Asexual reproduction of the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

The goal of this research is to enhance our knowledge of thecontributions of doliolids to the planktonic community as consumersand secondary producers. The objectives are to quantify asexualreproduction and carbon release rates of Dolioletta gegenbauriphorozooids at four food concentrations and four temperaturesin order to determine their impact as producers throughout thewater column. Although doliolids are abundant in numerous regionsof the coastal ocean, and are considered to be major planktonicgrazers, data on rates of asexual reproduction are scarce. Laboratoryexperiments were conducted at 20°C at food concentrationsof 7, 20, 60 and 160 µg C l^-1 of Thalassiosira weissflogiiand Rhodomonas sp., and at 60 µg C l^-1 at 16.5, 20, 23.5and 26.5°C, to quantify the phorozooid release rates ofgonozooids, and the amount of carbon released. Results fromthese experiments suggest that release rates increased at 20°Cas concentration increases from 7 to 160 µg C l^-1. Releaserates remained similar as the temperature increased from 16.5to 26.5°C at a phytoplankton concentration of 60 µgC l^-1. Food concentration and temperature has an effect on phorozooidreproductive longevity, size of gonozooids released, and theamount of carbon released asexually. Doliolid reproduction ratesare a function of environmental food concentrations and temperatures,and the results imply that doliolids can be important secondaryproducers in the neritic environment.     

Grazing rates for three life history stages of the doliolid Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

Grazing rates for Dolioletta gegenbauri averaged 2.5 ml zooid^–1h^–1 for trophozooids, 2.7 for phorozooids and 5.8 forgonozooids. In situ and laboratory rates were comparable forboth trophozooids and phorozooids.     

Laboratory-measured grazing and ingestion rates of the salp, Thalia democratica Forskal, and the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (4–5µm diameter) alone or in combination with Peridinium trochoideum(16–18 µm diameter) at concentrations of 0.15–0.70mm³ x 1^–1. Grazing rates (ml x zooid^–1 x 24 h ^–1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC^–1x 24 h^–1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (10⁶ µm³x zooid^–1 x 24 h^–1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC^–1 x 24 h^–1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C^–1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m³) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day. ¹Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5     

Lipid composition of the pelagic tunicate Dolioletta gegenbauri (Tunicata, Thaliacea)

The free-swimming sexual stage (gonozoid) of the doliolid, Doliolettagegenbauri, was abundant at a site in the NE Atlantic (58W,20N) during June 1996. Lipid analysis indicated that theseorganisms were comprised mainly of polar lipid with only lowlevels of neutral storage lipid (triacylglycerols) and thisis consistent with a life history strategy of rapid somaticgrowth and gamete production. Fatty acid analysis of the gonozoidssuggested a diverse microplanktonic diet, comprising diatoms,flagellates and dinoflagellates. The fatty acid compositionof D.gegenbauri was dominated by 20:5(n–3) and 22:6(n–3),and is of high nutritional value to predators, particularlyfish. The results are discussed in relation to the organisms'life history strategy and their potential nutritional impacton higher trophic levels.     

Feeding rates of the doliolid, Dolioletta gegenbauri, on diatoms and bacteria

Wild doliolids fed equally efficiently on radiolabelled bacteria>5 µm in size and diatoms >100 µm in size.Feeding by attached asexual buds accounted for 80% of the clearancerates of phorozooids and oozooids     

Iodine binding and peroxidase activity in the endostyle of Salpa fusiformis,Thalia democratica,Dolioletta gegenbauri and Doliolum nationalis (Tunicata,Thaliacea)

Summary The protothyroid region in the endostyles of four species of tunicates was examined by means of autoradiography and cytochemistry, at both the light and electronmicroscopic levels. To reveal the primary binding site for iodine, autoradiography was carried out on endostylar tissue from animals that had been incubated with high activity ¹²⁵I^- over a short period of time. The specific iodine binding enzyme, a peroxidase, was traced by its reaction with DAB. In accordance with previous findings, the iodinebinding cells proved to be the same as those containing the peroxidase. There were also strong indications of a secondary uptake of iodinated compounds and subsequent release into the body fluid. Together with the ultrastructural features, the data provided strong evidence indicating that these cells constitute a protothyroid region, which partly functions as an endocrine organ, possibly homologous with the vertebrate thyroid gland. Since the number of zones varied between the species, the numeration of the protothyroid region also varied. However, in all the examined endostyles, the protothyroid region was seen to be situated dorsolaterally to the glandular regions of the endostyle concerned with food capture.     

A monograph of the order Pyrosomatida (Tunicata, Thaliacea)

The taxonomy of the order Pyrosomatida is revised based on theexamination of over 300 samples from all parts of the worldoceans. The order consists of a single family (Pyrosomatidae),two subfamilies (Pyrostremmatinae and Pyrosomatinae), threegenera (Pyrostremma, Pyrosomdla and Pyrosoma) and 8 species(Pyrostremma spinosum, P. agassizi, Pyrosomella verticillata.P. operculata, Pyrosoma atlanticum, P. aherniosum, P. ovatumand P. godeauxi n.sp.). The species are briefly described anddata on their distribution are provided. A key to the speciesis given. A cladistic analysis of the distribution of relevantcharacter states is made and ideas on evolutionary developmentare put forward. Biogeographical data are summarized and inconjunction with that the likely modes of speciation in thisgroup are briefly discussed.     

