Marine zooplanktonic diversity: a view from the South Atlantic

Approximately 7000 marine zooplanktonic species have been described so far for the World Ocean; in the South Atlantic the presence of 40% of these has been confirmed, and an additional 20–30% are expected to be recorded in the future. The overall number of described species is very low when compared with other communities, and yet it may not be too far from the final, complete inventory. Very ample geographic distributional ranges, compositional similarity between the major oceanic basins, and declining species description rates suggest that the undescribed fraction of marine zooplankton is nowhere as large as those suggested for the biosphere as a whole. It is anticipated that the highest proportions of new species will be among the groups associated with the sea-floor (meroplanktonic and benthopelagic forms). However, the fact that a high proportion of the marine zooplanktonic species has already been described does not imply that the corresponding taxonomic systems are adequate and that our understanding of this community is better than that of others where undiscovered species are still the overwhelming majority. For most marine zooplanktonic species we have extremely scarce biological and ecological information. Furthermore, the taxonomy of several quite speciose groups is in such a state of disarray that synonyms by far outnumber “good species”.