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47. Free-Living Copepoda (Crustacea) of the Gulf of Mexico
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Copepods are a widely distributed and abundant group of microcrustaceans. They show an amazing diversity of forms, adapted to different kinds of environments. The group contains free-living and associated forms, the latter includingcommensalsandparasites.Free-livingcopepods occur mainly in marine and freshwater environments in benthic, littoral, and planktonic habitats, but they are present in terrestrial and semiterrestrial habitats as well (Reid 1986). Copepods are also symbiotic with all major animal groups living in the aquatic environment. They have been considered the most abundant animals on the face of the earth (Humes 1994), mainly because of their overwhelmingabundanceintheoceans ;anestimated1.37×1021 copepods inhabit the pelagic realm as part of the plankton. Taxonomically, copepods represent a subclass of the Crustacea (Huys and Boxshall 1991); the group contains 11 orders, one of which was described recently (Ho et al. 2003). Overall, copepods are arranged into about 200 families and more than 1650 genera (Mauchline 1998). The overall species diversity of copepods has been estimated by several authors; figures are variable, from less than 10,000 species (Kaestner 1970, Bowman and Abele 1982, Brusca and Brusca 1990) to more than 11,000 (Huys and Boxshall 1991, Humes 1994, Boxshall and Halsey 2004).Ifweconsiderthegeneralestimationthatonlyabout 2–15% of the living species of animals is known, the corresponding potential number of copepod species reaches a figure over 75,000 (Humes 1994). Moreover, at a conservative rate of at least 100 species described per year, the last decade(1994–2004)musthaveaddedmorethan1000new species to the Copepoda. In terms of diversity, the parasitic and associated copepods represent an important part of the Copepoda. Two of the 5 major orders of the Copepoda (i.e., Poecilostomatoida, Siphonostomatoida) are mostly parasitic forms and the other 3 (Calanoida, Cyclopoida, Harpacticoida) are primarily free-living but have a share of parasitic or associated forms. The estimated numbers of associated copepods is close to 4300 species (Ho 2001). Species are continuously being described from all over the world, so these figures grow every year. Hence, the task of settling the diversity of copepods in a large, complex system such as the Gulf of Mexico was really challenging. Planktonic Copepoda of the Gulf of Mexico There are very few published accounts dealing with the planktonic copepods in the Gulf before the first half of the 841 47 Free-Living Copepoda (Crustacea) of the Gulf of Mexico Eduardo Suárez-Morales, John W. Fleeger, and Paul A. Montagna Copepoda. After Wilson 1932. 842 ~ Free-Living Copepoda (Crustacea) Polanco 1968, Deevey 1979, Turner et al. 1979, Turner and Collard 1980, Ferrari and Bowman 1980). The knowledge of the Gulf copepod fauna has not been geographically homogeneous; the northern sector is much better known, for surveys on the group started there long before any substantial effort was attempted in the southern part (Suárez-Morales and Gómez-Aguirre 1996). In the southern Gulf, the earliest surveys were those by Aguayo-Saviñón (1965) and Polanco (1968) in Veracruz, Mexico. After a gap of almost 2 decades, studies in this sector were intensified during the 1980s (Campos 1980, 1982, Salas-Marmolejo 1981, Suárez-Morales 1989a, 1989b) and 1990s (Suárez-Morales 1990, 1991a, 1991b, 1997, Suárez-Morales, Gasca, and Sosa 1990, Suárez-Morales and Gasca 1991, Alvarez-Silva 1996, López-Salgado and Suárez-Morales 1996, Escamilla and Suárez-Morales 1999). Campos and Suárez-Morales (1995) published a taxonomic account of 190 species of Copepoda that covered the southern Gulf and part of the western Caribbean. More recently, López-Salgado, Gasca, and Suárez-Morales (2000) recorded 106 species in the central eastern Gulf. General accounts of the literature on the planktonic copepods of the southern Gulf of Mexico were presented by Suárez-Morales and Gasca (1998) and Suárez-Morales (2003). General surveys of the zooplankton of the Gulf that include a section on Copepoda (e.g., Kanaeva 1960, Jromov 1965, 1967, Suárez-Caabro and Gómez-Aguirre 1965, De la Cruz 1966, 1972, Kolesnikov 1966, Kolesnikov and Alfonso 1966, Jromov and González 1967, Fabre 1976, 1985, 1986, Hopkins 1982, Björnberg 1971,Villalobos-Figueroa et al. 1996) were also considered as antecedents to assemble this overview. Published works in adjacent areas such as Florida and the Caribbean (Davis 1950, Bowman 1958, 1971, Owre 1962, Owre and Foyo 1964, 1967, Michel and Foyo 1976, Fleminger and Moore 1977, Fleminger 1979, Rocha 1986, Suárez-Morales 2000) were surveyed to set the distributional range of the planktonic species. Major...