The Asian date mussel (Arcuatula senhousia) dominates macrobenthic communities on the Midori River tidal flats on the island of Kyushu, the southernmost of Japan’s main islands. They form dense patches and create mats on the sediment surface. We conducted field surveys between May 2014 and April 2015 to assess the vertical distribution of sedimentary conditions (depth 0–12 cm) and determined the seasonal variation in density, biomass, and secondary production of A. senhousia on the tidal flats. Arcuatula senhousia density and biomass reached a maximum of 80,800 individuals per square meter (ind. m⁻²) in September and 4,988 g wet weight (WW) m⁻² in August, respectively. We defined a sediment layer with >10 mg dry weight (DW) of byssus as the byssus layer. From May to November, the integrated standing stock of sedimentary nitrogen (N) within the byssus layer derived from A. senhousia (150.7 g N m⁻² 7 months⁻¹) was as high as the secondary production of A. senhousia (161.8 g N m⁻² year⁻¹). Thus, this study clearly indicates that accumulated sedimentary nitrogen within the byssus layer plays a considerable role in nutrient cycling in the Midori River tidal flats.

The present study investigated the distribution of Batillaria multiformis and B. attramentaria in the tidal flats of Southern Kyushu. These two species are the dominant inhabitants of tidal flats and play an important role in conserving the environmental condition of the coastal area. Since it is difficult to distinguish between the two species based on shell morphology, the polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) technique was used for identification. Among the 55 tidal flats surveyed, Batillaria species were found in 32, mainly along the coasts of Kagoshima Bay and East China Sea. Furthermore, these species were not observed in certain tidal flats, although their presence in these tidal flats was confirmed from 1999 to 2003. The reason for their absence or decline has been discussed here. Batillaria multiformis was distributed along the neighboring tidal flats of inner Kagoshima Bay and around Nagashima Island, whereas B. attramentaria was isolated along a few scattered tidal flats facing to the Pacific Ocean or East China Sea. The difference in the distribution of two species might be attributed to their developmental system—B. multiformis and B. attramentaria employ planktonic and direct developmental systems, respectively.

An advanced underwater camera was used for recording coral spawning at a flow-through seawater aquarium. A colony of Acropora digitifera from the reef flat of Sesoko Island, Okinawa, Japan was transferred to a flow-through aquarium and photographed continuously for 5 days at 10 min intervals using an underwater digital camera equipped with a lens wiper. LED lighting was provided. The number of gamete bundle-like particles between the coral and seawater surface was counted on the photographs obtained. The gamete bundle release started around 22:00 pm on 31 May, 2015 (2 h and 50 min after sunset and 3 days before full moon). Spawning was estimated to continue for < 2 hours. The present study indicates that an underwater camera with a lens wiper system will help elucidate the details of coral spawning.

Accurately determining the species richness and/or abundance using quantitative sampling methods is important for understanding community structures. The quadrat method has been one of the most commonly used quantitative methods for estimating benthic animals in tidal flats. However, it is difficult to implement this method in biodiversity surveys of benthic fishes, as they can move across the quadrat, thus altering the observations. In the present study, we introduced the quantitative sampling method for benthic fishes in tide-pools located in tidal flats by employing an improved quadrat with a net and sinkers. This setup prevented the movement of fishes across quadrats, unlike the conventional quadrat method which allowed the easy movement of fishes. This improved quadrat method can be useful in surveying fish biodiversity in tide-pools in a wide range of tidal flats. The potential advantages of this method include 1) determining the accurate biodiversity of fishes in a tidal flat tide-pool, 2) easily comparing the biodiversity per unit area among multi-sampling sites, and 3) easily increasing the number of quadrats in field surveys. We believe that our improved quadrat method will simplify and promote the study of fishes in tidal flats.

“Mating stacks” have been widely documented in calyptraeid slipper limpets, which are protandric and exhibit sequential hermaphroditism. Gigantopelta is a genus of peltospirid snails endemic to deep-sea hydrothermal vents containing two species, one distributed on the East Scotia Ridge in the Southern Ocean and another on the Southwest Indian Ridge in the Indian Ocean. Here, we report the observation that both species form extensive (often >15 individuals) “snail chains”. These chains are potentially analogous to ‘mating stacks’ of calyptraeids, or alternatively, maybe a behaviour to facilitate spermatophore transfer. Both Gigantopelta species apparently have separate sexes and are sexually mature at a small size. However, it remains unclear whether they undergo sex change during their life.

High-concentration pure glycerol has been used as a medium for permanent preservation of micro-crustacean specimens. However, glycerol-mounted permanent slide preparations are rare because of the difficulty in sealing the coverslip over the long term. I devised a glycerol-mounted permanent preparation method, especially for a small dissected piece of a micro-crustacean using a glass depression slide and a coverslip with secure sealing, in order to overcome some of the disadvantages of the popular permanent mountants that solidify, such as discoloration of specimens and difficulty in remounting. Unique characteristics of the preparation method are: (1) the central glycerol being of a few millimeters in diameter, which embeds the specimen and is retained in the depression center by a paraffin wax circle painted on the depression bottom; (2) the marginal glycerol, which fills up the clearance between the glass slide and the coverslip and prevents intrusion of the sealant into the clearance; (3) sealing with nail polish first and Canada balsam second, where the latter can seal securely over the long term and the former, being a fast-drying sealant, prevents intrusion of the latter into the marginal glycerol. By following this method, even a small dissected piece can be easily found under a microscope and taken out from the preparation for detailed examination with a low risk of going missing. The procedure to make the preparation is presented in detail.

Jellyfish-fish interactions have long been reported, most of these related to medusae as ichthyoplankton predators. Conversely, associations are much less documented, most involving scyphozoan jellyfishes in comparison to cubozoans. We report for the first time the association between the cubozoan Tamoya haplonema and stromateid fish, along with a review of all published cubomedusae-fish interactions. Four individuals of Peprilus cf. crenulatus, were observed swimming around the tentacles and subumbrellar cavity of an individual of T. haplonema during a SCUBA dive on the southern coast of Brazil. This behavior has been noted before, in which fish roam around the tentacles, avoiding them, and may move inside the subumbrellar cavity if threatened. In the review of cubomedusae-fish interactions, over 20 reports involve predation on fish whilst only 6 involve associations, which is much less than the over 80 associations described for scyphomedusae. This emphasizes the scarcity of reports on associations compared to predation, as well as of interactions of fishes with cubozoans if compared to scyphozoans. This could be due to host preference or even the large spatial and temporal variability in the occurrence of the former. Furthermore, even though there are no indications of species-specific interactions, reports of associations with cubozoans only involve fish species from the families Carangidae and Stromateidae, which produce pelagic young that have the highest potential for these associations. Future studies may address the possibility of size relationships in jellyfish-fish associations, as well as potential host preferences by the fish consorts.