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Holocene Molluscan Assemblages in the Magellan Region*

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SCI. MAR., 63 (Supl. 1): 15-22 SCIENTIA MARINA 1999 MAGELLAN-ANTARCTIC: ECOSYSTEMS THAT DRIFTED APART. W.E. ARNTZ and C. RÍOS (eds.) Holocene molluscan assemblages in the Magellan region* SANDRA GORDILLO Centro Austral de Investigaciones Científicas (CADIC, CONICET) C.C. 92, 9410 Ushuaia, Tierra del Fuego, Argentina. Present address: Cátedra de Estratigrafía y Geología Histórica, Universidad Nacional de Córdoba, Avda. Vélez Sárfield, 5000 Córdoba, Argentina. SUMMARY: In the Magellan region, much of the shoreline of the Beagle Channel coast (54°53’S; 67° - 68°W) is bordered by Holocene raised beaches, which contain a large number of molluscs and other shelled taxa. The purpose of this work is to document the presence of various molluscan assemblages deposited with little or no postmortem transportation. An epi- faunal Chlamys patagonica palaeocommunity (ca. 8,000 - 7,000 BP) and three infaunal (Tawera gayi, Ameghinomya anti- qua - Hiatella solida and Ameghinomya antiqua - Ensis macha) palaeocommunities (ca. 4,400 - 4,000 BP) were recognized. All the assemblages studied represent shallow, subtidal, cold-temperate environments. Based on comparisons with modern benthic communities in this region, these associations show that no remarkable ecologic and climatic changes occurred dur- ing the period ca. 8,000 - 4,000 BP. Thus, an apparent stability of modern marine communities over a period of several thou- sand years is suggested. Key words: Holocene, molluscan assemblages, Magellan region. RESUMEN: ASOCIACIONES DE MOLUSCOS DEL HOLOCENO EN LA REGIÓN DE MAGALLANES. En la región de Magallanes, gran parte de la costa del Canal del Beagle (54°53’S; 67°-68°O) está caracterizada por la presencia de playas elevadas del Holo- ceno, que contienen un gran número de moluscos y otros taxones. El objetivo de este trabajo es documentar la presencia de distintos tipos de asociaciones de moluscos depositadas sin previo transporte o escaso transporte postmortem. Se reconocieron una paleocomunidad epifaunal de Chlamys patagonica (ca. 8.000 - 7.000 AP) y tres paleocomunidades infau- nales de Tawera gayi, Ameghinomya antiqua-Hiatella solida y Ameghinomya antiqua-Ensis macha (ca. 4.400 - 4.000 AP). Todas estas asociaciones representan ambientes marinos costeros templado-fríos. Al comparar las asociaciones estudiadas con las unidades equivalentes actuales no se han detectado cambios ecológicos y climáticos durante el período considerado ca. 8.000 - 4.000 AP, lo que sugiere un período de estabilidad de las comunidades de moluscos de varios miles de años. Palabras clave: Holoceno, asociaciones de moluscos, región de Magallanes. INTRODUCTION (allochthonous assemblages), which have little palaeoecological interest. This is not the case of the Holocene marine molluscs are widely preserved mollusc assemblages considered in this work, in the geological record. Nevertheless, the majori- which have two characteristics used as tools for ty of these fossil molluscan assemblages -closely palaeoecological interpretations: (1) they were associated with the offshore to beach gradient- deposited in situ (autochthonous assemblages), or consist of preburially transported assemblages with little preburial transport (parautochthonous assemblages), and (2) the species are living taxa in *Accepted February 15, 1999. the Magellan region. As used here, the term “sub- HOLOCENE MOLLUSCA IN THE MAGELLAN REGION 15 fossil” refers to animal remains of Holocene age, completed with Quaternary sediments: Pleistocene i.e. up to 10,000 years old. glacial deposits and Holocene marine terraces. The purpose of this work is to document the sys- Holocene raised beaches border much of the shore- tematics of the subfossil species, the taphonomic line of the Beagle Channel coast. During the evidence and the mollusc assemblage types. In addi- Holocene, the palaeogeographic evolution of the tion, the trophic relationships and the ecological and Beagle Channel terraces system has been mainly palaeoecological characteristics of the species are controlled by glacioisostatic uplift and partly by discussed. neotectonic activity, notably by displacements on The Beagle Channel (54°53’S, 67°-68°W) is several minor faults (Rabassa et al., 1989; Gordillo located in the Magellan region within the Fuegian et al., 1992). Andes environment. Late Jurassic volcanic rocks According