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Citizens of the Sea: National Geographic Showcase of Marine Wonders

When more than two thousand scientists from countries across the world set out ten years ago to document the species living in the sea, little did anyone imagine the wonders they would find–or how, at the end of decade-long search, we would have a better appreciation of just how much we don’t know about what’s...

When more than two thousand scientists from countries across the world set out ten years ago to document the species living in the sea, little did anyone imagine the wonders they would find–or how, at the end of decade-long search, we would have a better appreciation of just how much we don’t know about what’s in the liquid realm of our oceanic planet.

The Census of Marine Life was well reported by National Geographic News over the ten years, drawing huge audiences to features like: 13 Stunning Photos From 10-Year Sea Census, Pictures: Hard-to-See Sea Creatures Revealed, and Photos: New Species, “Living Fossils” Found in Atlantic.

Now the distinguished marine biologist, Nancy Knowlton, has collected many of the highlights of these and other discoveries of the Census of Marine Life in a new National Geographic book, Citizens of the Sea.

Citizens of the Sea book cover.jpg

The diversity of ocean life is celebrated in a book from National Geographic, Citizens of the Sea: Wondrous Creatures from the Census of Marine Life (National Geographic Books; ISBN: 978-1-4262-0643-6; Sept. 14, 2010; $25; hardcover).

Click image to enlarge photo.


Nancy Knowlton is the Sant Chair for Marine Science at the Smithsonian National Museum of Natural History, in Washington, D.C., and a scientific leader of the Census of Marine Life. She founded the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography of the University of California, San Diego. She is a member of the National Geographic Society’s Committee for Research and Exploration. She has devoted her life to studying, celebrating and striving to protect the life-forms that live in the ocean–the citizens of the sea.

Drawing not only from the Census of Marine Life and other sources, Knowlton has also used her life’s work and knowledge to focus her book on such topics as the homes, movements, mating rituals, social dynamics, feeding habits, defense mechanisms, and predation of sea creatures.


This baby slipper lobster is completely transparent before growing a thick shell. Its bizarre eyes may confuse predators while it floats in the plankton. Click on image to enlarge photo. 

(Peter Parks/, p. 39)

Citizens of the Sea is also a practical and engaging educational tool. In his foreword to the book, National Geographic Ocean Fellow Enric Sala writes, “Drawing on the many discoveries of the Census of Marine Life, Nancy Knowlton’s book explores all the key issues — the diversity of ocean life and why it matters, how ocean creatures make a living, how we are changing life in the ocean, and what we can do to keep the ocean healthy. Nancy’s deep knowledge of the sea and its citizens, gained by thousands of hours studying them underwater, is a gift to the reader.”

But let’s hear from Knowlton…

Interview with Nancy Knowlton by David Braun

Video by David Braun

Why did you write this book?

Well the simple answer is that the Census asked me to synthesize the decade of Census discoveries for a wide audience. But the reason I said yes is that I have been collecting in my head wonderful stories about ocean creatures for as long as I have studied the ocean. So this seemed like a wonderful opportunity to share them in the context of the Census.


Coral reefs are full of hungry creatures, but the coloration of this poisonous sea slug (Phyllidia ocellata) warns predators that it is off the menu. Click on image to enlarge photo.

(Darlyne A. Murawski/, p. 37)

You have been an ocean scientist for more than 35 years, yet you were surprised that in writing this book you learned a lot. What were some of the things you were surprised you didn’t know?

I knew about the broad outlines of ocean diversity, threats to the ocean, wondrous things that ocean organisms can do. But as I explored each topic in preparation for writing, the details really grabbed me. Yes I knew that there were lots of microbes in the ocean, but I didn’t know that for every pound of larger organisms there are five to ten pounds of microbes. Or that seals use their whiskers with as much sensitivity as monkeys use their hands. Or that sooty shearwaters clock about one million miles during their lifetimes flying back and forth between the arctic and the antarctic. The book is filled with literally hundreds of such details, almost all of which were new to me.

What should we ordinary people know about the sea and why?

We depend on the ocean for food, jobs, and medicines, and it brings pleasure to millions of people every year. The ocean is also in serious trouble from overfishing, pollution, and the twin consequences of greenhouse gas emissions – warming and acidification. We still have time to turn things around, but the ocean needs our help now.


“Smiling” for the camera, this colorful ember parrotfish (Scarus rubroviolaceus) shows off its impressive chops, which can easily pulverize coral. Click on image to enlarge photo.

(Paul Sutherland/, p. 148)

The book draws heavily from the Census of Marine Life, a ten-year project involving thousands of scientists to assess and understand what lived, lives, and will live in the oceans. Do we have more of a sense of the scale of what we don’t know about the oceans because of the Census?

