Ascidian Research Articles

Effects of biological filtration by ascidians on microplastic composition in the water column

Plastic pollution, a widespread environmental challenge, significantly impacts marine ecosystems. The degradation of plastic under environmental conditions results in the generation of microplastic (MP; <5 mm) fragments, frequently ingested by marine life, including filter-feeders such as ascidians (Chordata, Ascidiacea). These organisms are integral to benthic-pelagic coupling, transporting MP from the water column through marine food web.Here, we explored the effect of filtration and digestion by the solitary ascidian Styela plicata on the composition of MP in the water column and on the sinking rates of faecal matter, focusing on differences between two distinct plastics, polystyrene (PS) and the biodegradable polylactic acid (PLA). The ascidians efficiently removed 2–5 μm particles within 2 h of filtration. Following digestion and secretion process, PS concentrations in water increased while PLA concentration remained stable. Some particles were egested into the water column repackaged inside faecal pellets, which significantly increased the pellets' drag force and sinking velocity. Raman spectral analysis of digested MP revealed distinct spectrum alterations due to coating by organic substances. These findings highlight the role of ascidians — and other filter-feeders— in modifying the structure of MP in their environment. Research into such modifications is crucial for understanding the MP cycle and its consequences in marine environments.

Halosquirtibacter laminarini gen. nov., sp. nov. and Halosquirtibacter xylanolyticus sp. nov., marine anaerobic laminarin and xylan degraders in the phylum Bacteroidota

The bacterial group of the phylum Bacteroidota greatly contributes to the global carbon cycle in marine ecosystems through its specialized ability to degrade marine polysaccharides. In this study, it is proposed that two novel facultative anaerobic strains, DS1-an-13321T and DS1-an-2312T, which were isolated from a sea squirt, represent a novel genus, Halosquirtibacter, with two novel species in the family Prolixibacteraceae. The 16S rRNA sequence similarities of these two strains were 91.26% and 91.37%, respectively, against Puteibacter caeruleilacunae JC036T, which is the closest recognized neighbor. The complete genomes of strains DS1-an-13321T and DS1-an-2312T each consisted of a single circular chromosome with a size of 4.47 and 5.19 Mb, respectively. The average amino acid identity and the percentage of conserved proteins against the type species of the genera in the family Prolixibacteraceae ranged from 48.33 to 52.35% and 28.34–37.37%, respectively, which are lower than the threshold for genus demarcation. Strains DS1-an-13321T and DS1-an-2312T could grow on galactose, glucose, maltose, lactose, sucrose, laminarin, and starch, and only DS1-an-2312T could grow on xylose and xylan under fermentation conditions. These strains produced acetic acid and propionic acid as the major fermentation products. Genome mining of the genomes of the two strains revealed 27 and 34 polysaccharide utilization loci, which included 155 and 249 carbohydrate-active enzymes (CAZymes), covering 57 and 65 CAZymes families, respectively. The laminarin-degrading enzymes in both strains were cell-associated, and showed exo-hydrolytic activity releasing glucose as a major product. The xylan-degrading enzymes of strain DS1-an-2312T was also cell-associated, and had endo-hydrolytic activities, releasing xylotriose and xylotetraose as major products. The evidence from phenotypic, biochemical, chemotaxonomic, and genomic characteristics supported the proposal of a novel genus with two novel species in the family Prolixibacteraceae, for which the names Halosquirtibacter laminarini gen. nov., sp. nov. and Halosquirtibacter xylanolyticus sp. nov. are proposed. The type strain of Halosquirtibacter laminarini is DS1-an-13321T (= KCTC 25031T = DSM 115329T) and the type strain of Halosquirtibacter xylanolyticus is DS1-an-2312T (= KCTC 25032T = DSM 115328T).

The genome sequence of the Orange-tipped sea squirt, Corella eumyota Traustedt, 1882.

We present a genome assembly from an individual specimen of Corella eumyota (the Orange-tipped sea squirt; Chordata; Ascidiacea; Phlebobranchia; Corellidae). The genome sequence is 129.3 megabases in span. Most of the assembly is scaffolded into 7 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 14.53 kilobases in length.

