Two new taeniogyrinid sea cucumbers collected in the intertidal zone of southern Japan, Taeniogyrus verruculosus sp. nov. and Scoliorhapis sesokoensis sp. nov. are described. Both species possess a small body size (approximately 30–40 mm), light body color (translucent white in preserved specimens), ten tentacles, and numerous verrucous surfaces on the body, within which small (mostly less than 70 µm in length) sigmoid-hook ossicles are present. The two new species have a very similar external appearance to each other, however they do differ in the number of tentacle digits: T. verruculosus possesses up to eight digits, whereas S. sesokoensis possesses up to six. In both species, wheel papillae are not present. T. verruculosus possesses only a few small (mostly less than 30 µm in diameter) wheel ossicles in the anterior dorsal skin, which are not present in S. sesokoensis. Additionally, the DNA barcode sequences of two new species were determined and are available in the DDBJ/NCBI/GenBank databases under the accession numbers.

View full abstract

Optics-based surveys for large unicellular zooplankton were carried out in five different oceanic areas. New identification criteria, in which “radiolarian-like plankton” are categorized into nine different groups, are proposed for future optics-based surveys. The autonomous visual plankton recorder (A-VPR) captured 65 images of radiolarians (three orders: Acantharia, Spumellaria and Collodaria) and 117 phaeodarians (four taxa: Aulacanthidae, Phaeosphaerida, Tuscaroridae and Coelodendridae). Colonies were observed for one radiolarian order (Collodaria) and three phaeodarian taxa (Phaeosphaerida, Tuscaroridae and Coelodendridae). The rest of the radiolarian orders (Taxopodia and Nassellaria) and the other phaeodarian taxa were not detected because of their small cell size (< ca. 400 µm).

View full abstract

Biomass and body elemental composition of the giant jellyfish Nemopilema nomurai in the southwestern Japan Sea were studied using specimens collected with mid-water trawl nets during September and October 2006, 2007, and 2009. The average biomass of N. nomurai was calculated as 0.26–0.93 g wet weight (WW) m⁻³. Body elemental composition of N. nomurai was water=95.8% of WW, carbon=6.6% of dry weight (DW), nitrogen=1.7% of DW, and phosphorus=0.14% of DW. Carbon requirements for growth and respiration were estimated in per unit area using biomass data. For growth analysis, size-frequency distributions of bell diameter (BD) were examined from specimens collected using set-nets in Wakasa Bay during August–January in 2005–2007 and the growth rate was calculated as 1.5 cm d⁻¹. For growth production, individual daily increase of total body weight derived from BD growth was summed for populations collected with mid-water trawl nets. Respiratory oxygen consumption in N. nomurai was estimated from electron transport system activity as 8.4 µLO₂ gWW⁻¹ h⁻¹ at 20°C. Based on these values, the carbon requirement for growth and respiration was predicted as 0.1–0.33 mgC m⁻³ d⁻¹. Biomass and carbon requirement data of N. nomurai were compared to the biomass of the common squid Todarodes pacificus and copepod production, respectively, in the Japan Sea. In the present study, it was demonstrated that when mass incidences of N. nomurai occurred in the Japan Sea, the biomass of N. nomurai was substantial and equivalent to that of the common squid. The amount of zooplankton consumed as prey by N. nomurai was not large enough to influence the biomass of zooplankton as a whole; however, it was critical for dense aggregations in a small area.

View full abstract

Copepod nauplii are the primary food item for early-stage marine fish larvae, but their feeding selectivity on the nauplii of different copepod species has not been well studied. This study revealed feeding selectivity in the dominant preflexion larvae of three fishes Sebastiscus marmoratus, Sebastes sp. and Ammodytes japonicus in the Seto Inland Sea, Japan, in spring and winter. Copepod nauplii and eggs numerically constituted 80–91% of the prey items in their guts. Chesson’s preference index for the nauplii of various copepod species was positive for Calanus sinicus and Paracalanus parvus sensu lato, negative for Acartia omorii, and negative or neutral for Oithona similis. This result is probably attributable to the size and swimming behavior of the prey species. The preference index in A. japonicus larvae was not significantly different between the nauplii of different species, suggesting that the larvae are less selective than the other two fishes. The preference index for Calanus eggs was very high, especially in Sebastiscus marmoratus and Sebastes sp., and most of the eggs in the guts were shrunken, probably due to digestion. In terms of volume, C. sinicus nauplii and eggs in gut contents represented 36–72% of total copepod nauplii and >80% of total copepod eggs, respectively, because of high selectivity by fish larvae and their large individual volumes compared with the dominant copepods. This indicates that C. sinicus is the most important prey species for early fish larvae despite their low abundance in the environment.

View full abstract

Two North American ectosymbionts, a cambarincolid branchiobdellidan, Cambarincola mesochoreus, and an entocytherid ostracod, Ankylocythere sinuosa, were recorded for the first time in Japan, on the red swamp crayfish, Procambarus clarkii, from an urban stream in Tokyo. Although the immediate origin of the hosts and ectosymbionts is unknown, it is highly probable that they were recently imported into Japan. A single C. mesochoreus was also found on an alien atyid shrimp, Neocaridina davidi, in the same stream as the infected Pr. clarkii. This demonstrates the possibility that C. mesochoreus may find this shrimp to be a new potential host.

View full abstract

A lot of confusion (over the last 90 years) surrounds the naming of the Californian carybdeid population, sighted near La Jolla and Santa Barbara, since its first description by Stiasny in 1922. The specimens were first identified as Carybdea rastonii and later as Carybdea marsupialis but the identification was doubted by several scientists. To clear up the confusion, specimens of the Californian population were compared to specimens of all known carybdeid species. This comparison revealed that the Californian population represents an undescribed carybdeid species, named Carybdea confusa n. sp., being identified by the combination of the following characters: Gastric phacellae (single rooted, single stemmed), velarial canals (2 velarial canal roots/octant; canals multiple-branched with rounded tips) and pedalial canal (knee bend with thorn-like appendage).

View full abstract

We investigated the cell size reduction and size restoration of Eucampia zodiacus, an organism causing bleaching of aquacultured nori seaweed (Pyropia yezonensis), in laboratory culture observations. Mean cell size (apical length) of four E. zodiacus strains, which at the beginning of the experiment ranged between 59.2–73.4 µm, decreased to approximately 10 µm after 265–315 days with increasing number of cell divisions. The mean reduction rates in cell size ranged from 0.04 to 0.28 µm division^-1 at 5 µm intervals of cell size. The rates were almost stable at cell sizes between 35 and 60 µm, and then declined with decreasing cell size. When the mean cell sizes reached <15 µm, they restored cell size. However, the restored-size cells ranged from 22.7–34.0 µm and were smaller than the maximum size (ca. 80 µm) observed in field samples from the Harima-Nada, eastern part of the Seto Inland Sea, Japan. Cell size restored to over 80 µm was observed only once, in the H31-C strain, when the mean cell size decreased to around 50 µm. The process of size restoration that was observed only once in the H31-C strain, was clearly different from the other size restoration mechanisms, suggesting that E. zodiacus has two different processes by which cell size is restored: sexual reproduction via auxospore formation and vegetative cell enlargement.

View full abstract

This study presents new evidence of the extensive trophic role of gelatinous zooplankton by documenting typically non-marine predators, mallard ducks, feeding on hydrozoans in shallow, coastal environments.

View full abstract