Nychthemeral variations of Tintinnina (Ciliata: Oligotrichida) near the Rocas Atoll (South Atlantic) and relationships with other microzooplanktonic components

Abstract

A major consideration in the study of microzooplankton is the scarcity of data from oceanic waters of the South Atlantic. We examined tintinnines and other surface water microzooplanktonic organisms at a fixed oceanic station near the Atol das Rocas Island (northeastern Brazil) at different times of the day, from 14 to 16 March, 1999. Tintinnines dominated and were represented by 42 species. The greatest diversities and abundances of microzooplankton were found in diurnal samples, although large fluctuations were regularly observed. The greatest diversity and abundance of was observed during the daytime at 06:00 and 14:00, and during the night at 19:00 and at 21:30. The most frequent and abundant species were Rhabdonellopsis apophysata (Cleve) Kofoid & Campbell, 1929, Rhabdonella amor (Cleve 1900) Brandt, 1907 , R. elegans Jörgensen, 1924, Undella claparedei (Entz, Sr., 1885) Daday, 1887, Epiplocylis undella (Ostenfeld & Schmidt 1901) Jörgensen, 1924 , and Eutintinnus apertus Kofoid & Campbell, 1929. Copepods and crustacean larvae were very abundant during the day, especially at 07:00 and 14:00. The Foraminifera were abundant only at 06:00, 09:00, 10:00, and 14:00. Other microzooplanktonic groups were observed occasionally. Vertical migration, patchy distributions, and the ‘island effect’ are the principal hypotheses suggested to explain the patterns observed.