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Meso- and bathypelagic distribution and abundance of chaetognaths in the Atlantic sector of the Southern Ocean

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Polar Biol (2009) 32:1359–1376 DOI 10.1007/s00300-009-0632-3 ORIGINAL PAPER Meso- and bathypelagic distribution and abundance of chaetognaths in the Atlantic sector of the Southern Ocean Svenja Kruse · Ulrich Bathmann · Thomas Brey Received: 5 December 2008 / Revised: 3 April 2009 / Accepted: 3 April 2009 / Published online: 19 April 2009 © Springer-Verlag 2009 Abstract We conducted multinet sampling during winter and summer in the Southern Ocean (Atlantic sector) to investi- gate the eVect of water mass, season and water depth on abun- dance and species composition of meso- and bathypelagic chaetognaths. Eukrohnia hamata (mean 115 ind. 1,000 m¡3) and Sagitta marri (mean 51 ind. 1,000 m¡3) were dominant, complemented by E. bathypelagica (mean 19 ind. 1,000 m¡3) and E. bathyantarctica (mean 19 ind. 1,000 m¡3) below 1,000 m. A further six species were identiWed, among them the rare bathypelagic species Heterokrohnia fragilis and the sub- tropical Eukrohnia macroneura that is new to the Antarctic. Water depth and season were the principal determinants of abundance and species composition patterns, indicating verti- cal seasonal migration and vertical segregation of species. The life cycles of E. hamata and S. marri were studied additionally. Their maturity stages were vertically segregated and prolonged reproductive periods are suggested for both species. Keywords Chaetognatha · Antarctica · Bathypelagial · Distribution · Abundance · Life cycle Introduction Chaetognaths represent a major component of the world’s marine zooplankton. In the Southern Ocean they contribute signiWcantly to the total zooplankton stock, at times reach- ing up to 30% of the total zooplankton abundance (Piatkowski 1985; Froneman and Pakhomov 1998; Pakhomov et al. 1999, 2000). As main predators of copepods (Øresland 1990, 1995) chaetognaths may consume up to 5.2% of the standing stock per day (Froneman and Pakhomov 1998). Hence, they are of great importance for the energy transfer from copepods to highe

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