Saving the Sea: What We Know and What We Need to Know

A sense of urgency and high drama today pervades the subject of conservation of the world's organic diversity. Most of the attention, however, is being lavished on land and freshwater habitats, especially in the tropics. The many extinctions that humans have already brought about and will undoubtedly continue to cause thanks to the large-scale and rapid destruction of these environments amply justify this urgency. No such atmosphere of crisis surrounds marine conservation despite widely publicized cases of disease and pollution in the sea. One reason for the more relaxed attitude about the sea is that there have been few extinctions among marine species in historic time. Some marine mammals (the Caribbean monk seal and Atlantic gray whale, for example) and flightless marine birds (including the great auk) have disappeared, but their numbers are small compared to the hundreds of larger land vertebrates that humans have exterminated. I know of only one well-documented case of historic extinction among marine invertebrates; this extinction, involving the northwestern Atlantic eelgrass-associated limpet Lottia alveus (J. Carlton, D. Lindberg, G. Vermeij, and E. Dudley, in preparation) may be unique among historic extinctions in apparently not being attributable to human agency. This state of affairs should not, I believe, lead to complacency. In fact, it should encourage us to embark on the kind of careful documentation and conservation planning for which many observers believe time may already have run out for the biotas of the land and freshwater. To survey the field of marine conservation and to chart its future course, the Society for Conservation Biology held a symposium entitled "Conservation Biology in Marine Ecosystems" at Davis, California, on the morning of August 19, 1988. The papers brought together in the present issue of Conservation Biology offer radically different approaches to the scientific study of marine conservation, ranging from experimental ecology to paleobiology. Quinn and his collaborators explore the relationship between habitat size and the short-term fates of intertidal populations of snails. By tracking populations of equal initial density on similar habitats of different sizes separated by inhospitable territory, Quinn et al. found no evidence in favor of the widely held view that habitats of large size are associated with population persistence. Although this is a short-term result from only one set of experiments, it forces us to question the wisdom of always favoring a few large reserves over a larger number of smaller ones in order to halt the disappearance of species. Estes and coworkers report on the complex interactions among the sea otter (a once-endangered top predator) and other members of the shallow-water nearshore biota of the temperate North Pacific. It is clear from their work that most competitive and predatorprey relationships among species in this biota would have been altered permanently and drastically had the sea otter been exterminated globally. Another important result is that communities in which sea otter populations have recovered are not necessarily identical to communities living at times before otters were exploited by humans. The results graphically illustrate the ecological cascade that extinction may engender; but perhaps even more importantly, they show that the ecological and evolutionary environment of surviving species may be altered greatly following the extinction of a species with a role as pivotal as that of the North Pacific sea otter or the extinct grazing Steller's sea cow. Two papers deal with the potential effects of invading species. In his survey of species transported deliberately