Development and circuitry of the tunicate larval Motor Ganglion, a putative hindbrain/spinal cord homolog

The Motor Ganglion (MG) is a small collection of neurons that control the swimming movements of the tunicate tadpole larva. Situated at the base of the tail, molecular and functional comparisons suggest that may be a homolog of the spinal cord and/or hindbrain ("rhombospinal" region) of vertebrates. Here we review the most current knowledge of the development, connectivity, functions, and unique identities of the neurons that comprise the MG, drawn mostly from studies in Ciona spp. The simple cell lineages, minimal cellular composition, and comprehensively mapped "connectome" of the Ciona MG all make this an excellent model for studying the development and physiology of motor control in aquatic larvae.

The appendicularian Oikopleura dioica can enhance carbon export in a high CO2 ocean

Gelatinous zooplankton are increasingly recognized to play a key role in the ocean's biological carbon pump. Appendicularians, a class of pelagic tunicates, are among the most abundant gelatinous plankton in the ocean, but it is an open question how their contribution to carbon export might change in the future. Here, we conducted an experiment with large volume in situ mesocosms (~55-60 m3 and 21 m depth) to investigate how ocean acidification (OA) extreme events affect food web structure and carbon export in a natural plankton community, particularly focusing on the keystone species Oikopleura dioica, a globally abundant appendicularian. We found a profound influence of O. dioica on vertical carbon fluxes, particularly during a short but intense bloom period in the high CO2 treatment, during which carbon export was 42%-64% higher than under ambient conditions. This elevated flux was mostly driven by an almost twofold increase in O. dioica biomass under high CO2 . This rapid population increase was linked to enhanced fecundity (+20%) that likely resulted from physiological benefits of low pH conditions. The resulting competitive advantage of O. dioica resulted in enhanced grazing on phytoplankton and transfer of this consumed biomass into sinking particles. Using a simple carbon flux model for O. dioica, we estimate that high CO2 doubled the carbon flux of discarded mucous houses and fecal pellets, accounting for up to 39% of total carbon export from the ecosystem during the bloom. Considering the wide geographic distribution of O. dioica, our findings suggest that appendicularians may become an increasingly important vector of carbon export with ongoing OA.

Comparative Transcriptomic Analysis Reveals the Functionally Segmented Intestine in Tunicate Ascidian

The vertebrate intestinal system consists of separate segments that remarkably differ in morphology and function. However, the origin of intestinal segmentation remains unclear. In this study, we investigated the segmentation of the intestine in a tunicate ascidian species, Ciona savignyi, by performing RNA sequencing. The gene expression profiles showed that the whole intestine was separated into three segments. Digestion, ion transport and signal transduction, and immune-related pathway genes were enriched in the proximal, middle, and distal parts of the intestine, respectively, implying that digestion, absorption, and immune function appear to be regional specializations in the ascidian intestine. We further performed a multi-species comparison analysis and found that the Ciona intestine showed a similar gene expression pattern to vertebrates, indicating tunicates and vertebrates might share the conserved intestinal functions. Intriguingly, vertebrate pancreatic homologous genes were expressed in the digestive segment of the Ciona intestine, suggesting that the proximal intestine might play the part of pancreatic functions in C. savignyi. Our results demonstrate that the tunicate intestine can be functionally separated into three distinct segments, which are comparable to the corresponding regions of the vertebrate intestinal system, offering insights into the functional evolution of the digestive system in chordates.

Transcriptome landscapes that signify Botrylloides leachi (Ascidiacea) torpor states

Harsh environments enforce the expression of behavioural, morphological, physiological, and reproductive rejoinders, including torpor. Here we study the morphological, cellular, and molecular alterations in torpor architype in the colonial urochordate Botrylloides aff. leachii by employing whole organism Transmission electron (TEM) and light microscope observations, RNA sequencing, real-time polymerase chain reaction (qPCR) quantification of selected genes, and immunolocalization of WNT, SMAD and SOX2 gene expressions. On the morphological level, torpor starts with gradual regression of all zooids and buds which leaves the colony surviving as condensed vasculature remnants that may be 'aroused' to regenerate fully functional colonies upon changes in the environment. Simultaneously, we observed altered distributions of hemolymph cell types. Phagocytes doubled in number, while the number of morula cells declined by half. In addition, two new circulating cell types were observed, multi-nucleated and bacteria-bearing cells. RNA sequencing technology revealed marked differences in gene expression between different organism compartments and states: active zooids and ampullae, and between mid-torpor and naive colonies, or naive and torpid colonies. Gene Ontology term enrichment analyses further showed disparate biological processes. In torpid colonies, we observed overall 233 up regulated genes. These genes included NR4A2, EGR1, MUC5AC, HMCN2 and. Also, 27 transcription factors were upregulated in torpid colonies including ELK1, HDAC3, RBMX, MAZ, STAT1, STAT4 and STAT6. Interestingly, genes involved in developmental processes such as SPIRE1, RHOA, SOX11, WNT5A and SNX18 were also upregulated in torpid colonies. We further validated the dysregulation of 22 genes during torpor by utilizing qPCR. Immunohistochemistry of representative genes from three signaling pathways revealed high expression of these genes in circulated cells along torpor. WNT agonist administration resulted in early arousal from torpor in 80% of the torpid colonies while in active colonies WNT agonist triggered the torpor state. Abovementioned results thus connote unique transcriptome landscapes associated with Botrylloides leachii torpor.

Nkx2-1 and FoxE regionalize glandular (mucus-producing) and thyroid-equivalent traits in the endostyle of the chordate Oikopleura dioica

The endostyle is a ventral pharyngeal organ used for internal filter feeding of basal chordates and is considered homologous to the follicular thyroid of vertebrates. It contains mucus-producing (glandular) and thyroid-equivalent regions organized along the dorsoventral (DV) axis. Although thyroid-related genes (Nkx2-1, FoxE, and thyroid peroxidase (TPO)) are known to be expressed in the endostyle, their roles in establishing regionalization within the organ have not been demonstrated. We report that Nkx2-1 and FoxE are essential for establishing DV axial identity in the endostyle of Oikopleura dioica. Genome and expression analyses showed von Willebrand factor-like (vWFL) and TPO/dual oxidase (Duox)/Nkx2-1/FoxE as orthologs of glandular and thyroid-related genes, respectively. Knockdown experiments showed that Nkx2-1 is necessary for the expression of glandular and thyroid-related genes, whereas FoxE is necessary only for thyroid-related genes. Moreover, Nkx2-1 expression is necessary for FoxE expression in larvae during organogenesis. The results demonstrate the essential roles of Nkx2-1 and FoxE in establishing regionalization in the endostyle, including (1) the Nkx2-1-dependent glandular region, and (2) the Nkx2-1/FoxE-dependent thyroid-equivalent region. DV axial regionalization may be responsible for organizing glandular and thyroid-equivalent traits of the pharynx along the DV axis.

Current status (as of end of 2020) of marine alien species in Turkey

The 2020's update of marine alien species list from Turkey yielded a total of 539 species belonging to 18 taxonomic groups, 404 of which have become established in the region and 135 species are casual. A total of 185 new alien species have been added to the list since the previous update of 2011. The present compilation includes reports of an ascidian species (Rhodosoma turcicum) new to the marine fauna of Turkey and range extensions of six species. Among the established species, 105 species have invasive characters at least in one zoogeographic region, comprising 19% of all alien species. Mollusca ranked first in terms of the number of species (123 species), followed by Foraminifera (91 species), Pisces (80 species) and Arthropoda (79 species). The number of alien species found in seas surrounding Turkey ranged from 28 (Black Sea) to 413 (Levantine Sea). The vectoral importance of the Suez Canal diminishes when moving from south to north, accounting for 72% of species introductions in the Levantine Sea vs. only 11% of species introductions in the Black Sea. Most alien species on the coasts of Turkey were originated from the Red Sea (58%), due to the proximity of the country to the Suez Canal. Shipping activities transported 39% of alien species, mainly from the Indo-Pacific area (20%) and the Atlantic Ocean (10%). Misidentified species (such as Pterois volitans, Trachurus declivis, etc.) and species those classified as questionable or cryptogenic were omitted from the list based on new data gathered in the last decade and expert judgements. The documented impacts of invasive species on socio-economy, biodiversity and human health in the last decade as well as the legislation and management backgrounds against alien species in Turkey are presented.

