Doliolum Nationalis Research Articles

Basin-scale distribution of salps and doliolids in the transition region of the North Pacific Ocean in summer: Drivers of bloom occurrence and effect on the pelagic ecosystem

The large-scale distribution of thaliaceans in relation to environmental variables was investigated over 4500 km in the transition region of the North Pacific (36°N–43.6° N, 141.5° E–164.5° W) in the summer of 2016–2019. Three main patterns occurred in the thaliacean bloom formations with specific and annual variabilities. Thalia democratica, the most dominant thaliacean species in this region, formed an intensive bloom (>100 ind m−3) of up to 300 km, mainly south of the subarctic boundary between 160° E and 180°. The bloom was accompanied by a dense water mass which was associated with high nutrient concentration and N/P ratio, indicating that this species thrived under the influence of the HNLC water mass from the subarctic region. A Dolioletta gegenbauri bloom was observed east of 180° and the north of the subarctic boundary in association with higher chlorophyll a levels. Doliolum denticulatum and Doliolum nationalis increased with sea surface temperature and pico-sized chlorophyll a, suggesting adaptation to oligotrophic subtropical waters. Estimated grazing and downward flux by Thalia democratica bloom corresponded to 63–80% and 20–26% of daily primary production, respectively, indicating that the bloom enhanced the biological pump in the HNLC-like environment dominated by small phytoplankton. Doliolids function as important components of the microbial food web through the consumption of varied organic matter. Thaliaceans utilise the specific niche which suspension-feeding copepods find difficult to colonise, indicating that bottom-up control of oceanographic conditions determines the mesozooplankton community and food-web structure in the transition region.

Composition and distribution of zooplankton species in the subtropical areas of the Northwestern Pacific Ocean

Based on the investigation data of 44 stations in the area 28°－35° N, 147°－154° E of the Northwestern Pacific Ocean by the research ship 'Songhang' in March 2019, we analyzed species composition and distribution of zooplankton to understand zooplankton community structure in the subtropical areas of the Northwestern Pacific Ocean. The results showed that a total of 456 zooplankton species (including planktonic larvae and unidentified species) were recorded in the surveyed area, which were belonged to 8 categories and 14 groups. There were 163 species of copepods, as the dominant group. The dominant species included 9 warm-water species, Eudoxoides spiralis, Neocalanus gracilis, Pleuromamma gracilis, Sagitta enflata, Doliolum nationalis, S. hexaptera, Euchirella rostrata, Nannocalanus minor and Mesocalanus tenuicornis, and one temperate species, Calanus jashnovi. Both the warm current indicator species S. hexaptera and the cold current indicator species C. jashnovi occurred simultaneously in the subtropical area, indicating that the Kuroshio Current and the Oyashio Current had an important impact on the diversity and temporal-spatial distribution of marine zooplankton. The average biomass was (31.64±23.81) mg·m-3, and the average abundance was (22.2±17.6) ind·m-3. The average values of purity index (C), eveness index (J), Shannon diversity index (H) and richness index (D) were 0.09±0.10, 0.76±0.10, 4.88±0.71, and 23.53±8.08, respectively. The spatial distribution of the four indices were uneven and irregular. During the study period, species composition of zooplankton in the Northwest Pacific was rich, species distribution was uneven, and community structure was stable.

Influence of monsoon-driven hydrographic features on thaliacean distribution in waters around Taiwan, western North Pacific Ocean

Abstract Background The mesoscale distribution of thaliaceans associated with hydrographic conditions in the waters around Taiwan was investigated during two different monsoon seasons in 2004 in order to elucidate possible influences of hydrological conditions driven by seasonal monsoons on distributional patterns of thaliaceans. Results In total, 18 thaliacean species, belonging to 12 genera and 3 families, were identified in our samples. Thalia rhomboides, Doliolum denticulatum, Doliolum nationalis, Thalia orientalis, Pyrosoma verticillatum, and Thalia democratica were the six predominant species and contributed 93% to the total thaliacean collection by number. Thaliacean assemblages were similar in composition between seasons, but abundances and species numbers were higher in summer than in winter. Spatial distribution patterns of doliolids and salps clearly differed and were closely associated with hydrographic characteristics. Doliolids were mainly found in lower-salinity and nutrient-rich shelf and neritic waters; among them, D. denticulatum could be used as an indicator species of the China Coastal Current. Most salp species showed higher abundances in warm oceanic waters, such as the Kuroshio Current, Kuroshio Branch Current, and South China Sea Surface Current. Conclusions This study showed that the succession of water masses driven by monsoons affects seasonal and particularly spatial distributions of abundances of the thaliacean assemblage in the area studied.

