Patterns of sarcodine feeding in epipelagic oceanic plankton

Abstract

The range of in situ prey composition was determined in marine planktonic acanthana, foraminifera and radiolana collected by divers, and quantitatively compared with the prey available, as determined by surface plankton hauls on cruises in the Florida Current, Gulf Stream and Sargasso Sea. A relatively large percentage of the sarcodines (60% of acantharia, 48% of foraminifera and 46% of radiolana) had no detectable prey Of those which had fed on identifiable prey, there was considerable overlap between sarcodine species m the types of prey captured. Nevertheless, some partitioning of food resources was evident Foraminifera consumed greater numbers of diatoms and copepods than other prey types, radiolana consumed more untinnids and mollusc larvae, and acantharia consumed mostly tintinnids. Copepods and their naupln dominated the biomass consumed for all three groups, though mollusc larvae were significant for both acantharia and radiolana. The results of parameters univariate statistical analyses earned out on each major predator group and multivariate analysis on a species-by-speaes basis confirmed that there was evidence for some partitioning of prey resources among the major sarcodine predators. The partitioning appeared to follow pnmanly morphological rather than taxonomic cnteria, however, and may have been at least partially a mechanical effect. Introduction There are three major groups of planktonic marine sarcodines: the acantharia (class Acantharea), the foraminifera (class Granuloreticulosea, order Foraminiferida) and the radiolana (classes Phaeodarea and Polycystinea). All three groups include organisms which are fascinating and unique in a variety of ways, not the least of which is that most of the members of each group construct some form of skeleton or shell (composed of celestite, calcite and opal respectively). Indeed, the composition, structure and diversity of these skeletons has been one of the major characters studied, and their biomineralization remains one of the main focuses of research on each of these groups of organisms. In general, because of their different skeletal structures, these groups have not lent themselves well to joint studies: the CaCO3 tests of foraminifera dissolve in most preparations for radiolana, the SiO2 skeletons of which are commonly cleaned with acid. For their part, the SrSO4 spines of Acantharia dissolve in most commonly used preservatives, confounding the identification of these species. Additionally, the taxonomy of the radiolaria is notoriously difficult, there being well over a thousand species. As a result, most investigations of sarcodines have been fairly narrowly focused taxonomically, in spite of the fact that the organisms appear to be very similar in terms of their general trophic status and gross morphology. Several studies have investigated the basic trophic biology of representatives of each of the various sarcodine groups, and these studies have indicated an important and complex role for sarcodines in planktonic ecosystems. Some