In Hokkaido, Japan, the toxic dinoflagellate Alexandrium catenella (A. tamarense species complex Group I) is the source of frequent contamination of bivalves with paralytic shellfish toxins over the last 40 years, whereas A. pacificum (Group IV) has rarely been reported. Recently, A. pacificum cells were identified based on their morphology and DNA sequences in Hakodate and Funka bays, southern Hokkaido. To understand their seasonal occurrence, A. pacificum and A. catenella cells in the two bays were detected using microscopy and multiplex polymerase chain reaction (PCR) over a 2-year period (May 2018–May 2020). Microscopic observation showed that cells of A. pacificum, a species without the ventral pore between the 1′ and 4′ plates, occurred in Hakodate Bay from July to November 2018 and in July 2019, with a maximum cell density of 4450 cells L⁻¹ in November 2018. It also occurred in Funka Bay in October 2018, with a maximum cell density of 50 cells L⁻¹. Multiplex PCR using Alexandrium species-specific primers showed a similar seasonal occurrence of A. pacificum in Hakodate Bay. In contrast, A. catenella was found from February to May in Funka Bay but its occurrence was uncertain in Hakodate Bay because the microscopy and PCR tests were not simultaneously positive. The occurrence of A. pacificum was limited to the period (July to November) of optimum water temperature for growth (15–25℃), suggesting that the occurrence of motile cells was affected by water temperature. When A. pacificum bloomed at a relatively high density in Hakodate Bay during autumn 2018, warmer water temperature and lower salinity in the surface layer were observed compared to the previous 5 years. These environmental conditions were thought to be established due to warmer air temperatures, a longer sunshine duration, and a large amount of precipitation from October to November 2018. Such environmental and meteorological conditions were suggested to be suitable for the growth of A. pacificum in Hakodate Bay.

Limacina helicina, a species of Pteropoda (Cuvier, 1804), plays an important role in the food web and carbon cycle in subpolar and polar regions. The presence of aragonite unsaturated water in the Pacific sector of the Arctic Ocean necessitates the need to examine damage caused by ocean acidification on species with aragonite shells. According to previous studies that examined the impact of acidification on shell-bearing species by employing incubation experiments, young stages (veligers and juveniles) are more vulnerable than adults. In the present study, vertical distribution of the young stages of L. helicina in the Arctic Ocean during autumn was observed to evaluate the effects of environmental factors on their distribution. Veligers and juveniles showed high abundances from the surface to 30 m depth in the basin regions around the Chukchi Plateau (Stations 39, 45, and 49) but were restricted to a depth of 20–30 m, overlying a strong halocline formed by the inflow of less saline water. Veligers were predominant in the basin regions, indicating that active reproduction occurred in September. Since adult females involved in reproduction were abundant in the shelf regions, their reproduction patterns varied with different periods and regions. Unsaturated aragonite waters and damaged shells were not observed in the study area, possibly due to dilution by sea ice melt water inflowing from the shelf regions. This study showed that the distribution of the young stages of L. helicina was predominantly concentrated in the upper 30 m of the basin due to stratification with a strong halocline in the shallow layers caused by the inflow of sea ice melt water.

The prey of whale sharks (Rhincodon typus) visiting the northern Satsunan area (western North Pacific Ocean) was investigated using microscopic and metabarcoding analysis of their faecal pellets. The stable isotope ratios of the dorsal fin and faecal pellets from the whale sharks were compared with those of their potential prey (plankton and fish larvae). Microscopic analysis identified protozoans (foraminifera) and metazoans (copepods, ostracods, and amphipods) but unclassified material was predominant in their faecal pellets. Metabarcoding analysis detected metazoans in the faecal pellets, represented by copepods, ostracods, amphipods, hydrozoans, and tunicates. Comparison of stable isotope ratios (δ¹³C and δ¹⁵N) from their dorsal fin and faecal pellets with those of zooplankton in the northern Satsunan area showed different feeding histories for the whale sharks appearing in the northern Satsunan area.