Jet propulsion in salps (Tunicata: Thaliacea)

This paper describes the locomotion of salps by jet propulsion, from a combination of measurements of chamber pressures, static thrust, and electromyographic activity, with kinematic records of free-swimming and tethered salps. From such measurements, estimates are made of the thrust exerted, the drag incurred, and the work performed by single salps, and by chains of linked individuals. It is concluded that salp jet propulsion is a more economical process than is jet propulsion in other animals.     

Distribution and vertical migration of salps (Tunicata, Thaliacea) near Bermuda

Sampling near Bermuda by trawling and SCUBA diving yielded 16species of salps in August 1989 and March-April 1990. Severalspecies occurred in the surface waters only at particular timesof the day. suggesting diel vertical migrations on differentschedules. At the time of sampling, salps were present in lownumerical abundances and constituted only a small fraction ofthe total zooplankton biomass.     

Jet propulsion in Doliolum (Tunicata: Thaliacea)

The jet propulsion of doliolid gonozooids is described from a combination of kinematic, chamber pressure, and muscle electrical records. Doliolids respond to light mechanical stimuli by a rapid contraction of the locomotor muscle bands, producing a single jet pulse which drives the animal forwards or backwards at instantaneous velocities up to 21.4cm·s^?1 (over 50 body lengths·s^?1). Spike potentials from the (multiply innervated) locomotor muscle fibres are variable in size and probably are non-propagating. Maximum chamber pressures during the jet pulse range up to 500 Pa, doliolids ≈4.5 mm long perform around 4 × 10^?6 J work per contraction. Although the locomotor system is specialized for single rapid escape movements, the same movements are used at irregular intervals to maintain the horizontal position of the animal (which is denser than sea water) in the water column. The locomotor system is less economical than that of salps.     

Phosphate excretion rate ofSalpa fusiformis Cuvier (Tunicata : Thaliacea)

The rate of phosphate excretion bySalpa fusiformis was measured for animals of various weights at temperatures of 12.5 to 25 °C. Blastozooids excreted only small, often undetectable quantities of phosphate, in contrast to oozooids, in which the effects of individual weight and temperature were mainly studied. Excretion rate and specific excretion rates were independent of body weight (as total protein). The specific excretion rate increased exponentially with temperature, giving a Q10 of 4.54 (3.17 to 6.43) over the whole temperature range. Using the measurements of Andersen & Nival (1986) on the ammonia excretion rate ofS. fusiformis, we calculated the atomic N/P ratio, which appeared, for oozooids, similar to N/P ratios reported for other zooplanktonic species.     

Short communication. Determination of generation time and asexual fecundity of doliolids (Tunicata, Thaliacea)

The goal of this study was to provide temporal information on the generation time of Dolioletta gegenbauri and some of the life cycle's components. At 20C and 90 g C l^-1 of ingestible phytoplankton. D.gegenbauri's life cycle is completed in 20.5 days. Phorozooids 5 mm produce on average 11.0 gonozooids day^-1 over a period of 8-18 days. Utilizing field data on the abundance and size distribution of an assemblage of phorozooids and nurses, in conjunction with experimentally obtained rates, indicates that asexual production per cubic meter by phorozooids with that of nurses should result in rapid colonization of a wide shelf by doliolids, as observed during July and August 1981 on the southeastern continental shelf of the USA.      

Filtration and ingestion rates of Salpa fusiformis Cuvier (Tunicata : Thaliacea): Effects of size,individual weight and algal concentration

Filtration and ingestion rates of Salpa fusiformis Cuvier were determined while fed Phaeodactylumtricomutum Bohlin at concentrations of 2?64 × 10³ cells·ml^?1. Filtration and ingestion rates increase exponentially with increasing length and body protein. The relations between protein content and body length, and between filtration rate and weight are similar for blastozooids and oozooids. A capture efficiency of the order of 6–32% is calculated: Salpa fusiformis seems to have a low retention efficiency, but its very high filtration rate gives it pride of place amongst filter-feeders. Specific filtration rates are independent of weight; specific ingestion rates are independent of weight for blastozooids, but for oozooids they seem to diminish with increasing weight. The mean daily ration (μg C ingested · μg body C^?1) is 107% for a blastozooid and 117% for an oozooid. Specific filtration rates decrease exponentially as particle concentration rises, as for many other filter-feeders, and the specific ingestion rate follows an Ivlev relation.     

