to the recent drastic sea-ice reduction during summer months. The importance of the effects of this atmospheric turbulence on the marine ecosystem in this region, however, is not fully understood. To evaluate the effects of atmospheric turbulence on the marine ecosystem, high-frequency sampling (daily) from five layers of the microplankton community between 0 and 30m at a fixed station in the Chukchi Sea from 10 through 25 September 2013 was conducted. During the study period, a strong wind event (SWE) was observed on 18 and 19 September. The abundance of microplankton was 2.6 to 17.6 cellsmL-1, with a maximum abundance being reported at 20m on 22 September, while diatoms were the most dominant taxa throughout the study period. The abundance of diatoms, dinoflagellates and ciliates ranged between 1.6 and 14.1, 0.5 and 2.4 and 0.1 and 2.8 cellsmL-1, respectively. Diatoms belonging to 7 genera consisting of 35 species (Cylindrotheca closterium and Leptocylindrus danicus were dominant), dinoflagellates belonging to 7 genera consisting of 25 species (Prorocentrum balticum and Gymnodinium spp. were dominant) and ciliates belonging to 7 genera consisting of 8 species (Strobilidium spp. and Strombidium spp. were dominant) were identified.Within the microplankton species, there were 11 species with abundances that increased after the SWE, while there was no species with an abundance that decreased following the SWE. It is conjectured that atmospheric turbulences, such as that of an SWE, may supply sufficient nutrients to the surface layer that subsequently enhance the small bloom under the weak stratification of the Chukchi Sea Shelf during the autumn months. After the bloom, the dominant diatom community then shifts from centric-dominated to one where centric/pennate are more equal in abundance.

Background Despite its ecological importance, little information is available regarding the spatial and vertical changes in the calanoid copepod community over large geographical regions. This study investigated the spatial and vertical patterns in calanoid copepod abundance and community structure using zooplankton samples collected between depths of 0 and 2,615 m across the North Pacific from 0° to 56°N. Results A total of 211 calanoid copepod species belonging to 66 genera and 24 families were identified. Calanoid copepod abundance decreased with increasing depth, and few latitudinal differences were detected. Across the entire region, species diversity peaked near 500 to 2,000 m in depth. The calanoid copepod community was separated into seven groups with distinct spatial and vertical distributions. For all groups, the number of species was low (28 to 37 species) in the subarctic region (north of 40°N) and high (116 to 121 species) in the subtropical-tropical region. The deepest group in the subtropical-tropical region was composed of cosmopolitan species, and this group was also observed in deep water in the subarctic region. Conclusions In deep water, most of the calanoid copepod community consisted of cosmopolitan species, while an endemic community was observed in the subarctic region. Because the food of deep-sea calanoid copepods originates from the surface layer, sufficient and excess flux in the eutrophic subarctic region may be responsible for maintaining the endemic species in the region.

Background An optical plankton counter (OPC) was used to examine spatial and temporal changes in the zooplankton size spectra in the neighboring waters of Japan from May to August 2011. Results Based on the zooplankton biovolume of equivalent spherical diameter (ESD) in 45 bins for every 0.1 mm between 0.5 and 5.0 mm, a Bray-Curtis cluster analysis classified the zooplankton communities into six groups. The geographical distribution of each group varied from each of the others. Groups with a dominance of 4 to 5 mm ESD were observed in northern marginal seas (northern Japan Sea and Okhotsk Sea), while the least biovolume with a dominance of a small-size class (0.5 to 1 mm) was observed for the Kuroshio extension. Temporal changes were observed along the 155° E line, i.e., a high biovolume group dominated by 2 to 3 mm ESD during May shifted to other size spectra groups during July to August. These temporal changes were caused by the seasonal vertical descent of dominant large Neocalanus copepods during July to August. As a specific characteristic of the normalized biomass size spectra (NBSS), the slope of NBSS was moderate (−0.90) for the Neocalanus dominant spring group but was at −1.11 to −1.24 for the other groups. Theoretically, the slope of the NBSS of the stable marine ecosystem is known to settle at approximately −1. Conclusions Based on the analysis by OPC, zooplankton size spectra in the neighboring waters of Japan were separated into six groups. Most groups had −1.11 to −1.24 NBSS slopes, which were slightly higher than the theoretical value (−1). However, one group had a moderate slope of NBSS (−0.90) caused by the dominance of large Neocalanus copepods.