I think we now know that the ocean is much more diverse than we realized before. For example, we found that in just six square yards of reef there are more different kinds of crabs than in all the seas of Europe. But the diversity is so high that we still don’t have even a rough estimate of how many marine species there are.

Your colleague, Sylvia Earle, famously says that every teaspoon of seawater brims with life. In your book you state that there are more microbes in the ocean than stars in the universe. How important are the microbes to the ocean ecosystem, and ultimately to us?

They produce every other molecule of oxygen that we breathe, and the entire chemistry of the planet is essentially created by microbes–basically they rule the world!


Fast-growing giant kelps (Macrocystis pyrifera) form cold-water forests that many fish, invertebrates, and mammals call home. Click on image to enlarge photo.

(Phillip Colla/, p. 79)

The book is full of weird and wonderful animals, from diving reptiles to transparent fish. Do you think there are still big discoveries to be made about life in the sea?

We have barely scratched the surface when it comes to ocean exploration. Only two men have been to the deepest ocean trench, making it less visited than the moon! Even on shallow coral reefs, most of the organisms have yet to be studied or named by scientists.

The decline of the health of the oceans is well documented, almost a daily drum beat of doom. But your book points out that some recovery is being achieved and some species are “back in business.” Can you talk a little about the success of conservation and how people can get behind the momentum to make it stronger.

My husband [marine scientist Jeremy Jackson] and I used to be called Drs. Doom and Gloom, and it is true that there is a lot of bad news when it comes to the health of the ocean. But lately we have tried to draw attention to the good news stories that are out there — we have started a program called “Beyond the Obituaries” to celebrate and learn from the successes we have.

There are fisheries that have been restored to health, populations of turtles and whales have come back where they are protected, and some bays and estuaries that are much less polluted than they used to be.

Because of telling these stories, NGS fellow Enric Sala recently reintroduced us as Drs. Hope and Change. There are many opportunities for people to help, both as individuals by making sustainable choices about lifestyle, as well as by supporting organizations that are making a difference.

Related National Geographic video: “Dumbo” Other Deep-Sea Oddities Found 

Fun Facts from Citizens of the Sea

  • The Bob Marley worm (Bobmarleya gadensis) is named for its “dreadlock” tentacles, while the giant clam, Tridacna gigas, is so named from the Greek for something so large that three bites are needed to eat it.
  • Some sea animals have amazing camouflage strategies, like the kelp crab that lives in kelp, looks like kelp and even has a few hooks for attaching kelp to its body; and squid, octopus and cuttlefish that can change their color to match in a new background in a matter of seconds.
  • At 200 tons — twice the weight of the largest dinosaurs — the blue whale is the largest animal ever to live on the planet.
  • The smallest fish is less than one-third of an inch long and weighs a mere 7/100,000th of an ounce.
  • There may be a billion types of bacteria in the ocean. There can be 20,000 different kinds in just a quart of seawater.
  • The claw of a mantis shrimp moves as fast as a .22-caliber bullet.
  • Antarctic icefish have antifreeze in their bodies.
  • Seals use their whiskers to feel objects the way monkeys use their hands.
  • Seaweed products can be found in everything from toothpaste to chocolate milk.
  • Coral reefs are the rain forests of the sea. Up to one-third of all ocean species live on reefs, even though if reefs were squashed together, they would all fit into an area the size of Texas.
  • Cone snails are walking pharmacies, each containing hundreds of potential drugs.
  • Herring mate in schools that can be 25 feet long.

Book Details: Citizens of the Sea: Wondrous Creatures from the Census of Marine Life (National Geographic Books; ISBN: 978-1-4262-0643-6; Sept. 14, 2010; $25; hardcover).

This book review by David Braun draws from publicity materials provided by National Geographic Communications (including a copy of Citizens of the Sea) and interviews with Nancy Knowlton.

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Meet the Author

Author Photo David Max Braun
More than forty years in U.S., UK, and South African media gives David Max Braun global perspective and experience across multiple storytelling platforms. His coverage of science, nature, politics, and technology has been published/broadcast by the BBC, CNN, NPR, AP, UPI, National Geographic, TechWeb, De Telegraaf, Travel World, and Argus South African Newspapers. He has published two books and won several journalism awards. In his 22-year career at National Geographic he was VP and editor in chief of National Geographic Digital Media, and the founding editor of the National Geographic Society blog, hosting a global discussion on issues resonating with the Society's mission and initiatives. He also directed the Society side of the Fulbright-National Geographic Digital Storytelling Fellowship, awarded to Americans seeking the opportunity to spend nine months abroad, engaging local communities and sharing stories from the field with a global audience. A regular expert on National Geographic Expeditions, David also lectures on storytelling for impact. He has 120,000 followers on social media: Facebook  Twitter  LinkedIn