Phylogenomic and morphological relationships among the botryllid ascidians (Subphylum Tunicata, Class Ascidiacea, Family Styelidae)

Ascidians (Phylum Chordata, Class Ascidiacea) are a large group of invertebrates which occupy a central role in the ecology of marine benthic communities. Many ascidian species have become successfully introduced around the world via anthropogenic vectors. The botryllid ascidians (Order Stolidobranchia, Family Styelidae) are a group of 53 colonial species, several of which are widespread throughout temperate or tropical and subtropical waters. However, the systematics and biology of this group of ascidians is not well-understood. To provide a systematic framework for this group, we have constructed a well-resolved phylogenomic tree using 200 novel loci and 55 specimens. A Principal Components Analysis of all species described in the literature using 31 taxonomic characteristics revealed that some species occupy a unique morphological space and can be easily identified using characteristics of adult colonies. For other species, additional information such as larval or life history characteristics may be required for taxonomic discrimination. Molecular barcodes are critical for guiding the delineation of morphologically similar species in this group.

Identification of DNA (de)methylation-related genes and their transcriptional response to environmental challenges in an invasive model ascidian

Marine invasive species are constantly challenged by acute or recurring environmental stresses during their range expansions. DNA methylation-mediated stress memory has been proposed to effectively affect species' response and enhance their overall performance in recurring environmental challenges. In order to further test this proposal in marine invasive species, we identified genes in the DNA methylation and demethylation processes in the highly invasive model species, Ciona robusta, and subsequently investigated the expression patterns of these genes under recurring salinity stresses. After a genome-wide comprehensive survey, we found a total of six genes, including two genes of DNA methyltransferase 3a (DNMT3a1 and DNMT3a2), and one gene of DNA methyltransferase 1 (DNMT1), methyl-CpG-binding domain protein 2 (MBD2), methyl-CpG-binding domain protein 4 (MBD4) and ten-eleven-translocation protein 1 (TET1). Phylogenetic reconstruction and domain arrangement analyses showed that the deduced proteins of the identified genes were evolutionarily conserved and functionally similar with their orthologs. All genes were constitutively expressed in all four tested tissues. Interestingly, we found time-dependent and stress-specific gene expression patterns under high and low salinity stresses. Under the recurring high salinity stresses, DNMT3a1 and TET1 conformed to the definition of memory genes, while under the recurring low salinity stresses, two DNMT3a paralogues were identified as the memory genes. Altogether, our results clearly showed that the transcriptional patterns of (de)methylation-related genes were significantly influenced by environmental stresses, and the transcriptional memory of some (de)methylation-related genes should play crucial roles in DNA methylation-mediated stress memory during the process of biological invasions.

Characterization of vanadium of biological origin for possible applications in physics experiments

For the first time, vanadium of biological origin, extracted from centrifugal fraction of vanadium-storing blood cells of the Ascidia sydneiensis samea species, was characterized as regards its isotopic composition and content of natural radioactive elements potassium (K), thorium (Th) and uranium (U). The natural abundance of vanadium isotopes has been confirmed with high accuracy, thus excluding a possible selectivity within bio-chemical reactions of vanadium concentration in blood cells from seawater. A large potassium concentration (up to 5500 × 10^-6 g g^-1) was found in the blood cell samples. The concentration of thorium was determined to be about 30 × 10^-9 g g^-1, while the uranium concentration was about 150 × 10^-9 g g^-1. Hence, a highly efficient two-stage purification approach with a total vanadium recovery of better than 70% was developed and applied. The final concentrations of K < 100 × 10^-6 g g^-1 and of U/Th < 0.5 × 10^-9 g g^-1 in the purified vanadium-containing samples were achieved. Vanadium extracted from centrifugal fraction of vanadium-storing blood cells after two-stage purification approach could be utilized in various applications, where a high chemical purity compound is required. However, to be used as a source of radiopure vanadium in ultra-low-background experiment aimed to search for ⁵⁰V beta decay, it should be further purified by Electron Beam Melting against residual potassium.

UV-B radiation bearings on ephemeral soma in the shallow water tunicate Botryllus schlosseri

Sedentary shallow water marine organisms acquire numerous protective mechanisms to mitigate the detrimental effects of UV radiation (UV-R). Here we investigated morphological and gene expression outcomes in colonies of the cosmopolitan ascidian Botryllus schlosseri, up to 15-days post UV-B irradiation. Astogeny in Botryllus is characterized by weekly repeating sets of asexual budding, coinciding with apoptotic elimination of functional zooids (blastogenesis). Ten UV-B doses were administered to three clusters: sublethal, enhanced-mortality, lethal (LD₅₀ = 6.048 kJ/m²) which differed in mortality rates, yet reflected similar distorted morphotypes, and arrested blastogenesis, all intensified in the enhanced-mortality/lethal clusters. Even the sub-lethal doses inflicted expression modifications in 8 stress proteins (HSP 90/70 families and NIMA) as well as morphological blastogenesis. The morphological/gene-expression impacts in surviving colonies lasted for 15 days post irradiation (two blastogenic-cycles), where all damaged and arrested zooids/buds were absorbed, after which the colonies returned to their normal blastogenic-cycles and gene expression profiles, and initiated new buds. The above reflects a novel colonial maintenance strategy associated with the disposable-soma tenet, where the ephemeral soma in Botryllus is eliminated without engaging with the costs of repair, whereas other colonial components, primarily the pool of totipotent stem cells, are sustained under yet unknown colonial-level regulatory cues.

Tunicate gastrulation

Tunicates are a diverse group of invertebrate marine chordates that includes the larvaceans, thaliaceans, and ascidians. Because of their unique evolutionary position as the sister group of the vertebrates, tunicates are invaluable as a comparative model and hold the promise of revealing both conserved and derived features of chordate gastrulation. Descriptive studies in a broad range of tunicates have revealed several important unifying traits that make them unique among the chordates, including invariant cell lineages through gastrula stages and an overall morphological simplicity. Gastrulation has only been studied in detail in ascidians such as Ciona and Phallusia, where it involves a simple cup-shaped gastrula driven primarily by endoderm invagination. This appears to differ significantly from vertebrate models, such as Xenopus, in which mesoderm convergent extension and epidermal epiboly are major contributors to involution. These differences may reflect the cellular simplicity of the ascidian embryo.

Core and Dynamic Microbial Communities of Two Invasive Ascidians: Can Host-Symbiont Dynamics Plasticity Affect Invasion Capacity?

Ascidians (Chordata, Ascidiacea) are considered to be prominent marine invaders, able to tolerate highly polluted environments and fluctuations in salinity and temperature. Here, we examined the seasonal and spatial dynamics of the microbial communities in the inner-tunic of two invasive ascidians, Styela plicata (Lesueur 1823) and Herdmania momus (Savigny 1816), in order to investigate the changes that occur in the microbiome of non-indigenous ascidians in different environments. Microbial communities were characterized using next-generation sequencing of partial (V4) 16S rRNA gene sequences. A clear differentiation between the ascidian-associated microbiome and bacterioplankton was observed, and two distinct sets of operational taxonomic units (OTUs), one core and the other dynamic, were recovered from both species. The relative abundance of the dynamic OTUs in H. momus was higher than in S. plicata, for which core OTU structure was maintained independently of location. Ten and seventeen core OTUs were identified in S. plicata and H. momus, respectively, including taxa with reported capabilities of carbon fixing, ammonia oxidization, denitrification, and heavy-metal processing. The ascidian-sourced dynamic OTUs clustered in response to site and season but significantly differed from the bacterioplankton community structure. These findings suggest that the associations between invasive ascidians and their symbionts may enhance host functionality while maintaining host adaptability to changing environmental conditions.

