Author''s Note In 2001, when the first edition of Creatures of the Deep was published, I wrote that we were embarking on a great century of discovery in the deep ocean. That prediction is on course. In 2007, fishermen off New Zealand hauled to the surface the largest colossal squid ever seen by humans (though still never observed alive in its natural habitat). In 2010, researchers reported on the Census of Marine Life, a decade-long investigation into life in the oceans that described some 6,000 potential new species, mainly in the deep sea. Soon after that announcement, scientists raised the estimated number of oceanic species named and known to science from 220,000 to 240,000, an increase of 20,000 new species that make their homes in the sea. Thanks to an expedition that launched from Japan in June 2012, we were able to watch the first video of a living giant squid in the wild. Also in 2012, after a gap of 50 years, we shared the excitement of the second manned visit to the deepest spot in the ocean--Challenger Deep, at the southern end of the Mariana Trench--undertaken by filmmaker James Cameron. There''s much, much more.

For example, in 2006, on the North Icelandic Shelf near Grimsey Island on the Arctic Circle, researchers from Bangor University in Wales dredged up what they took to be 400-year-old specimens of the clam Arctica islandica . The age of one of the clams was subsequently determined to be 507 years, which was confirmed by carbon dating. The longest-lived noncolonial animal with an accurately determined life span, this clam was named Ming, a tribute to the fact that it had started life during the Chinese Ming Dynasty. While there is no way of knowing just how much longer Ming might have lived had the clam been left on the ocean floor, its discovery does lead us to wonder what secrets to a long and happy life are to be found in the cold waters north of Iceland. Around the deep-sea hydrothermal vents, researchers have discovered the scaly-foot snail--a gastropod with a hard-shell foot adapted to withstand hot conditions--and the furry abominable crab, also known as the Yeti crab. Found in the South Pacific Ocean in 2005, this crab has a fur coat, which seems strangely out of place for a creature living near a site where supercritical water (whose physical properties lie between those of a gas and a liquid) pours out from the hottest parts of the vents at temperatures up to 867 degrees F (464 degrees C). And there is not just one Yeti crab but several and perhaps many; different species appear to live at different hydrothermal vents. Yeti crabs have also been discovered at so-called cold vents, or cold methane seeps, where water transports dissolved elements from the seabed.

Oregon State University''s Andrew Thurber and his colleagues uncovered a notable new Yeti species, Kiwa puravida , during an Alvin submarine cruise off Costa Rica in 2006. A microbe specialist, Thurber studied how the new Yeti rhythmically swings its chelipeds, or claws (which are covered in dense setae and epibiotic bacteria), above the methane seep in what appears to be a form of symbiosis with the bacteria. These Yeti are thought to farm the bacteria, caring for them, nurturing them and perhaps consuming them, much like the ants that stand guard over subdued aphids, feeding from their sugary secretions and, as needed, eating the aphids. Many such "tiny fauna" stories reveal the lives of microbes--the bacteria, archaeans and other mostly single-cell organisms called protists--that live in symbioses with squid, jellyfish and zooplankton, providing a source of food as well as light for communication and more. Microbes are so hardy that they can live inside rocks that lie 1,900 feet (580 m) below the deep seafloor. Most estimates of biological diversity in the sea hover around one million species, but according to some biologists, 10 million species is not out of the question. Clearly, we are still at the beginning of the grand adventure that is the human effort to understand these species and their relationships with one another. But if every species has a story, then an ecosystem is like a multilayered epic novel, one that details the relationships between the novel''s characters.

As a setting, the ocean has the most extensive--and some of the richest--ecosystems on our planet. Ecosystem is one of those fuzzy words, overused and dimly understood. The Oxford Dictionary defines it simply as "a biological community of interacting organisms and their physical environment." For our purposes, this means all life in the sea, as well as the sea itself, including the seamounts and trenches, the midocean ridge and the nutrient matter floating through the deep. The ecosystem is the network of all the above and their interactions. The question is: Where does an ecosystem begin and end? Some conversations confine an ecosystem to a small space about the size of a room, a house or a neighborhood; other discussions consider the ocean ecosystem as one system; some, like scientist James Lovelock, regard Earth and its atmosphere as one ecosystem. What we''re talking about here resides somewhere between these extremes. We might usefully consider an ecosystem from the point of view of an animal, its community of interacting organisms and its physical environment.

In the case of a sea cucumber filtering matter from the ocean floor, this environment may be relatively small. But for a barnacle on a humpback whale that migrates about 5,000 miles (8,000 km) twice a year, it''s clearly extensive. Yet even the sea cucumber inching along the seafloor depends on matter drifting down from a surface that may be seven miles (11 km) away. A killer whale''s ecosystem may extend to prey that swims thousands of miles upriver, such as salmon. Of course, it''s not just a matter of our being intrigued and delighted at the richness of this planet''s ecosystems, although that would be enough. When I set out to write the first edition of this book, I was determined to unravel the stories about true and imagined monsters of the deep sea, even to rehabilitate the image of those monsters, if possible. Over time, the public''s perception of some has, indeed, been transformed for the good, while others are perennially regarded as monsters, with or without justification. These creatures range in size from tiny microbes to giant squid.

Some are conventionally ugly but harmless. Others are beautiful but dangerous. Yet without question, among these "monsters" are potential sources of medicine and examples of life strategies and genetic designs that may inspire future inventions, innovations and artistic creations. At the same time, humans continue to place incredible life-threatening challenges in the path of many ocean species, reducing and even eliminating populations through pollution, hunting, collisions at sea, fishing-gear entanglements, noise, indiscriminate overfishing and, more than anything else, injury and death through unintended catches by commercial fishermen. This so-called bycatch includes an annual tally of an estimated 300,000 whales and dolphins, millions of sharks and untold numbers of turtles, seals and fish. Thus we are in a race both to identify the problems and to solve them, even as we struggle to get a better idea of which species we may be threatening and even losing.