Because sea stars are the primary predators of the Japanese scallop, Mizuhopecten yessoensis, they are being removed from scallop fishing grounds, despite the lack of information on their predatory impacts. We experimentally examined the predatory behavior of the sea stars Asterias amurensis and Distolasterias nipon on the Japanese scallop. In the first experiment, we hypothesized that sea stars respond to distant chemical cues from live scallops. However, the results showed that neither A. amurensis nor D. nipon responded to the chemical cues of live intact animals, though it is commonly known that they respond to the chemical cues of carrion. We also examined the effects of the relative sizes of the sea stars to the scallop on their predator-prey relationship. We altered the body size ratios of the Japanese scallop to A. amurensis in the summer and winter, and to D. nipon in the summer, and observed the scallops’ survival. In all experiments, logistic regression models were applied to changes in survival under different prey-to-predator size ratios, which were calculated by dividing the scallop size by the sea star size. Our results suggested that survival of the Japanese scallop rapidly increases with increasing body size. The ratios at which mortality was 50% provide an important parameter in estimating the predation risk from sea stars in scallop fishing grounds. Our study will contribute to the effective and responsible management of Japanese scallop mariculture.

We investigated the life history traits of a population of the sesarmid crab, Clistocoeloma villosum on the southern coast of Izu Peninsula, the known eastern range limit of the species distribution. Traits investigated included new recruitment, reproduction, and overwintering ability, to determine whether the species had become established at the edge of its distribution range. During the study period, 902 individual C. villosum were obtained, including 479 males, 386 non-ovigerous females, 2 ovigerous females, and 35 sex-undetermined juveniles. Because population numbers and changes in the size structure were consistent over the study period, it is highly likely that C. villosum had overwintered successfully in the study site. Additionally, intermittent new recruitment of juvenile crabs was apparent over the year. However, only two ovigerous females were recorded in August, so the reproductive period was very short compared with most sesarmid crabs in East Asia. Such weak reproductive activity together with the likelihood of planktonic larval recruitment via the warm Kuroshio Current most likely indicates that the southern Izu Peninsula population of C. villosum represents a sink population.

The benthic ctenophore Vallicula multiformis Rankin, 1956 (Ctenophora, Platyctenida) was originally described from Jamaica. We found the species in an aquarium during our survey of jellyfish from Palawan Island, the Philippines. Molecular analysis of the species confirmed the morphology-based identification of the samples. This discovery is the first report of the occurrence of species from the western Pacific area.

A new occurrence of the hydrozoan Olindias muelleri and the first case of an associated envenomation were recorded from the eastern Aegean Sea. A total of eight adult medusae of O. muelleri were collected near the surface on 22 and 23 June 2018 in Boyalık Bay, Turkey following a sting report by a bather. Medusae were identified as O. muelleri using morphological keys and confirmed through COI-based DNA barcoding. The presence of O. muelleri may have not been noticed in the past in the region or it could stem from a recent range expansion from other parts of the Mediterranean Sea. Monitoring is needed to better understand the spread of O. muelleri and the threat it presents for human health and coastal tourism in Çeşme.

The brackish-water calanoid copepod known as Pseudodiaptomus inopinus in the mainland of Japan consists of two genetically separate species. One is P. japonicus, which was once synonymized with P. inopinus but was recently revived. This paper describes the other species as Pseudodiaptomus yamato n. sp., which is confirmed to have morphological differences from P. inopinus s.s. based on specimens from the type locality (Lake Taihu, China) of the latter. We also redescribe P. japonicus and P. inopinus s.s. for comparative purposes. The three species are distinguishable by the combination of the following morphologies: 1) weak or prominent posterior round projections of the female last pediger; 2) relative length of posterior processes of the female genital operculum; 3) presence or absence of medial spinules on the first exopodal segment of the female leg 5; and 4) the size of spinules at the center of the ventral surface of the male second urosomite. Significant inter-population variation is observed in some spinules of P. japonicus. The past and present records indicate that Pseudodiaptomus yamato n. sp. is endemic to Japan and confined to the coasts affected by the warm Kuroshio Current from western Kyushu to the middle of Honshu, while P. japonicus is widespread in northern East Asia without overlapping the range of P. yamato n. sp. The range of Pseudodiaptomus inopinus s.s. most certainly does not extend to those of P. yamato n. sp. and P. japonicus.

Digestion time and feeding of the pelagic chaetognath Zonosagitta nagae, which occurs predominantly in warm waters around Japan, were investigated in the laboratory. Young individuals of Z. nagae ranging from 4.1–7.6 mm in body length were used for the experiments with adult females of the copepod Acartia steueri as prey. The mean digestion time of Z. nagae was 115±3 minutes at 20°C. Temporal change in individual’s feeding intensity was observed every 1.5 h for 24 h to determine the diel feeding pattern, feeding interval, feeding rates and daily ration. Almost all individuals showed no clear diel rhythm within 24-h at 20°C under 12L:12D cycle; time interval between feeding was 4.5–6 h (mode) for individuals that ingested multiple copepods. The number of copepods ingested by a chaetognath ranged from 0 to 5 and on average 2.6 copepods were consumed a day per individual. Specific daily ration in most individuals corresponded to ca. 50% of its dry weight while some individuals showed the extremes of non-feeding or voracious feeding (>200% d⁻¹), indicating that some of the young Z. nagae had an intermittent feeding mode, which would be adaptive to save energy expenditure at low prey densities and to reduce mortality by lowering the risk of predation.

Lingula species are brachiopods inhabiting the tidal flats. In Japan, they are threatened by the marine pollution and decreasing habitat. Although these brachiopods are endangered in Japan, little is known about their life history. The aim of this study was to examine the life history characteristics of Lingula anatina after settlement in Kasari Bay, Amami-Oshima Island, Kagoshima, Japan, by measuring the gonad index and seasonal changes in size distribution. The results revealed that the breeding season of this species is from summer to early autumn, which is longer than that of other populations in Japan. Their settlement starts in winter after the planktonic stage, and they reach maturity after two or three years. Their longevity is more than four years and they breed every year. Lingula species are under taxonomic revision; therefore, for convenience, we named the species in Amami-Oshima as Lingula anatina.

The Seven-arm Octopus, Haliphron atlanticus, was observed holding a coronate medusa, Periphyllopsis braueri, by the remotely-operated vehicle (ROV) Dolphin-3K. The jellyfish was held by the aboral surface within the arms of the octopus. Although obscured at first, the lappets and tentacles of the jellyfish became exposed as the octopus turned toward the ROV. Based on recent reports, it appears that gelatinous prey species are important components of the diet of Haliphron. Furthermore, gelatinous prey may be generally underappreciated as a food source and important trophic link in open-ocean, deep-sea, pelagic food webs.