• J.P. Grassle, 1980; J.P. Grassle, pers. comm., 1993). Most of the species differ in some of their life-history characteristics, such as larval development type, brood size, and generation time. Thus, the use of sibling species within this complex as bioassays of environmental degradation hinges on understanding the ecological consequences of their life-history variation.
  • Cryptic sibling species have now been discovered in important commercial species, including the oyster Crassostrea, the shrimp Penaeus, and the stone crab Menippe, with important implications for conservation and management (Knowlton, 1993). Examples exist for both exploited and protected species. Identification of the Spanish mackerel Scomberomorus maculatus as two species that mature at different ages and sizes (Collette et al., 1978) dictates the avoidance of using life history data of the first species for management of the second species. Use of molecular techniques has also suggested that the common dolphin (Delphinus delphis) is actually two species that may have different distributions and abundances (Rosel et al., 1994), and therefore different requirements for protection.

These types of discoveries help to foster an appreciation of the true extent of marine biodiversity, and add a considerable new dimension to estimates of how many species exist in the ocean. It is clear, however, that molecular techniques provide one of the most powerful means for revealing a new understanding of the ocean's complexity (see Box 3).

Habitat and Ecosystem Diversity

Advanced instrumentation and sampling have revealed new species assemblages in novel habitats in the oceans, such as hydrothermal vents (J.F. Grassle, 1986; Tunnicliffe, 1991), whale carcasses (C.R. Smith et al., 1989), wood debris (Turner, 1973, 1981), and sites of hydrothermal, brine, and hydrocarbon seepage (Williams, 1988; Kennicutt et al., 1989; Southward, 1989; MacDonald et al., 1990). As with the discovery of new genomes and new species, it is doubtful that hydrothermal vents or whale skeleton biotas have closed the final chapter on the discovery of novel habitats or ecosystems in the sea. Are there, for example, unique biotas in the abyssal depths of the mid-Atlantic Ocean singularly tied to sinking masses of the pelagic seaweed Sargassum? Moreover, new discoveries are unlikely to be limited to just the vast deep-sea depths. Discovery of novel chemoautotrophic associations, shallow and deep (reviewed in Bennett et al., 1994), is a striking reminder that the biodiversity of the majority of the Earth's surface may be dependent on yet undiscovered and unanticipated habitat diversity. Continually improving capabilities for exploring large regions of the ocean floor and water column (e.g., see Box 12) now set the stage for searching the sea in ways impossible to imagine only a few years ago.

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