The present study was conducted to elucidate the distribution of the invasive alien snail Laguncula pulchella and its effect on the native mollusk populations in the Orikasa River Estuary, Iwate Prefecture after the 2011 Great East Japan Earthquake. Laguncula pulchella was the most abundantly distributed in the area with sandy sediment among the three survey areas. Although the number of L. pulchella increased in an area with gravelly sediment during the second year of the study period, the higher gravel content (>54%) might have inhibited the distribution of L. pulchella in another gravelly area. The clam Ruditapes philippinarum was the dominant species and main prey of L. pulchella in the study area. There was a positive correlation between predator and prey sizes, and the coefficient (0.53) tended to be lower than that reported by the earlier studies. In the estuary, L. pulchella might have preyed on clams smaller than its preferred size. The density of R. philippinarum decreased within the distribution area of L. pulchella; however, its density was maintained in the areas with gravelly sediment. These results indicate that the heterogeneity of sediment with gravel after the earthquake limited the distribution of L. pulchella, and thereby contributed to the maintenance of the native mollusk populations.

The objective of the present study was to elucidate the distribution characteristic of Neripteron pileolus (Neritidae, Gastropoda), one of the endangered species in Japan, at two tidal flats around the river mouth in Tokushima Prefecture, Shikoku Island. We investigated the distribution of gastropods including Neripteron pileolus and several environmental variables at (1) 70 (small scale) and 124 stations (large scale) at a reed marsh in the Yoshino River Estuary in October 2004 and 2007; and (2) 130 stations at the Katsuura River Estuary in October 2005. Assimineidae spp., Neripteron pileolus, and Cerithidea moerchii were the dominant species in the reed marsh at the Yoshino River. The population density of Neripteron pileolus in the Yoshino River was higher than that in the Katsuura River. Further, the reed density was almost similar between the Yoshino and Katsuura Rivers. However, the number of dead leaves of reed in the Yoshino River was 14 times higher than that in the Katsuura River. The small-sized Neripteron pileolus (< 11 mm) were found to be attached to the dead leaves of reed. The multi-regression analysis and decision tree at different time and space revealed that the number of dead leaves of reed is the most important environmental variable affecting the distribution of Neripteron pileolus

Ikedosoma elegans (Ikeda, 1904) (Annelida: Echiura: Thalassematidae) is a rare, large deep-burrowing spoon worm that has been observed only in Japan. This species was first described based on the specimens collected from Misaki, Sagami Bay (Kanagawa Prefecture), eastern Japan, in 1902. Since the first description, this species has not been collected until the recent studies, which reported that I. elegans was collected from Hamana Lake (Shizuoka Prefecture), Boso Peninsula (Chiba Prefecture), and probably Amakusa, Ariake Sea (Kumamoto Prefecture). Furthermore, the specimen collected from Takasu, Seto Inland Sea (Okayama Prefecture) in 1975 was identified to be I. elegans. In this study, we present a new locality of this species in Japan. We collected a large individual of I. elegans with a probably commensal scale worm (Polynoidae: Polynoinae) by using a yabby pump in a mud flat in the Doki River Estuary, which is facing the Seto Inland Sea, in Marugame (Kagawa Prefecture), northern Shikoku Island. To the best of our knowledge, the present study is the first record of I. elegans from Shikoku Island and the second record from the Seto Inland Sea, following a 42-year-old record from Takasu, Okayama.

The red-eared slider, Trachemys scripta elegans, is a freshwater turtle native to the South Central United States of America and Northeastern Mexico. It was introduced into Japan in the late 1960s and is currently the dominant and widely distributed species throughout the country. The species is salt tolerant, and its distribution has recently expanded into tidal flats; however, its ecology in the tidal flats is unknown. The aim of the present study was to analyze the diet of T. s. elegans inhabiting the tidal flats. We collected 46 individuals from the tidal flats and adjacent freshwater waterway of the Tanakagawa River in the Mie Prefecture in November 2014 and from April to November 2015. We compared the intestinal content of the turtles from both the habitats. They consumed a wide variety of plants and animals in both the habitats, with no difference between the habitats in terms of food intake per body weight. There was a higher ratio of animal to plant matter in juveniles and adults from the tidal flats than that in those from the freshwater waterways. In this animal matter, there was a high incidence of decapod species, such as the tidal flat crabs Helice tridens and Macrophthalmus japonicus. To the best of our knowledge, the present study is the first to suggest that the red-eared slider affects the tidal flat ecosystems by preying on the native tidal flat organisms.

The Japanese sea cucumber Apostichopus japonicus exhibits aestivation during high temperature season. During aestivation, they migrate to sheltered and dark microhabitats(under the surface of rocks and underneath rocks)and stop feeding and moving. Aestivation is commonly observed in the sea cucumbers inhabiting warm areas. However, in Hokkaido, which is a cool temperate zone, there is a controversy whether the sea cucumbers aestivate because of the relatively low temperature even during summer. A field experiment was conducted to verify the occurrence of aestivating individuals in Funka Bay, Hokkaido. A total of 50 cages were set up at 7 m depth, in which an individual sea cucumber and a concrete block with chambers were placed in each cage. We observed the attaching point of each individual within a cage by SCUBA diving every alternative day from late July to the mid-November 2012 for 4 months. The observations revealed that aestivation often occurred intermittently during the experiment period. The longest successive aestivation period was 12 d; however, several individuals did not aestivate. The mean bout of successive aestivating period was estimated to be 3 d. A maximum of 25% and 75% of the individuals exhibited aestivation and attached onto the shaded sites, respectively. These values correlated positively with the seawater temperature. The body weight of the sea cucumbers significantly decreased during the summer months. These results confirmed that the sea cucumbers in Funka Bay aestivate during summer even in the cool temperate zone. The aestivation behavior, such as moving into sheltered areas under rocks and decrease in body weight, will significantly affect the efficiency and quantity of sea cucumber fishing.