Pelagic Tunicates Research Articles

The Effects of Microplastics on Dolioletta gegenbauri (Tunicata, Thaliacea).

Oceanographic studies revealed the abundance of minute plastic particles in coastal regions. Such particles, called microplastics, are abundant in sizes smaller than 100µm ESD (Equivalent Spherical Diameter) and can be collected and ingested by planktonic copepods. Those animals are the most abundant metazoans on our planet. Abundantly co-occurring with planktonic copepods in subtropical and temperate neritic waters are doliolids (Tunicata, Thaliacea), which can dominate subtropical shelves because of their high asexual reproductive performance. Our studies were designed to examine the effects of polystyrene beads at low abundance, compared with phytoplankton, on abundantly occurring gonozooids of Dolioletta gegenbauri. Our findings reveal that such abundance of microplastic particles, in the presence of environmental concentrations of phytoplankton, reduces rates of feeding, growth, and oxygen consumption of this tunicate. Feeding rates on phytoplankton in the presence of beads were reduced by up to 58%, growth rates by up to 85%, and oxygen consumption rates by up to 33%. We conclude that such microplastic particles could limit the often in situ encountered pronounced proliferation of this tunicate species (Deibel in: Bone (ed) The biology of pelagic tunicates, Oxford University Press, Oxford, 1998).

Inclusion of jellyfish in 30+ years of Ecopath with Ecosim models

Abstract A review of the functional role of jellyfish in Ecopath with Ecosim (EwE) models by Pauly et al. [Pauly, D., Graham, W., Libralato, S., Morissette, L., and Deng Palomares, M. L. 2009. Jellyfish in ecosystems, online databases, and ecosystem models. Hydrobiologia, 616: 67–85.] a decade ago concluded that recreation of jellyfish population dynamics in models required additional ecological research and the careful consideration of their unique biology during model construction. Here, amidst calls for ecosystem-based management and the growing recognition of jellyfishes' role in foodwebs, we investigate how jellyfish are implemented in EwE models and identify areas requiring improvement. Over time, an increasing percentage of models have included jellyfish. Jellyfish were often linked to the wider ecosystem, with many predators and prey included in models. However, ecotrophic efficiency, a measure of the extent to which they are used by higher trophic levels, was frequently set at low values, suggesting that jellyfish are still perceived as under-utilized components of the ecosystem. Moving forward, greater care should be taken to differentiate the functional roles played by ctenophores, cnidarians, and pelagic tunicates. Additionally, when feasible, early life stages should be incorporated as multi-stanza groups to more accurately depict jellyfishes' complex life cycle.

Salp metabolism: temperature and oxygen partial pressure effect on the physiology of Salpa fusiformis from the California Current

AbstractSalps are pelagic tunicates that play an important role in carbon cycling by filter feeding and packaging waste into dense fecal pellets that sink rapidly to the deep ocean. There has been limited research on salp physiology and no studies that examine how changes in environmental factors such as temperature and dissolved oxygen impact basic physiological processes. Here I examine temperature and oxygen partial pressure effect on metabolism in blastozooids of Salpa fusiformis. Routine metabolic rates of 1.66 and 3.95 μmol O2 g−1 h−1 wet weight at 10°C and 17°C, respectively, resulted in a Q10 = 3.45. The observed decrease in metabolism associated with decreased temperature, as well as hypoxia tolerance, is explored in the context of observed vertical migrations into hypoxic waters in the California Current, and potential impacts on carbon output. Metabolic rates for S. fusiformis are compared to metabolic rates published for other species of salps and gelatinous zooplankton. Expansion of this work across a broader set of species is critical to quantify the impact climate change may have on salps and their role in marine carbon cycling.

Updated checklist of the marine gelatinous macrofauna from the Azores

Updated checklist of the marine gelatinous macrofauna from the Azores

Diet and trophic interactions of a circumglobally significant gelatinous marine zooplankter, Dolioletta gegenbauri (Uljanin, 1884).

