Burrow-dwelling shrimps, formerly known as “thalassinids,” are attracting the attention of researchers as ecosystem engineers. This review focuses on the ecology of upogebiid shrimps worldwide, especially their life history and burrow traits. The mud shrimp has a larval period consisting of three to four zoeal stages with one decapodid stage. The time required for maturity and longevity has been estimated to be 1–3 years and 3–5 years, respectively. However, data on shrimp lifespan may be updated with the development and application of age determination methodologies. The structure of the shrimp burrow is mainly U- or Y-shaped and is similar among species but with some interspecific differences. Mud shrimps are filter feeders due to the ventilation activity in the U-shaped structure, and inhabit burrows with an inner diameter that fits their body. Burrow connections were recorded between burrows of males and females. Some juvenile mud shrimps may branch off from adult burrows to create their own burrows. This review discusses the response of shrimp populations in areas affected by the 2011 Great East Japan Earthquake. Owing to long maturation times, the recovery of these populations was slow in habitats affected by tsunamis. These results highlight the future effects of climate change on shrimp populations.

Photograph records of four holothurian individuals upon which colonial ascidians were associated epizoically are reported from the waters around Akajima Island, Kerama Islands, Okinawa, Japan. Although holothurians are known to be hosts of many organisms, these new observations add a new perspective to understanding the ecological role of holothurians as mobile scaffolds. Some ascidians have limited capabilities of locomotion, but we believe an association with holothurians would increase the mobility of ascidians. On the other hand, such associations may be beneficial as part of the holothurians’ chemical defenses, since some ascidians and/or harbored cyanobacteria produce bioactive compounds. Even though these observed cases may be temporary associations, it is apparent holothurians are ecosystem engineers on coral reefs not only due to their feeding behavior, but also due to their associated fauna.

This paper reports an effective and easy method to culture the ctenophore Bolinopsis mikado. Fifteen adult B. mikado individuals were maintained in a kreisel tank, and fertilized eggs, which were detected in the following days, were all raised together in the same tank. From the early development stage to day 13, the B. mikado cydippid larvae were only fed Artemia nauplii. The cydippid larvae were able to easily catch the Artemia nauplii excreted by adult B. mikado; therefore, they were considered capable of growing on excrement. Adult B. mikado individuals were removed from the tank when the cydippid larvae reached approximately 5 mm in length (day 14). The cydippid larvae were then transferred to a circular tank with a water spray chamber. Approximately 21 days after the early development stage, cydippid larvae had grown to lengths of approximately 20 mm and were then bred in the same manner up to the 5th generation. The greatest advantages of this culture method are that it is less cumbersome and only requires feeding and observation until the cydippid larvae attain a size that enables them to pursue live Artemia nauplii. Thus, damage to the living body due to water exchange and the labor involved are reduced, thereby allowing stable breeding of B. mikado.

Molecular analysis is a common tool for marine ecological and biological research. For genomic analysis of zooplankton, ethanol preservation and freezing are often used to preserve samples until analysis. However, these methods have disadvantages, such as the loss of morphological information. Recently, 10% Lugol’s iodine solution (10% Lugol) has been shown to be an effective preservative of plankton samples for molecular analysis, even after 18 months. However, that study only reported a PCR-based molecular study using copepods. We tested the preservation effectiveness of 10% Lugol on various zooplankton over 33 months by comparing them to samples preserved by freezing or in 5% formalin seawater. The results revealed that the total amounts of DNA extracted from crustacean and gelatinous zooplankton preserved in 10% Lugol were the same or higher than those preserved in formalin or by freezing. Gel electrophoresis of the extracted DNA indicated that the DNA of the samples preserved in 10% Lugol was not fragmented during the preservation period. PCR amplification of a partial 18S rRNA gene using DNA extracted from various zooplankton taxa (siphonophores, copepods, ostracods, doliolids, polychaetes, pteropods, euphausiids, and chaetognaths) was successful. Sequences of morphologically identified species preserved in 10% Lugol had BLAST hits to sequences of these species deposited in Genbank, with a similarity of 100%, which indicated there was no sequence alteration during the preservation period. Thus, we conclude that 10% Lugol is a suitable preservative for molecular analysis of various zooplankton taxonomic groups.

A new species of sapphirinid copepod, Sapphirina doliolettae n. sp. was described from the Kuroshio Extension region in the western North Pacific Ocean. The new species is similar to S. nigromaculata and S. scarlata with respect to the following characteristics: 5-segmented antennule, one inner marginal process on caudal rami, and slender endopods with two apical spines on leg 4. However, it can be distinguished from these congeners by a combination of the following characteristics: the relative length of each segment of the antennule and antenna in both sexes, the width of the fourth pedigerous somite in females, the shape of the anterolateral corner of the genital somite in males and terminal process length of 3rd endopodal segment of leg 2 in males. The mitochondrial cytochrome oxidase subunit I sequences of S. doliolettae showed high interspecific variabilities from other Sapphirina species, including S. nigromaculata (20.2%) and S. scarlata (21.6–21.8%).