The seasonal and inter-annual changes in the asymmetry of female insemination and the male leg 5 of the planktonic calanoid copepods Metridia okhotensis and M. pacifica were investigated in the Okhotsk Sea. An inter-species comparison of both parameters was also carried out on seven Metridia species collected from oceans throughout the world. For M. okhotensis from the Okhotsk Sea, most of the females showed left-side insemination (annual average: 95.7%) and most of the males showed left-side asymmetry (99.7%) of the long inner process of the second exopodal segment in the fifth leg throughout the year. However, sympatric M. pacifica showed different ratios of asymmetry for female insemination and male morphotypes with a left : right = 1 : 2 ratio throughout the year. For the seven Metridia species from the global oceans treated in this study, ratios of asymmetry for female insemination and male morphotypes were correlated with each other. One-sided insemination (i.e., only left or only right insemination) was a common pattern for various Metridia species from global oceans, but their ratios varied by species. Previously, low hatching rates (29-68%) of eggs were reported for various Metridia spp. in laboratory experiments, but the reasons for these low rates were unclear. Because each spermatheca of Metridia spp. is connected to the oviduct on the same side, either left or right, this suggests that half of the eggs produced by unilaterally inseminated females remain unfertilized. The morphology of the genital structures and literature data of the egg hatching rates of Metridia spp. indicate that almost half of the eggs produced by females are not viable and are, thus, wasted.

Winter ice cover of the Arctic Ocean makes year-round zooplankton sampling by plankton net a difficult task. Therefore, the collection of copepods with a sediment trap can be a powerful tool. In the present study, we analysed the seasonal changes in the population structures of five dominant planktonic copepods (Oncaea parila, Calanus hyperboreus, Metridia longa, Paraeuchaeta glacialis and Heterorhabdus norvegicus), which were collected using a sediment trap rotated at 10-15day intervals moored at 184-260m in the Northwind Abyssal Plain (75 degrees 00N, 162 degrees 00W) of the western Arctic Ocean from October 2010 to September 2012. Oncaea parila C6F with egg sacs occurred throughout the year, and the total abundance and composition of early copepodid stages (C1-C3) had two peaks each year. Calanus hyperboreus was dominated by C6F throughout the year, and their maturation was observed during February to May. Metridia longa C6F had a clear seasonality in lipid accumulation and gonad maturation: high lipid accumulation was observed from October to February, whereas gonad maturation occurred from March to September. Paraeuchaeta glacialis C6F also showed seasonality in lipid accumulation and gonad maturation, although their seasonal patterns varied from those of M. longa: high lipid individuals were abundant from February to April and mature individuals dominated from October to November. Heterorhabdus norvegicus showed seasonal changes in population structure as well: C1, C5, and C6M dominated from April to May, November to February and August to October, respectively. The life cycle patterns of these species are compared with those reported from other areas. While the results obtained by a sediment trap are inevitably subject to collection bias (i.e. passive collection at a fixed depth), a sediment trap should be considered as a powerful tool for the evaluation of the life cycle of planktonic copepods, especially in ice-covered oceans.

Several aspects of the ecology of planktonic copepods (vertical distribution, abundance, community structure, population structure and body size) were evaluated and compared between communities in the autumn, in the Okhotsk Sea and the adjacent Oyashio region in the western North Pacific. Vertically, copepods were concentrated primarily at depths of 250 to 500m in the Okhotsk Sea but near the surface in the Oyashio region. The abundances of most of the copepods were greater in the Oyashio region with the exception of Metridia okhotensis, which showed significantly greater abundance in the Okhotsk Sea (30 times greater) and dominated the copepod community, accounting for approximately 70% of total copepod abundance. The population structure of the dominant copepods in the Okhotsk Sea was dominated by late copepod stages, suggesting that these copepods were in the resting phase. The prosome lengths of most of the copepods were larger in the Okhotsk Sea than in the Oyashio region and the larger body size is probably due to the lower habitat temperatures. The special ecological characteristics of planktonic copepods in the Okhotsk Sea are possibly related to the development of a strong pycnocline in the Okhotsk Sea. The consequences of differences in copepod communities between regions were discussed from the viewpoints of life cycle timing and the scale of active vertical flux.

