In 1934, Stiasny described cubomedusan specimens from Station 279 of the Discovery Expedition 1925–27 in the Gulf of Guinea, West Africa as Tamoya haplonema. He also presented line drawings of the habitus that raised some doubts on the identification of the species. In the collections of the Natural History Museum of London, the described specimens were still available and in good condition due to their storage in formalin. More specimens could be found in other European museums. The formalin made a genetic analysis impossible but as all anatomical structures were excellently preserved, a direct comparison was possible with the structures in Tamoyahaplonema and Tamoya ohboya from the Americas. Due to the morphological comparison with the American Tamoya species it could be confirmed that the African Tamoya specimens are an up-to-now undescribed new Tamoya species, Tamoya anacamori sp. nov., described herein.
Change in abundance and composition of the zooplankton community was studied at the innermost part of Onagawa Bay, northeastern Japan, before and after the Tohoku Earthquake and tsunami of 2011. Abundance of zooplankton groups did not drastically decrease just after the tsunami except for cladocerans and the larvae of benthic organisms. The decrease of the former may have been caused by their resting eggs being swept away by the tsunami or buried in the sediment just before their spring increase, while that of the latter by a population decline of their adults. The number of cladoceran species decreased from 7 to 5, with increasing dominance of Podon leuckarti after the tsunami. The percentage of the genera Acartia and Oithona, combined, was 73% of all copepod genera before the tsunami and increased to 85% after the tsunami. Zooplankton abundance increased with the increase of chlorophyll concentration from 2013, two years after the tsunami. The basic structure of the breakwater broken by the tsunami was reconstructed by the end of 2014 with a shallower sill depth, and the water exchange between the inside and outside of the breakwater became restricted. As a result, dissolved oxygen concentration decreased not only on the bottom but also in the water column and the species diversity of copepods decreased at the innermost station. Long-term monitoring should be continued.
Burrows produced by marine invertebrates often harbor other small commensal invertebrates. The mud shrimp Upogebia is known to coexist with the myid bivalve Cryptomya in a burrow produced by the shrimp. Both species are filter-feeders, and thus interspecific competition or trophic niche segregation may occur in the burrow. Samples for carbon and nitrogen stable isotope analysis were collected from a tidal flat near the tidal inlet of Akkeshi Lake, Hokkaido, northern Japan in April 2013. In addition, stratified benthos sampling was conducted on the tidal flat in August 2018, to clarify the interspecific relationship between U.major and C.busoensis in the burrow. The stratified benthos sampling showed the vertical distribution of these species, and indicated that both species filter water from the same part of the burrow for feeding. The stable carbon and nitrogen isotope analysis showed that important food sources for both U. major and C. busoensis are marine phytoplankton and microphytobenthos. In addition, C. busoensis is likely to consume terrestrial organic matter whereas U. major is unable to utilize it. The partial trophic segregation between the species increases the potential benthic filtering because it allows the Upogebia burrow complex to consume a wide variety of organic matter, and it might reduce interspecific competition between the filter-feeding host and its commensal species. These results demonstrate how ecologically similar macrobenthos can coexist in a burrow.
Mesochaetopterus is a bioluminescent polychaete that belongs to the family Chaetopteridae. It secrets a blue luminescent mucus as a response to mechanical stimulation similar to the species in Chaetopterus (Chaetopteridae). However, unlike Chaetopterus, the biochemical properties of Mesochaetopterus bioluminescence are largely unexplored. In this study, we examined the basic biochemical properties of the bioluminescence seen in Mesochaetopterus japonicus and compared them to those seen in Chaetopterus. The comparison revealed that similar blue luminescence peaked at approximately 460 nm were induced by the addition of Fe2+ and H2O2, suggesting that bioluminescence in M. japonicus and Chaetopterus has similar basic biochemical properties. On the other hand, the gel filtration analyses showed that the elution volumes of active proteins were different between Mesochaetopterus and Chaetopterus. The molecular weights of these proteins were estimated to be 150 kDa and 90 kDa (approximately) for Mesochaetopterus and Chaetopterus, respectively.
A new species of viviparid gastropod belonging to the genus Heterogen Annandale, 1921, is described from the Pleistocene Katata Formation of the Kobiwako Group in the southern part of Lake Biwa, central Japan. This new species is continuously recorded from the Nijigaoka Clays (1.2 Ma) to the Hiraen Clays (0.8 Ma) of the Katata Formation. This new species, Heterogen praelongispira sp. nov. is similar to the extant H. longispira in Lake Biwa, but the details of shell morphology are different from those of H. longispira, including fine-to-deep suture, flattened whorl side, and oval shape of embryonic shell.
Mysid specimens collected at Lombok Island, Indonesia were examined and assessed taxonomically. These specimens share morphological characteristics with species of the subgenus Javanisomysis (genus Anisomysis). They are separable from the other four known species of the subgenus by the structure of the fourth male pleopod, and the condition and pattern of sub-segmentation in the third to eighth thoracopodal carpopropodi of both sexes. The male pleopod is long and reaches the posterior end of the sixth abdominal somite, excluding the apical barbed setae, and the first segment of the pleopod is broader in the proximal one-fourth to one-third. The third to eighth thoracopodal carpopropodi are divided distally into two segments. The population from Lombok Island thus is considered an undescribed species of the subgenus. On the basis of characteristics of the fourth male pleopod, a key to species of the subgenus is provided.
