Vickerman (1992)

'Biome: Ma, marine; To, terrestrial; Fw, freshwater: ^Lifestyle: PP, primary producers; P. parasitic; F, free-living; C. consumers; D, detritivores. 'Barnes (1989) contributed the number of species described. JThe species estimate for Zoomastigina was from Vickerman (1992) and Rupert and Barnes(1994)

Differences at higher phyletk levels Differences in biodiversity between marine and terrestrial systems are perhaps most pronounced at higher taxonomic levels (Table 16.1; May 1988, 1992; Ray and Grassle 1991; Angel 1993). Over half of the phyletic diversity of animals arc unique to the open ocean, most probably because life has existed there for longer than elsewhere. In contrast, almost all fungal and plant phyla are terrestrial. Overall, there are more marine phyla than terrestrial phyla, and marine phyla are more evenly distributed with respect to extant species richness, a measure of present-day radiation (Figure 16.4). The most successful terrestrial phyla have more species than their marine counterparts; the most successful phyla are those which have adapted well to existence on land and in the water. The functional diversity of marine organisms, reflected in some part by this phyletic diversity, is even more profound. Indeed, the evolution of functional diversity on earth began as life's first prokaryotes attempted to use fundamentally different biochemical pathways in an ocean of primary compounds. Life on earth faced a harsh environment without an atmosphere to stabilize the climatc, and thus a variety of extreme habitats existed. Under such circumstances, there emerged a plethora of respiratory and metabolic pathways, leading to very different ways of living (Fenchel and Finlay 1994; Truper 1992). Many of the original functional groups still exist on earth, but not on land, and so are hidden from human perspective. These organisms dwell in environments extreme to our view, i.e. deep down in the earth's core, geysers, hot thermal vents or anoxic sediments (Bolliger et al. 1991;

Figure 16.4 The rank abundance of species abundance per phyla for all four eukar-yotic kingdoms. The data were drawn from Table 16.1. Phyla were grouped into a single biome if all or almost all (>80% species) occurred in only one biome (see Table 16.1)

Gold 1992). The fact that we frequently overlook these life forms, or that they fail to comply with a narrow species concept distilled chicfly from data on tetrapods, does not diminish their importance to ecosystem processes. These organisms could become even more important in the near future, as hostile environments increase because of anthropogenicaliy caused environmental degradation. The microbial world of both the pelagic and the benthic open are poorly understood, in part because suitable culture techniques have yet to be developed. Recent molecular techniques should increase our knowledge about this group of organisms (Bergh et al. 1989; Giovan-noni et al. 1990; Bolligcr et al. 1991; Fuhrman et al. ยก992, 1993).

Are open-ocean communities cosmopolitan? Ocean basins are the pelagic equivalent of continents: each has a distinctive biota, and the pelagic species are widely distributed within a basin (Angel 1993; McGowan and Walker 1993). This impression is reinforced by the distribution of conspicuous elements such as Physalia the Portuguese man-of-war, across the globe's oceans. The degree of endemism within ocean basins is generally unknown, and sampling is too sparse to rule out its potential importance. Planktonic diversity, especially the smallest plankton, may be an order of magnitude higher than the number of described species would suggest, given the current rate that taxa are being discovered (Waterbury et al. 1979; Li et al. 1983; Piatt and Li 1986; Chrisholm et al. 1988; Fuhrman et al. 1992). The supposedly cosmopolitan nature of the plankton is quite possibly a vaxonomic artifact (a result of inadequate data and lumping), or the pattern may be real, but anthropogenic, as a result of species introductions (Carlton 1989; Carlton and Gelter 1993). Although most deep-sea benthic organisms have planktonic larvae that inhabit the pelagic realm, many benthic organisms have direct development (e.g. species of gastropod) or brood their young (isopods), and are thus capable of extreme regional differentiation. Vinogra-dova (1979a,b) estimated that 85% of deep-sea fauna was endemic to one ocean. Dispersal in time through the production of dormant spores exists as a strategy among some oceanic species. The significance of such a mode of dispersal is unclear.

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