Gelatinous zooplankton play a crucial role in marine planktonic food webs. However, primarily due to methodological challenges, the in situ diet of zooplankton remains poorly investigated and little is known about their trophic interactions including feeding behaviour, prey selection and in situ feeding rates. This is particularly true for gelatinous zooplankton including the marine pelagic tunicate, Dolioletta gegenbauri. In this study, we applied an 18S rRNA amplicon metabarcoding approach to identify the diet of captive-fed and wild-caught D.gegenbauri on the midcontinental shelf of the South Atlantic Bight, USA. Sequencing-based approaches were complimented with targeted quantitative real-time polymerase chain reaction (PCR) analyses. Captive-fed D.gegenbauri gut content was dominated by pico-, nano- and micro-plankton including pico-dinoflagellates (picozoa) and diatoms. These results suggested that diatoms were concentrated by D.gegenbauri relative to their concentration in the water column. Analysis of wild-caught doliolids by quantitative real-time PCR utilizing a group-specific diatom primer set confirmed that diatoms were concentrated by D.gegenbauri, particularly by the gonozooid life stage associated with actively developing blooms. Sequences derived from larger metazoans were frequently observed in wild-caught animals but not in captive-fed animals suggesting experimental bias associated with captive feeding. These studies revealed that the diet of D.gegenbauri is considerably more diverse than previously described, that parasites are common in wild populations, and that prey quality, quantity and parasites are likely all important factors in regulating doliolid population dynamics in continental shelf environments.

Immunological response to bacterial infection in a pelagic tunicate: Inflammation in the salp Thalia democratica

Thaliaceans are pelagic tunicates that play a key role in trophic chains of the oceans. In the field of tunicate immunity, a notable gap is the lack of data on their inflammatory response. The common salp, Thalia democratica, possesses scant immunocytes, represented by a phagocytic line (hyaline amebocytes) and a mast cell-like line (granular cells). We aimed to provide the first investigation of defense reactions upon exposure to a large amount of bacteria (Bacillus clausii). We detected (i) bacterial phagocytosis by hyaline amebocytes, (ii) degradation of phagocytizing hyaline amebocytes in the tunic after transcellular diapedesis from the hemocoel, and (iii) release of heparin, histamine, and TNF-α by granular cells. Cell degranulation and phagocytosis occurred in epidermal cells lining the hemocoel, and an excess of mucus was observed in the post-branchial gut, causing a functional inhibition of cilia and microvilli. These findings indicate multi-step events comparable to an inflammation involving responses at both tissue and organismal levels.

Surface mesozooplankton assemblages in a tropical coastal upwelling ecosystem: Southeastern Arabian Sea

The spatio-temporal variation of mesozooplankton assemblages and the relative environmental variables were assessed in a coastal upwelling system. Remarkable seasonal variations were found in the mesozooplankton community structure and Chl-a concentration due to the seasonal shift in the environmental variables. Copepods were found to be the dominant group during the winter monsoon (WM) and spring inter monsoon (SIM) seasons whereas, cladocerans (Evadne tergestina and Penilia avirostris) were dominant during the summer monsoon (SM) which may be attributed to the availability of preferential food and favorable environmental conditions (viz., temperature and salinity etc.). Multivariate statistical analysis revealed that the distribution and their possible spatio-temporal pattern of dominant copepods (Acrocalanus gibber, Acartia danae, Nanocalanus minor and Oncaea venusta), siphonophores (Chelophyes appendiculata and Diphyes chamissonis) and pelagic tunicates (Doliolida sp.) synchronized with their specific food habits and adaptive mechanism. The present findings emphasize the significance of the trophic relationship between Chl-a concentration and mesozooplankton abundance in the coastal waters of Kochi, southeastern Arabian Sea.

