Elsa Vázquez

Toxicity of Hg, Cu, Cd, and Cr on early developmental stages of Ciona intestinalis (Chordata, Ascidiacea) with potential application in marine water quality assessment

The toxicity of mercury, copper, cadmium and chromium on sperm viability, fertilisation, embryogenesis and larval attachment of Ciona intestinalis was examined. Fertilisation rate (FR) showed a small decrease even at the highest metal concentration tested. The median effective concentrations (EC50) reducing rates of embryogenesis and larval attachment by 50% were 54 microg Hg/l (0.27 microM), 46 microg Cu/l (0.72 microM), 838 microg Cd/l (7.46 microM), 10,318 microg Cr/l (198 microM), and 35 microg Hg/l (0.18 microM), 34 microg Cu/l (0.54 microM) and 11,755 microg Cr/l (226 microM), respectively. Therefore, Hg is three times more toxic than Cu (on a molar basis), ca. 30 times more toxic than Cd and ca. 1000 times more toxic than Cr to early stages of C. intestinalis. Rates of larval attachment and embryogenesis were the most sensitive endpoints, although the latter is more advisable for routine assessment of seawater quality because of its greater simplicity. In addition to bivalves and sea-urchins, ascidian embryos can provide biological criteria for seawater quality standards taking into account the sensitivity of a chordate and contributing to the detection of harmful chemicals with no marked effect on the species currently in use in seawater quality bioassays.

Zoogeography of the Antarctic ascidian fauna in relation to the sub-Antarctic and South America

Abstract This study of the relationships between the Antarctic, sub-Antarctic and South America biogeographical regions used both existing and new data. We constructed a presence/absence matrix of 237 species for 27 biogeographical divisions which included the Amsterdam-Saint Paul and Tristan da Cunha islands. Species and areas were classified using cluster analysis combined with MDS ordination. Six main groups were obtained from the species classification: 1) Amsterdam-Saint Paul, and 2) Tristan da Cunha species, 3) species from the Macquarie Province, 4) species from the sub-Antarctic Region, 5) Antarctic species and species distributed in the cold regions, 6) South American species. The biogeographical components were dominated by the endemic (although it is not as high as in other groups), Antarctic-South America and Southern Hemisphere elements. Except for Amsterdam-Saint Paul, Tristan da Cunha and Bouvet, the areas considered were grouped together with Macquarie being rather related to New Zealand regions. We speculate that the Antarctic Region may have acted as an “evolutionary incubator”, providing a centre of origin for sub-Antarctic and South American ascidians.

A standardisation of Ciona intestinalis (Chordata, Ascidiacea) embryo-larval bioassay for ecotoxicological studies

A standardisation of the ascidian Ciona intestinalis embryo-larval bioassay for marine pollution assessment has been developed. The minimum percentage of embryogenesis success was established to assess the quality of the biological material used; minimum sample size and number of replicates per treatment were also estimated. The suitability of artificial and natural seawater for the incubation of ascidian embryos and larvae was compared, and the optimum conditions of temperature, salinity, pH, density of embryos in the vials and the sperm/egg ratio were investigated. On the basis of the 10th percentile of the distribution of larval abnormalities, we proposed a threshold of 50% normal larvae in the control in order to consider the test of acceptable biological quality. According to our results n=5 is a sufficiently high replication to detect 5% differences among treatment means with a power of P=90% and alpha=0.05, and a sampling size >/=222 allows a 95% confidence in the estimate with an error of 0.05. Egg density did not affect larval development within the range 1-20 eggs/ml, and the optimum sperm/egg ratio which fertilise 100% of the eggs was 3000-30,000 sperm/egg (i.e. 10(8)-10(7) sperm/ml). There were not significant differences between the two water types tested, and the optimum tolerance ranges were 18-23 degrees C temperature, 34-42 ppt salinity (42 ppt was the highest salinity tested), and 7.4-8.8 pH. The median effective concentration (EC(50)) of copper (Cu) causing a 50% reduction of normal hatched larvae was 54.2 microg/l (0.85 microM), which shows a sensitivity of this species similar to the commonly used bivalve and sea-urchin tests. The ascidian embryo-larval bioassay is an accurate, reliable, simple and rapid method that can be used in ecotoxicological studies.

Chapter Five: Effects of the Prestige Oil Spill on the Biota of NW Spain: 5 Years of Learning

On 19 November 2002, the oil tanker Prestige broke into two and sank in the Atlantic Ocean 260 km off the north-western coast of Spain, releasing about 63,000 tonnes of Bunker C oil. The accident represented one of the largest environmental catastrophes in the history of European navigation. More than 1000 km of coastline and a huge variety of habitats were affected, ranging from supralittoral, intertidal and sublittoral levels to oceanic and bathyal environments. In this chapter, we review published results regarding the impact of the Prestige oil spill on marine organisms, at levels of biological organisation ranging from the molecular to the ecosystem. Although some research is still in progress, all results indicate a strong initial impact during the first year after the spill, mainly on intertidal communities and fishing resources, with recovery by 2004.

