Reproductive biology of the ascidians Styela rustica and Halocynthia pyriformis from Kongsfjorden, Svalbard, Arctic
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Ascidians are abundant and well-represented members of worldwide benthic communities, including Antarctica and the Arctic. These organisms exhibit different reproductive patterns usually related to a latitudinal gradient, as do many marine invertebrate species. Reproductive seasonality varies from one or two annual peaks in cold and temperate water species to continuous reproduction throughout the year in warm water species. Styela rustica (Linnaeus 1767) and Halocynthia pyriformis (Rathke 1806) are solitary species with external fertilization and a wide distribution range, from the North Atlantic to the Arctic. The reproductive patterns of these two species were assessed for Arctic populations by year-round sampling and structural analysis of the gonads. Both species are hermaphrodites and showed marked seasonality in oocyte maturity and spawning; S. rustica peaked during the boreal summer and H. pyriformis in late spring. The two species also showed marked differences in mature oocyte sizes: H. pyriformis almost doubled those of S. rustica and, while spermatocytes of H. pyriformis were mature year-round, the maturity of male and female gametes was synchronized in S. rustica. The species thus showed an annual reproductive cycle coupled with a higher production period in the ecosystem, but also exhibited different strategies developed under the same environmental pressures.
KeywordsPolar ecosystems Tunicates Life cycles Reproductive ecology
We would like to thank the SCUBA divers of AWI involved in sampling the species and installing the cages, namely Saskia Brandt, Daniel Carstensen, Wolfgang Nikolaus Probst, Bettina Saier, Philipp Schubert, Max Schwanitz, Christian Wecke, Ulrich Kunz, and José Velez. We are indebted to the station staff, Thorsten Wilhelm, Anne Hormes, Anne Theuerkauf, Jens Kuba and Kai Marholdt, as well as to Roland Neuber, who retrieved the cages and fixed the samples. We thank the three anonymous reviewers for their valuable suggestions. We are grateful for financial and logistic support provided by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and the Secretaría de Ciencia y Tecnología (SECyT).
This study was funded by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) and the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). The work was partially funded by PICTO (Ref 36326 and 2010–0019) (ANPCyT-DNA) and the Secretaría de Ciencia y Tecnología (SECyT 05/I602).
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Conflict of interest
The authors declare that they have no conflicts of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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