Radiolarian Characteristics of Major Oceanographic Environments: ABSTRACT

Abstract

Plankton samples from major oceanographic environments (mainly DUCA high-speed net tows) and evaluated by radiolarian species and microplankton-group (foraminiferan, pteropod, diatom, copepod, etc) compositions, diversities, and densities have been used to characterize the radiolarian components of these major oceanographic environments. Eastern and western high productivity boundary currents contain high standing crops of polycystine radiolarians, with the eastern boundary current revealing a higher radiolarian standing crop and diversity than the western boundary current region. The eastern boundary current also reveals its greater upwelling by containing more deep water upwelled individuals in the surface water than does the more mesotrophic western boundary current. Open ocean oligotrophic gyres are dominated by colonial radiolarian species and other species containing algal symbionts. Some extremely eutrophic shelf regions exhibit very low diversities and densities of polycystine radiolarians although the general microplankton standing crop is extremely high. Seasonal studies of the south Texas shelf exhibit olig trophic to eutrophic conditions (which can be characterized by the radiolarian fauna) that can be related to the seasonal physical oceanography of the area. The evaluation of detailed vertical samples has suggested radiolarian interactions with other planktonic groups, such as a decrease in radiolarians during the blooming of solitary centric diatoms. Vertical samples also suggest interactions among different groups of radiolarians such as the situation in which polycystine radiolarians may be competitively excluded on either a large (regional) or small (patchy) scale by the presence of ancantharian radiolarians. Several radiolarian characteristics of major oceanographic environments can be and have been used to interpret paleo-oceanographic environments. End_of_Article - Last_Page 688------------