Cellular and molecular mechanisms of regeneration in colonial and solitary Ascidians

Regenerative ability is highly variable among the metazoans. While many invertebrate organisms are capable of complete regeneration of entire bodies and organs, whole-organ regeneration is limited to very few species in the vertebrate lineages. Tunicates, which are invertebrate chordates and the closest extant relatives of the vertebrates, show robust regenerative ability. Colonial ascidians of the family of the Styelidae, such as several species of Botrylloides, are able to regenerate entire new bodies from nothing but fragments of vasculature, and they are the only chordates that are capable of whole body regeneration. The cell types and signaling pathways involved in whole body regeneration are not well understood, but some evidence suggests that blood borne cells may play a role. Solitary ascidians such as Ciona can regenerate the oral siphon and their central nervous system, and stem cells located in the branchial sac are required for this regeneration. Here, we summarize the cellular and molecular mechanisms of tunicate regeneration that have been identified so far and discuss differences and similarities between these mechanisms in regenerating tunicate species.

The biology of the extracorporeal vasculature of Botryllus schlosseri

The extracorporeal vasculature of the colonial ascidian Botryllus schlosseri plays a key role in several biological processes: transporting blood, angiogenesis, regeneration, self-nonself recognition, and parabiosis. The vasculature also interconnects all individuals in a colony and is composed of a single layer of ectodermally-derived cells. These cells form a tube with the basal lamina facing the lumen, and the apical side facing an extracellular matrix that consists of cellulose and other proteins, known as the tunic. Vascular tissue is transparent and can cover several square centimeters, which is much larger than any single individual within the colony. It forms a network that ramifies and expands to the perimeter of each colony and terminates into oval-shaped protrusions known as ampullae. Botryllus individuals replace themselves through a weekly budding cycle, and vasculature is added to ensure the interconnection of each new individual, thus there is continuous angiogenesis occurring naturally. The vascular tissue itself is highly regenerative; surgical removal of the ampullae and peripheral vasculature triggers regrowth within 24-48 h, which includes forming new ampullae. When two individuals, whether in the wild or in the lab, come into close contact and their ampullae touch, they can either undergo parabiosis through anastomosing vessels, or reject vascular fusion. The vasculature is easily manipulated by direct means such as microinjections, microsurgeries, and pharmacological reagents. Its transparent nature allows for in vivo analysis by bright field and fluorescence microscopy. Here we review the techniques and approaches developed to study the different biological processes that involve the extracorporeal vasculature.

Effects of polystyrene microplastics on early stages of two marine invertebrates with different feeding strategies

Nowadays, microplastics represent one of the main threats to marine ecosystems, being able to affect organisms at different stages of their life cycle and at different levels of the food web. Although the presence of plastic debris has been reported in different habitats and the ability to ingest it has been confirmed for different taxa, few studies have been performed to elucidate the effects on survival and development of marine animals. Thus, we explored the effects of different environmental concentrations of polystyrene microbeads on the early stages of two invertebrate species widespread in the Mediterranean shallow waters: the pelagic planktotrophic pluteus larvae of the sea urchin Paracentrotus lividus and the filter-feeding sessile juveniles of the ascidian Ciona robusta. We evaluated the effects on larvae and juvenile development and determined the efficiency of bead ingestion. The feeding stages of both species proved to be extremely efficient in ingesting microplastics. In the presence of microbeads, the metamorphosis of ascidian juveniles was slowed down and development of plutei altered. These results prompted the necessity to monitor the populations of coastal invertebrates since microplastics affect sensitive stages of life cycle and may have consequences on generation recruitment.

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.

Observations on the symbiotic relationship between the caridean shrimp Odontonia sibogae (Bruce, 1972) and its ascidian host Herdmania momus (Savigny, 1816)

Symbiotic relationships between shrimps and other invertebrates are a very common phenomenon in tropical environments. Although the caridean shrimp-ascidian association has been known for many years, the nature of this relationship is still unclear. The current study investigated the association between the caridean shrimp Odontonia sibogae (Bruce, 1972) and solitary ascidians. A combination of field work conducted along the Red Sea coast of Israel and laboratory experiments, conducted during 2015–2016, revealed a clear preference of the shrimps for the ascidian species Herdmania momus (Savigny, 1816), with a low survival ability of the shrimp outside their host's body. The shrimps usually inhabit their host as pairs of male and female or pair of females, but never as pairs of males. Out of the 53 studied females, 51% were observed to bear between 156–1,146 embryos, throughout the course of the year. As these ascidian hosts are known to create large aggregates, we suggest that males may possibly wander among the ascidians occupied by females in order to increase their reproductive success. To date, this is the first study to record the shrimp Dactylonia ascidicola (Borradaile, 1898) inhabiting the ascidian H. momus; and the first study to investigate in depth the ascidian-shrimp association in the Red Sea. It thus provides a platform for future research into the physiological and behavioral adaptations required for such a unique association.

Natural acidification changes the timing and rate of succession, alters community structure, and increases homogeneity in marine biofouling communities

Ocean acidification may have far-reaching consequences for marine community and ecosystem dynamics, but its full impacts remain poorly understood due to the difficulty of manipulating pCO₂ at the ecosystem level to mimic realistic fluctuations that occur on a number of different timescales. It is especially unclear how quickly communities at various stages of development respond to intermediate-scale pCO₂ change and, if high pCO₂ is relieved mid-succession, whether past acidification effects persist, are reversed by alleviation of pCO₂ stress, or are worsened by departures from prior high pCO₂ conditions to which organisms had acclimatized. Here, we used reciprocal transplant experiments along a shallow water volcanic pCO₂ gradient to assess the importance of the timing and duration of high pCO₂ exposure (i.e., discrete events at different stages of successional development vs. continuous exposure) on patterns of colonization and succession in a benthic fouling community. We show that succession at the acidified site was initially delayed (less community change by 8 weeks) but then caught up over the next 4 weeks. These changes in succession led to homogenization of communities maintained in or transplanted to acidified conditions, and altered community structure in ways that reflected both short- and longer-term acidification history. These community shifts are likely a result of interspecific variability in response to increased pCO₂ and changes in species interactions. High pCO₂ altered biofilm development, allowing serpulids to do best at the acidified site by the end of the experiment, although early (pretransplant) negative effects of pCO₂ on recruitment of these worms were still detectable. The ascidians Diplosoma sp. and Botryllus sp. settled later and were more tolerant to acidification. Overall, transient and persistent acidification-driven changes in the biofouling community, via both past and more recent exposure, could have important implications for ecosystem function and food web dynamics.

Whole-Body Regeneration in the Colonial Tunicate Botrylloides leachii

The colonial marine invertebrate Botrylloides leachii belongs to the Tunicata subphylum, the closest invertebrate relatives to the vertebrate group and the only known class of chordates that can undergo whole-body regeneration (WBR). This dramatic developmental process allows a minute isolated fragment of B. leachii's vascular system, or a colony excised of all adults, to restore a functional animal in as little as 10 days. In addition to this exceptional regenerative capacity, B. leachii can reproduce both sexually, through a tadpole larval stage, and asexually, through palleal budding. Thus, three alternative developmental strategies lead to the establishment of filter-feeding adults. Consequently, B. leachii is particularly well suited for comparative studies on regeneration and should provide novel insights into regenerative processes in chordates.Here, after a short introduction on regeneration, we overview the biology of B. leachii as well as the current state of knowledge on WBR in this species and in related species of tunicates. Finally, we highlight the possible future directions that research might take in the study of WBR, including thoughts on technological approaches that appear most promising in this context. Overall, we provide a synthesis of the current knowledge on WBR in B. leachii to support research in this chordate species.