Mesoscale anticyclonic eddies have been observed south of the Aleutian Islands. Eddies farther east, in the Gulf of Alaska, are known to transport coastal water and coastal zooplankton to the offshore open ocean. The impacts of mesoscale anticyclonic eddies formed south of the western Aleutian Islands (Aleutian eddies) on the zooplankton community are not fully understood. In the present study, we describe zooplankton population structures within an Aleutian eddy and outside the eddy during July 2010. Based on the sea-level anomaly, the Aleutian eddy was formed south of Attu Island (172 degrees 54'E) in February 2010, and it moved southeastward in the next 5 months. Large oceanic copepods, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica were more abundant inside the eddy than the outside. Inside the eddy, the life stage distribution of N. cristatus was more advanced than that outside, and Neocalanus spp. had accumulated more lipids. These conditions probably reflect the greater primary production in the eddy, production enhanced by nutrients advected into the eddy. The Aleutian eddy contained mostly oceanic copepods because it was formed in the offshore water and/or eddy-eddy interaction occurred after its formation. The sufficient food condition in the eddy presumably resulted in higher growth and survival rates of these oceanic copepods, resulting in the greater abundance, advanced development stages and greater lipid accumulation.

Seagrasses are known to have allelopathic activity to reduce growth of phytoplankton. We found growth-inhibiting bacteria (strains E8 and E9) from Zostera marina possessing strong activity against the toxic dinoflagellate Alexandrium tamarense. Strain E9 markedly inhibited growth of A. tamarense even with initial inoculum size as small as 2.9 cells ml(-1). This bacterium also had growth-inhibiting effects on the red-tide raphidophytes Chattonella antiqua and Heterosigma akashiwo, the dinoflagellate Heterocapsa circularisquama, and the diatom Chaetoceros mitra. Small subunit (SSU) ribosomal DNA (rDNA) sequencing analysis demonstrated that the most probable affiliation of these strains was Flavobacteriaceae, and proved that another inhibitory bacterial strain (E8) was the same species as strain E9. Two other bacterial strains (E4-2 and E10), showing different colony color and isolated from the same seagrass sample, revealed no growth-inhibiting activity. Interestingly, strain E4-2 showed the same sequences as E8 and E9 (100 %), and strain E10 matched E8 and E9 with 99.80 % similarity. Growth-inhibiting bacteria against the toxic dinoflagellate Alexandrium tamarense associated with seagrass, such as Flavobacterium spp. E8 and E9, are able to repress shellfish poisoning besides the allelopathic activity of seagrass itself.

To examine seasonal changes in the mesozooplankton community, analyses were made on the swimmer samples (>1 mm) collected by a sediment trap mooring at 184 m depth on the Northwind Abyssal Plain in the western Arctic Ocean during October 2010–September 2011. The zooplankton swimmer flux ranged from 5 to 44 ind. m−2 day−1 and was greater during July to October; copepods were the dominant taxon. Based on the zooplankton swimmer flux, cluster analysis classified samples into three groups (A, B-1 and B-2). The occurrence of each group showed clear seasonality; group A was observed during July to October, group B-1 was seen in November to January and group B-2 during March to June. The seasonal variability in population structures of four dominant copepod swimmers was clearly different between the species. Most Calanus hyperboreus were copepodid stage 6 female (C6F) throughout the year. For Metridia longa and Paraeuchaeta glacialis, C6Fs dominated during January to May, and early copepodid stages increased during June to October. Heterorhabdus norvegicus was dominated by stage C5 during November to February, and C6F/M during March to May. Since Pacific copepods (Neocalanus cristatus) occurred in significant number during August–September, possible causes are discussed.