Antarctic ascidians: an isolated and homogeneous fauna

Several biogeographical studies have already been performed on the ascidians of the Antarctic region. However, new data obtained in the last few years have led us to a revision of the biogeography of this fauna. To examine the biogeographical structure of the Antarctic region, we divided it into 10 sectors, depending on the principal geographical features, and then applied cluster analysis and a multi-dimensional scaling ordination to a presence/absence matrix of species for each biogeographical area. Our study shows that Antarctic ascidians are a very homogeneous fauna, with a high level of endemism in the whole region (25–51% of Antarctic endemic species per sector), but with a low percentage of sector endemism (only up to 10%). This probably results from isolation arising from the Antarctic Convergence, and the vast geographical distances from adjacent regions, as well as from the relative constancy of the hydrographical conditions and the dispersal of organisms through circumpolar currents. In fact, cosmopolitan species represented only 0–7% of the total ascidian fauna in all sectors. Only the Bellingshausen Sea (low sample size), Bouvetøya (young and isolated, with an impoverished ascidian fauna) and the South Sandwich Islands (also young and isolated) are relatively separated. The insular sectors were more closely related to the South America and sub-Antarctic regions than the continental ones, showing a latitudinal gradient.

Ontogenetic changes in phototaxis during larval life of the ascidian Polyandrocarpa zorritensis (Van Name, 1931)

Ontogenetic changes in larval photoresponses of Polyandrocarpa zorritensis (Ascidiacea, Styelidae) were studied by characterizing the swimming trajectories of individual larvae exposed to white light. The same individuals were tested repeatedly from release to settlement to remove the effects of interindividual variation in behavior. Swimming speed and overall level of activity varied significantly over time, eventually decreasing near the end of larval life. The youngest larvae swam in large spirals or straight trajectories. Late-stage larvae, used short vertical hops to contact the substratum repeatedly with the anterior papillae. This observation supports the hypothesis that papillae function in selection of a site as well as in adhesion. P. zorritensis become photopositive at the end of larval life, a behavior which probably functions in selection of microhabitats rather than in depth regulation.

A Non-Swimming Ascidian Larva: Protostyela longicauda (Styelidae)

The ascidian Protostyela longicauda broods larvae that have a unique, non-locomotory tail. In hatched larvae, the tail is a simple strand of tunic without cellular components or external fins, extremely elongated and anteriorly directed. Before hatching, the tail consists of a mass of secretory cells that release fibrillar material to the tunic. Notochord, neural tube, and muscle cells are absent, but presumptive chordal cells are found at earlier embryonic stages. The anterior part of the trunk bears three conical adhesive papillae and five pairs of ampullae, which elongate at metamorphosis. The tunic of the trunk and tail is sticky from the first moment after hatching and adheres readily to any object; the papillae make contact later. This species attaches to algal fronds in wave-swept, rocky intertidal habitats. Field observations on adult populations revealed a strongly aggregated, philopatric pattern of distribution, as well as within-patch patterns of colonization of some algal species as substrate. Restricted dispersal of short-lived larvae in these communities diminishes the risk of being swept away and is consistent with the aggregated pattern found. We suggest that, upon release of the larva, the sticky tail rapidly becomes entangled with algae, thereby allowing the papillae, oriented at about 30? to the tail, to contact the substrate and achieve permanent fixation. We therefore interpret these non-swimming larvae as facilitating philopatry. Additional key words: tunicate larvae, caudal complex, dispersal, distribution, philopatry Structural and morphological variations in invertebrate larval forms, driven by strong selective pressures, reflect profound differences in the biology of the species-in duration of larval period, in feeding mode, dispersal ability, and mortality-even in taxonomically close groups (reviewed in Giangrande et al. 1994). A vast literature is concerned with debating the adaptive value of diverse larval strategies (reviewed in McEdward 1995). Indeed, major developmental and morphological changes in larval forms may accompany corresponding changes in life-history strategies of the species (Wray 1995). Among ascidians, the typical tadpole larva has a locomotory tail, sensory structures (ocellus, otolith) for orientation, and papillae and ampullae for anchoring. Adult organs are present in a rudimentary state (Cloney & Torrence 1984; Svane & Young 1989). In some species, adult features develop precociously (a phenomenon called adultation by Jeffery & Swalla 1992); in others, the locomotor tail system is enhanced (caudalization, Jeffery & Swalla 1992); and in some a To whom correspondence should be addressed. cases, the free-swimming larval stage is completely suppressed (anural development). In general, larvae of solitary ascidians tend to be simpler than those of colonial species, which more often feature adultation and/or caudalization. While some biologists focus on the developmental mechanisms (Jeffery & Swalla 1990, 1992; Satoh 1994), these phenomena also have life-history consequences. Adultation reduces the interval between hatching and metamorphosis, while caudalization enhances swimming and hence dispersal. For dispersal, the most drastic dichotomy is between urodele and anural modes of development (Bates 1993; Satoh 1994). Anural forms have been reported in some members of the family Molgulidae and in two species of Styelidae (Pelonaia corrugata MILLAR 1954 and Polycarpa tinctor MILLAR 1962). Most anural species are unattached inhabitants of sand-flat substrates, which are far more homogeneous than hard substrates (Berrill 1931, 1975). But some anural species inhabit high-energy habitats, such as shallow subtidal communities along rocky shores, and appear specifically adapted to such environments (Young et al. 1988). Recently, another anural species has also been reported to inhabit rocky, This content downloaded from 157.55.39.58 on Sun, 11 Dec 2016 04:28:38 UTC All use subject to http://about.jstor.org/terms