Anthropogenic factors influencing invasive ascidian establishment in natural environments

Marine environments are constantly impacted by bioinvasions. Invasive ascidians (Chordata, Tunicata) are well-known for their ability to rapidly overgrow any available substrate. While the majority of studies have investigated the factors contributing to the successful establishment of ascidians on artificial substrates, the anthropogenic factors that contribute to such establishment on natural substrates have rarely been investigated. Here, we studied non-indigenous ascidians presence on natural substrate for the first time, using underwater field surveys at eight natural sites along the Israeli Mediterranean coast, in order to provide an analysis of factors assisting their establishment. The findings revealed that sites exposed to extended sewage-spill events experimented a reduction in native ascidian species. Understanding which factors alter ascidian population is essential for further monitoring efforts, to protect areas that are more susceptible to invasion, and for developing effective management tools to control further spread of invasive species in natural environments.

Flow cytometric characterization of hemocytes of the solitary ascidian, Halocynthia roretzi

Internal defense of ascidians relies, at least partially, on cells circulating in body fluids and infiltrating in tissues, referred to as hemocytes, although structure and composition of ascidian hemocytes still remain unclear. In the present study, we investigated hemocyte types and their functions of the solitary ascidian Halocynthia roretzi using flow cytometry. Based on morphology, cellular activities and intracellular parameters from the flow cytometry, we identified eight hemocyte types including, three granulocytes (Gr-1, Gr-2, and Gr-3), 4 hyalinocytes (Hy-1, Hy-1', Hy-2, and Hy-3) and lymphocyte-like (Ly-like) cells. The granulocyte Gr-1 accounted for 30% of the total circulating hemocytes and exhibited highest density of lysosomes and oxidative activity. Gr-1 was deeply involved in phagocytosis and degradation of foreign material. Hyalinocytes consist of two main populations, Hy-1 and Hy-2, and each accounted for 30% of the circulating hemocyte. Hy-1 displayed lysosomal content, an inducible oxidative activity, and no proteases, while Hy-2 expressed highest density of intracellular proteases, no lysosomes and a low oxidative activity. It was believed that Hy-2 may represent an important link between cellular and humoral immune reactions. Hy-1 did not show phagocytosis activity. Hy-3 and the Ly-like cells presented a similar profile except for their size and complexity, and Hy-3 may represent an intermediate differentiation/maturation step between Ly-like cells and other hemocyte populations. This first characterization of the hemocyte populations of H. roretzi provides a solid basis to investigate further their respective roles and functions in physiological and pathological contexts.

Hematological Analysis of the Ascidian Botrylloides leachii (Savigny, 1816) During Whole-Body Regeneration

Whole-body regeneration (WBR)-the formation of an entire adult from only a small fragment of its own tissue-is extremely rare among chordates. Exceptionally, in the colonial ascidian Botrylloides leachii (Savigny, 1816) a fully functional adult is formed from their common vascular system after ablation of all adults from the colony in just 10 d, thanks to their high blastogenetic potential. While previous studies have identified key genetic markers and morphological changes, no study has yet focused on the hematological aspects of regeneration despite the major involvement of the remaining vascular system and the contained hemocytes in this process. To dissect this process, we analyzed colony blood flow patterns using time-lapse microscopy to obtain a quantitative description of the velocity, reversal pattern, and average distance traveled by hemocytes. We also observed that flows present during regeneration are powered by temporally and spatially synchronized contractions of the terminal ampullae. In addition, we revised previous studies of B. leachii hematology as well as asexual development using histological sectioning and compared the role played by hemocytes during WBR. We found that regeneration starts with a rapid healing response characterized by hemocyte aggregation and infiltration of immunocytes, followed by increased activity of hemoblasts, recruitment of macrophage-like cells for clearing the tissues of debris, and their subsequent disappearance from the circulation concomitant with the maturation of a single regenerated adult. Overall, we provide a detailed account of the hematological properties of regenerating B. leachii colonies, providing novel lines of inquiry toward the decipherment of regeneration in chordates.

Morula cells as key hemocytes of the lectin pathway of complement activation in the colonial tunicate Botryllus schlosseri

The complement system is deeply rooted in the evolution of humoral mechanism of innate immunity. In addition to the alternative pathway of complement activation, lectins and associated serine proteases exert important roles in the recognition of non-self and activation of the effectors. In the colonial tunicate Botryllus schlosseri, we identified, characterized and studied the expression of three orthologues of genes involved in the lectin pathway of complement activation of vertebrates, i.e., genes for a mannose-binding lectin (MBL), a ficolin and a mannose-associated serine protease 1 (MASP1). All the genes are transcribed by hemocytes, and specifically by morula cells, the same immunocytes responsible for the transcription of C3 and Bf orthologues. The transcription levels of MASP1 and ficolin orthologues are not affected by zymosan challenge, indicating a constitutive expression of complement system associated serine proteases, whereas the MBL orthologue is up-regulated after 15 min of zymosan exposure. Collectively, our data suggest the presence of a complete lectin activation pathway in Botryllus.

Asymmetric and Unequal Cell Divisions in Ascidian Embryos

Asymmetric cell division during embryogenesis contributes to cell diversity by generating daughter cells that adopt distinct developmental fates. In this chapter, we summarize current knowledge of three examples of asymmetric cell division occurring in ascidian early embryos: (1) Three successive cell divisions that are asymmetric in terms of cell fate and unequal in cell size in the germline lineage at the embryo posterior pole. A subcellular structure, the centrosome-attracting body (CAB), and maternal PEM mRNAs localized within it control both the positioning of the cell division planes and segregation of the germ cell fates. (2) Asymmetric cell divisions involving endoderm and mesoderm germ layer separation. Asymmetric partitioning of zygotically expressed mRNA for Not, a homeodomain transcription factor, promotes the mesoderm fate and suppresses the endoderm fate. This asymmetric partitioning is mediated by transient nuclear migration toward the mesodermal pole of the mother cell, where the mRNA is delivered. In this case, there is no special regulation of cleavage plane orientation. (3) Asymmetric cell divisions in the marginal region of the vegetal hemisphere. The directed extracellular FGF and ephrin signals polarize the mother cells, inducing distinct fates in a pair of daughter cells (nerve versus notochord and mesenchyme versus muscle). The directions of cell division are regulated and oriented but independently of FGF and ephrin signaling. In these examples, polarization of the mother cells is facilitated by localized maternal factors, by delivery of transcripts from the nucleus to one pole of each cell, and by directed extracellular signals. Two cellular processes-asymmetric fate allocation and orientation of the cell division plane-are coupled by a single factor in the first example, but these processes are regulated independently in the third example. Thus, various modes of asymmetric cell division operate even at the early developmental stages in this single type of organism.

Seasonal heterogeneity provides a niche opportunity for ascidian invasion in subtropical marine communities

Implications of changes in environmental conditions caused by seasonality and human alterations on the recruitment of non-native species and their biotic resistance to predation are poorly understood. Here, through the use of experimental recruitment panels and predation exclusion cages, we examined 1) whether a subtropical seasonality (i.e., tropical and temperate conditions) affects the recruitment and abundance of the non-native ascidian Ciona intestinalis, the cryptogenic Styela plicata and Ascidia sydneiensis, and native Hermandia momus in fouling communities in Hong Kong, 2) whether human environmental alterations (i.e., typhoon shelters and sheltered bays with different habitat alteration and seawater quality) affect the abundance of the ascidians, and 3) whether predation reduces the abundance of ascidians under different environmental conditions caused by seasonality and human alteration. Our experimental results indicate that seasonality provides a temporal niche for the recruitment of the ascidians; C. intestinalis and S. plicata recruited mostly in winter, whereas A. sydneiensis and H. momus recruited in summer. Ciona intestinalis was the only ascidian that prospered in anthropogenically altered environments where it monopolized communities. The marked seasonal recruitment of the ascidians obscured the effect of predation between seasons, whereas human alteration did not affect predation. The recruitment of the ascidians in subtropical communities appeared to correspond to their original temperate or tropical distributions, hence Ciona intestinalis, with a temperate native distribution, benefits from a temporal niche opportunity during winter conditions. We argue that seasonality, as an important ecological factor for recruitment and community ecology dynamics, must also be considered in the context of biological invasion.

