This study conducted laboratory experiments to investigate the relationship of polyps to water temperature and food concentrations in Aurelia malayensis from a subtropical zone. The growth of polyps was found to be unrelated to water temperature, while significant differences were observed between feeding and no-feeding experimental rearing schemes. Polyp size increased in all feeding schemes and decreased in all no-feeding schemes, suggesting a direct positive relationship between feeding and polyp growth. Polyp asexual reproduction was suppressed at a lower temperature (20°C) under a low food concentration and strobilation was observed even under constant water temperatures. These findings suggest that A. malayensis is adapted to an environment of high water temperature with low levels of fluctuation and low food concentrations. Ephyrae were produced at water temperatures of 25°C and 30°C at both high and low food concentrations in all four rearing schemes. At water temperatures of 30°C and with low food concentrations, the size of liberated ephyrae was significantly smaller than in the other three schemes. These results suggest that at high water temperatures and low food concentrations, small ephyrae are liberated. This study reveals the effects of water temperature and food concentration on the polyp stage of A. malayensis, suggesting that this species is particularly adapted to high water temperatures. This also suggests that in the future, as global warming progresses, medusae blooms of A. malayensis may occur. From this perspective, it is necessary to monitor the population dynamics of A. malayensis and focus intently on its trends.

Seasonal variation in the abundance of the large mucilage colony-forming diatom Thalassiosira diporocyclus was investigated from October 2020 to January 2022 in Minamata Bay. This diatom is a red-tide forming harmful species that causes the bleaching of seaweed culture (Pyropia thalli) due to nutrient exhaustion. The growth characteristics of T. diporocyclus were also examined in incubation experiments using a culture strain. Vegetative cells of T. diporocyclus were consistently detected in the water column throughout the year, making this first report that they have survived in the summer. The cell density of T. diporocyclus exhibited clear seasonal variation, with a peak (4.8×10³–8.5×10³ cells L⁻¹) in November and decrease in December in 2020 and 2021. High cell densities were observed in a narrower range of water temperature (21.0°C–21.2°C) and salinity (33.0–33.1). Nutrient concentrations increased throughout the water column in September, when stratification disappeared. However, the cause of the population decline in December remained unclear. Incubation experiments demonstrated positive growth of T. diporocyclus at 15°C–27°C and salinity levels of 25–35 (0.63±0.02–1.29±0.02 d⁻¹). Thalassiosira diporocyclus could actively grow in almost all seasons in Minamata Bay. These results suggest that T. diporocyclus has an autochthonous life cycle in Minamata Bay.

The 11 March 2011 Great East Japan Earthquake generated a massive tsunami that triggered an extraordinary release of floating transoceanic marine debris. That floating debris subsequently landed on coastlines from Midway Atoll to the Hawaiʻian Islands and from south central Alaska to central California of North America. Two species of Caprella (Crustacea: Amphipoda: Caprellidae) were collected from a large concrete fisheries dock (approximately 20 m length) that was part of the floating debris, on Agate Beach, near Newport, Oregon, USA, on 5 June 2012. The caprellids recovered from the dock are identified as Caprella cristibrachium Mayer, 1903 and C. mutica Schurin, 1935. Caprella cristibrachium had not been observed previously outside of the Bering Sea to the Far East Asia. The robust body somites and short antennae and basis of gnathopod 2 make C. cristibrachium suitable for attaching the filamentous macroalgae and/or marine invertebrates on the large tsunami fishing dock. Caprella mutica, originally recorded from the Far East Asia, was previously introduced to Oregon, to other cold-water areas between northern California and Alaska, the eastern and western North Atlantic and to the southern hemisphere.

Owing to its particular mixotrophic nutrition, Prorocentrum cf. balticum has recently been suggested to contribute significantly to the biological pump in the world’s oceans. However, the physiological attributes that facilitate its distribution have not yet been investigated. We clarified the effects of temperature and light intensity on the growth of a strain of P. cf. balticum isolated from the Oyashio-Kuroshio Mixed Water region and then estimated its potential habitat in the western North Pacific in the context of global warming. In batch cultures maintained at 5°C–30°C, the highest growth was observed at 25°C, while the viable temperature range was estimated to be 6.03°C–29.4°C. At the six different light conditions tested (20–500 µmol m⁻² s⁻¹), growth rates were positively correlated with light intensity, except at 500 µmol m⁻² s⁻¹ where photoinhibition was observed. At 20°C, the maximum specific growth rate was calculated to be 0.661 day⁻¹ and the compensation light intensity and the saturation light intensity were 1.15 and 283 µmol m⁻² s⁻¹, respectively. These findings suggested that compared to other Prorocentrum species, P. cf. balticum is generally well suited to subtropical environments characterized by high light intensities. However, the potential to survive in mid-latitude environments that experience low temperatures during winter suggests a high probability of year-round occurrence at higher latitudes, including the Oyashio region, in the future.