In vivo absorption spectra and spectrally reconstructed absorption spectra from HPLC-determined pigment concentrations were obtained and compared for five different mixtures of two dinoflagellates (large cells, Prorocentrum micans and small cells, Prorocentrum minimum) with similar cell shapes and pigment compositions but significant differences in pigment contents and cell volume. Although the large cells contained 4-fold higher chlorophyll a content than the small cells, the observed intracellular chl a contents per unit cell volume (Ci) increased with decreasing cell volume. Exponentially grown cells with the abovementioned characteristics were prepared for use in mixing experiments with 0, 25, 50, 75, and 100% of P. minimum and vice versa for P. micans. The in vivo absorption values determined at nine wavelengths (412, 440, 480, 510, 532, 555, 650, 676, and 700 nm) were significantly associated with the biomass with respect to either cell volume or chl a concentration and were inversely correlated with Ci (p <0.01). The observed package effect [Q*a (λ)] indicated an overestimation of absorption spectra at all wavelengths by reconstruction. The fractional reduction of pigment absorption due to Q*a (λ) was wavelength dependent regardless of the mixing ratio of the two populations. The results showed that the product of equivalent spherical diameter and Ci should be considered for quantitative studies of Q*a (λ) in various chromatic-adapted species in cultures as well as in coastal waters.
Sea pens are ecologically important habitats for associated marine organisms, serving as ecosystem engineers in sandy or muddy seafloor environments. In such areas, sea pens can form habitats with high population densities known as “sea pen fields”. However, the presence and importance of sea pen fields have not been well studied in shallow waters in East Asia. Here, we report a sea pen field of Virgularia sp. aff. gustaviana in the shallow waters of Ushibuka Marine Park, in the Amakusa Islands of southern Japan. The average colony numbers of the field across all depths (7–20 m) was 10.3 colonies/m2 (live colonies) to 13.6 colonies/m2 (all: live+dead colonies+holes), and the area of the sea pen field was at least ∼50,000 m2. At a depth of 15 m, the substratum consisted of sand and fallen leaves of terrestrial origin, and the highest sea pen density was observed (averages=17.2 live colonies/m2, =25.8 total (live+dead+holes) colonies/m2). At a depth of 20 m, the substratum consisted of broken shells and rocks and had the lowest density (live colonies: average=0.8 colonies/m2, all: average=1.0 colonies/m2). There were significant differences in colony number of Virgularia sp. aff. gustaviana between the “sand”, “sand+leaves”, and “broken shells/rocks” substrates. We hypothesize that the strength of the water currents caused by local geographic features and tidal movements produce suitable sedimentation and habitat for this species of sea pen. Therefore, we suggest that preserving the natural coastline is crucial to protect this and other sea pen fields in shallow waters and their benthic marine communities.
Feeding experiments with a natural microplankton assemblage and egg production experiments with the neritic copepod Acartia steueri were conducted simultaneously in an inlet on the Sanriku coast during autumn. Diapausing egg production status of A. steueri was also investigated. Further, A. steueri dominated during September to October and then gradually decreased until December, before disappearing after January. The dominant microplankton in natural waters during the study period were dinoflagellates, followed by centric and pennate diatoms and oligotrich ciliates. A. steueri fed only on dinoflagellates and oligotrich ciliates at rates of 87.0–309 and 17.7–71.5 cells ind−1 d−1, respectively. Egg production rate of A. steueri ranged from 1.6 to 15.0 eggs female−1 d−1 and significantly increased as ingestion rates of dinoflagellates and oligotrich ciliates increased. The copepod began producing diapausing eggs in October, and by late December, 86% of the eggs produced were diapausing. The population’s egg production rate was highest in September (18,961 eggs m−3 d−1) and gradually decreased through the end of December. These dietary and diapausing egg production seasons of A. steueri in the Sanriku area are significantly different from the results of previous studies in the temperate zone, where the copepod mainly fed on diatoms and produced diapausing eggs during spring. A. steueri can alter its feeding habits and the timing of diapausing egg production in response to changes in habitat. The flexibility of this species to environmental change has likely allowed expansion of its geographical distribution.
This paper describes “inverse rapping” as a characteristic mating behavior in Pagurus nigrofascia. The behavior involves one hermit crab pulling another crab’s shell towards itself causing the shells to hit against each other. This is the first evidence that males perform inverse rapping as a mating behavior in a Pagurus species. Two experiments were conducted to describe the inverse rapping in detail and to discuss its function. In Experiment A, we clarified when (mating season or non-mating season) and to whom (males or females) males displayed this behavior. A focal male that had not been guarding in the field was placed together with another crab and their interaction was observed, especially inverse rapping. Males showed inverse rapping mainly with a female that was close to copulation in the mating season, especially when the male guarded the female. In Experiment B, we examined the female’s response to male inverse rapping and tested the effect of the presence of a neighboring conspecific on the occurrence of the behavior. Most females reduced struggling and/or withdrew into their shells in response to male inverse rapping. The presence of neighboring crabs did not affect inverse rapping. Our findings suggest that inverse rapping is a mating behavior in P. nigrofascia, and that inverse rapping may benefit males in the initiation and/or continuation of precopulatory guarding because it can help to restrain struggling females. This behavior has not been observed in other sympatric Pagurus species and appears to be a characteristic mating behavior of P. nigrofascia.