A biogeographical study of Laurencia and Hypnea species of the Macaronesian region

Abstract

Most of the Macaronesian islands, except the Cape Verde Islands. were included by FELDMANN (1946) in the Lusitano-African region. In more re­cent studies, VAN DEN HOEK (]984) included the Azorean archipelago in the Warm Temperate NE At­lantic region and the Azores flora is also incorporat­ed in the list of benthic marine algae of the North Atlantic Ocean (SOUTH & TITTLEY 1986). PRUD' HOMME VAN REINE (1988) assigned to the Azores an intermediary position between the subtropical Maca­ronesian islands (Madeira, Salvages and Canaries) on the one side and the warm temperate Eurafrican coasts on the other side. On the contrary, the Cape Verdean seaweed flora is characterized as tropical on account of the predominance of alga! species with a tropical distribution (FELDMANN 1946; VAN DEN HoEK 1975, 1984). LAWSON & JOHN (1987), however, on the basis of an ordination (reciprocal averaging) oí a large number of tropical and subtropical seaweed flo­ras around the Atlantic Ocean, concluded that the Cape Verde Islands belong to the Warm Temperate African flora, including also the Canarian, the Mau­ritanian and the Senegalese floras. PRUD'HOMME VAN REINE & V􀀁 DEN HOEK {1988), however, found out a separate and individual position, with a distinct E America imprínt for the Cape Verdean seaweed flora. Thus, additional studies are needed to better under­standing the biogeographícal position of the seaweed floras present in the Macaronesian archipelagos. In the Macaronesian region the assembled sea­weed flora of each archipelago is clearly dominated by members of Rhodophyta (PRUD'HoMME VAN REINE 1988; LEVRING 1974; GIL-RODRÍGUEZ & APONSO­CARIULLO 1980; PRUD'HOMME VAN REINE & VAN DEN HOEK 1988). Among those red algae, the genera Lau­rencia and Hypnea have several species, mainly in in­tertidal and shallow sublittoral habitats. Nevertheless, it is possible to find an latitudinal gradient in the respective florula size and compositíon for each arch­ipelago. This íact provides a sound opportunity to study the biogeographical relationships within the different Macaronesian archipelagos and with sur­rounding areas. The present study is carried out to determine the taxonomical status of several species of these two genera and to further contribute to the biogeographi­cal relationships of the Macaronesian archipelagos seaweed floras.