Abstract | Introduction | Presentation | Diversity | Main marine currents | The different oceanic zones : Summary of the species - Marine currents and other maps | Cosmopolitanism and endemism |
Species indicative of continental drift | Species whose localization is difficult to explain | Anthropic mechanisms | Conclusion
Anthropic mechanisms :
Three processes are involved in dispersion due to human activity: transport by sea, canal cutting, and aquacultural exchange.
1/ Transport in ships' ballast :
Remy (1927 a , p.177 & fol.) analysed the geographical distribution of Acartia tonsa from its description in the bay of Port-Jackson ( Australia ). He concluded that its localisations, particularly on the European coast, could be due to marine transportation. Transport between Asia and the California-Oregon coast has introduced brackish-water species such as Pseudodiaptomus marinus (Fleminger & Kramer, 1988). Recently Carlton & Geller (1993, p.78), Mauchline (1998, p.505, Table 78) have provided more examples of this. Although difficult to pinpoint in marine planktonic Copepods, the following cases may be cited: Acartia omorii (Hirakawa, 1988: Japan > Chile), Acartia sinjiensis (Ueda & Hiromi, 1987: Japan > Australia), Centropages typicus (McAden et al., 1987: NW Atlantic > N Gulf of Mexico), Centropages abdominalis (Hirakawa, 1986: Japan > Chile), Oithona davisae (Nishida, 1986 a: Japan > California; Hirakawa, 1988: California > Chile) and perhaps Acartia plumosa (Ueda & Hiromi, 1987: Angola-Congo > South Yemen), Paracartia grani is perhaps also an example of this transport mechanism (tropical to temperate East Atlantic Coast > Norway, and > Mediterranean).
Williams et al. (1988) analysed the ballast of ships from Japan arriving in various Australian ports. Six species originating from or present in Japanese waters: Calanus sinicus, Centropages abdominalis, C. yamadei, Labidocera bipinnata (= rotunda ), Pontellopsis tenuicauda, Corycaeus affinis, hitherto unreported in Australian waters, were observed. Fourteen species of less definite origin and other unidentified copepods were also recorded in the ballast. Only Acartia sinjiensis mentioned above succeeded in acclimatising to the river-mouth at Brisbane.
Choi & al. (2005) studied the contents of the ballast water of ships in the San Francisco harbor coming from Asia (mainly from Japan) and other regions. Among the forms observed, 39 species of pelagic copepods are identified, whose majority would not be observed in the San Francisco Estuary. Among those noted in the estuary, some were already normally resident there, the others could not become acclimatized in the new environment or reproduce there because of their low number and their dispersal (apart the few known exceptions). The water ballast can play the role of an incubator for harpacticides, as suggested by the study of Gollasch, Lenz, Dammer & Andres (2000), and thus support the expatriation of the forms having eggs in diapause. The occurrence of Acartia omorii in Dunkirk harbor (France), indeed the first indication from outside the Pacific (Seuront, 2005), shows the importance of these anthropic transports at the present time.
2/ Opening of the Suez Canal :
Following the opening of the Suez Canal (1869), exchanges with the Red Sea were slow in starting (thirty years or so due to ecological conditions). More recently, penetration of species into the eastern Mediterranean (lessepsian migration according to Por, 1969; 1971) was reported by Sewell (1948, p.441) and later by Berdugo (1968), Casanova (1973), Lakkis (1976; 1984; 1990 ). These authors reported: Acartia fossae, Calanopia elliptica, C. media, Euchaeta concinna, ? Labidocera madurae, L. pavo. Conversely, Corycaeus brehmi and Centropages ponticus would appear to have passed from the Mediterranean to the Red Sea .
The forms that indicate this mechanism seem relatively limited (M. L. Furnestin, 1979, p.217) or difficult to pinpoint since 206 species (i.e. 76.2 % of all the species in the Red Sea ) are common to both seas. Sea transport may also have favoured this exchange, particularly for those species that lay long-lasting eggs (diapause).
3/ Indirect introduction :
The development of aquaculture, and in particular the introduction of shellfish may have extended the territory of species such as Paracartia grani described by Sars (1904 b) from animals living in an oyster bed south of Bergen. This species was later reported on the Portugal coast (Candeias, 1932), at Dinard (Franc, 1951), in the Arcachon basin (Lubet, 1953), and later on the African coast by Gaudy & Séguin (1964) at Dakar and as far as Angola by Marques (1958). It was only more recently that it was reported in the Mediterranean by Rodriguez & Vives (1984) in the port of Malaga, by Euzet (1998, pers. comm .) in oyster beds in the Etang de Thau and as far as the Gulf of Saronikos by Siokou-Frangou (1997). Sars, however, (1904 b; 1921) emphasised the temperate-hot character of this genus and regarded the Norway form as a relict of fauna corresponding to a period of ocean warming.
Fleminger & Kramer (1988) considered that Pseudodiaptomus marinus, originating in Asian estuaries, was introduced in this way to a man-made bay (Mission Bay, San Diego).