The oral sensory structures of Thaliacea (Tunicata) and consideration of the evolution of hair cells in chordata

We analyzed the mouth of three species, representative of the three orders of the class Thaliacea (Tunicata)--Pyrosoma atlanticum (Pyrosomatida), Doliolum nationalis (Doliolida), and Thalia democratica (Salpida)--to verify the presence of mechanoreceptors, particularly hair cells. In vertebrates, hair cells are well-known mechanoreceptors of the inner ear and lateral line, typically exhibiting an apical hair bundle composed of a cilium and stereovilli but lacking an axon. For a long time, hair cells were thought to be exclusive to vertebrates. However, evidence of a mechanosensory organ (the coronal organ) employing hair cells in the mouth of tunicates, considered the sister group of vertebrates, suggests that tunicate and vertebrate hair cells may share a common origin. This study on thaliaceans, a tunicate group not yet investigated, shows that both P. atlanticum and D. nationalis possess a coronal organ, in addition to sensory structures containing peripheral neurons (i.e., cupular organs and triads of sensory cells). In contrast, in T. democratica, we did not recognize any oral multicellular sensory organ. We hypothesize that in T. democratica, hair cells were secondarily lost, concomitantly with the loss of branchial fissures, the acquisition of a feeding mechanism based on muscle activity, and a mechanosensory apparatus based on excitable epithelia. Our data are consistent with the hypothesis that hair cells were present in the common ancestor of tunicates and vertebrates, from which hair cells progressively evolved.

A contribution to the knowledge of the thaliacean faunas of the eastern mediterranean and the red sea

ABSTRACT In the sector of the Mediterranean east of the 22nd meridian, five species of Salpidae (Thalia democratica, Salpa fusiformis, Ihlea punctata, Pegea confoederata and Cyclosalpa pinnata polae) and five species of Doliolidae (Doliolum denticulatum, Doliolum nationalis, Doliolina sp., Doliolina intermedium (?)' and Dolioletta sp.) were caught during a series of cruises. At the same time, four species of Salpidae (Thalia democratica, Salpa cylindrica, Brooksia rostrata and Ritteriella amboinensis) and two species of Doliolidae (Doliolina mulleri krohni and Doliolum denticulatum) were recorded in the Gulf of Elat (Gulf of 'Aqaba), Two further species, Salpa maxima and Dolioletta gegenbauri tritonis, previously recorded from this area, were not found again in these last catches. Pyrosomidae are missing in both areas. The two faunas are very different, having in common only a few widely distributed species.

Taxonomic Study of Family Doliolidae (Urochordata: Thaliacea: Doliolida) from Korea

Four species in two genera of the family Doliolidae are identified and re-described in Korean waters: Doliolum denticulatum Quoy and Gaimard, 1834, Doliolum nationalis Borgert, 1894, Dolioletta gegenbauri (Uljanin, 1884), and Dolioletta tritonis (Herdman, 1888). Dolioletta gegenbauri is newly recorded in Korean fauna. A key to species of the family Doliolidae in Korea is provided.

Thaliacean distribution and abundance in the northern part of the Levantine Sea (Crete and Cyprus) during the eastern Mediterranean climatic transient, and a comparison with the western Mediterranean basin

First results are presented on the composition, abundance and vertical distribution of the thaliacean fauna in the Levantine basin obtained from stratified tows at three deep-sea sites in 1993: SE off Crete, and SW and NE off Cyprus. Samples with a 10 m2-MOCNESS (mesh size 1.67 mm) were poor in species and specimens as compared to samples with a 1 m2-double-MOCNESS (0.333 mm). Of the 12 species identified, six species belonged to the most abundant Doliolida, predominated by the phorozooids of Doliolum nationalis, five species belonged to the Salpida and one to the Pyrosomatida. Thaliaceans, most abundant by species and numbers SE off Crete, comprised ≤0.2% of the local mesozooplankton standing stocks. Presumably, they did not contribute substantially to the vertical flux generating the locally increased biomass and activity of the microbial benthos at the 4,300 m deep Cretean site. Most doliolids and salps were collected from the epipelagic and upper mesopelagic layers, and appeared to be most abundant close to the deep maximum of chlorophyll-a. Samples below 150 m were rarely rich in specimens, although two species performed diel migrations from the mesopelagic zone into the surface layers where some vertical segregation was evidenced. The aspect of niche separation is discussed.