Determination of naturally derived propionic, benzoic, and sorbic acids in seafood, meats, and fruits during storage

Propionic acid, benzoic acid, and sorbic acid are common preservatives in processed foods, but their natural concentrations in raw foods are not well understood. In Korea, if propionic acid or benzoic acid exceeds certain levels in processed plant-based foods, manufacturers must prove they are naturally occurring to avoid recalls. This regulation applies to both local and imported products, with non-compliance leading to economic costs and damage to brand reputation. To address this, further research is needed to build a database of naturally occurring preservatives in raw foods and develop food safety standards. This study quantified the levels of propionic, benzoic, and sorbic acids in 37 raw foods stored at different temperatures for 2 weeks, using gas chromatography and high-performance liquid chromatography. The changes in acid concentrations during storage were examined, with preservatives identified by mass spectrometry. Sensory evaluation and total viable count were used to assess spoilage in seafood and meat samples. The matrix effects were evaluated, and the quantification methods were validated using seven food matrices. The intra- and interday accuracies and precisions (% relative standard deviation, %RSD) values met the Codex guidelines. In general, the propionic acid contents of most seafood and meat samples increased during storage, with the highest content being found in manila clams. Interestingly, the fresh sea squirt sample contained a higher propionic acid content (456mg/kg) than the other samples. However, benzoic acid and sorbic acid were not detected in most samples, with the exception of the jujube and apple samples.

Illuminating the richness of the ascidian fossil record: a new exceptionally diverse assemblage of ascidian spicules from the Middle Miocene of Bosnia and Herzegovina

AbstractAscidians, or sea squirts, are sac‐like sessile tunicates commonly found in modern seas. Although the oldest ascidians, or at least ascidian‐like tunicates, are mid‐Cambrian in age, the quality of the ascidian fossil record is extraordinarily poor. It mostly consists of isolated finds or low‐diversity assemblages, often represented by mineral spicules. Our study reports the world's most diverse assemblage of ascidian spicules, originating from the Middle Miocene Bogutovo Selo near Ugljevik, Bosnia and Herzegovina. This material includes 31 spicule types, with four assignable to species (Lissoclinum cf. perforatum, Polysyncraton cf. bilobatum, Didemnum cf. vexillum and D. cf. leopardi) and 10 to genera, all belonging to aplousobranchiate ascidians. Comparing our findings with those of two other studies that use modern biological nomenclature, our assemblage shows a closer resemblance to the distant Eocene Australian assemblage than to the Miocene ascidians from Eastern Paratethys. This suggests the persistence of a once‐homogeneous and widely distributed Eocene fauna into the Miocene, while the Eastern Paratethyan basin developed an endemic fauna after the isolation of Eastern Paratethys from the open sea. Some taxa of our assemblage currently inhabit the Mediterranean Sea. The discovery of one species in distant South African waters suggests that tectonic and environmental changes during the Late Miocene, including the closure of the Gibraltar Strait and prior disconnection from the Indian Ocean, may have limited its survival to remote refugia. The study underscores the importance of including spicules in reconstructing ascidian faunas in the geological past, an area that has been surprisingly understudied.

Palatability of ascidians: a meta-analysis of the predation effect on ascidians

Ascidians are marine sessile animals that have evolved many strategies to reduce predation. Previous manipulative experiments with ascidian tissues or pellets have shown that they have chemical defenses that render them unpalatable. However, predation-exclusion experiments on a community scale have shown that ascidians are almost entirely eaten when exposed to predators. Based on these contrasting results, we performed a meta-analysis to assess the importance of study site, experiment design, ascidian sociability, and predator identity to the efficacy of the ascidian defense. Our study is the first quantitative review of predation on ascidians, and it emphasizes the importance of ecological interactions beyond the specific defense tactics of the organisms. We found that multiple factors can interfere with the effectiveness of the ascidian defense. Palatability studies have shown evidence for ascidian defense mechanisms; however, they depend on the identity of the predators (e.g. fish, crab, amphipod). We did not find evidence of ascidian defense in community studies. There is a lack of field experiments, mainly on solitary ascidians, that evaluate their predation risk in communities. Research on ascidian defense mechanisms is also geographically biased toward the temperate region in the Northern Hemisphere. The commonly held belief that ascidians possess active defenses may be overestimated, and the defenses that do exist are probably restricted to only a few species. This misconception has been caused mainly by methodological and geographical bias that has resulted in tests being performed only on species with previous evidence of defenses. Therefore, we need more worldwide studies focusing on the ecological relationships between ascidians and predators, specifically in natural communities under field conditions.

