Cubomedusae and Scyphomedusae
Geographic and vertical distribution

Studies on Cubo- and Scyphomedusae in the South Atlantic Ocean mainly directed to distribution pattern and zoogeography are scarce. Kramp (1961) constitutes the most recent available source that included the study area, and Kramp (1970) presented a review on Rhizostomeae of the world with a zoogeographic emphasis. Larson (1986) summarized information for the antarctic seas, including the South Atlantic up to 30ºS, but based mainly on pelagic species, inhabitants of the outer region of the continental shelf and open sea. Pagès et al. (1992) and Mianzan (1986b, 1989) attempted to clarify the state of formal knowledge in the southeastern and southwestern Atlantic Ocean, respectively.

In the present account, data on the distribution of each species are derived from a compilation of all available literature records and personal research data, so some new records are included. [A distribution map for each species is provided in the multimedia field of their records in the Species module]. Some of the species have wide distributional ranges, following the continental shelf in the neritic forms or occupying most of the Atlantic Ocean in the oceanic ones. However, most of the species have seldom been found, so instead of using latitudinal range tables, we prefer to present the information as distribution maps.

Several species reported from the equatorial Northen Hemisphere (Paraphyllina ransoni, Linuche unguiculata and Cephea cephea) are included due to the high probability of finding them in tropical waters of the South Atlantic. However, others reported from locations far north of the Equator and not included in the present account, such as Cassiopea frondosa and Cassiopea xamachana (Caribbean Sea), should be mentioned.

Endemism is rare in Cubo- and Scyphomedusae in the South Atlantic, and many of the species could be considered cosmopolitan. Other areas show strong endemism, as the Indo-West Pacific for the Rhizostomeae (Kramp, 1970). The Atlantic, however, has only a few species recorded exclusively there.

As with other gelatinous forms (e.g. Ctenophora), coastal species from the southwestern Atlantic Ocean fit well with local biogeographic schemes proposed in the literature (Mianzan, 1989a; Mianzan et al., 1988; Ramírez et al., 1990). Warm-water forms, like the Cubomedusae and Rhizostomeae, tend not to penetrate higher latitudes (35º and 39ºS, respectively). However, the Semaeostomeae dominate the fauna in southern latitudes (in particular the families Cyaneidae and Ulmaridae), through the region influenced by the Malvinas (= Falkland) Current (cold waters up to 35°S). The Coronatae, with a few exceptions, are oceanic, so they are not common along the coast. The wide South American continental shelf creates good conditions for the development of populations of coastal species.

Conditions are different in the southeastern Atlantic Ocean. African scyphomedusa surveys include an important number of coronate species — a consequence of the narrow continental shelf of west Africa. The influence of the cold waters of the Benguela stream might explain the presence of some of the semaeostome species observed, even though the low temperatures and constantly fluctuating physical environment nearshore may account for their paucity (Gibbons et al., 1992). The equatorial and oceanic waters generate the necessary environmental stability to allow high diversity. It is also likely that some species from the Indian Ocean pass to the Atlantic, like Tamoya haplonema (see Möller, 1980b; Cornelius, 1997b), advected by the Aghulas current (see "General biological features of the South Atlantic" in this volume).

Abundance and biomass were discussed by Larson (1986). South Atlantic oceanic scyphomedusae, mainly the coronates Periphylla periphylla, Atolla chuni and Atolla wyvillei, seem to increase in numbers of individuals and biomass with increasing latitude from 30ºS to 80ºS. This implies that these species are not randomly distributed, but that they tend to occur in response to factors such as hydrographic conditions and prey distribution.

Vertical distribution of scyphomedusae is not random. It is affected by light, pressure, presence of prey, stage of life cycle and temperature, salinity and oxygen gradients (Larson, 1986; Fearon et al., 1992; Arai, 1997). The Coronatae are well studied and the vertical profiles of total abundance in antarctic and subantarctic waters show that the peaks of their populations are typically between 500 and 1000 m depth (Larson, 1986). Some species are capable of strong vertical displacement. Atolla vanhoeffeni migrates at least 200 m upward (Arai, 1997), and Periphylla periphylla seems to have a diel migration range of at least 500 m (Mianzan, unpublished observations).