A taxonomic revision of the genus Thalia Blumenbach, 1798; Weelia Yount, 1954; Brooksia Metcalf, 1918 (Salpida: Salpidae) from East Coast of Peninsular Malaysia

The marine pelagic tunicates of Family Salpidae Lahille, 1888 presence in the coastal waters of Terengganu was studied for the first time. Samples were collected from April to July 2016 using 200µm Bongo net; hauled vertically from a stationary vessel; and preserved in 5% buffered formaldehyde. A total of 4 species under this family were found, observed and identified: Thalia rhomboides (Quoy and Gaimard 1824); Thalia sibogae (van Soest 1973); Weelia cylindrica (Cuvier 1804) and Brooksia rostrata (Traustedt 1893). All species were identified as new records in Malaysian waters. The description on morphological characteristics and a key to the solitary and aggregate of the recorded species is added. The distribution was analyzed from the 18 sampling stations in theTerengganu waters including Pulau Bidong, Pulau Yu and Pulau Kapas. The collected data was then compiled with previous available global literature on the distribution and occurrence of these four species, consequently updating the biodiversity of Malaysian fauna and its worldwide biogeography distribution.

Consumption of pelagic tunicates by cetaceans calves in the Mediterranean Sea

Gelatinous zooplankton, including jellyfish, ctenophores and pelagic tunicates, constitutes fragile marine animals that live in the water column, and represent an important resource for marine food webs through their seasonal pulses. Although there is scarce evidence on the occurrence of gelatinous zooplankton in stomach contents of apex, endothermic predators such as cetaceans, the ecological significance of such observations requires consideration. In this study, we report on the occurrence of pelagic tunicates in the stomach of three individual calves of two cetacean species from the western Mediterranean, and collate all previous reports of gelatinous zooplankton in cetacean diets. We then briefly discuss the possible dietary significance of these observations.

Mammoth grazers on the ocean's minuteness: a review of selective feeding using mucous meshes.

Mucous-mesh grazers (pelagic tunicates and thecosome pteropods) are common in oceanic waters and efficiently capture, consume and repackage particles many orders of magnitude smaller than themselves. They feed using an adhesive mucous mesh to capture prey particles from ambient seawater. Historically, their grazing process has been characterized as non-selective, depending only on the size of the prey particle and the pore dimensions of the mesh. The purpose of this review is to reverse this assumption by reviewing recent evidence that shows mucous-mesh feeding can be selective. We focus on large planktonic microphages as a model of selective mucus feeding because of their important roles in the ocean food web: as bacterivores, prey for higher trophic levels, and exporters of carbon via mucous aggregates, faecal pellets and jelly-falls. We identify important functional variations in the filter mechanics and hydrodynamics of different taxa. We review evidence that shows this feeding strategy depends not only on the particle size and dimensions of the mesh pores, but also on particle shape and surface properties, filter mechanics, hydrodynamics and grazer behaviour. As many of these organisms remain critically understudied, we conclude by suggesting priorities for future research.

Pyrosome consumption by benthic organisms during blooms in the northeast Pacific and Gulf of Mexico.

Pyrosome consumption by benthic organisms during blooms in the northeast Pacific and Gulf of Mexico.

Plankton food for benthic fish: de visu evidence of trophic interaction between rainbow wrasse (Coris julis) and pelagic tunicates (Pegea confoederata)

Salps (pelagic tunicates) are rarely observed in nature and trophic interactions involving them mainly rely on the inspection of stomach contents of their potential predators. Moreover, salps have soft bodies that are hardly identified in potential consumers. We involved recreational SCUBA-divers and photographers in collecting de visu evidence of i) massive occurrence of salps and ii) trophic interactions involving salps as preys and benthic animals as consumers. Direct evidence of trophic interactions between salps and benthic fish was documented by photographic frames. We detected a long colony of the salp Pegea confaederata being transported by currents close to the substrate on top of Banco di Santa Croce, an underwater rocky outcrop in the Gulf of Naples (Italy). An individual of the rainbow wrasse Coris julis attacked the above-mentioned salp colony by selectively detaching individuals and biting their stomach. Our report of a trophic interaction between labrids and salps is the second in fifty years and the previous one was only indirect. In this study, citizen science allowed detecting both neglected marine animals like salps and trophic interactions involving them. Visual, direct evidence of predation on salps by benthic fish adds further knowledge about patterns of living-matter fluxes between plankton and benthos, opening new questions on the potential of global change in modifying the efficient circulation of organic matter in marine systems.

