Molluscan diversity from the Western Ghat rivers of Karnataka was studied and 14 species of freshwater molluscs were recorded. Melanoides tuberculata was found throughout the study period whereas Brotia costula and Parreysia spp. were rarely observed. The species diversity of molluscs was more in pre-monsoon than post-monsoon. The molluscs were more abundant in the upstream of the rivers Netravathi and Souparnika than the midstream and downstream. Filopaludina bengalensis was restricted to the Sharavathi river and their abundance was observed in the midstream of the Sharavathi river. Kruskal Wallis test showed a significant difference in abundance and species richness with the seasons. This shows that seasonal changes bring about variations in the molluscan diversity of the Western Ghat rivers of Karnataka.

The present study was carried out to design a simple, new and accurate method for identification of the morphologically similar four species (forms A and B of P. shikueii, P. mictodonta, and P. wilsoni) of the Perinereis nuntia species complex by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) patterns of the internal transcribed spacer (ITS). Restriction digestion analysis in the following two steps generated a specific restriction pattern for each species: (1) by the first digestion of amplified ITS fragments with AluI, we can distinguish the two forms of P. shikueii from P. mictodonta and P. wilsoni; (2) by the subsequent digestion of ITS fragments with Cfr10I, we can distinguish between the forms A and B of P. shikueii, and by that with HinfI, we can distinguish P. mictodonta from P. wilsoni. Our result indicates that this method enable easy and accurate identification of these taxa. We additionally examined the distributions of the two forms of P. shikueii in Japan, Korea and Taiwan using this new method. The form B was distributed in a wide range in western Japan and Korea, whereas the form A was distributed in few limited sites in the inner parts of the Seto Inland Sea and the Ariake Sea in Japan, the western and southern coasts of Korea, and the western coast of Taiwan.

Intertidal distribution of Haustorioides amphipods were studied in relation to the tidal fluctuation at four sandy beaches in Japan and Korea, to understand their behavioral responses to environment during tidal fluctuations. Presence or absence of Haustorioides individuals (including four species: H. japonicus, H. koreanus, H. munsterhjelmi, and H. nesogenes) were generally recorded at 2 m intervals from the drift line to the swash zone at various tidal conditions including high tides and low tides. Generalized linear mixed models demonstrated that the occurrence of Haustorioides amphipods at the sampling points were best described by a model with suction (the tension of moisture in the sediment) as an explanatory variable. Other environmental variables at the sampling points (slope angle, distance from the shoreline at the sampling time, and height from the sea level at the sampling time) were relatively poor predictors. The model showed that the probability occurrence of the amphipods was highest at the suction value of 0.76 kPa. Thus, the tidal migration behavior of these Haustorioides amphipods can be explained by suction dynamics rather than the swash conditions. This response was common to all four species and appears to be consistent over various tidal conditions.

The relationship between diet isotopic signatures and the extent of the tissue-diet isotope fractionation factors have been shown previously in controlled feeding studies, but this relationship remains poorly resolved for marine invertebrates in a natural setting. Using isotope analysis of gut contents, this study investigated the variability in tissue-diet isotopic fractionation factors (Δδ¹³C and Δδ¹⁵N) between scallop tissues (i.e. muscle and digestive gland) and gut content in the Japanese scallop Mizuhopecten yessoensis (Jay, 1857) and assessed how the growth rate of juvenile scallops and gut content quality (as carbon to nitrogen (C/N) molar ratios) would affect the values of tissue-diet isotopic fractionation. Tissue-diet isotopic fractionation factors (Δδ¹³C and ∆δ¹⁵N) varied according to tissue, which averaged 1.7‰ and −0.1‰ for N in muscle and digestive gland, and 3.4‰ and 1.2‰ for C in muscle and digestive gland, respectively. Muscle-gut ∆δ¹⁵N isotopic factors negatively correlated with growth rate, suggesting that the juvenile δ¹⁵N signatures were strongly dependent on food quantity. The influence of diet quality on ∆δ¹⁵N was also evident, where ∆δ¹⁵N decreased as C/N molar ratios in gut contents increased. The wide difference in Δδ¹³C and ∆δ¹⁵N from accepted standard values may be, in part, a consequence of using gut contents as a dietary proxy. Results of this study have implications for diet reconstruction studies of this scallop species reared under field conditions.

The northern Satsunan area, comprising the mouth of Kagoshima Bay and Osumi Strait, is an important spawning and nursery ground for Japanese jack mackerel Trachurus japonicus in Japan. Upwellings frequently occur at the mouth of the bay during winter and spring, and the consequent nutrient supply promotes phytoplankton blooms. This study examined how T. japonicus utilizes upwelling (Kagoshima Bay) and non-upwelling areas (Osumi Strait) as larval nursery grounds. Densities and growth rates (measured as the average width of the last three otolith increments) of T. japonicus larvae in both areas were compared to determine the upwelling influence on nursery ground formation. The mouth of the bay had lower temperature and salinity but higher chlorophyll-a concentrations and prey density than that of the strait. Densities of larvae were consistently higher in the bay than in the strait, indicating that the main nursery of T. japonicus is formed in Kagoshima Bay. No significant differences were observed in the growth rates of larvae among areas, suggesting that lower temperatures and prey availability are growth limiting factors in the mouth of the bay and the strait, respectively, and the Osumi Strait could also provide a favorable nursery area.

This study reports an effective and simple method for culturing the comb jellyfish, Beroe cucumis. The method for breeding another comb jelly, Bolinopsis mikado, was published by Ikeda et al. (2022), in which Bolinopsis mikado was bred stably and in large numbers, and then provided as food to developing Beroe cucumis. Fertilized eggs were found in a 235-L tank two days after five parental Beroe cucumis were housed in the tank, and the parental individuals were isolated from the tank the next day. The day after the eggs were found, Beroe cucumis larvae (0.54 ± 0.04 mm long (n = 9)) were observed in the tank daily and were fed Bolinopsis mikado. The Beroe cucumis larvae were only fed Bolinopsis mikado during the early stages of development. They reached a total length of approximately 10 mm in 17 days, and by day 20, when most had grown large (approximately 12 mm and over) enough to not pass through the 3-mm perforated plates, they were moved to a 145-L display tank. Thereafter, they were reared in the same manner and were successfully propagated cumulatively for more than five generations. The greatest advantage of this culture method is that the larvae need only be fed and observed until they reach the size required for display. Therefore, stable breeding of Beroe cucumis can be achieved by feeding its larvae with Bolinopsis mikado, reducing labor and stress on the organisms from frequent water changes.