Large-scale patterns in marine harpacticoid (Crustacea, Copepoda) diversity and distribution

Abstract

The zoogeographic distributions of 1,747 species of shallow-sea benthic Harpacticoida from 370 genera and 51 families reported in the Northern Hemisphere (Atlantic and Arctic Oceans and the European seas) were analyzed. Faunal diversity analysis revealed that the Northeast Atlantic and the North and Mediterranean Seas contain the richest faunas, while certain Arctic regions and internal seas (Caspian, Azov and Aral Seas) are the poorest ones. The distribution of families and genera was also briefly analyzed. Most families are widely distributed (probably cosmopolitan), though others are restricted to boreo-subtropical or even tropical zones, and no purely Arctic families were discovered. Many more genera are present in (or even restricted to) the tropics/subtropics compared with the Arctic/Subarctic zone. Over 15% of species and 55% of genera can be still considered either widespread or cosmopolitan. Cluster-analysis of the regions by species composition revealed six main clusters: Arctic (central Arctic basin, Kara, Laptev, East Siberian, Chukchi and Beaufort Seas), Boreal (North Atlantic Ocean, and North, Baltic, White and Barents Seas), Mediterranean, Ponto-Caspian (Black, Azov, Caspian and Aral Seas), Central East Atlantic, and Central West Atlantic. The distinction between the Mediterranean and Ponto-Caspian faunas is considered in particular, as the latter is not an exact derivative of the Mediterranean one but instead has more atlanto-boreal features. The percent of regional endemics, mean species occurrence and number of families correlate with total species richness, which primarily reflects the degree of exploration in a given region. After removing this effect, the abovementioned features show significant latitudinal trends, with a few endemics present in polar waters. The distribution patterns of different life-forms also vary according to their dispersal abilities. At both global and regional scales, bentho-pelagic forms are the most widely distributed, followed by phytal species, whereas benthic species, especially interstitial, have a more restricted distribution. Overall, our results confirm and statistically validate the main features of marine harpacticoid biogeography asserted a quarter of a century ago by Abele [In: Abele LG (ed) The biology of crustacea. Academic Press, New York, pp 242–304, 1982] and Wells (Syllogeus 58:126-135, 1986).