General biological features of the South Atlantic
The distribution of biomass

The distribution of biomass in pelagic waters of the South Atlantic seems to be also reflected by that of the numbers of species present, yet this relationship is not straightforward. Indeed, while for most groups diversity in the tropics is several times that at the pole, on these large scales higher numbers of taxa are recorded in the Transition Zone, rather than at the equator (Gb4). Thus, biologically poorest waters host the highest numbers of species. It should be noticed that the estimate reproduced in (Gb4) is partially an artifact of lumping the time-averaged record in a single graph. Insofar as it is the accumulated inventory resulting from sampling the same area throughout several seasons and years, restricted time offsets would most probably lower the Figures indicated, especially for the colder-water areas in general, and for the Transition in particular. Nevertheless, high degrees of mixture of warm- and cold water organisms in the same sample are very common in the Transition, as is evident from the curve for the ostracods (Gb4), derived from data collected during a single cruise. In the eastern South Atlantic further enhancements of specific diversity at transitional latitudes are also derived from the advection of Indian Ocean waters via eddies and rings associated with the Agulhas Current.

From the ecological point of view this Transition is probably quite dissimilar from the domains that bound it from north and south. These organisms are almost exclusively expatriates from the neighboring systems, since very few zooplankters seem to thrive here better that in Subantarctic or Subtropical waters. Thus, they most probably are "terminal" assemblages (sensu Beklemishev, 1969) of organisms circumstantially brought together, with little chances of surviving and reproducing. In consequence, because they do not share an evolutionary history, their interactions are loose, rather than based on mutual adaptation (Boltovskoy, 1986).