Horizontal distribution of Thetys vagina Tilesius (Tunicata, Thaliacea) in the Japan Sea during spring 2004

The occurrence of the salp Thetys vagina was observed in theJapan Sea during spring 2004. Catches up to 187 kg wet weight(WW) per 2.18 x 10⁵ m³ (equal to 0.9 g WW m^–3) were collectedwith 10-m diameter surface-water otter trawl nets. The horizontaldistribution indicated that the high biomass was related tothe area with high chlorophyll a (Chl a) concentration, whichwas located around the subarctic front with the warm TsushimaCurrent. Five prey taxa were identified from the gut contentsof individuals from the high Chl a area. The diatom Coscinodiscusspp. (13–55 µm in diameter) dominated numerically.Another significant prey was the large diatom Coscinodiscuswailesii (219–313 µm) that is an indicator of thespring bloom in this area. The mass occurrence of T. vaginathus appears related to phytoplankton availability, though themechanisms remain uncertain.     

Pyrosoma atlanticum (Tunicata, Thaliacea): diel migration and vertical distribution as a function of colony size

A large population of the colonial pelagic tunicate Pyrosomaatlanticum occurred in April 1991 in offshore waters of theLigurian Sea (Northwestern Mediterranean). The high numbersof colonies caught allowed their vertical distribution and dielmigration in the 0–965 m water column to be describedas a function of their size. Daytime depths and amplitudes ofthe migration were correlated with colony size. The amplitudeof the migration ranged from 90 m for 3-mm-length colonies to760 m for 51-mm-length colonies, with a mean amplitude of 410m for the whole population, all sizes pooled. The results ofhorizontal hauls at a given depth around sunrise and sunsetshowed a marked diurnal symmetry of the migratory cycle relativeto noon, and that migration of the population was not cohesive.For example, the larger the colonies, the later after sunsetthey reached the upper layers during their upward migration.     

Transport Speed of the Mucous Feeding Filter in Clavelina lepadiformis (Aplousobranchiata,Tunicata)

The transport speed of latex spheres trapped in the mucous feeding filter of 30 specimens of Calvelina lepadiformis (Müller 1776) was measured by microscopical examination and a stop watch. The speed across the gill screen increased from 24 μm s^?1 in small animals to 220 μm s^?1 in large ones. The net translocation speed of the food roll behind the dorsal Lamina was generally much slower but revealed a similar trend (7–78 μm s^?1). The increased feeding filter speed in larger animals was parallelled by an increased branchial circumference in such a way that the duration of water filtration through each part of the filter remained almost constant (between 38 and 56 s as means for all groups of animals). The amount of filter secreted by large animals approached 150 cm² h^?1 or 2.5 m² week^?1. Based on available data on water filtration rates it could be calculated that the speed of water through the filter was of the same order of magnitude as the observed translocation speed of the filter.     

Effect of temperature on the filtration rate and percentage of assimilation ofSalpa fusiformis Cuvier (Tunicata: Thaliacea)

The effect of temperature on filtration and ingestion rates ofSalpa fusiformis Cuvier was determined over the temperature range 13–22°C at a constant algal concentration. Filtration and ingestion rates increased with temperature up to an optimum (19.7 to 20.2°C) beyond which they decreased. Food assimilation for this salp species was determined while fed onPhaeodactylum tricornutum Bohlin orHymenomonas elongata Stein at different algal concentrations. The percent assimilation varied between 28 and 39% (mean: 32%) with the diatomP. tricornutum as food, and between 39 to 81% (mean: 64%) with the flagellateH. elongata. Assimilation did not seem to depend on the algal concentration but it was greater with the flagellate than with the diatom, the latter having a higher ash content.     

Differences in embryological development in two closely related species: Ihlea racovitzai and Ihlea magalhanica (Tunicata,Thaliacea)

Differences in the early stages of embryological development confirm the validity of the closely related salp species Ihlea racovitzai and Ihlea magalhanica. In the latter 8–12 oocytes and thus 8–12 follicles and uterine sacs are observed in the ovary; however most of them undergo a progressive degradation and only two embryos complete their development. In Ihlea racovitzai two embryos also develop but from the very beginning only the two successful follicles are found.     

Stolon development and some aspects of musculature in the characterization of Ihlea racovitzai (van Beneden, 1913) and Ihlea magalhanica (Apstein, 1894) (Tunicata,Thaliacea)

Summary A new contribution to the characterization of the salps Ihlea racovitzai and I. magalhanica, particularly their reproductive features, is presented. In both species two oocytes develop in the aggregate form, in the solitary form stolon growth is continuous. Buds grow continuously from the zone of deployment to the distal region without forming blocks or intermediate pieces. In Ihlea racovitzai the exit of the stolon and the resulting release of buds occurs later than in I. magalhanica. In the latter it takes place at the beginning of the strobilation of the stolon, which means an earlier and perhaps more continuous release of buds. The opening for the release of the buds is ventral and anterior to the nucleus in I. magalhanica and ventrolateral and posterior to the nucleus in I. racovitzai. Differences in the pattern of body muscle VII and the atrial retractors in the solitary forms are underlined.