Zoogeography of the southern New Zealand, Tasmanian and southern African ascidian fauna

Abstract We studied the relationships among the ascidian fauna of southern New Zealand, Tasmania, and southern Africa, considering main currents and surface water temperature. We constructed a presence/absence matrix of 494 ascidian species from these regions (which were also divided into provinces) for 28 biogeographical worldwide regions using published records. Biogeographical areas were classified using cluster analysis combined with non‐metric multidimensional scaling ordination. The region classification separated Vema Seamount because of the low number of citations and the high number of ascidian endemism owing to an island effect. The Tasmanian, southern African and southern New Zealand regions formed separate groups. The ascidian fauna was dominated by endemic species in southern New Zealand (43%) and southern Africa (45%), whereas southern Australian species dominated the Tasmanian fauna (41%).

Response of two mytilids to a heatwave: the complex interplay of physiology, behaviour and ecological interactions

Different combinations of behavioural and physiological responses may play a crucial role in the ecological success of species, notably in the context of biological invasions. The invasive mussel Xenostrobus securis has successfully colonised the inner part of the Galician Rias Baixas (NW Spain), where it co-occurs with the commercially-important mussel Mytilus galloprovincialis. This study investigated the effect of a heatwave on the physiological and behavioural responses in monospecific or mixed aggregations of these species. In a mesocosm experiment, mussels were exposed to simulated tidal cycles and similar temperature conditions to those experienced in the field during a heat-wave that occurred in the summer of 2013, when field robo-mussels registered temperatures up to 44.5°C at low tide. The overall responses to stress differed markedly between the two species. In monospecific aggregations M. galloprovincialis was more vulnerable than X. securis to heat exposure during emersion. However, in mixed aggregations, the presence of the invader was associated with lower mortality in M. galloprovincialis. The greater sensitivity of M. galloprovincialis to heat exposure was reflected in a higher mortality level, greater induction of Hsp70 protein and higher rates of respiration and gaping activity, which were accompanied by a lower heart rate (bradycardia). The findings show that the invader enhanced the physiological performance of M. galloprovincialis, highlighting the importance of species interactions in regulating responses to environmental stress. Understanding the complex interactions between ecological factors and physiological and behavioural responses of closely-related species is essential for predicting the impacts of invasions in the context of future climate change.

Agnezia monnioti and Styela gagetyleri, New Deep-Sea Ascidians Specialized for Life within and below the Oxygen Minimum Layer in the Arabian Sea

Two new species of solitary ascidians from the deep sea off Oman, Arabian Sea, are described. Agnezia monnioti n. sp. is from the abyssal plain at 3162 m depth. Whereas many deep-sea ascidians have reduced branchial ciliation and exploit the velocity gradient in the benthic boundary layer to induce internal flow, this species has strong ciliation and a siphonal arrangement that appears inappropriate for using ambient water currents for filtration. Styela gagetyleri n. sp. is found at a depth of 368 m, which is in the middle of a persistent oxygen minimum zone. The branchial sac of this species has a reduced number of folds and therefore fewer cilia for food collection and less surface area for oxygen exchange than shallowwater congeners. We hypothesize that reduced filtration capacity is made possible by an unusually high flux of organic material to the sea floor in this region. The observed reduction in branchial surface area in a persistent hypoxic zone suggests that branchial complexity in ascidians is more important for feeding efficiency than gas exchange. Affinities of these species with other members of their respective genera are discussed and an appendix with the synonyms and localities of species in the genus Agnezia is included. Additional key words: filter feeding, Indian Ocean, monsoons, Tunicata, Urochordata,