A microfluidic chip for immobilization and imaging of Ciona intestinalis larvae.

Sea squirts (Tunicata) are chordates and develop a swimming larva with a small and defined number of individually identifiable cells. This offers the prospect of connecting specific stimuli to behavioral output and characterizing the neural activity that links these together. Here, we describe the development of a microfluidic chip that allows live larvae of the sea squirt Ciona intestinalis to be immobilized and recorded. By generating transgenic larvae expressing GCaAMP6m in defined cells, we show that calcium ion levels can be recorded from immobilized larvae, while microfluidic control allows larvae to be exposed to specific waterborne stimuli. We trial this on sea water carrying increased levels of carbon dioxide, providing evidence that larvae can sense this gas.

Exploring the antibacterial potential of tunicate-associated bacteria (Ascidiacea) at the shipwreck site of Menjangan Kecil Waters, Karimunjawa

Menjangan Kecil Island is situated south of Karimunjawa Island and boasts a rich diversity of coral reefs and associated marine life, including tunicates. Tunicates, also known as sea squirts, produce secondary metabolites to defend against predators. This study aims to explore the antibacterial potential of tunicate-associated bacteria from shipwrecks in Menjangan Kecil Waters. The research adopts an exploratory descriptive approach. Seventy-two bacterial isolates were recovered from five tunicate specimens. Fifteen isolates exhibited antibacterial activity against Vibrio harveyi, with two isolates, KJ1.3.02.05 and KJ1.4.02.02, displaying the highest activity. Molecular identification via 16S rRNA gene amplification revealed that KJ1.3.02.05 was Sinomicrobium oceani (99.64% similarity), and KJ1.4.02.02 was Bacillus haynesii (98.64% similarity).

Adaptive alien genes are maintained amid a vanishing introgression footprint in a sea squirt.

Human transport of species across oceans disrupts natural dispersal barriers and facilitates hybridization between previously allopatric species. The recent introduction of the North Pacific sea squirt, Ciona robusta, into the native range of the North Atlantic sea squirt, Ciona intestinalis, is a good example of this outcome. Recent studies have revealed an adaptive introgression in a single chromosomal region from the introduced into the native species. Here, we monitored this adaptive introgression over time, examining both the frequency of adaptive alleles at the core and the hitchhiking footprint in the shoulders of the introgression island by studying a thousand Ciona spp. individuals collected in 22 ports of the contact zone, 14 of which were sampled 20 generations apart. For that purpose, we developed a KASP multiplex genotyping approach, which proved effective in identifying native, nonindigenous and hybrid individuals and in detecting introgressed haplotypes. We found no early generation hybrids in the entire sample, and field observations suggest a decline in the introduced species. At the core region of the introgression sweep, where the frequency of C. robusta alleles is the highest and local adaptation genes must be, we observed stable frequencies of adaptive alien alleles in both space and time. In contrast, we observed erosion of C. robusta ancestry tracts in flanking chromosomal shoulders on the edges of the core, consistent with the second phase of a local sweep and a purge of hitchhiked incompatible mutations. We hypothesize that adaptive introgression may have modified the competition relationships between the native and invasive species in human-altered environments.