Measurement of refractive indices of tunicates\u2019 tunics: light reflection of the transparent integuments in an ascidian Rhopalaea sp. and a salp Thetys vagina

BackgroundTunic is a cellulosic, integumentary matrix found in tunicates (Subphylum Tunicata or Urochordata). The tunics of some ascidian species and pelagic tunicates, such as salps, are nearly transparent, which is useful in predator avoidance. Transparent materials can be detected visually using light reflected from their surfaces, with the different refractive indices between two media, i.e., tunic and seawater, being the measure of reflectance. A larger difference in refractive indices thus provides a larger measure of reflectance.ResultsWe measured the refractive indices of the transparent tunic of Thetys vagina (salp: Thaliacea) and Rhopalaea sp. (ascidian: Ascidiacea) using an Abbe refractometer and an ellipsometer to estimate the light reflection at the tunic surface and evaluate the anti-reflection effect of the nipple array structure on the tunic surface of T. vagina. At D-line light (λ = 589 nm), the refractive indices of the tunics were 0.002–0.004 greater than seawater in the measurements by Abbe refractometer, and 0.02–0.03 greater than seawater in the measurements by ellipsometer. The refractive indices of tunics were slightly higher than that of seawater. According to the simulation of light reflection based on rigorous coupled wave analysis (RCWA), light at a large angle of incidence will be completely reflected from a surface when its refractive indices are smaller than seawater. Therefore, the refractive index of integument is important for enabling transparent organisms to remain invisible in the water column.ConclusionIn order to minimize reflectance, the refractive index should be similar to, but never smaller than, that of the surrounding seawater. The simulation also indicated that the presence or absence of a nipple array does not cause significant difference in reflectance on the surface. The nipple array on the tunic of the diurnal salp may have another function, such as bubble repellence, other than anti-reflection.

Pelagic tunicates in the China Seas

ABSTRACTThe biogeography of pelagic tunicates belonging to the two taxonomic classes Larvacea and Thaliacea was analysed using seven sampling stations along the coastal regions of Taiwan which contribute to all the China Seas surrounding Taiwan. The collected data were then compared with the information in the available literature about pelagic tunicate species diversity in the China Seas (Bohai Sea, North Yellow Sea, East China Sea and South China Sea) and previous studies on these organisms in Taiwan waters to get a better understanding of their biodiversity, abundance and distribution. A total of 19 species of pelagic tunicates were observed and identified to the speciel level: five species belonging to the class Larvacea, in the two families Oikopleuriidae and Fritillariidae; 14 species belonging to the class Thaliacea, in the families Salpidae and Doliolidae. We summarised morphological characteristics of the recorded species which were found to be useful for identification, and we provided further information about their global distribution and ecological preferences. Our results revealed that pelagic tunicates occurred in the China Seas with high species richness throughout the year. This is the first account on the class Larvacea from Taiwan. Comparing our results with available records from all China Seas, Taiwan proved to be a species diversity hotspot for pelagic tunicates, especially for the family Salpidae. The waters of southern Taiwan showed a higher species richness compared to the northern counterpart. The doliolid Doliolum denticulatum can be designated as an indicator of the low-temperature China Coastal Current species.

Trans-Atlantic variability in ecology of the pelagic tunicate Salpa thompsoni near the Antarctic Polar Front

The distribution, density, demography and feeding dynamics of the pelagic tunicate Salpa thompsoni were investigated during the trans-Atlantic ANTARKTIS XXVIII/3 expedition to the Southern Ocean, on board RV Polarstern, between January and March 2012. Net samples were collected using an RMT-8 at four major sampling regions in the proximity of the Antarctic Polar Front (APF): along a 10°E transect, Salpastan, 12°W eulerian study, and the South Georgia Basin. Salps, mostly S. thompsoni, were found at all but one station and with few exceptions contributed <<40% to total zooplankton in terms of both abundance and biomass. Salp abundance and biomass was lowest (6.2 ind.1000m−3 and 0.8mgDWm−3) north of the APF along the 10°E transect and highest (3150 ind.1000m−3 and 20.5mgDWm−3) at the Salpastan station south of the APF. Size distributions of S. thompsoni aggregates and solitaries, and their developmental dynamics, were similar in all locations except the Salpastan region. In aggregates, the overall salp size distributions were strongly right-tailed with the mass of the distribution always concentrated in the left where small aggregates (6–10mm) dominated. During the eulerian study at 12°W, several cohorts of aggregates and solitaries were traceable allowing assessment of the daily growth rates of S. thompsoni. Estimated in situ growth rates of aggregates and solitaries were 0.53±0.18 and 2.83±0.42mmday−1, respectively, and the complete S. thompsoni life cycle duration (sexual+asexual) during austral summer at the APF region may have been as short as 2–3 months. The rapid growth rates of S. thompsoni found in this study urgently require further research to re-evaluate salp life cycle in the Southern Ocean.