Analysis of the Appendicularia class (subphylum Urochordata) as a possible tool for biomonitoring four estuaries of the tropical region

This study aims to characterize the differences between physical and chemical parameters of water quality indicators and eutrophication in four estuaries of the state of Rio de Janeiro and relate them to full density of the species that belong to the Appendicularia class with the purpose of seeking bioindicators for estuarine areas. The estuaries studied were from the rivers Macaé, São João, Bracuí, and Perequê-Açu. The physicochemical parameters monitored for evaluation of the water bodies and used for the correlation with the appendicularians were pH, temperature, nitrite, nitrate, N-ammonia, total nitrogen, phosphate, total phosphorus, dissolved oxygen (DO), suspended particulate matter (SPM), chlorophyll a, heterotrophic bacteria, and fecal coliform. The estuaries Bracuí and São João showed enhanced qualities of water and lower degrees of eutrophication than Macae and Perequê-Açu estuaries. The species of the Appendicularia class found in this study were Oikopleura longicauda (Vogt, 1854), Oikopleura dioica Fol, 1872, Oikopleura fusiformis Fol, 1872, and Fritillaria haplostoma Fol, 1872. The density of appendicularians and O. longicauda was inversely related to the nutrient values and SPM; nonetheless, no species of appendicularians could be used as a bioindicator of any estuary in the current study. Studies on the quality of estuary waters and the search for other bioindicators belonging to other zooplankton groups are recommended to confirm the obtained results and to expand the knowledge of these coastal environments.

Recurrent phagocytosis-induced apoptosis in the cyclical generation change of the compound ascidian Botryllus schlosseri

Colonies of the marine, filter-feeding ascidian Botryllus schlosseri undergo cyclical generation changes or takeovers. These events are characterised by the progressive resorption of adult zooids and their replacement by their buds that grow to adult size, open their siphons and start filtering. During the take-over, tissues of adult zooids undergo extensive apoptosis; circulating, spreading phagocytes enter the effete tissues, ingest dying cells acquiring a giant size and a round morphology. Then, phagocytes re-enter the circulation where they represent a considerable fraction (more than 20%) of circulating haemocytes. In this study, we evidence that most of these circulating phagocytes show morphological and biochemical signs of apoptosis. Accordingly, these phagocytes express transcripts of orthologues of the apoptosis-related genes Bax, AIF1 and PARP1. Electron microscopy shows that giant phagocytes contain apoptotic phagocytes inside their own phagocytic vacuole. The transcript of the orthologues of the anti-apoptotic gene IAP7 was detected only in spreading phagocytes, mostly abundant in phases far from the take-over. Therefore, the presented data suggest that, at take-over, phagocytes undergo phagocytosis-induced apoptosis (PIA). In mammals, PIA is assumed to be a process assuring the killing and the complete elimination of microbes, by promoting the disposal of terminally differentiated phagocytes and the resolution of infection. In B. schlosseri, PIA assumes a so far undescribed role, being required for the control of asexual development and colony homeostasis.

Territoriality and Conflict Avoidance Explain Asociality (Solitariness) of the Endosymbiotic Pea Crab Tunicotheres moseri

Host monopolization theory predicts symbiotic organisms inhabiting morphologically simple, relatively small and scarce hosts to live solitarily as a result of territorial behaviors. We tested this prediction with Tunicotheres moseri, an endosymbiotic crab dwelling in the atrial chamber of the morphologically simple, small, and relatively scarce ascidian Styela plicata. As predicted, natural populations of T. moseri inhabit ascidian hosts solitarily with greater frequency than expected by chance alone. Furthermore, laboratory experiments demonstrated that intruder crabs take significantly longer to colonize previously infected compared to uninfected hosts, indicating as expected, that resident crabs exhibit monopolization behaviors. While territoriality does occur, agonistic behaviors employed by T. moseri do not mirror the overt behaviors commonly reported for other territorial crustaceans. Documented double and triple cohabitations in the field coupled with laboratory observations demonstrating the almost invariable success of intruder crabs colonizing occupied hosts, suggest that territoriality is ineffective in completely explaining the solitary social habit of this species. Additional experiments showed that T. moseri juveniles and adults, when searching for ascidians use chemical cues to avoid hosts occupied by conspecifics. This conspecific avoidance behavior reported herein is a novel strategy most likely employed to preemptively resolve costly territorial conflicts. In general, this study supports predictions central to host monopolization theory, but also implies that alternative behavioral strategies (i.e., conflict avoidance) may be more important than originally thought in explaining the host use pattern of symbiotic organisms.

Contaminant cocktails: Interactive effects of fertiliser and copper paint on marine invertebrate recruitment and mortality

Understanding interactive effects of contaminants is critical to predict how human activities change ecosystem structure and function. We examined independent and interactive effects of two contaminants (fertiliser and copper paint) on the recruitment, mortality, and total abundance of developing invertebrate communities in the field, 2, 4, 6, and 8 weeks after substrate submersion. Contaminants affected community structure differently, and produced an intermediate community in combination. Fertiliser increased recruitment and decreased mortality of active filter feeders (ascidians and barnacles), while copper paint decreased recruitment and increased mortality of some taxa. Contaminants applied together affected some taxa (e.g. Didemnid ascidians) antagonistically, as fertiliser mitigated adverse effects of copper paint. Recruitment of active filter feeders appears to be indicative of nutrient enrichment, and their increased abundance may reduce elevated nutrients in modified waterways. This study demonstrates the need to consider both independent and interactive effects of contaminants on marine communities in the field.

Desiccation as a mitigation tool to manage biofouling risks: trials on temperate taxa to elucidate factors influencing mortality rates

The desiccation tolerance of biofouling taxa (adults and early life-stages) was determined under both controlled and 'realistic' field conditions. Adults of the ascidian Ciona spp. died within 24 h. Mortality in the adult blue mussel Mytilus galloprovincialis occurred within 11 d under controlled conditions, compared with 7 d when held outside. The Pacific oyster Crassostrea gigas was the most desiccation-tolerant taxon tested (up to 34 d under controlled conditions). Biofouling orientated to direct sunlight showed faster mortality rates for all the taxa tested. Mortality in Mytilus juveniles took up to 24 h, compared with 8 h for Ciona, with greater survival at the higher temperature (18.5°C) and humidity (~95% RH) treatment combination. This study demonstrated that desiccation can be an effective mitigation method for a broad range of fouling taxa, especially their early life-stages. Further work is necessary to assess risks from other high-risk species such as algae and cyst forming species.

It's a wrap: encapsulation as a management tool for marine biofouling

Encapsulation of fouled structures is an effective tool for countering incursions by non-indigenous biofoulers. However, guidelines for the implementation of encapsulation treatments are yet to be established. This study evaluated the effects of temperature, biomass, community composition, treatment duration and the biocide acetic acid on biofoulers. In laboratory trials using the model organisms Ciona spp. and Mytilus galloprovincialis, increasing the temperature or biomass speeded up the development of a toxic environment. Total mortality for Ciona spp. occurred within 72 and 24 h at 10 and 19°C, respectively. M. galloprovincialis survived up to 18 days, with high biomass increasing mortality at 10°C only. In a field study, three-month-old and four-year-old communities were encapsulated with and without acetic acid. Mortality took up to 10 days for communities encapsulated without acetic acid, compared to 48 h with acetic acid. The insights gained from this study will be useful in developing standardised encapsulation protocols.