Primer registro de Dolioletta gegenbauri (Uljanin, 1884) y Doliolum nationalis Borgert, 1893 en aguas chilenas (Tunicata, Doliolida)

Dolioletta gegenbauri (Uljanin, 1884) and Doliolum nationalis Borgert, 1893 are reported for the first time for Chilean waters. The organisms studied included 31 specimens of Dolioletta gegenbauri, divided among 8 phorozooids, 15 gonozooids and 8 nurses, plus 20 specimens of Doliolum nationalis, which were all phorozooids. All the specimens were collected in Mejillones Bay, Chile (23oS) between 0 and 100 m depth, in October 2001.

Complete nucleotide sequence of the mitochondrial genome of Doliolum nationalis with implications for evolution of urochordates

The evolutionary history of the diverse lifestyles adopted by urochordates has attracted intense interest because it may effect the evolutionary history of vertebrates. Here, we report the complete mitochondrial (mt) DNA sequence of the pelagic thaliacean doliolid Doliolum nationalis. The doliolid mt genome shares the unusual tRNAs of trnM( uau) and trnG( ucu) with other ascidians, such as Halocynthia and Ciona. On the other hand, the gene order of the doliolid mt genome is significantly different from that of any ascidian species or vertebrate reported to date. Phylogenetic analyses of the amino acid sequences of 12 protein-coding genes strongly support the sister-grouping of doliolids and the Phlebobranch ascidian Ciona, with the Stolidobranch ascidian alocynthia as the outgroup, thereby providing strong support for the paraphyly of ascidians, as has been suggested by 18S rDNA studies. Given the paraphyletic nature of ascidians, it seems likely that the common ancestor of ascidians and thaliaceans was sessile, as are the present-day ascidians, and that the thaliaceans subsequently evolved a pelagic lifestyle.

On endostyle ultrastructure in two new species of doliolid-like tunicates

The endostyle is a glandular and ciliated groove lining the pharyngeal floor of tunicates. This paper describes the histological structure of this organ in two new species of doliolid-like animals, Doliopsis bahamensis and Paradoliopsis harbisoni, and compares it with that of Doliolum nationalis. The results confirm the distinction between the Doliolida and the other Thaliacea.

Ciliary specializations in branchial stigmatal cells of protochordates

Tissues from the pharynx of five representative species of the protochordates (subphylum Tunicata, the three classes Ascidiacea, Thaliacea and Appendicularia, and subphylum Cephalochordata) were examined in both thin sections and freeze-fracture replicas. In all species, the stigmatal cilia of the branchial chamber are neatly arranged and move continuously to propel sea-water in a fixed direction for respiration and feeding of the organism. A number of specializations are found in the basal region of these cilia and are represented by: a) bridges connecting axonemal doublets numbers 5 and 6; b) dense fibrous material linking the doublet microtubules of the axoneme to the ciliary membrane, sometimes in the shape of longitudinal strands or as clusters of filaments; c) intramembrane particles (IMPs) associated with the P-face of the membrane, often arranged in clusters evenly aligned along the ciliary shaft in relation to the underlying axonemal doublets. Ciliary specializations are distributed along the plane of the effective stroke of the beat in both the ascidian Botryllus schlosseri and in the thaliacean Pyrosoma atlanticum and the amphioxus Branchiostoma lanceolatum, whereas in the thaliacean Doliolum nationalis and the appendicularian Oikopleura dioica a more uniform distribution of these specializations all around the basal portion of the cilia is observed. Whatever the disposition of the ciliary specializations in all the examined species, they are always present at the base of the water-propelling cilia. Some morphological evidence suggests that these specializations play a mechanical function in tethering the ciliary membrane to the axoneme. We propose that they help maintain the orientation of the cilia during beating, enhance their stiffness and improve their efficiency.

Doliolids in the German bight in 1989: Evidence for exceptional inflow into the North Sea

Doliolids were found in samples taken with a Continuous Plankton Recorder (CPR) in October 1989 between 55°14'N 03°32'E and 55°20'N 06°13'E during a tow between Newcastle and Esbjerg. Densities were estimated at >100 m−3 for about 112 km of tow. A sub-sample of specimens in sufficiently good condition to be reliably identified were referred to Doliolum nationalis Borgert. Substantial numbers of doliolids were found on a CPR tow between Harwich and Gothenburg which passed through the same area in that month and specimens were found nearer to the Danish coast in November and south-west of Helgoland in December. The distribution of doliolids in CPR samples taken in the North Sea in the last three months of 1989 is shown in Figure 1.