Use of tunicate meal (pleated sea squirt Styela plicata) protein as a partial replacement of menhaden fish meal protein in the diet of juvenile Black Sea Bass

AbstractObjectiveThe pleated sea squirt Styela plicata (subphylum Tunicata), an invasive marine invertebrate in coastal waters of southeastern North Carolina, was investigated as an alternative protein source to fish meal (FM) in the diet of juvenile Black Sea Bass Centropristis striata.MethodsSix different isoproteic and isolipidic diets were formulated to replace 0.0, 8.3, 16.7, 25.0, 33.3, and 41.6% of FM protein with tunicate meal (TM) protein by supplementing 0, 5, 10, 15, 20, and 25% TM in the diets. The experimental system consisted of eighteen 75‐L tanks supported by a recirculating seawater system in an indoor, climate‐controlled laboratory. Juveniles (average weight = 7.1 g) were stocked at a density of 15 fish/tank (N = 3 tanks/treatment) and were fed the test diets daily to apparent satiation for 55 days.ResultReplacement of FM protein with TM protein caused slight declines in dietary amino acid concentrations (notably arginine, methionine, and tryptophan) at higher replacement levels. At terminal sampling, no significant differences in survival (87–96%), percent body weight gain (157–228%), feed conversion ratio (1.50–1.71), or proximate composition were observed among dietary treatment groups. However, significant positive linear trends were found between incremental levels of TM and final fish weight, body weight gain, and specific growth rate. Whole‐body fatty acid composition reflected dietary levels.ConclusionResults indicate that TM protein can be used to replace at least 41.6% of the FM protein in the diet for juvenile Black Sea Bass without adverse effects on survival, growth, feed utilization, or whole‐body proximate composition.

The genome sequence of the Orange-tipped sea squirt, Corella eumyota Traustedt, 1882

We present a genome assembly from an individual specimen of Corella eumyota (the Orange-tipped sea squirt; Chordata; Ascidiacea; Phlebobranchia; Corellidae). The genome sequence is 129.3 megabases in span. Most of the assembly is scaffolded into 7 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 14.53 kilobases in length.

Global level of methylation in the sea lamprey (jawless vertebrate) genome is intermediate between invertebrate and jawed vertebrate genomes.

In eukaryotes, cytosine methylation is a primary heritable epigenetic modification of the genome that regulates many cellular processes. In invertebrate, methylated cytosine generally located on specific genomic elements (e.g., gene bodies and silenced repetitive elements) to show a "mosaic" pattern. While in jawed vertebrate (teleost and tetrapod), highly methylated cytosine located genome-wide but only absence at regulatory regions (e.g., promoter and enhancer). Many studies imply that the evolution of DNA methylation reprogramming may have helped the transition from invertebrates to jawed vertebrates, but the detail remains largely elusive. In this study, we used the whole-genome bisulfite-sequencing technology to investigate the genome-wide methylation in three tissues (heart, muscle, and sperm) from the sea lamprey, an extant agnathan (jawless) vertebrate. Strikingly, we found that the methylation level of the sea lamprey is very similar to that in sea urchin (a deuterostome) and sea squirt (a chordate) invertebrates. In sum, the global pattern in sea lamprey is intermediate methylation level (around 30%), that is higher than methylation level in the genomes of pre-bilaterians and protostomes (1%-10%), but lower than methylation level appeared in jawed vertebrates (around 70%, teleost and tetrapod). We anticipate that, in addition to genetic dynamics such as genome duplications, epigenetic dynamics such as global methylation reprograming was also orchestrated toward the emergence and evolution of vertebrates.

Vanadium Accumulation and Reduction by Vanadium-Accumulating Bacteria Isolated from the Intestinal Contents of Ciona robusta

The sea squirt Ciona robusta (formerly Ciona intestinalis type A) has been the subject of many interdisciplinary studies. Known as a vanadium-rich ascidian, C. robusta is an ideal model for exploring microbes associated with the ascidian and the roles of these microbes in vanadium accumulation and reduction. In this study, we discovered two bacterial strains that accumulate large amounts of vanadium, CD2-88 and CD2-102, which belong to the genera Pseudoalteromonas and Vibrio, respectively. The growth medium composition impacted vanadium uptake. Furthermore, pH was also an important factor in the accumulation and localization of vanadium. Most of the vanadium(V) accumulated by these bacteria was converted to less toxic vanadium(IV). Our results provide insights into vanadium accumulation and reduction by bacteria isolated from the ascidian C. robusta to further study the relations between ascidians and microbes and their possible applications for bioremediation or biomineralization.

