Unlike much hard-shelled micro-plankton, radiolarians are distributed to all depths of the oceans, and individual species are variously restricted to horizontal and vertical provinces. Furthermore, these provinces are not static, but become modified geographically and bathymetrically as the water masses and currents responsible for these habitats change. This makes them uncommonly useful for studying oceanographic conditions in both present-day oceans and the preserved sedimentary record. There are by now a large number of sources of data relating to the ecology and distribution of radiolarians. However, these studies are generally of regional scale within individual oceans, and we believe it is timely to summarize this information on a worldwide basis.
We have undertaken a compilation of currently accessible (published and unpublished) data on Radiolaria (Polycystina) distributions from plankton and sediment trap samples, and from surface sediment materials. The database we have assembled covers a total of 307 polycystine taxa (145 spumellarians and 162 nassellarians, plus 18 family and order-level categories), in 6719 samples from the World Ocean (3492 from the Pacific, 2186 from the Atlantic, 696 from the Indian Ocean, and 345 from the Arctic; see
Table 1 and
A deterrent to this scale of synthesis has been disagreement in the taxonomic concepts among authors and the consequent fragmentation of the distributional significance of radiolarian species. Thus, the initial phase of this project was to list the taxa included in the various publications and then identify forms that are the same based on descriptions, illustrations and synonymy lists, rather than on the names under which they were cited (which vary widely between publications). The process we used to achieve this conformity is elaborated in the Methods section. The first stage of results from this project is the production of an atlas of distribution patterns of Recent radiolarians, which is the subject of this report. The basic displays are world maps showing species abundances above and below 150 m and in sediment trap and surface sediment samples. In addition to the maps, we have also plotted latitudinal sections of vertical distributions. Equitability and specific diversity, radiolarian fluxes (sediment traps), assessment of seasonality as a function of latitude (sediment traps), and biogeographic zonations, are also presented.
These displays will allow the reader to view the results of numerous regional studies simultaneously, to reveal the relationships between the radiolarian distributions and worldwide water mass and circulation patterns. Furthermore, comparison of distributions in the water column with those on the sea floor provide insights into the dynamics of settling shells. This information will help users to interpret future changes in distributions as they are affected by climatic and oceanographic changes. And paleontologists will be better able to interpret past climatic and oceanographic conditions. Finally, the maps may point up reports of species far from otherwise restricted local distributions, thus suggesting re-examinations of taxonomic relationships.
It should be stressed that this work is not aimed at solving taxonomic or nomenclature problems, but at illustrating our current knowledge of the geographic distribution of polycystine taxa. Neither does it include all the Recent polycystine species described because the forms covered are restricted to those cited in the 88 sources used. However, the size of this database and its geographic coverage allow assuming that all but the extremely rare Recent forms have been accounted for. Because one of our goals was assessing objectively the overall number of polycystine species, even taxa with only one single record were incorporated in the database (see Appendix 2).
This atlas is a presentation of data, and therefore we have generally refrained from making interpretations of the illustrations, or drawing conclusions from them.