Radiolarians in the Adriatic Sea plankton (Eastern Mediterranean)

Abstract

         Samples for the study of radiolarians in the Southern Adriatic were collected during five cruises at three stations along the Dubrovnik transect (stations S-100 to S-1000) from April 1993 through February 1995. Moreover, samples were collected during 21 cruises at the deepest station, S-1000/1200, from June 2001 through December 2009. Samples were taken in 2 to 8 vertical layers with a Nansen net 53 μm equipped with a closing system. In the central part of the southern Adriatic Pit, a total of 95 radiolarian taxa were recorded: 32 species of spumellaria, 46 species of nassellaria and 17 species of phaeodaria. The present research added 49 taxa to the known radiolarian fauna of the Adriatic Sea. The most common species were the phaeodarian Challengeria xiphodon, the spumellarian Stylodictya multispina and the nassellarian Cornutella profunda, which were present in 99% of the vertical series. Radiolarians were rarely present in coastal areas and in the central Adriatic, whereas the highest abundances were recorded in the deepest parts of the south Adriatic Pit. Phaeodaria represented 20-86 % of the total average abundance. As a rule, very low abundances were noted in the euphotic layer except during October 2001, when a maximum of 169 ind. m^-3 was recorded. Juvenile forms of the species Eucyrtidium acuminatum represented 98 % of the total number in these samples. In most cases, the maximum abundances were found in layers between depths of 200-300 m. The populations of most species were renewed by incoming eastern Adriatic currents from the Ionian Sea.