Pelagic biogeography: background, gaps and trends.

BOLTOVSKOY DEMETRIO

Pelagic Biogeography ICoPB II

UNESCO Press

Lugar: Paris; Año: 1998; p. 53 - 64

Because pelagic biogeography is intimately associated with many widely different fields of marine research, its boundaries as a science are vague and imprecise. The "classical" approach to biogeography, which involves the study of the geographic distribution of taxonomic entities, however, is somewhat better defined, and is chiefly based on identifications and counts. The major oceanic provinces of the World Ocean were more or less adequately defined by about the middle of this century, mostly on the basis of qualitative (presence-absence) distributional data. During the 60's and 70's, counts - in addition to identifications - became widespread. This quantitative information strongly modified some earlier concepts of the structure and dynamics of several marine systems, but changes to the basic biogeographic schemes established by 1950-1960 were generally minor. Although various regional and global studies showed that floral and faunal patterns allow recognition of a larger number of distinct areas than the 9 defined in the earlier studies (4 paired ones in the two hemispheres: Polar, Subpolar, Transitional, and Subtropical; and the Tropical or Equatorial), this basic scheme is still the most widely accepted, which suggests that, for the time being, this is as much biogeographic detail as we can produce at ocean-wide scales without raising significant disagreements. The fact that biogeographic boundaries in the pelagic realm have not experienced major changes in the last 30-40 years is partly due to the soundness of the early divisions established, partly to methodological artifacts, partly to the increasing state of disarray of the systematics of many groups, and partly to the decline in taxonomic and distributional studies (between 1985 and 1993 the share of publications on the geographic distribution of marine organisms dropped about 4-fold). Some of the issues that ought to be addressed in order to further our understanding of pelagic biogeography include: (1) More intensive coverage of some poorly known areas, such as the south Atlantic and south Pacific oceans; (2) Investigation of seasonal and multiannual changes by means of sediment traps and varved sediments. For this purpose a better understanding of the processes which govern coupling between specific makeups in the epipelagic (plankton samples), mid-depths (sediment traps), and the surface sediments (cores) is necessary; (3) Efforts at a more efficient utilization of the information available, which in turn requires the generation of widely accessible and acceptable, standardized, taxonomic and geographic databases.