Details

Autor(en) / Beteiligte

• Koutsoukos, EAM
• Fauth, G
• Kotzian, C B
• Falcetta, M M

Titel

Distribution of Recent foraminifera, ostracods, and micromolluscs in shore sediments of Easter Island (Isla de Pascua), southeastern Pacific

Ist Teil von

• Anuário do Instituto de Geociências, 2006-01, Vol.29 (1), p.269-270

Erscheinungsjahr

2006

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Easter Island, a small volcanic island with an area of approximately 106 km super(2), lies 2,230 miles west of the Chilean coast at latitude 2710' S. As the easternmost outpost of the Polynesian region, and one of the most isolated islands in the Pacific Ocean, Easter Island has a marine fauna with an Indo-Pacific affinity. Characteristically, there is a high level of endemism for several taxonomic groups, including foraminifera (e.g., Adelosina pascuaensis), ostracods (e.g., Cytheroloidea keiji pasquaensis, Macrocyprina rattrayi, Neonesidea supercaudata, Loxocorniculum mayburyae, Quadracythere allows, Tenedocythere titanikos, Triginglymus nesiotes, Cletocythere nautes, Xestoleberis polys, Xestoleberis tetragons and Aglaiocypris cylindratas; all described in R. Whatley, R. Jones & K. Woutrs, 2000. Revista Espanola de Micropaleontologia, 32 (1): 79-106) and micromolluscs (dominated by microgastropods of the families Hipponicidae and Caecidae). Nine sediment samples, mainly calcareous in composition and biogenic in origin, with scattered fragments of volcanic rocks, were collected in June 1979 at four different shore sites (water depth less than 1 m at the time of collection): Anakena Bay, Ovahe Bay and La Perouse Cove, on the East coast, and Hanga Roa Cove, on the North coast. Amphistegina lessonnii is the dominant species in all the samples. A relatively well diversified miliolid assemblage, represented by 28 species belonging to Adelosina, Amphisorus, Hauerina, Heterillina, Marginopora, Miliolinella, Nodobacularia, Quinqueloculina, Spiroloculina and Triloculina, is consistently found only in the Anakena and Ovahe bays, typically reflecting the more protected biotopes of these sites, with low wave energy, finer-grained sediments and sea-grass substrate. This environmental setting is also reflected by the relative abundance in the foraminiferal assemblage of Discorbis mira, Homotrema rubrum, Planorbulina acervalis and P. mediterranensis, together with subordinate numbers of rotaliids, represented by 23 species belonging to Ammonia, Anomalina, Bolivina, Cibicides, Elphidium, Eponides, Fissurina, Glabratella, Gypsina, Heterostegina, Lamarckina, Lenticulina, Loxostomum, Planulina, Poroeponides, Rectobolivina, Reussella, Siphogenerina, Spirillina and Stomatorbina. In addition, the ostracod and microgastropod diversity and abundance are also much higher at these sites. The absence of a well diversified miliolid assemblage in the coves of La Perouse and Hanga Roa (where only rare Amphisorus were recorded), and of the genera Ammonia, Discorbis and Elphidium, points out to less protected biotopes, with moderate to strong wave activity, induced by the high-energy winds prevailing on the SW coast, with steep cliffs, coarser-grained sediments and a rocky shoreline.