The strawberry conch, Strombus luhuanus, is exploited as a fishery resource during its reproductive season in Japan, and the degree of fishery exploitation might therefore affect the reproductive potential of this species. From May to August in 2003 and 2004, we compared population and reproductive parameters of S. luhuanus, including population density, size frequency, density of egg masses, egg tube length and diameter, and egg size and number, between a highly exploited population in Uranouchi Inlet and a less exploited population around Okinoshima island. Both sites are located along the Pacific coast of Shikoku. Mean shell length of the Uranouchi population was greater than that of the Okinoshima population, and egg tube length and diameter of the Uranouchi population were larger than those of the Okinoshima population, but the density of egg masses was much lower in Uranouchi than at Okinoshima. This suggests that fishery operations can disturb the mating and/or breeding of this species resulting in reduced fecundity of the Uranouchi population. Conchs engaged in reproductive behavior, as well as conch egg masses, were observed more frequently on mixed sediment with sand and pebbles than on uniform sediment composed either of mud, sand, or pebbles. Sediment type might be important for the reproduction of S. luhuanus; but immature conchs were also most abundant on mixed sediment. This type of sediment might, however, be preferred by S. luhuanus irrespective of state of maturity, for other reasons such as ease of burrowing to avoid predation.

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Arthritica reikoae (Suzuki & Kosuge 2010) is an ovoviviparous microbivalve inhabiting estuarine tidal flats in inner bays in Japan. Although A. reikoae is the dominant bivalve species in the tidal flats, its ecological characteristics remain largely unknown. We conducted ecological studies of populations in Tokyo Bay. The field research revealed that in the summer of 2010, more than 90% of adult A. reikoae bred as females. This species might be hermaphroditic similar to other congeneric species. Mature A. reikoae held 13.0 ± 5.7 (Mean ± S.D.) shelled larvae, and the shell length of the larvae just before release was about 0.3 mm. The breeding cycle was estimated to be 20 days based on laboratory culturing. A. reikoae produces large benthic larvae with limited dispersal but high survival. A. reikoae inhabits estuaries and brackish lakes where it may be exposed to a wide range of salinity. The results of a salinity tolerance experiment indicated that A. reikoae is euryhaline, which lets it inhabit such environments. The population density significantly increased through the breeding season, and the maximum density reached 1,578.4 indiv./100 cm² in the estuary of the Tama River.

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We investigated macrozoobenthos fauna in 26 tidal flats existing in foreshores, lagoons, tidal rivers and small artificial channels along the entire coast of Tokyo Bay to evaluate the distribution and population rarity of the tidal flat species. A total of 98 species were recorded, of which 31 were regarded as rare species that need to be conserved. The rare species were found mainly in artificial channels with a salt marsh. Among these rare species, the mud snails Batillaria multiformis, Cerithidea rhizophorarum, and Cerithideopsilla djadjariensis; the varunid crabs, Chasmagnathus convexus and Helicana japonica; the sesarmid crab Sesarmops intermedium; and the camptandriid crab Deiratonotus cristatus are considered rare not only in Tokyo Bay, but also along the coasts of the Japanese main islands, suggesting these species should be the first focus of conservation. Furthermore, the occurrence of rare species tended to be restricted to the eastern shore of Tokyo Bay, where tidal flats (Obitsu Estuary, Edogawa Drain and Tamagawa River) and artificial channels with a salt marsh are located. From the viewpoint of ecological connectivity between the tidal river and the artificial channels, these findings suggest that restoration of tidal flats with salt marshes along the shoreline of the bay is important to conserve the biodiversity of tidal-flat macrozoobenthos in Tokyo Bay.

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The distribution pattern of Pillucina pisidium in intertidal Zostera japonica beds at Uchinoura, Tanabe Bay, Wakayama, Japan was studied and compared with other environments. P. pisidium was distributed widely throughout the study area. The mean density (± SD) of P. pisidium was 1,892.9 ± 3,795.3 and 394.7 ± 265.1 individuals/m² in the Z. japonica beds and the bare sandy bottom, respectively. The mean wet weight at each location was 32.4 ± 46.7 and 14.4 ± 13.8 g/m², respectively. Despite the large differences between the two means, neither differed significantly between the two locations. The density and the wet weight of P. pisidium were each compared among the four areas: area facing the open ocean, area within an enclosed inlet, river mouth area and tidal flat area. Both were highest in the Z. japonica beds in the area facing the open ocean and lowest in the bare sandy bottom in the area within enclosed inlet. The mean shell length of P. pisidium was highest in the area facing the open ocean and lowest in the river mouth area. The density and the wet weight of P. pisidium were each both negatively correlated with the total organic carbon (TOC) and the silt-clay content in the sediment. These results show that P. pisidium is densely distributed in the intertidal zone, especially in Z. japonica beds, with low TOC and silt-clay contents. In conclusion, Z. japonica beds presumably play an important role in providing suitable habitats for P. pisidium.

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The feeding behavior of the leucosiid crab Pyrhila pisum was observed, and its diet composition was analyzed, on a sandy tidal flat of Hakata Bay, Fukuoka, Japan during the day from May to September in 2011 and 2012. Pyrhila pisum were seen mostly wandering, resting, or engaging in mating behavior; only a few crabs exhibited feeding behavior. The crabs were carnivorous, eating various small organisms including bivalves, snails, hermit crabs, brachyuran crabs, isopods, amphipods, flatworms, and fish, but their diet was highly biased to bivalves, especially Arcuatula senhousia and Venerupis philippinarum. In addition, diet preferences differed annually: A. senhousia predominated as prey through the 2011 survey, but in 2012 V. philippinarum predominated in the early season while A. senhousia became the dominant prey later. Pyrhila pisum usually ate small, thin-shelled shallowly buried living animals, but large, dead V. philippinarum occurred abundantly in the early season of 2012, and P. pisum could easily consume their soft tissues. In contrast, P. pisum did not actively capture benthic animals such as hermit crabs, snails, or varunid crabs, which were abundantly on the tidal flat, and showed no interest in jellyfish, green algae, or vascular plant detritus for both male and female crabs. The preference for bivalves was similar, but males tended to eat more snails (Batillaria sp. and Nassarius festivus) than females did, probably because their larger chelipeds better allowed them to handle snails. In sum, P. pisum is a predator of small and slow-moving benthic animals distributed on or just under the substrate's surface and a scavenger biased to preying on bivalves.

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In order to predict the expansion of the golden mussel (Limnoperna fortunei) population in Lake Kasumigaura, Japan, we investigated its spatial distribution in 2012 and compared it to the distribution in 2006. In 2012, mussels were found in 104 (83.2%) of 125 sampling sites evenly spaced around the entire shoreline of the lake. No mussels were found near the mouth of the Koise River at the north end of the lake. On average, the mussel density (the number collected in 10 minutes by a single researcher) at a given site was 3.8 times higher in 2012 than in 2006. Colonization of a vacant site from the nearest inhabited site was explained primarily by distance, whereas habitat classification of a vacant site had no significant effect. There was a 50% probability that golden mussels would colonize a vacant site as distant as 10.96 km from the nearest inhabited site within six years. Given this colonization potential, we predict that golden mussels will spread over the entire shoreline by 2018 at the latest.

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