The sakura-ebi [Lucensosergia lucens (Hansen, 1922)] fishery in Suruga Bay, Japan, sharply declined in 2018 and has not yet recovered (140 tons was reported for the spring catch in 2021). I have proposed two causal hypotheses to explain the slump:1) a decline in the spawning population in the inner area of the bay due to excessive fishing in the spring season and a shift in the spawning peak from early summer to late summer-autumn, and 2) a decline in biological productivity in the inner and western area of the bay after the 1980s due to recent coastal development and environmental deterioration. A delay in the spawning peak may causes a shift in the main spawning area from the inner area to the western area of the bay.

Test the first hypothesis; we performed numerical experiments to investigate the transport processes of eggs and larvae of L. lucens in Suruga Bay, focusing on the physical effects of the current with a different peak in the spawning season and in the area using the particle tracing method. Particles regarded as eggs and early larvae were passively transported in flow fields for 1 month after being deployed at three locations: a) off the mouth of the Fuji River, the inner area, b) off the mouth of the Abe River, the western area, and c) off the mouth of the Oi River, in the southwestern area. The particles were tracked by two ocean circulation models using simplified hydrographic conditions in September 2007 and with predicted and real observations of current flow from 1 June to 1 October, 2020.

In the first experiment, using simplified conditions without considering the effect of the Kuroshio current, approximately half of the particles deployed in the 0–24 m layer off the mouth of the Fuji River remained in the inner area of the bay after 1 month. Nearly 90% of the particles remained in the bay. However, only 22% of the particles deployed off the mouth of the Abe River and less than 10% deployed off the mouth of the Oi River remained in the bay after 1 month. In the case where the particles were deployed in the 24–60 m layer off the mouth of the Fuji River, 100% remained in the bay. In the second experiment with predicted and real observations of the current flow, 54% of the particles that were deployed off the mouth of the Fuji River remained in the bay, whereas only 23% from off the mouth of the Abe River and 15% from off the mouth of the Oi River remained in the bay after 1 month. In Sagami Bay, 76% of the particles that were deployed in the 25–45 m layer off the mouth of the Sakawa River were run out from the bay after 1 month. These results indicate the importance of the retention area in the inner area of Suruga Bay, where the eggs and larvae can stay for a long time.

A good correlation was observed between the spawning peak during 1991 to 1997 and catch per unit effort (CPUE) (catch [kg] per 30 min tow) of the 0-year class shrimp, suggesting that earlier spawning in July causes an increase in the 0-year class shrimp population for the autumn catch.

Thus, I believe that the first hypothesis is correct. Delays in peak spawning time cause a shift in the main spawning area from the inner area to the western and southwestern area of Suruga Bay, and therefore cause a remarkable loss of larvae to outside the bay. To restore the shrimp stock, it is essential to reduce fishing effort during the spring catch to facilitate spawning of larger eggs in June/July in the inner area, and hence many larvae remain and grow in the bay. Distinct differences exist in the hydrographic conditions between Suruga Bay and the neighbouring Sagami Bay. The eggs and larvae in Sagami Bay are easily run out from the bay, and hence the population cannot be maintained to the level of commercial fishery.

In recent years, learning styles involving observation and experimentation have been recommended for schools as a form of active learning. The National Institute of Polar Research is promoting the improvement and increased production of resin-embedded zooplankton specimens for use in marine education. Based on trials and questionnaires completed by current teachers, we created a marine educational workshop kit comprising resin-embedded specimens, observation tools, a booklet, worksheets, introductory videos for participants, and workshop programs. The kit is designed mainly for junior high school students and can be used for remote (online) workshops to facilitate online learning necessitated by the COVID-19 pandemic. We have requested school teachers to try using the kit and identify various applications of the kit. We began loaning out the kits in November 2021. We hope that many teachers who have not had the chance to conduct marine education will start using this kit.