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Recent progress in study on calcareous algae and algal sediments

2017; Wiley; Volume: 26; Issue: 3 Linguagem: Inglês

10.1111/iar.12213

1440-1738

Yasufumi Iryu, Davide Bassi,

Marine and coastal plant biology

Calcareous algae are characterized by biologically precipitated deposits of calcium carbonate, forming an artificial biological assemblage that cuts across taxonomic boundaries. They are one of the most important framework and sediment producers in reefs and carbonate platforms from the Proterozoic. Calcareous algae and algal sediments have been, therefore, a major target of paleontological and geological sciences. The International Fossil Algae Association (IFAA), an international group of scientists who are interested in any aspect of fossil and living algae, organizes an international symposium every 4 years. Okinawa was selected to host the 11th International Symposium on Fossil Algae (Figure 1) because of great contributions to the study of calcareous algae by Japanese scientists such as Ryuji Endo, Wataru Ishijima, and Kenji Konishi (Iryu, 2004) and easy accessibility to modern and Pleistocene coral reefs for which many sedimentological and paleontological studies have been performed for more than 100 years (e.g. Iryu et al., 2006). The Symposium was held on September 14–18, 2015 with the support of the Geological Society of Japan and the Palaeontological Society of Japan. A total of 13 scientists from five countries attended the symposium. Pre-symposium field excursions (September 14–15) visited modern dasycladacean meadows (Figure 2) and Pleistocene carbonate deposits on Okinawa-jima, Central Ryukyus and coral reefs off Kerama Islands. The next 2 days (September 16–17) were devoted for the scientific sessions at the University of the Ryukyus. A special session was organized to discuss “Morphology versus molecular evidence in determining algal taxonomy and phylogeny.” A post-symposium excursion was conducted on September 18. We visited the Shuri Castle and then observed Pleistocene carbonate successions on southern Okinawa-jima. Although the number of participants was limited, there were prolonged discussions for every presentation. This thematic section collects recent studies on calcareous algae and algal sediments by IFAA members. Five papers are assembled here, covering Devonian to modern materials from Europe, Africa, and Japan. The first article in this issue is by Hubmann and Reuter (2017). Based on newly collected material from the type locality in the Eastern Alps, Austria, they emend the taxonomic description of Zeapora (Bryopsidales, Chlorophyta). Although this genus was regarded to be endemic in the alpine Noric Terrane, Litanaella is shown to be a younger synonym of Zeapora. This indicates that Zeapora had a circum-tropical distribution in the Early to Middle Devonian similar to that of modern Halimeda. Granier, Azerêdo, and Ramalho (2017) perform a taxonomic reassessment of Cylindroporella? lusitanica Ramalho from the Upper Jurassic (Oxfordian) in Portugal and ascribe this species to the new genus Barattoloporellopsis. With its unique body plan, this species is likely to be a primitive dasycladalean alga (Dasycladales, Chlorophyta), a “missing link” between the modern taxa (from the Cretaceous onwards) and their Jurassic ancestors. Bucur, Săsăran, and Pascariu (2017) examine well preserved specimens of Petrascula bugesiaca Bernier, collected from Cretaceous conglomerates in the Romanian South Carpathians. Since Bernier’s (1979) discovery of this species from Tithonian limestones in the Southern Jura Mountains (French−Switzerland), it has not been reported elsewhere. Detailed anatomical analysis indicates that this species can be ascribed to the dasycladalean Petrascula Gümbel. The latest Barremian–earliest Aptian dasycladalean assemblage in Lebanon are characterized by relatively high diversity of Triploporellaceae species. Maksoud, Granier, and Azar (2017) describe a new Triploporellaceae species, Triploporella? edgelli. Because studied specimens lack calcified secondary segments, its taxonomic position cannot be determined at present. Ohba et al. (2017) report the occurrence and distribution of 12 present-day dasycladalean species in Okinawa-jima, Ryukyu Islands, and discussed their paleontological implications. Dasycladalean algae mostly grow on coral rubble and rocks, often forming large meadows in calm shallow lagoons. Dasycladus vermicularis (Scopoli) Krasser and Neomeris annulata Dickie, however, occur in deeper waters (15–89 and 0–30 m, respectively), putting into question the common paleontological interpretation that the occurrence of dasycladalean algae is linked to very shallow water habitats. We hope that this thematic section will provide insights into some of the investigations that have been undertaken recently on calcareous algae and algal sediments of various ages all over the globe and will stimulate further studies and collaboration among workers. We greatly acknowledge J. Aguirre, G. Amado-Filho, F. Barattolo, I. Bucur, M.A. Conrad, B. Granier, T. Grgasović, J. Ledesma Vazquez, M. Parente, W. Prud’homme van Reine, M. Reolid, M. Rasser, and F. Schlagintweit. We wish to thank T. Muto, the Editor-in-Chief of Island Arc, for his efficient assistance in bringing this thematic section to fruition.