Knowledge about the taxonomic and size composition of mesozooplankton is of critical importance for both fisheries and oceanography. In this study, we collected an annual time series of mesozooplankton samples in Funka Bay and analysed them using ZooScan to reveal the seasonal changes in taxonomic and size structure. Both zooplankton abundance and biovolume peaked in April and were dominated by an appendicularian Oikopleura labradoriensis which has been reported as being are being important food source for flatfish larvae. Furthermore, Noctiluca scintillans was abundant from September to December. The occurrence of this species may be related to the recent increase in the transport of Tsugaru Warm Current water into the bay. The Normalized Biomass Size Spectra (NBSS) was significant for 16 of 21 sampling dates. Insignificant NBSS, with an extremely flat slope, was observed for January–March. Significant NBSS with a flat slope was observed in April. Then, the relatively steep slopes of the NBSS were the case from mid-May to December. These seasonal changes in the slope of NBSS suggest that the energy transfer efficiency for higher trophic levels varied seasonally. The observed slopes of the NBSS in Funka Bay ranged from −1.09 to −0.30, which was flatter than the theoretical value (−1) and the previously reported values for the oceanic region of the western North Pacific. This suggests that the energy transfer efficiency to organisms at higher trophic levels in the Funka Bay is higher than in the adjacent oceanic region.

The temporal changes in the behavior of vegetative cells and cysts of the noxious red tide flagellates Chattonella (C. antiqua and C. marina) were investigated in Ago Bay, central Japan, mainly in 2013. In this study, in situ germination flux (cells m⁻² day⁻¹) was measured in May, June, and October 2013, using a ‘plankton emergence trap/chamber (PET chamber)’. Vegetative cells occurred in April and increased from May, forming a bloom in July with cyst production, and subsequently decreased thereafter. This change in the occurrence of the vegetative cells was considered to be controlled primarily by temperature and secondarily by nutrients and biotic factors. The PET chamber experiment showed that cyst germination in May contributed largely to forming the initial vegetative population to initiate blooming. An experiment to elucidate the effect of storage temperature on the germinability of cysts in the sediment showed that newly produced cysts (immature dormant cysts) mature (acquire germinability) under low storage temperature (10°C) within at least one month, indicating that cysts need to experience a cold season in the sediment for their maturation. The PET chamber experiment conducted in October before a cold season also confirmed that cysts scarcely germinated from the cyst population, containing many immature dormant cysts, in the in situ sediment. However, these cysts could act as seeds to form the initial population of the subsequent bloom in the next season, since the cysts will mature by then. Consequently, Chattonella cysts were concluded to play crucial roles in the population dynamics.

This study investigated the host-epibiont relationship between calanoid copepods and suctorian ciliates collected widely from the northern North Pacific Ocean. Mid- and deep-water adult female calanoids without dormant stages were found to be infested with suctorians, probably because of their larger size, longer intermolt duration and longevity in comparison to males and surface water species. A total of 259 calanoids belonging to sixteen species were infested with five suctorian species. Among them, Candacia columbiae, Gaetanus minutus, Lucicutia bicornuta, Metridia similis, Pleuromamma scutullata, and Racovitzanus antarcticus were reported to be infested with suctorians for the first time in the present study. Ephelota coronata infested only Metridia pacifica and displayed a strong host preference, whereas the other suctorians displayed a weaker host preference. Any suctorian species that infested Metridia pacifica and M. similis attached almost exclusively to their urosome. Suctorians might avoid or could not stay attached to the anterior parts of these fast-swimming copepods. The attachment sites of Actinocyathula pleuromammae and Paracineta gaetani extended to the anterior part of the copepod body as the number of attached suctorians increased, suggesting they were obliged to attach to suboptimal parts that were exposed to faster flow speed.

Ernst Haeckel described four new chirodropid species in 1880. Chirodropus gorilla was seen only on a few occasions along the Western coasts of Africa, while Chirodropus palmatus (from St. Helena Island) was never recorded again. Type specimens of both species are lost, leading some scientists to doubt the validity of C. palmatus. New specimens assignable to C. gorilla from European and South African Museum collections shed light on the identification of both species. Among the C. gorilla samples, small mature individuals with more pedalial branches than in the larger specimens were discovered. Further observations on living specimens of the smaller chirodropid from Cameroon suggested that they must be C. palmatus because there were only two chirodropid species described from West African waters; comparison with Haeckel’s descriptions and drawings confirmed the identification. Additionally, our data showed that Chirodropus palmatus must be classified into the family Chiropsalmidae and accommodated in its own genus, Chimaerus gen. nov. We also revised definitions of the families Chirodropidae and Chiropsalmidae and re-described both species.