Environmental drivers of salp Thalia democratica population dynamics from in situ observations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 561:189-201 (2016) - DOI: https://doi.org/10.3354/meps11915 Environmental drivers of salp Thalia democratica population dynamics from in situ observations Maria Pascual1,*, Michael G. Neubert2, José Luis Acuña3, Andrew R. Solow2, Carlos Dominguez-Carrió1, Joaquín Salvador1, Alejandro Olariaga1, Verónica Fuentes1 1Institut de Ciències del Mar, 08003 Barcelona, Spain 2Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 3Universidad de Oviedo, 33003 Oviedo, Spain *Corresponding author: mpascual@icm.csic.es ABSTRACT: Thalia democratica blooms are a recurrent phenomenon in many coastal areas of the Mediterranean Sea and have significant ecological effects. To better understand the environmental drivers of salp blooms, we conducted 8 surveys to sample T. democratica in contrasting seasonal, temperature and chlorophyll conditions. In each survey, short-term variations in the abundances of different salp stages were assessed by sampling the same population at 30 min intervals. Using these data, we estimated the parameters in a set of stage-classified matrix population models representing different assumptions about the influence of temperature and chlorophyll on each stage. In the model that best explains our observations, only females are affected by changes in water temperature. Whether this is a direct influence of temperature or an indirect effect reflecting low food availability, female reproduction cessation seems to slow population growth under unfavourable conditions. When conditions become favourable again, females liberate the embryo and change sex to male, allowing for mating under extremely low salp densities and triggering the bloom. In contrast to previous findings, our results suggest that females, rather than oozooids, are responsible for the sustainability of salp populations during latency periods. KEY WORDS: Matrix population models · Pelagic tunicate ecology · Population latency · Gelatinous zooplankton blooms Full text in pdf format Supplementary material PreviousNextCite this article as: Pascual M, Neubert MG, Acuña JL, Solow AR and others (2016) Environmental drivers of salp Thalia democratica population dynamics from in situ observations. Mar Ecol Prog Ser 561:189-201. https://doi.org/10.3354/meps11915 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 561. Online publication date: December 15, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

One tunic but more than one barcode: evolutionary insights from dynamic mitochondrial DNA inSalpa thompsoni(Tunicata: Salpida)

The DNA barcode within the mitochondrial cox1 gene is typically used to assess the identity and diversity of animals under the assumption that individuals contain a single form of this genetic marker. This study reports on a novel exception from the pelagic tunicate Salpa thompsoni Foxton. Oozoids caught off South Georgia and the Antarctic Peninsula generated barcodes consisting of a single prominent DNA sequence with some additional, subtler signals of intra-individual variation. Further investigation revealed this was due to duplicated and/or minicircular DNAs. These could not simply be explained as artefacts or nuclear copies of mitochondrial DNA, but provided evidence for heteroplasmy arising from a dynamic mitochondrial genome. Genetic variation of this sort may allow S. thompsoni to ecologically benefit from asexually driven population blooms without incurring the genetic cost of an excessive mutational load. Analysis of the prominent barcode sequence data yielded low haplotype (h < 0.61) and nucleotide (π < 0.0014) diversities, and no evidence for genetic structure between sampling locations as assessed using analysis of molecular variance. These results are consistent with the impact of population blooms and the mixing effect of Southern Ocean currents on S. thompsoni genetic diversity.