to Iturraspe et al., (1989) the Beagle (Lemaire Fm.; Borello, 1969) follow the potential Channel shows an average temperature at 2 m depth Paleozoic-early Mesozoic basement (Lapataia Fm.; of 6.5°C, with a maximum of 10°C (February) and a Borello, 1969). Cretaceous marine rocks overlay minimum of 3°C (August); and salinity varies from this formation (Yahgan Fm.; Kranck, 1932). Eocene 27 to 31‰. continental beds (Slogget Fm.; Caminos, 1980) The localities considered in this work (Fig. 1) intruded by eruptive rocks (Quartino et al., 1989) were selected on the basis of the features of the represent the Tertiary. The stratigraphical scheme is molluscan assemblages previously studied by FIG. 1. – Map of the Beagle Channel showing sampling locations. LR: Lago Roca; RO: Río Ovando; ER: Entre Ríos; LV: Laguna Verde; BG: Bahía Golondrina and GA: Isla Gable. 16 S. GORDILLO Gordillo (1993) and Gordillo et al. (1993). In the TABLE 1. – List of the total fauna of molluscs collected in the western sector, Figure 1 shows the Cormoranes studied area. Archipelago which includes the Lago Roca (LR), Río Ovando (RO), Entre Ríos (ER) and Laguna Class GASTROPODA Cuvier 1797 Subclass PROSOBRANCHIA Milne Edwards 1848 Verde (LV) sites. Low islands where Holocene Order ARCHAEOGASTROPODA Thiele 1925 deposits contain molluscs buried in situ cap this Family PATELLIDAE Rafinesque 1815 Nacella magellanica (Gmelin 1790) area. At present, this area is disconnected from the Nacella deaurata (Gmelin 1790) Beagle Channel and is occupied by fresh water. Family TROCHIDAE Rafinesque 1815 Calliostoma (Swainson 1840) sp. The exposed profile of the LR site is a greyish silty Margarella violacea (King & Broderip 1831) massive bed 3.0 m above sea level (a.s.l.) radiocar- Order MESOGASTROPODA Thiele 1925 bon dated by Gordillo et al. (1993) at 7518 +/- 58 Family LITTORINIDAE J.E. Gray 1840 Eatoniella kerguelensis (Smith 1875) BP (NZ # 7730). Shells of the RO were dated by Family CERITHIDAE Fleming 1822 Rabassa et al. (1986) at 4425 +/-55 BP (SI # 6735). Ataxocerithium pullum (Philippi 1845) Eumetula michaelseni (Strebel 1906) The ER and the LV sites can be correlated, accord- Family CALYPTRAEIDAE Blainville 1824 ing to their elevation (near 2.5 - 3.0 m a.s.l.), with Calyptraea pileolus d’Orbigny 1841 Crepipatella dilatata (Lamarck 1822) the Río Ovando site. In the central sector the exis- Family NATICIDAE Forbes 1828 tence of a profile with molluscs in life position Falsilunatia limbata (d’Orbigny 1840) close to the Golondrina bay (BG; Fig. 1), 5 km east Order NEOGASTROPODA Thiele 1929 Family MURICIDAE Rafinesque 1815 of Ushuaia, must be mentioned. Finally, in the east- Trophon geversianus (Pallas 1774) ern sector, molluscs without signs of transportation Xymenopsis muriciformis (King 1831) Family BUCCINIDAE Rafinesque 1851 near 3 m above m.s.l. were also found on Gable Meteuthria martensi (Strebel 1905) Island (IG; Fig. 1). Pareuthria plumbea (Philippi 1845) Subclass PULMONATA Cuvier 1797 Order BASOMMATOPHORA Schmidt 1855 Family SIPHONARIIDAE Gray 1840 MATERIAL AND METHODS Siphonaria lessoni (Blainville 1824) Class BIVALVIA Linné 1758 Subclass PALAETAXODONTA Korobkov 1954 Molluscs from each assemblage mentioned in Order NUCULOIDA Dall 1889 Family MALLETIIDAE H. & A. Adams 1858 Figure 1, i.e. LR, RO, ER, LV, BG and IG, were Malletia cumingi (Hanley 1860) identified, counted and measured in size. Shell size Family Nuculanidae H. & A. Adams 1858 Nuculana striata (King 1831) range (SSR) of the main taxa, relative abundance of Subclass PTERIOMORPHA Beurlen 1944 the articulated valves (AV) and orientation of the Order PTERIOIDA Newell 1965 shells (life position or horizontal position) were cal- Family PECTINIDAE Rafinesque 1815 Chlamys patagonica (King & Broderip 1831) culated. Biodiversity of the preservable groups was Family LIMIDAE Rafinesque 1815 also considered. The Shannon index (H´) as an esti- Limatula pygmaea (Philippi 1845) Order MYTILOIDA Férussac 1822 mate of species richness was coupled with the Shan- Family MYTILIDAE Rafinesque 1815 non evenness (E) as a measure of evenness and with Mytilus edulis chilensis Hupé 1854 the Simpson index (D) as a measure of dominance. Perumytilus purpuratus (Lamarck 1797) Aulacomya atra (Molina 1782) Diversity was calculated separately for each assem- Subclass HETERODONTA Neumayr 1884 blage. High values of the Shannon index indicate a Order VENEROIDA H. & A. Adams 1856 Family LEPTONIDAE J.E. Gray 1847 combination of many species and an even distribu- Neolepton