• The brown tides that led to the demise of the bay scallop industry of southern New England in the 1980s were caused by a protist that was previously unknown and had no genus or species name (Sieburth et al., 1988).
  • Major estuarine fish kills have now been associated with a previously undescribed "phantom" dinoflagellate whose existence and identity were only announced in 1992 (Burkholder et al., 1992).
  • In the open ocean, the prochlorophytes, a group of marine, free-living, bacterial primary producers, were not discovered until the late 1980s—and yet they are now known to account for up to 40 percent of the chlorophyll in some ocean regions (Chisholm et al., 1988; R.J. Olson et al., 1990; S.W. Chisholm, pers. comm., 1994).
  • Species of marine nonphotosynthetic microbes—bacterial taxa now known as Eubacteria and Archaea—are now being discovered at a rapid rate thanks to new molecular genetic techniques and are the basis (along with enhanced awareness of the widespread abundances of marine viruses [Bergh et al., 1989; Proctor and Fuhrman, 1990]) for rapidly evolving concepts of marine microbial diversity and the role of microbes in global geochemical cycles (Box 3).
  • What was once thought to be a single species of algal symbiont in the Caribbean star coral (that is in fact at least three coral species, as discussed later) is now known to be three major groups of symbionts (Rowan and Powers, 1991, 1992) that occur at different depth zones (Rowan and Knowlton, in press). The ecological significance of these findings is currently being investigated, including the possibility that the symbiont species have different propensities for expulsion from the three coral species, which may help to explain the phenomenon of variable coral-bleaching episodes (N. Knowlton, pers. comm., 1994).

There are numerous undescribed species in even the most familiar of ocean environments—ranging from the common harpacticoid copepods and worms of shelf muds to the tiny nematodes and highly colorful sea slugs in tropical lagoons. Table 1 provides a glimpse of the magnitude of underdescribed diversity of marine invertebrates at the level of individual taxa. At the level of entire ecosystems, there are environments such as the deep sea and polar regions that are so undersampled that hundreds of new species are discovered during each expedition to a new area. Indeed, knowledge of the ecology and evolutionary history of the deep sea has been fundamentally altered by the discovery that the diversity of abyssal communities is dramatically higher than previously thought (J.F. Grassle, 1991; J.F. Grassle and Maciolek, 1992).

None of these estimates of underdescribed marine biodiversity takes into account the innumerable and ecologically important benthic and planktonic protists, which alone may comprise at least 34 phyla and 83 classes (Corliss, 1994), nor the vast complexity of the undescribed parasites that live on and in other marine organisms. New views of the true scale of marine biodiversity dictate substantial rethinking of current understanding of the processes that create and

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