Euchonoides is a genus of small sabellid worms composed of two valid species, E. moeone from Hawaii and E. bicincta from Kamchatka and Kurile Islands. We report here a third species from sandy mud sediments in Suruga Bay, Japan. Euchonoides shizuoka sp. nov. is characterized by several unique, distinctive features as follows: a laterally notched collar; a wide glandular ridge on chaetiger 2; enlarged thoracic chaetigers 5–8; distinctive glandular shields on thoracic chaetigers 6–8; an enlarged abdominal chaetiger 1; swollen pad-like structures on the ventral side of abdominal chaetiger 2; a pre-pygidial depression with lateral wings and an anterior bordering margin. A comprehensive description based on the external morphology and supplemented with scanning electron microscopy images, light microscopy, and line drawings, is provided.

Few studies have been carried out correlating environmental factors to spiny lobster Panulirus argus nutritional condition, topic undeveloped in Cuba. This study aimed to quantify the impact of biotic (food availability) and abiotic (temperature, salinity, and dissolved oxygen) environmental factors on lobster’s nutritional condition. Twelve sites, located in the Gulf of Batabanó, were sampled on Dry and Rainy seasons during 2011–2017 period. Blood refractive index (BRI) and total weight/carapace length relationship (Kcl) were determined. Benthos trawling was carried out to estimate benthic food availability (BFAI). Temporary variations of environmental variables showed a significant decrease only for BFAI. Salinity and dissolved oxygen were high during Dry season, but temperature was significantly less. BFAI did not show differences between Dry and Rainy, it was significantly correlated with both Kcl and BRI. Kcl was significantly impacted only by site variations (43.5% deviance explained). BRI was significantly impacted by site and BFAI variations (57.9% deviance explained). Among environmental variables only BFAI showed spatio-temporary variations like BRI, decreasing gradually from 2011 to 2017, partially explaining variations on lobster’s nutritional condition. Decreased food availability, which could be due to unfavorable environmental quality, causes lobster’s nutritional conditions to decline.

Red tides of harmful dinoflagellates Karenia spp. have recently occurred along the coast of Hokkaido, northern Japan, causing concern about the mass mortality of aquatic organisms. This study aimed to verify the lethal effects of Karenia mikimotoi on reared juveniles of two bivalves, the Yesso scallop Mizuhopecten yessoensis and Sakhalin surf clam Spisula sibyllae, and two echinoderms, the short-spined sea urchin Strongylocentrotus intermedius and Japanese common sea cucumber Apostichopus japonicus, which are industrially important species in Hokkaido. Their juveniles were exposed to seawater with four different densities of red tide-causing K. mikimotoi from 0 to 4.5×10⁴ cells mL⁻¹ for 48 h and then kept in the seawater without K. mikimotoi for 96 h for follow-up. The survival of the individuals was recorded every two days. The analysis using Firth’s bias-reduced logistic regression model showed that K. mikimotoi significantly affected the survival of the Yesso scallop, Sakhalin surf clam, and short-spined sea urchin within 96-h follow-up of the 48-h exposure, but did not significantly affect the survival of the Japanese common sea cucumber. The median lethal doses of K. mikimotoi at the end of follow-up were estimated as 2.40×10⁴ cells mL⁻¹ for the Yesso scallop, 3.32×10⁴ cells mL⁻¹ for the Sakhalin surf clam, and 4.45×10⁴ cells mL⁻¹ for the short-spined sea urchin. These results suggested that the sensitivities of species to K. mikimotoi toxicity differ.

We describe Paranthura oriens sp. nov. based on specimens collected from Tateyama, Chiba, Japan. Paranthura is the most speciose genus in Anthuroidea, with five groups defined by the condition of the pleonites. Our new species belongs in Group E, defined by having dorsally fused pleonites 1–5. It differs from the other 17 species in Group E in the following combination of characters: (1) the apical edge of the telson is rounded, not sharp, (2) the uropodal endopod is triangular and tapering, and (3) the uropodal exopod is narrow, 2.72–2.84 times longer than wide. We determined a partial cytochrome c oxidase subunit I (COI) nucleotide sequence for the new species.

Acartia omorii is a predominant planktonic calanoid copepod during winter and spring in temperate coastal waters of the Northwest Pacific. Seasonal occurrence of A. omorii in warm-temperate bays has been known to be restricted to the period with water temperatures below 20°C. However, we found an adult male of A. omorii in a sample from the eastern Seto Inland Sea in September 2023, when the water temperature exceeded 27°C. Rare summer occurrence of A. omorii in the same region was confirmed by re-examining the samples collected at >20°C in previous studies. Previous experimental studies on the species have shown that their biological functions related to population growth increase with rising temperature at around 20°C, which is inconsistent with the field observation that seasonal occurrence of the planktonic population ends when temperatures exceed 20°C. The reason for this inconsistency could be explained by mass mortality of the female after laying resting eggs, before the high temperature becomes detrimental to their biological functions. Individuals appearing in mid-summer are considered likely those hatched from resting eggs.