Pelagic Mysidacea and Decapoda have important roles in marine ecosystems. However, information on their life histories is extremely limited. This study aimed to evaluate the life cycles of pelagic Mysidacea and Decapoda in the Oyashio region, Japan. Production of the four dominant species was estimated by combining body mass (DM) data and abundance data Mysidacea belonging to 5 species from 5 genera occurred in the study area. Their abundance and biomass ranged between 11.7-50.1 ind. m(-2) and 1.2-7.9 g wet mass (VIM) m(-2), respectively. Six species from 6 genera belonged to Decapoda, and their abundance and biomass ranged between 9.0-17.3 ind. M-2 and 3.0-17.3 g WM M-2, respectively. Based on body length histograms, there were two to four cohorts for the three dominant mysids and one dominant decapod on each sampling date. Life histories of the two numerically dominant mysids (Eucopia australis and Boreomysis californica) followed similar patterns: recruitment of young in May, strong growth from April to June, and a longevity of three years. Life cycles of the two minor species (the mysid Meterythrops microphthalma and the decapod Hymenodora frontalis) were not clear because of their low abundance. The timing of recruitment of the young and the strong juvenile growth for the two dominant mysids corresponds with the season when their prey is abundant. The annual production of the dominant mysid species was 14.0 mg DM M-2 (B. californica) and 191.8 mg DM m(-2) (E. australis). Annual production/biomass (P / B) ratios ranged between 0.242 (H. frontalis) and 0.643 (M. microphthalma). Compared with other regions, the Oyashio region showed high production and low P / B ratios. The high production in the Oyashio region may be related to the high biomass of these species. Because of the low temperature conditions (3 degrees C), pelagic mysids and decapods in the Oyashio region may have slower growth, longer generation times and lower P / B ratios than in other oceans.

The assimilation efficiency of zooplankton is an essential parameter required to estimate energy transfer to higher trophic levels in marine ecosystems. However, little information is available for large oceanic copepods, especially the Neocalanus and Eucalanus species dominant in the subarctic Pacific. In this study, the assimilation efficiencies of the C5 stages of Neocalanus cristatus, Neocalanus flemingeri and Eucalanus bungii were evaluated using eight phytoplankton species as food. The average assimilation efficiencies of N. cristatus, N. flemingeri and E. bungii ranged between 45 and 66%, 44 and 66% and 34 and 65%, respectively. The assimilation efficiency was highly variable depending on the food phytoplankton species. In all species, the assimilation efficiency showed a significant negative relationship with the ash content of the phytoplankton (r2 = 0.79–0.87, p < 0.001). The assimilation efficiency of large-body sized N. cristatus for large-sized diatoms was higher than for the other copepod species. In population models of N. cristatus, changes in assimilation efficiency affect the growth and survival rates of the population. The Lagrangian ensemble model (LEM) for N. cristatus showed that, for assimilation efficiencies less than 57%, the population could not be maintained. Because variations in assimilation efficiency may have significant effects on the copepod population, their variability should be incorporated into marine ecosystem models in the future.

Stratified zooplankton sampling was conducted in the subarctic Pacific in June 2009 at four stations along 47°N from 0 to 3,000 m depth to evaluate longitudinal changes in population structure and vertical distribution of the dominant copepod species. At the westernmost station (160°E), the population structure of Eucalanus bungii and Metridia pacifica was dominated by early copepodid stages. In E. bungii, nauplii were abundant and adult females had developed ovaries at 160°E, while at the three stations to the east (167°E, 174°E and 179°W), no E. bungii nauplii were collected, and the resting stages were dominant. This suggests the species was reproducing near 160°E and in diapause in the east. In all three Neocalanus species analyzed (N. cristatus, N. flemingeri and N. plumchrus), late copepodid stages were dominant at the eastern three stations. Lipid accumulation in the fifth copepodid stage of Neocalanus spp. was greater in the west than in the east. This probably resulted from better food conditions and lower temperatures in the west, where copepods could consume more food during development than in the east.