Interactions of gelatinous zooplankton within marine food webs

Gelatinous zooplankton (GZ) comprise a taxonomically and functionally diverse group of marine organisms which includes ctenophores, cnidarians and pelagic tunicates, sharing a soft, mostly transparent body texture, a high body water content and a lack of exoskeleton. They range in size from less than a millimetre to nearly 2 m for the cnidarian jellyfish Nemopilema nomurai, and comprise some of the fastest growing metazoans on Earth (Hopcroft et al., 1998), sometimes surpassing crustacean zooplankton in their contribution to secondary production (i.e. in subtropical waters; Jaspers et al., 2009). They feed on a wide range of prey sizes, with predator–prey ratios comparable in some cases to those of baleen whales and krill (Deibel and Lee, 1992), and with prey removal rates which are similar to those of their non-gelatinous competitors (Acuna et al., 2011). In spite of early work pointing to gelatinous zooplankton as a trophic dead end (Verity and Smetacek, 1996), evidence is rapidly accumulating which shows that they may potentially channel energy from the picoplankton-sized, microbial loop organisms up to the higher trophic levels, including fish (Llopiz et al., 2010). However, this pathway is still largely neglected in most food web investigations even though it is now becoming clear that GZ represent a major fraction of the diet of several commercially important fish species such as bluefin tuna (Thunnus thynnus) (Cardona et al., 2012).

Tunicates: exploring the sea shores and roaming the open ocean. A tribute to Thomas Huxley.

This review is a tribute to the remarkable contributions of Thomas Huxley to the biology of tunicates, the likely sister group of vertebrates. In 1851, the great biologist and philosopher published two landmark papers on pelagic tunicates in the Philosophical Transactions of the Royal Society. They were dedicated to the description of the adult anatomy and life cycle of thaliaceans and appendicularians, the pelagic relatives of ascidians. In the first part of this review, we discuss the novel anatomical observations and evolutionary hypotheses made by Huxley, which would have a lasting influence on tunicate biology. We also briefly comment on the more philosophical reflections of Huxley on individuality. In the second part, we stress the originality and relevance of past and future studies of tunicates in the resolution of major biological issues. In particular, we focus on the complex relationship between genotype and phenotype and the phenomenon of developmental system drift. We propose that more than 150 years after Huxley's papers, tunicate embryos are still worth studying in their own right, independently of their evolutionary proximity to vertebrates, as they provide original and crucial insights into the process of animal evolution. Tunicates are still at the forefront of biological research.

Biogeochemistry and ecology of Pyrosoma spinosum from the Central Arabian Sea.

A swarm of pelagic tunicate (Pyrosoma spinosum) was found in the surface open waters of the Arabian Sea during late southwest monsoon (September 2007). The swarm site was characterized by moderate southwesterly wind (approximately 7 m s-1), relatively low sea-surface temperature (approximately 26°C), shallow mixed layer (approximately 50 m), and substantial macro-nutrient concentrations (surface values: 2.5 μM nitrate, 0.3 μM phosphate, 0.9 μM silicate, and 5.0 μM ammonium). Despite adequate macronutrient availability, the swarm site was characterized by low diversity of phytoplankton (>5 μm) and mesozooplankton in the upper 200 m. Low chlorophyll a concentration (27.3 mg/m2 in the upper 120 m) at the swarm site was dominated (90% to 95% in the upper 40 m) by the Synechococcus (20 × 106 /ml). Silicate deficiency in surface waters upwelled or entrained from the thermocline may be a key factor for the dominance of smaller autotrophs (flagellates and cyanobacteria) that seems to offer favorable conditions for episodic occurrence of swarms of these filter feeders. Low carbon content (37% of total dry weight) and the lower molar(carbon-to-nitrogen) ratio (5) in P.spinosum suggestgrowth of these organisms is carbon-limited. Wedescribe various physicochemical and biological conditions at the P.spinosum swarmlocation and at two other nearby sites not affected by it. The biological factors predominantly high densities of Synechococcus and flagellates were best suited conditions for the proliferation of pyrosome biomass in the central Arabian Sea.