A year round comparative study on the population structures of pelagic Ostracoda in Admiralty Bay (Southern Ocean)

Abstract

The population structures of the three dominant planktonic halocyprid Ostracoda species in Admiralty Bay (King George Island, Antarctic Peninsula) were followed throughout the course of a year in zooplankton samples collected once every three weeks from February 1993 to January 1994. The sampling was conducted at two stations: A in the central part of Admiralty Bay (400-0 m) and B in the entrance to the Bay from the Bransfield Strait (400-0 m). The samples were taken using a WP-2 net (square mouth opening of 0.196 m 2 and 200 lm mesh) hauled vertically from the bottom to the surface. Changes in the age structures of the populations of three species Alacia belgicae, Alacia hettacra and Metaconchoecia isocheira were tracked. Their population structures differed. The changes in A. belgicae suggested that it reproduces year-round, whereas both A. hettacra and M. isocheira probably complete their life cycles within a year. The cycle in A. hettacra probably starts earlier in the year than that of M. isocheira. Populations of A. belgicae and M. isocheira were more advanced in their development at station A, than at station B, but A. hettacra was more advanced at the latter. Advection appears to play a role in maintaining the populations in the shelf waters. Comparisons between populations in the shelf area (Admiralty Bay) and in open ocean waters (Croker Passage) show that the M. isocheira population is older in shelf water whereas the age structure of A. belgicae population is not influenced by the locality.

Species composition, seasonal abundance and population structure of chaetognaths in Admiralty Bay (Antarctic)

“…In the Atlantic sector, most of the studies have been carried out in the areas around the Antarctic Peninsula (Boysen-Ennen and Piatkowski 1988;Piatkowski 1989;Siegel and Piatkowski 1990;Bielecka and Żmijewska 1993;Øresland 1995;Kittel 1996;Duro et al 1999;Duro and Gili 2001;Kulagin 2010). However, the research on zooplankton in Admiralty Bay has been focused on the taxa other than chaetognaths, or on the general characteristics of the whole formation (Menshenina and Rakusa-Suszczewski 1992;Wasik and Mikołajczyk 1992;Żmijewska 1992;Freire et al 1993;Siciński et al 1996;Kittel et al 2001;Blachowiak-Samolyk and Angel 2007). This study provides the first comprehensive description of Chaetognatha in Admiralty Bay.…”

“…from the bottom (270-500 m) to the surface. In summer 2007/2008, Kruse et al (2009) estimated the body length of E. hamata in the Lazarev Sea. The range for the body length was between 7 and 29 mm , and the mean length of the individual stages was higher by 5-8 mm than that observed in Admiralty Bay.…”

“…Hitherto, investigations on the zooplankton in this bay have mainly concerned its particular components, e.g. Tintinnina (Wasik and Mikołajczyk 1992), Copepoda (Żmijewska 1992), Euphausiacea (Stępnik 1982), Ostracoda (Blachowiak-Samolyk and Angel 2007) or the whole plankton community (Menshenina and Rakusa-Suszczewski 1992;Freire et al 1993;Siciński et al 1996;Kittel et al 2001). Although chaetognaths are a very important group in the Antarctic waters, one of the most numerous after copepods, the information on their biology and ecology in Admiralty Bay is still very incomplete.…”