Fine structure of spermatids and sperm of Dolioletta gegenbauri and Doliolum nationalis (Tunicata: Thaliacea): implications for tunicate phylogeny

In Dolioletta gegenbauri and Doliolum nationalis, collected in 1987 in the bay of Villefranche-sur-mer (French Mediterranean Sea), spermiogenesis is essentially the same. Early spermatids have a round head, a flagellum arising from a single centriole with short microtubules at 45° to its base, several mitochondria, and an acrosome 50 nm thick and 250 nm long with its long axis parallel to the plasma membrane. The acrosomal contents are dense, with a central denser plate. The nuclear envelope next to the acrosome is thickened and concave. In elongating nuclei, strands of chromatin become oriented parallel to the length of the nucleus and then twist helically. Although the mitochondria surround the nucleus, they remain relatively short and do not fuse into a single mitochondrion as in sperm of other tunicates. In very late doliolid spermatids, the acrosome undergoes exocytosis, and exposes fibrous material that stays associated with the tip of the sperm; no acrosomal tubule forms. Exocytosis at this stage may be triggered by fixation. If so, exocytosis probably occurs naturally at some time before fusion of sperm and egg. Sperm have elongate heads (1 μm×10 μm), with the anterior two-thirds of the nucleus surrounded by mitochondria. Spermiogenesis in doliolids, compared to that in other tunicates, is most like that in solitary members of the class Ascidiacea, except that in the latter the sperm mitochondria fuse and the acrosome appears incapable of exocytosis. In contrast, previous work has shown that salps (class Thaliacea) and colonial didemnid ascidians have an acrosomeless sperm with a spiral mitochondrion, while the class Appendicularia has a sperm with a midpiece, a compact head and an acrosome capable of exocytosis and acrosomal tubule formation. By outgroup comparison with echinoderms and acraniates, appendicularian sperm are plesiomorphic within the Tunicata. Thus, gamete morphology indicates that (1) solitary ascidians and doliolids had a common ancestor, (2) the popular idea that doliolids gave rise to appendicularians is incorrect, and (3) the Thaliacea are polyphyletic, doliolids having arisen very early from the ascidian lineage and salps having arisen later.

東支那海黄海に於けるプランクトンの分布に就て

This is the second report of my observation on the plankton in the Eastern China Sea and Yellow Sea. This observation has been studied from April to June, for the years 1949-1950. The methode emploved in the present work was the same at that the former investigation, the plankton samples were obtained by vertical hauls and filtered through a plankton net made of 20 bolting silk at 22 fishining grounds. As dominants species in phytoplankton the following kinds can be recorded; Coscinodiscus janishii and C. asteromphalus at April, Rhizosolenia hebetata ƒ. semispina, R. alata ƒ. indica, R. alata ƒ. gracillima at May, Stephanopyxis Palmeriana, Thalassiothrix longissima, Chaetoceras spp. at June. In zooplankton Paracalanus aculeatus, Oithona similis, Nauplii oƒ Copepoda can be seen from April to June. Other kinds different from above mentioned can be recorded namely Noctiluca scintillans, Peridinium divergens at May, and Oikopleura longicauda, Doliolum nationalis at June.

Occurrence of Dolioletta gegenbauri (Uljanin) in the North Sea

IN a recent issue of NATURE, Delsman1 refers to the appearance of large numbers of Doliolum nationalis at Den Helder in 1910–12, presumably carried there from the English Channel. It may be of interest to record the presence of another doliolid in the North Sea this year. The material was collected in the course of investigating the relations between herring and the plankton by means of the Hardy plankton indicator2, and was forwarded to Prof. Garstang, who kindly identified phorozoids and gonozoids as Dolioletta gegenbauri (Uljanin). Oozoids were also present, but the identification of these is as yet uncertain.

Tunny in the North Sea

AMONG the notes in the “Calendar of Nature Topics” in NATURE of July 15 are two paragraphs on the occurrence of tunny in the North Sea. This fish seems, indeed, to have become much more common there in recent times than it was some decades ago. A fisherman here, now concerned with Indian fishery investigations, recently told me that he remembers perfectly well that it was in the year 1911 (well-known also by an exceptionally heavy storm) that the big creatures, hitherto unknown, first came under the attention of those engaged in herring fishing on the North Sea. This particularly interested me, as 1911 was an exceptional year in its very warm and dry summer. My plankton investigations on the light-vessel Haaks off Den Helder, during the years 1910–1912, showed that the influence of this heat period was great also on the temperature of the sea and the development of the plankton. Diatoms, peridinians, and copepods, one after the other, successively attained maxima several times higher than in normal years1 and a southerly form like Doliolum nationalis pushed forward in great numbers to the latitude of Den Helder. Would it be possible that the tunny also in this remarkable year found its way into the North Sea and in subsequent summers has continued to frequent these northerly waters? It would be interesting to have further information upon the statement of my fisherman.