A Boolean Function for Neural Induction Reveals a Critical Role of Direct Intercellular Interactions in Patterning the Ectoderm of the Ascidian Embryo

A complex system of multiple signaling molecules often produce differential gene expression patterns in animal embryos. In the ascidian embryo, four signaling ligands, Ephrin-A.d (Efna.d), Fgf9/16/20, Admp, and Gdf1/3-r, coordinately induce Otx expression in the neural lineage at the 32-cell stage. However, it has not been determined whether differential inputs of all of these signaling pathways are really necessary. It is possible that differential activation of one of these signaling pathways is sufficient and the remaining signaling pathways are activated in all cells at similar levels. To address this question, we developed a parameter-free method for determining a Boolean function for Otx expression in the present study. We treated activities of signaling pathways as Boolean values, and we also took all possible patterns of signaling gradients into consideration. We successfully determined a Boolean function that explains Otx expression in the animal hemisphere of wild-type and morphant embryos at the 32-cell stage. This Boolean function was not inconsistent with three sensing patterns, which represented whether or not individual cells received sufficient amounts of the signaling molecules. These sensing patterns all indicated that differential expression of Otx in the neural lineage is primarily determined by Efna.d, but not by differential inputs of Fgf9/16/20, Admp, and Gdf1/3-r signaling. To confirm this hypothesis experimentally, we simultaneously knocked-down Admp, Gdf1/3-r, and Fgf9/16/20, and treated this triple morphant with recombinant bFGF and BMP4 proteins, which mimic Fgf9/16/20 and Admp/Gdf1/3-r activity, respectively. Although no differential inputs of Admp, Gdf1/3-r and Fgf9/16/20 signaling were expected under this experimental condition, Otx was expressed specifically in the neural lineage. Thus, direct cell–cell interactions through Efna.d play a critical role in patterning the ectoderm of the early ascidian embryo.

It is often difficult to understand a complex system of multiple signaling molecules in animal embryos only with experimental procedures. Although theoretical analysis might solve this problem, it is often difficult to precisely determine parameters for signaling gradients and kinetics of signaling molecules. In the present study, we developed a parameter-free method for determining a Boolean function for understanding a complex signaling system using gene expression patterns of signaling molecules and geometrical configurations of individual cells within the embryo. In the ascidian embryo, four signaling ligands, Ephrin-A.d (Efna.d), Fgf9/16/20, Admp, and Gdf1/3-r, coordinately induce Otx expression in the neural lineage at the 32-cell stage. In addition to determining a Boolean function, our method determined sensing patterns, which represented whether or not individual cells received sufficient amounts of the signaling molecules. The sensing patterns predicted that differential expression of Otx in the neural lineage is primarily determined by Efna.d, but not by differential inputs of Fgf9/16/20, Admp, and Gdf1/3-r. We confirmed this prediction by an experiment. As a result, we found that only Efna.d signaling pathway is differentially activated between ectodermal cells and the remaining signaling pathways are activated in all ectodermal cells at similar levels.

Diel Vertical Dynamics of Gelatinous Zooplankton (Cnidaria, Ctenophora and Thaliacea) in a Subtropical Stratified Ecosystem (South Brazilian Bight)

The diel vertical dynamics of gelatinous zooplankton in physically stratified conditions over the 100-m isobath (~110 km offshore) in the South Brazilian Bight (26°45’S; 47°33’W) and the relationship to hydrography and food availability were analyzed by sampling every six hours over two consecutive days. Zooplankton samples were taken in three depth strata, following the vertical structure of the water column, with cold waters between 17 and 13.1°C, influenced by the South Atlantic Central Water (SACW) in the lower layer (>70 m); warm (>20°C) Tropical Water in the upper 40 m; and an intermediate thermocline with a deep chlorophyll-a maximum layer (0.3–0.6 mg m^-3). Two distinct general patterns were observed, emphasizing the role of (i) physical and (ii) biological processes: (i) a strong influence of the vertical stratification, with most zooplankton absent or little abundant in the lower layer. The influence of the cold SACW on the bottom layer apparently restricted the vertical occupation of most species, which typically inhabit epipelagic warm waters. Even among migratory species, only a few (Aglaura hemistoma, Abylopsis tetragona eudoxids, Beroe sp., Thalia democratica, Salpa fusiformis) crossed the thermocline and reached the bottom layer. (ii) A general tendency of partial migrations, with variable intensity depending on the different species and developmental stages; populations tended to be more widely distributed through the water column during daylight, and to become more aggregated in the upper layer during the night, which can be explained based on the idea of the “hunger-satiation hypothesis”, maximizing feeding and minimizing the chances of being predated.

Predicting competitive shifts and responses to climate change based on latitudinal distributions of species assemblages

Many terrestrial plant and marine benthic communities involve intense competition for space as a means to survive and reproduce. Superior competitors can dominate other species numerically with high reproductive rates, indirectly with high growth rates that facilitate space acquisition, or directly with competitive overgrowth. To assess how climate change could affect competitive interactions, we examined latitudinal patterns in growth rates and overgrowth competition via field surveys and experiments with marine epibenthic communities. Epibenthic fouling communities are dominated by invasive tunicates, bryozoans, and other species that grow on docks, boats, and other artificial structures. Fouling communities are space limited, so growth rate and overgrowth competition play an important role in shaping abundance patterns. We experimentally assessed temperature-dependent growth rates of several tunicates and bryozoans in eight regions spanning the U.S. east and west coasts. Several species displayed positive growth responses to warmer temperature in the northern portions of their latitudinal ranges, and vice versa. We used photo surveys of floating docks in at least 16 harbors in each region to compare communities and overgrowth competition. There was a strong correlation across species and regions between growth rate and competitive ability, indicating that growth plays an important role in competitive outcomes. Because growth rates are typically temperature dependent for organisms that compete for space, including terrestrial plants, fungi, algae, bacteria, and sessile benthic organisms, global warming could affect competitive outcomes. Our results suggest that these competitive shifts can be predicted by species' relative growth rates and latitudinal ranges.

The sexual and mating system of the shrimp Odontonia katoi (Palaemonidae, Pontoniinae), a symbiotic guest of the ascidian Polycarpa aurata in the Coral Triangle

Theory predicts that monogamy is adaptive in symbiotic crustaceans inhabiting relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. We tested this prediction in the shrimp Odontonia katoi, which inhabits the atrial chamber of the ascidian Polycarpa aurata in the Coral Triangle. Preliminary observations in O. katoi indicated that males were smaller than females, which is suggestive of sex change (protandry) in some symbiotic organisms. Thus, we first investigated the sexual system of O. katoi to determine if this shrimp was sequentially hermaphroditic. Morphological identification and size frequency distributions indicated that the population comprised males that, on average, were smaller than females. Gonad dissections demonstrated the absence of transitional individuals. Thus, O. katoi is a gonochoric species with reverse sexual dimorphism. The population distribution of O. katoi in its ascidian host did not differ significantly from a random distribution and shrimps inhabiting the same host individual as pairs were found with a frequency similar to that expected by chance alone. This is in contrast to that reported for other socially monogamous crustaceans in which pairs of heterosexual conspecifics are found in host individuals more frequently than expected by chance alone. Thus, the available information argues against monogamy in O. katoi. Furthermore, that a high frequency of solitary females were found brooding embryos and that the sex ratio was skewed toward females suggests that males might be roaming among hosts in search of receptive females in O. katoi. Symbiotic crustaceans can be used as a model system to understand the adaptive value of sexual and mating systems in marine invertebrates.

Biogeography of Phallusia nigra: is it really black and white?

Ascidians (Chordata, Tunicata) are an important group for the study of invasive species biology due to rapid generation times, potential for biofouling, and role as filter feeders in an ecosystem. Phallusia nigra is a putative cosmopolitan ascidian that has been described as introduced or invasive in a number of regions in the Indo-Pacific Ocean (India, Japan, and Hawaii) and in the Mediterranean. The taxonomic description of P. nigra includes a striking smooth, black tunic and large size. However, there are at least two similar Phallusia species-P. philippinensis and P. fumigata-which also have dark black tunics and can be difficult to discern from P. nigra. The distribution of P. nigra broadly overlaps with P. philippinensis in the Indo-Pacific and P. fumigata in the Mediterranean. A morphological comparison of P. nigra from Japan, the Caribbean coast of Panama, and Brazil found that Atlantic and Pacific samples were different species and led us to investigate the range of P. nigra using morphological and molecular analyses. We sequenced 18S rDNA and cytochrome oxidase B of individual ascidians from the Red Sea, Greece, Singapore, Japan, Caribbean Panama, Florida, and Brazil. Our results show that identification of the disparate darkly pigmented species has been difficult, and that several reports of P. nigra are likely either P. fumigata or P. philippinensis. Here we include detailed taxonomic descriptions of the distinguishing features of these three species and sequences for molecular barcoding in an effort to have ranges and potential invasions corrected in the ascidian literature.

