Copepoda
Horizontal distribution

Many species are found over a range of depths (Vinogradov, 1968) and the geographical distributions of species with different bathymetric distributions varies. Cosmopolitan distributions are more typical of deep water species (e.g. Gaetanus tenuispinus, Pseudochirella obtusa, Paraeuchaeta barbata, Oncaea englishi, Oncaea mediterranea). Apparently bipolar species also tend to be deep water species (e.g. Aetideopsis minor, Chiridius polaris).

(Fig. Co.5a, Sapphirina nigromaculata)
(Fig. Co.5b, Pontellina platychela)
(Fig. Co.5c, Macrosetella gracilis)
(Fig. Co.5d, Pseuddiaptomus spp.)

Epipelagic copepods are rarely cosmopolitan due to their environment which is strongly influenced by climate and hydrography. However, quite a few epipelagic species have wide distributional ranges (see Co.12 Tables. Morphometric and distributional data for the species treated). For example Acrocalanus species, Mecynocera clausi, Eucalanus hyalinus, Pareucalanus sewelli, most Oithonidae, Sapphirinidae (Fig. Co.5a) and Corycaeidae have a widespread circumglobal tropical-subtropical distribution. It appears that only those species that are able to breed at latitudes that extend to 40ºS have such a widespread distribution. Those species which are endemic to the Atlantic Ocean are more usually epipelagic and have distributions which do not extend very far south, such that the South American and African continents present a barrier to their distribution. Examples of such species are Euchaeta marina, Euchaeta paraconcinna and Pontellina platychela (Fig. Co.5b). The distribution of these species exhibits another feature of low latitude distributions in the South Atlantic. These distributions are not symmetrical north and south of the equator. It appears that the coastal Brazilian Current carries such species further to the south on the eastern border of the South Atlantic.
(See tables in Co.12 Tables. Morphometric and distributional data for the species treated)

In the regions between the shore and neighbouring oceanic waters there are more restricted habitats occupied by coastal species. Coastal regions are highly influenced by the land and are inhabited by species which are variously adapted to the variability contributed by freshwater runoff and coastal upwelling. These species may de defined as coastal (e.g. some species of genera Centropages, Acartia, Paracalanus, Calanus, Temora, Oithona). They are restricted to varying degrees to the coast. Other species are more closely associated with the shore or low salinity water and may be defined as neritic or brackish water species (e.g. all or some species of Pseudodiaptomus, Acartia, Labidocera, Pontella). Whereas other species such as Calanoides carinatus thrive in upwelled water (e.g. Mensah, 1974). The distribution of the mostly estuarine genus Pseudodiaptomus illustrates the degree of local geographic restriction that can be found among such species (Fig. Co.5d). It is amongst some of these coastal species that resting eggs are known to occur which allow them to survive unfavourable conditions (e.g. Uye, 1985).

In addition to the already noted extension of tropical species down the coast of Brazil, other regions where strong currents dominate usually differ from neighbouring areas in that species penetrate with the currents. For example, the presence of Macrosetella gracilis and Oithona rigida in the southeastern Atlantic indicates the Agulhas Current and its retroflection south of South Africa (De Decker, 1984), and also demonstrates an extension of the Indian Ocean distribution of the species (Fig. Co.5c). In the Gulf of Guinea and in the Benguela current Calanoides carinatus and Metridia lucens dominate, whereas the neighbouring tropical Atlantic pelagic community is dominated by Subeucalanus subtenuis and Nannocalanus minor (see Fig. 12 in Heinrich, 1993). The main reason for the temporal changes in species composition and differences in biomass dominance in these tropical communities is the response to upwelling rather than being the result of horizontal advection.

In the polar and subpolar regions in the spring-summer season species diversity is low and the biomass of one to three species in the upper layers may reach 80%, whereas in the tropical oceanic zooplankton diversity is much higher. Calanoid species common in the Atlantic sector of the Antarctic-Subantarctic are: Calanoides acutus, Calanus propinquus, Calanus simillimus, Neocalanus tonsus, Rhincalanus gigas and Metridia gerlachei. Calanoides acutus, Calanus propinquus and Rhincalanus gigas are the main members of the Antarctic copepod community although not completely restricted by the Antarctic Convergence. Neocalanus tonsus plays a dominant role in the subantarctic zone and north of the Subtropical Convergence (Bradford-Grieve and Jillett, in press). All above-listed dominant copepods are epi- to mesopelagic species and are found in the Southern Hemisphere only; Calanoides acutus, Rhincalanus gigas, and Metridia gerlachei are restricted to Antarctic waters, whereas others have Antarctic-subantarctic distributions (see tables Co.12). They survive winter by dispersing to deep depths and vary in the timing of their ascent to the upper water layers. In biological spring Calanoides acutus is most abundant in the upper water layers, whereas at this time Rhincalanus gigas is more abundant in deeper layers. Later Calanus propinquus occupies the upper water layers and is followed by Rhincalanus gigas at slightly deeper depths. In the subantarctic surface waters Neocalanus tonsus dominates in the north and Calanus simillimus in the south. Rhincalanus gigas also dominates in southern subantarctic waters but in the deeper water layers (Voronina, 1984:185).

Although the evidence is not complete, it appears that in the South Atlantic from the equator to 60ºS, the frontal zones of the various water masses have an influence on the distributional patterns of many pelagic oceanic copepods. This pattern is often obscured when a species has a vertical distribution which crosses the vertical boundaries of a water mass.