Multi-Index Fusion Debris Flow Early Warning Model Based on Spatial Interpolation and Support Vector Machine

Debris flow early warning is an effective method to prevent major disasters, so a multi-index fusion debris flow early warning model based on spatial interpolation and a support vector machine is designed. Aiming at the discrete rainfall data in the study area, the collaborative Kriging spatial interpolation method based on Kriging spatial interpolation is adopted to process the rainfall data into multi-index fused surface data. The rainfall data after spatial interpolation are used as the input sample data of the support vector machine early warning model, and the optimal parameters of the support vector machine are calculated by the sea squirt algorithm, and then the debris flow early warning results are output. After experimental analysis, the model can obtain rainfall surface data. After calculation by the model, the accuracy of the early warning probability of debris flow is improved, and the early warning result is consistent with the actual result of debris flow.

Anciently duplicated genes continuously recruited to heart expression in vertebrate evolution are associated with heart chamber increase.

Although gene/genome duplications in the early stage of vertebrates have been thought to provide major resources of raw genetic materials for evolutionary innovations, it is unclear whether they continuously contribute to the evolution of morphological complexity during the course of vertebrate evolution, such as the evolution from two heart chambers (fishes) to four heart chambers (mammals and birds). We addressed this issue by our heart RNA-Seq experiments combined with published data, using 13 vertebrates and one invertebrate (sea squirt, as an outgroup). Our evolutionary transcriptome analysis showed that number of ancient paralogous genes expressed in heart tends to increase with the increase of heart chamber number along the vertebrate phylogeny, in spite that most of them were duplicated at the time near to the origin of vertebrates or even more ancient. Moreover, those paralogs expressed in heart exert considerably different functions from heart-expressed singletons: the former are functionally enriched in cardiac muscle and muscle contraction-related categories, whereas the latter play more basic functions of energy generation like aerobic respiration. These findings together support the notion that recruiting anciently paralogous genes that are expressed in heart is associated with the increase of chamber number in vertebrate evolution.

Distinct microbial communities in an ascidian-crustacean symbiosis.

Ascidians are marine invertebrates known to occasionally host symbiotic crustaceans. Although the microbiomes of both ascidians and free-living crustaceans have been characterized, there is no documentation of microbial communities in an ascidian-crustacean symbiosis. Samples of the solitary ascidian Ascidia sydneiensis and ambient seawater were collected in Belize. Four symbiotic amphipod crustaceans were retrieved from the branchial sac of the animal, and their microbiomes were compared with those from their ascidian host (tunic and branchial sac compartments) and seawater. Microbiome richness and diversity differed significantly between sample types, with amphipod microbiomes exhibiting significantly lower diversity than tunic and ambient seawater samples. Microbiome composition also differed significantly between sample types and among all pairwise comparisons, except for branchial sac and amphipod microbiomes. Differential operational taxonomic unit (OTU) analyses revealed that only 3 out of 2553 OTUs had significantly different relative abundances in amphipods compared with ascidian branchial sacs, whereas 72 OTUs differed between amphipod and tunic and 315 between amphipod and seawater samples. Thus, different body compartments of A. sydneiensis hosted distinct microbiomes, and symbiotic amphipods contained microbiomes resembling the region they inhabit (i.e., the branchial sac), suggesting that environmental filtering and co-evolutionary processes are determinants of microbiome composition within ascidian-crustacean symbioses.