Rocky intertidal zonation pattern in Antofagasta, chile: invasive species and shellfish gathering

Background

Biological invasions affecting rocky intertidal zonation patterns, yield information on species interactions. In the Bay of Antofagasta, northern Chile, the non-indigenous tunicate Pyura praeputialis, originally from Australia, has invaded (in the past century or so) and monopolized a major portion of the mid-intertidal rocky shore, displacing upshore the native mussel Perumytilus purpuratus. In Antofagasta the tunicate is subjected to intensive exploitation. Monitoring protocols show that in the past 10 years Antofagasta's tunicate population has experienced a drastic decline, affecting the intertidal zonation pattern.

Methodology/Principal Findings

A 12.5 km of coastline, on the southern eastern shore of the Bay of Antofagasta, was studied. Eight sites were systematically (1993–1994) or sporadically (2003–2014) monitored for the seaward-shoreward expansion or reduction of the tunicate Pyura praeputialis, and native mussel and barnacle bands. A notable reduction in the mid-intertidal band of P. praeputialis and a seaward expansion of the mussel, Perumytilus purpuratus, and barnacle bands was observed. We suggest that the major cause for the decline in the tunicate is due to its intensive exploitation by rocky shore Pyura-gathers. The rate of extraction of tunicates by professional Pyura-gathers ranged between 256–740 tunicates hour⁻¹. Between 2009–2014 the density of professional Pyura-gather ranged between 0.5–4.5 km⁻¹ per low tide. Hence, 10 professional Pyura-gathers working 1 h for 10 low tides per month, during 6 months, will remove between 307–888 m² of tunicates. A drastic decline in tunicate recruitment was observed and several P. praeputialis ecosystems services have been lost.

Conclusion and Significance

In Antofagasta, the continuous and intensive intertidal gathering of the invasive tunicate Pyura praeputialis, has caused a drastic reduction of its population modifying the zonation pattern. Thereby, native mussel Perumytilus purpuratus has regained its ecological center in the intertidal zone. We recorded a Pyura recruitment failure and loss of ecosystem services.

Polygodial: a contact active antifouling biocide

Ongoing investigation of the candidate antifouling (AF) biocide polygodial (PG) has revealed that this compound may be contact active, whereby it can confer effect while remaining bound within a stable matrix. To test this hypothesis, the AF activity of PG-laced coatings was compared to that of seawater in which PG-laced coatings had been soaked. Four coating types spanning high to low affinity for PG were examined and AF activity was assessed based on inhibition of settlement and metamorphosis of larvae of three fouling organisms: Ciona savignyi Herdman, Mytilus galloprovincialis Lamarck and Spirobranchus caraniferus Gray. Direct exposure to the coatings had a significantly greater impact on larval metamorphosis than indirect exposure to seawater in which the coatings had been soaked. In particular, metamorphosis was almost completely inhibited by high-affinity coatings containing ≥ 200 ng of PG per replicate, while corresponding soaking waters had no detectable effect. These findings support the assertion that PG is contact active.

When shape matters: strategies of different Antarctic ascidians morphotypes to deal with sedimentation

Climate change leads to increased melting of tidewater glaciers in the Western Antarctic Peninsula region and sediment bearing glacial melt waters negatively affects filter feeding species as solitary ascidians. In previous work the erect-forms Molgula pedunculata and Cnemidocarpa verrucosa (Order Stolidobranchiata) appeared more sensitive than the flat form Ascidia challengeri (Order Phlebobranchiata). Sedimentation exposure is expected to induce up-regulation of anaerobic metabolism by obstructing the organs of gas exchange (environmental hypoxia) or causes enhanced squirting activity (functional hypoxia). In this study we evaluated the possible relationship between ascidian morphotype and their physiological response to sedimentation. Together with some behavioural observations, we analysed the response of anaerobic metabolic parameters (lactate formation and glycogen consumption) in different tissues of three Antarctic ascidians, exposed to high sediment concentrations (200 mgL(-1)). The results were compared to experimental hypoxia (10% pO2) and exercise (induced muscular contraction) effects, in order to discriminate the effect of sediment on each species and morpho-type (erect vs. flat forms). Our results suggest that the styled (erect) C. verrucosa increases muscular squirting activity in order to expulse excessive material, while the flat-form A. challengeri reacts more passively by down-regulating its aerobic metabolism under sediment exposure. Contrary, the erect ascidian M. pedunculata did not show any measurable response to the treatments, indicating that filtration and ingestion activities were not reduced or altered even under high sedimentation (low energetic material) which could be disadvantageous on the long-term and could explain why M. pedunculata densities decline in the study area.

Vascular regeneration in a basal chordate is due to the presence of immobile, bi-functional cells

The source of tissue turnover during homeostasis or following injury is usually due to proliferation of a small number of resident, lineage-restricted stem cells that have the ability to amplify and differentiate into mature cell types. We are studying vascular regeneration in a chordate model organism, Botryllus schlosseri, and have previously found that following surgical ablation of the extracorporeal vasculature, new tissue will regenerate in a VEGF-dependent process within 48 hrs. Here we use a novel vascular cell lineage tracing methodology to assess regeneration in parabiosed individuals and demonstrate that the source of regenerated vasculature is due to the proliferation of pre-existing vascular resident cells and not a mobile progenitor. We also show that these cells are bi-potential, and can reversibly adopt two fates, that of the newly forming vessels or the differentiated vascular tissue at the terminus of the vasculature, known as ampullae. In addition, we show that pre-existing vascular resident cells differentially express progenitor and differentiated cell markers including the Botryllus homologs of CD133, VEGFR-2, and Cadherin during the regenerative process.

Marine natural products with P-glycoprotein inhibitor properties

P-glycoprotein (P-gp) is a protein belonging to the ATP-binding cassette (ABC) transporters superfamily that has clinical relevance due to its role in drug metabolism and multi-drug resistance (MDR) in several human pathogens and diseases. P-gp is a major cause of drug resistance in cancer, parasitic diseases, epilepsy and other disorders. This review article aims to summarize the research findings on the marine natural products with P-glycoprotein inhibitor properties. Natural compounds that modulate P-gp offer great possibilities for semi-synthetic modification to create new drugs and are valuable research tools to understand the function of complex ABC transporters.

Mini-review: impact and dynamics of surface fouling by solitary and compound ascidians

Globally, ascidians are a significant contributor to benthic marine fouling communities, but have remained poorly studied in this context. In some cases, such as in shellfish and finfish aquaculture, ascidians are the most problematic of all fouling organisms. The disproportionate impact of ascidian fouling in some specific geographic locations has been related directly to anthropogenic translocation of these organisms around the globe. In the case of ascidians, therefore, the economic issue of biofouling and the ecological ramifications of invasion are inextricably linked. This mini-review briefly discusses the introduction of non-native ascidians to areas where they have subsequently proven to be a significant fouling pest. The elements of ascidian reproductive ecology that support their aggressive fouling character are discussed and the scant information pertaining to their adhesion and adhesives is presented. Finally, strategies for mitigating ascidian fouling are examined. It is suggested that sufficient working knowledge currently exists to support the inclusion of one or more common ascidian species as 'standard' test organisms used for evaluation of novel fouling-resistant surfaces.

