The Silent Deep has been published at a critical time: the deep sea, which covers a vast part of our planet, is being gravely threatened by anthropogenic impacts, ranging from rising temperatures and increasing concentrations of carbon dioxide and pollutants to the effects of trawling the bottom at ever-increasing depths to extract a diminishing supply of fish. Tony Koslow, a deep-sea ecologist, very effectively sounds the alarm, especially about uncontrolled benthic trawling in international waters, an issue that the public is little aware of.
The Silent Deep is an enjoyable, illustrated history of the exploration and scientific investigation of the deep ocean from the 19th century to the present, one that will appeal to lay people as well as to scientists. Koslow spent six years writing this comprehensive treatise, and I applaud his attention to detail. Especially noteworthy is his use of the primary research literature, along with more general treatises and government reports. Moreover, even though Koslow tackles many, sometimes confusing subjects, he makes them coherent for the general public, yet shows scientific caution in the overall synthesis.
Although it is easy to suppose that anthropogenic impacts on deep-sea systems are associated with continental margins, Koslow demonstrates that this is not always true.... [P]ollutants are disseminated on a global scale, and concentrations are amplified through oceanic food webs.
The section on the impact of increasing levels of carbon dioxide on the ocean is particularly well orchestrated. Koslow describes the papers that first discussed the potential problems associated with fossil-fuel consumption and rising carbondioxide levels in the atmosphere, properly crediting Roger Revelle and Hans Suess for emphasizing these issues and the need for long-term monitoring. Although it is easy to suppose that anthropogenic impacts on deep-sea systems are associated with the continental margins, Koslow demonstrates that this is not always true. The atmospheric transport of chlorinated hydrocarbons and trace metals such as mercury is a case in point. These pollutants are disseminated on a global scale, and concentrations are amplified through oceanic food webs. The consequences for deep-sea animals are as yet unstudied, but they may well be far from trivial.
Koslow also gives a good description of the controversy concerning the number of animal species in the deep sea and the number of species that remain undescribed, beginning with the seminal study of Fred Grassle and Nancy Maciolek, who sampled macrofauna in sediments along the New Jersey and Delaware continental margin. These investigators extrapolated the rate of occurrence of new species in successive transect samples (one per kilometer) to the world's oceans below 1000 meters, arriving at a global estimate of 10 million new species in the deep sea. Their paper has been a galvanizing force in establishing initiatives to study biodiversity and document all species in the deep ocean worldwide, although some prominent researchers—Koslow included, he acknowledges—have criticized Grassle and Maciolek's projections as being overestimates.
Unfortunately, Koslow only briefly discusses the technological advances that have led to breakthroughs in our knowledge of the deep sea, such as the bathysphere, the submersible Alvin, the use of finer-mesh sieves, and camera systems for detecting scavenging species around bait. A more thorough presentation might have made it apparent that many discoveries would not have been possible without these and other technological advances. Autonomous instrumentation untethered to a ship, for example, has been used extensively over the past 50 years for both short- and long-term studies in the deep sea.
Koslow does stress, however, the importance of long time-series measurements in the deep sea, and notes that such research is now conducted at only two sites worldwide. The planned installation of cabled observatories in the North Pacific, North Atlantic, and Mediterranean will allow a new approach to long-term monitoring. Many countries and the European Union are financing these installations. An introduction to this frontier of deep-sea observation, which allows real-time data acquisition and control, would have provided the reader with insight into future long-term monitoring of the deep sea.
The only part of the book that I found laborious was chapter 11, which deals with ocean conservation and policy options. Here the author describes the myriad governing bodies involved with deep ocean issues, each of which is introduced, and subsequently discussed, by acronym. The resulting alphabet soup is unappealing. Had fewer agencies been described in detail, this section would have been far more readable, and the take-home message for the reader would have been much clearer.
Koslow's personal notes throughout the book establish his unique credibility in discussing deep-sea biology. His studies of the orange roughy provide good insight into the known natural history of this species and the subsequent decline of its extensive fishery. Koslow makes a concerted effort to relate earlier descriptive chapters to the sections dealing with fisheries management and with the critical international issues yet to be resolved.
Koslow describes the key discoveries in deep-sea biology that have led to our current, and still sketchy, knowledge. Considering how little of the ocean floor has been explored, we should not wonder why the deep ocean is still the most understudied expanse of the earth's surface. The Silent Deep illuminates the deep sea—both its wealth of biological diversity and its vulnerability to anthropogenic assaults—and persuasively argues for protection of this vast portion of the biosphere. I highly recommend this book to anyone interested in the deep ocean.