Growth Performance of a Newly Isolated and Culturable Thraustochytrid Strain from Sea Squirt Colonies

The world’s oceans and seas host &gt;100 known strains of thraustochytrids, a common group of marine eukaryotic unicellular protists, residing in diverse marine habitats, with many others to be isolated and cultivated. The thraustochytrids have become of considerable industrial interest due to health benefits gained from their high percentages of valuable bioactive compounds, revealing the needs for the isolation of new potential strains. Employing a recently developed isolation methodology (use of cell culture medium), we assess initial culture conditions and growth paces of newly isolated thraustochytrid cells (thraustochytrid sp. BSH), originated from the colonial tunicate Botryllus schlosseri, residing on Helgoland Island, Germany. Cells were cultivated under static versus agitated conditions, along with two inoculation sizes (0.5 × 106 and 1 × 106 cells/dish) and in three vessel types (35 mm Petri dishes and T25 and T75 flasks; containing 3, 5 and 15 mL medium, respectively). Cultures were observed under regular microscopy, confocal microscopy and H&amp;E staining. While cells in all conditions grew fast, results revealed the superiority of agitated cultivation in T75 flasks inoculated with 0.5 × 106 cells/dish (6.41 ± 1.91-fold increase/week). Further, 18S rDNA revealed high similarities (99.5–99.8) of strain BSH to two thraustochytrid strains from Monterey, California (USA), B. schlosseri colonies, elucidating a new understanding of these animals-protists associations.

Nutritional composition of sea squirts from Iwate Prefecture, Japan

n this study, due to the effects of the Great East Japan Earthquake in 2011, sea squirts were not exported overseas and were discarded without being used for food. We addressed the disposal issue by raising awareness of sea squirts and incorporating them into food. When the general food composition of peeled sea squirts from Iwate Prefecture was analyzed, it was confirmed that they had a high ash content of 5.9% protein, 0.3% fat, 6.3% carbohydrates, and 2.9% ash, similar to shellfish. The mineral content of sea squirts from Iwate Prefecture revealed high levels of magnesium, iron, and zinc, similar to those of shellfish. The analysis of free amino acids in sea squirts revealed high levels of taurine, glutamic acid, proline, and alanine, indicating high amino acid content related to the taste of sea squirts, particularly sweetness and umami. It was confirmed that sea squirts are rich in minerals and amino acids, making them functional foods beneficial to human health.

The distribution of the red-throated ascidian Herdmania momus shifts northwards in association with ocean warming in the Korean Peninsula

Abstract Climate change poses a major threat to marine ecosystems, with its effects felt worldwide. A major effect of climate change on marine ecosystems is the rise in water temperature, leading to a northward expansion of habitats for marine organisms. Herdmania momus, a species of ascidians (sea squirts), originally found in tropical and subtropical regions, was introduced to the Korean Peninsula. In this study, we examined the habitat of H. momus along the southeastern coast of the Korean Peninsula between 2016 and 2022. We found that H. momus settlements were observed across the entire survey area, with confirmed habitation in Busan in 2016, Ulsan in 2021, and Gyeongju (the northernmost location) in 2022. The observed habitation trend indicates a rapid geographical expansion, occurring approximately 79 years earlier than previously predicted. These observations demonstrate that marine organisms are undergoing a more rapid geographical expansion than previously projected. These unexpected findings should inform government policies related to proactive measures and strategies for managing the impact of climate change on marine ecosystems.

Stress granule-related genes during embryogenesis of an invertebrate chordate.

Controlling global protein synthesis through the assembly of stress granules represents a strategy adopted by eukaryotic cells to face various stress conditions. TIA 1-related nucleolysin (TIAR), tristetraprolin (TTP), and Ras-GTPase-activating protein SH3-domain-binding protein (G3BP) are key components of stress granules, allowing the regulation of mRNA stability, and thus controlling not only stress responses but also cell proliferation and differentiation. In this study, we aimed at investigating the roles of tiar, ttp, and g3bp during embryogenesis of the solitary ascidian Ciona robusta under both physiological and stress conditions. We carried out CRISPR/Cas9 to evaluate the effects of gene knockout on normal embryonic development, and gene reporter assay to study the time and tissue specificity of gene transcription, together with whole-mount in situ hybridization and quantitative real time PCR. To induce acute stress conditions, we used iron and cadmium as "essential" and "non-essential" metals, respectively. Our results highlight, for the first time, the importance of tiar, ttp, and g3bp in controlling the development of mesendodermal tissue derivatives during embryogenesis of an invertebrate chordate.