cobbi (Cooper & Preston 1910) tion of the specimens over the species. In relation to Family MONTACUTIDAE Clark 1855 Mysella cf.arturi (Cooper & Preston 1910) evenness, values close to the maximum of 1 show Family CONDYLOCARDIIDAE Bernard 1896 uniform abundances of the taxa. Finally, as domi- Carditella naviformis (Reeve 1843) nance increases diversity decreases (see equations in Carditopsis flabellum (Reeve 1843) Family MACTRIDAE Lamarck 1809 Magurran, 1988). Mulinia edulis (King 1831) Complementary observations of modern benthic Family SOLENIDAE Lamarck 1809 Ensis macha (Molina 1782) communities of the Beagle Channel were made in Family VENERIDAE Rafinesque 1815 the intertidal zone
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    8 May 1964 MEM. NAT. MUS. VICT. 26—1963 219 https://doi.org/10.24199/j.mmv.1964.26.12 STUDIES OF THE GENUS KATELYSIA ROMER 1857 (MOLLUSCA, LAMELLIBRANCHIATA). By Barbara J. Nielsen. Introduction. There has been confusion as to the validity of the species included in the genus Katelysia Romer 1857, and this suggested the necessity for an assessment of its representatives in Victoria. This was followed by detailed studies of two particular species Katelysia scalarina Lamarck 1818 and Katelysia rhytiphora ' Lamy 1935 to ascertain their validity as biological or natural ' species as against specific separation based on shell morphology alone. This includes the anatomy of the animals, statistical analyses of shell measurements and an investigation of breeding cycles. The third species K. peronii Lamarck 1818, is omitted because of insufficient material. Synonymy. Although Eduard Romer established the genus Katelysia for a group of Venus like lamellibranchs from southern Australia (genotype K. scalarina Lamarck 1818) in 1857 the name does not appear again in the literature until 1914 when Jukes-Brown used it in his revision of the family Veneridae. Later Lamy (1935, 1937) revised the Lamark'ian species consigned to it. Unfortunately, Lamy's work was by-passed by Australian conchologists," most basing their check-lists on Pritchard's and Gatliff s condensation (1903) of nine Lamarckian species of Venus into three species, Chione strigosa, C. scalarina and C. peronii. Katelysia first came into general usage in 1938, when Cotton and Godfrey revived the name and recorded three species from South Australia. Because of the numerous writers it is easiest to consider first the species listed in the four latest works of Kershaw (1955), Macpherson and Chappie (1951), Allan (1950) and Cotton and Godfrey (1938).
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    Revista Chilena de Historia Natural 73: 99-129, 2000 Zoogeografía de macroinvertebrados bentónicos de la costa de Chile: contribución para la conservación marina Zoogeography of benthic macroinvertebrates of the Chilean coast: contribution for marine conservation DOMINGO A. LANCELLOTII & JULIO A. VASQUEZ 1 Departamento de Biología Marina, Facultad de Ciencias del Mar, Universidad Católica del Norte, Casilla 117, Coquimbo, Chile, e-mail: [email protected] RESUMEN La diversidad de macroinvertebrados marinos ha recibido una atención creciente, no obstante, con un escaso tratamiento en el contexto biogeográfico. Este estudio analiza los registros de 1.601 especies de macroinvertebrados bentónicos pertenecientes a: Demospongiae, Anthozoa, Polychaeta, Mollusca, Crustacea, Echinodermata y Ascideacea, agrupados en 10 zonas y tratados desde una perspectiva zoogeográfica. Mollusca (611 especies), Polychaeta (403) y Crustacea (370) corresponden a los grupos mejor representados a lo largo de la costa chilena, determinantes en el patrón global de la biodiversidad. Este aumenta suavemente de norte a sur, interrumpido por máximos que sugieren esfuerzos diferenciales de estudio más que un comportamiento natural de la biodiversidad. El grado de agrupamiento entre las zonas muestra las tres unidades biogeográficas definidas recientemente por Lancellotti & V ásquez. Este arreglo, que representa lo exhibido por los grupos más diversos, se ve alterado en los grupos menos representados donde las diferencias obedecen al patrón de afinidades mostradas por las zonas comprendidas dentro de la Región Templada Transicional. El quiebre zoogeográfico alrededor de los 41° S, sugerido largamente en la literatura, sólo ocurre en Echinodermata y Demospongiae, evidenciando en los otros taxa la existencia de un área de transición entre los 35° y 48° S, caracterizada por un reemplazo gradual de especies.