Predation limits spread of Didemnum vexillum into natural habitats from refuges on anthropogenic structures

Non-indigenous species can dominate fouling assemblages on artificial structures in marine environments; however, the extent to which infected structures act as reservoirs for subsequent spread to natural habitats is poorly understood. Didemnum vexillum is one of few colonial ascidian species that is widely reported to be highly invasive in natural ecosystems, but which in New Zealand proliferates only on suspended structures. Experimental work revealed that D. vexillum established equally well on suspended artificial and natural substrata, and was able to overgrow suspended settlement plates that were completely covered in other cosmopolitan fouling species. Fragmentation led to a level of D. vexillum cover that was significantly greater than was achieved as a result of ambient larval recruitment. The species failed to establish following fragment transplants onto seabed cobbles and into beds of macroalgae. The establishment success of D. vexillum was greatest in summer compared with autumn, and on the underside of experimental settlement plates that were suspended off the seabed to avoid benthic predators. Where benthic predation pressure was reduced by caging, D. vexillum establishment success was broadly comparable to suspended treatments; by contrast, the species did not establish on the face-up aspect of uncaged plates. This study provides compelling evidence that benthic predation was a key mechanism that prevented D. vexillum’s establishment in the cobble habitats of the study region. The widespread occurrence of D. vexillum on suspended anthropogenic structures is consistent with evidence for other sessile invertebrates that such habitats provide a refuge from benthic predation. For invasive species generally, anthropogenic structures are likely to be most important as propagule reservoirs for spread to natural habitats in situations where predation and other mechanisms do not limit their subsequent proliferation.

Tolerance of the invasive tunicate Styela clava to air exposure

Styela clava is a subtidal invasive marine species in Northern Europe, Atlantic Canada, Australia and New Zealand. It grows attached to solid substrata, including boat hulls, ropes, moorings, piers and aquaculture equipment, all of which can aid its spread to new locations. It interferes with feeding of mussels and oysters, and increases their harvesting costs. Being subtidal, it could be assumed that tunicates would rapidly die in air and thus exposure to air would be a practical method to prevent their spread on boats and equipment. This study tested their survival when exposed to air for up to (1) 120 h at a constant temperature of 10 °C, (2) shade ambient 15-27 °C, and (3) full sun ambient 15-29 °C. Humidity was consistently high (78-100%). The results indicated that survival was longer when the air temperature was cooler. Larger individuals of S. clava generally survived for longer out of seawater than smaller individuals. The results predict that two weeks of exposure to air for two weeks could be an effective management method to eradicate S. clava from marine equipment when the air temperature is 10 °C. However, drying time would be less under conditions of low humidity and under direct sunlight.

Species-specificity of sperm motility activation and chemotaxis: a study on ascidian species

Egg-derived sperm-activating factors and attractants activate sperm motility and attract the sperm, respectively. These phenomena constitute the first communication signaling between males and females in the process of fertilization in many animals and plants, and in many cases, these are species-specific events. Thus, sperm motility activation and chemotaxis may act as a safety process for the authentication between conspecific egg and sperm, and help to prevent crossbreeding. Here, we examine species-specificity of sperm motility activation and chemotaxis in the ascidians belonging to the order Phlebobranchiata: Ciona intestinalis, Ciona savignyi, Phallusia mammillata, Phallusia nigra, and Ascidia sydneiensis. Cross-reactivity in both motility activation and chemotaxis of sperm was not observed between C. savignyi and P. mammillata, or between A. sydneiensis and Phallusia spp. However, there is a "one way" (no reciprocity) cross-reaction between P. mammillata and P. nigra in sperm activation, and between C. savignyi and A. sydneiensis in sperm chemotaxis. Furthermore, the level of activity is different, even when cross-reaction is observed. Thus, sperm motility activation and chemotaxis are neither "species-" nor "genus-" specific phenomena among the ascidian species. Moreover, the interaction between the sperm-activating and sperm-attracting factors (SAAFs) in the ascidian species and the SAAF receptors on the sperm cells are not all-or-none responses.

Competitive and demographic leverage points of community shifts under climate warming

Accelerating rates of climate change and a paucity of whole-community studies of climate impacts limit our ability to forecast shifts in ecosystem structure and dynamics, particularly because climate change can lead to idiosyncratic responses via both demographic effects and altered species interactions. We used a multispecies model to predict which processes and species' responses are likely to drive shifts in the composition of a space-limited benthic marine community. Our model was parametrized from experimental manipulations of the community. Model simulations indicated shifts in species dominance patterns as temperatures increase, with projected shifts in composition primarily owing to the temperature dependence of growth, mortality and competition for three critical species. By contrast, warming impacts on two other species (rendering them weaker competitors for space) and recruitment rates of all species were of lesser importance in determining projected community changes. Our analysis reveals the importance of temperature-dependent competitive interactions for predicting effects of changing climate on such communities. Furthermore, by identifying processes and species that could disproportionately leverage shifts in community composition, our results contribute to a mechanistic understanding of climate change impacts, thereby allowing more insightful predictions of future biodiversity patterns.

Dynamics of wood fall colonization in relation to sulfide concentration in a mangrove swamp

Wood debris are an important component of mangrove marine environments. Current knowledge of the ecological role of wood falls is limited by the absence of information on metazoan colonization processes over time. The aim of this study was to provide insights to their temporal dynamics of wood eukaryotic colonization from a shallow water experiment in a mangrove swamp. Combined in situ chemical monitoring and biological surveys revealed that the succession of colonizers in the mangrove swamp relates with the rapid evolution of sulfide concentration on the wood surface. Sulfide-tolerant species are among the first colonizers and dominate over several weeks when the sulfide content is at its maximum, followed by less tolerant opportunistic species when sulfide decreases. This study supports the idea that woody debris can sustain chemosynthetic symbioses over short time-scale in tropical shallow waters.

Biodiversity and abundance patterns of rock encrusting fauna in a temperate fjord

Fjords are semi-enclosed systems often with usually strong physical and chemical gradients. These gradients provide the opportunity to test the influence of various physical and chemical factors on biodiversity. However study area of this investigation, Trondheimsfjord, is a large water body where especially salinity gradient along the fjord is not well pronounced. The goal of this study was to establish within a temperate fjord a baseline identifying encrusting fauna on rocks and determine the factors driving changes along the length of the fjord and changing depths. There was no trend in species composition change and increase or decrease in number of species, diversity and number of individuals along the fjord. This was likely due to the relative homogeneity of both substrate (rocks) and environmental parameters. Nevertheless, the influence of fresh water inflow in the vicinity of the river mouth was apparent by the presence of characteristic brackish-water species at these locations. Multidimensional scaling analysis revealed three separate assemblages: intertidal, shallow and deep subtidal (below 50 m). Intertidal assemblages were species poor (one to 11 species) but relatively abundant (six to 2374 indiv./m(2) of rocks). Number of individuals and biomass was highest in the shallow subtidal (2059-13,587 indiv./m(2) of rocks). Overall the highest species number (45) was recorded at 50 m depth which is probably result of low competition pressure yet still relatively high nutrient concentration in comparison to shallower locations. Environmental parameters (i.e., tidal currents, wave action, salinity) change more drastically with depth than along the fjord and these changes are the major driving forces in shaping encrusting assemblages in Trondheimsfjord.

Remote identification of the invasive tunicate Didemnum vexillum using reflectance spectroscopy

Benthic coverage of the invasive tunicate Didemnum vexillum on Georges Bank is largely unknown. Monitoring of D. vexillum coverage is vital to understanding the impact this invasive species will have on the productive fishing grounds of Georges Bank. Here we investigate using reflectance spectroscopy as a method for remote identification of D. vexillum. Using two different systems, a NightSea Dive-Spec and a combination of LED light sources with a hyperspectral radiometer, we collected in-situ measurements of reflectance from D. vexillum colonies. In comparison to reflectance spectra of other common benthic substrates, D. vexillum appears to have a unique spectral signature between 500 and 600 nm. Measuring the slope of the spectrum between these wavelengths appears to be the most robust method for spectral identification. Using derivative analysis or principal component analysis, the reflectance spectra of D. vexillum can be identified among numerous other spectra of common benthic substrates. An optical system consisting of a radiometer, light source, and camera was deployed on a remotely operated vehicle to test the feasibility of using reflectance to assess D. vexillum coverage. Preliminary results, analyzed here, prove the method to be successful for the areas we surveyed and open the way for its use on large-scale surveys.