Reviewed by David Cordie (Edgewood College)
Johnsen, S. 2025. Into the Great Wide Ocean: Life in the Least Known Habitat on Earth. Princeton University Press, Princeton, NJ. 248 pp. ($24.95 cloth with 20% PS discount, $17.47 e-book with 30% PUP30 discount.)
When I think about marine organisms, my mind immediately conjures up images of colorful reefs teeming with hundreds of tiny fish. Asked to think deeper, I probably think of sharks (thanks Discovery Channel), then perhaps the weird creatures of the deep. It would be some time before I come to the subject of Sönke Johnsen’s Into the Great Wide Ocean: Life in the Least Known Habitat on Earth.
As the subtitle suggests, Johnsen is particularly interested in poorly understood regions of our planet. This work specifically focuses on the upper 1,000 feet of the pelagic zone of the ocean (the epipelagic for those in oceanography). No coastal environments, no deep sea, no seafloor: just surface waters far from land. The author’s logic for why the open ocean is far harder to study is reasonable. Coastal environments are easily accessible via scuba, and others at least have a bottom to explore with a camera-and-weight contraption dropped into the abyss. But the open ocean is not so simple. Everything needs to float, but not too much or else you reach the surface. And visitors have no landmarks in the open water. The author describes how studies to date have struggled and often failed to research this part of the world. Plankton nets—the most-used method of study this habitat—are akin to driving a bulldozer through an open-air concert and then trying to determine the ecology of the surviving organisms. (Author’s analogy, not mine.) One can tell a lot about the physical characteristics of an organism, but nothing about its behavior or communal relationships.
The book discusses this ecosystem in eight chapters, each one covering some physical or ecological aspect of the open ocean. Three chapters on gravity, pressure, and light discuss how water affects these three parameters. Each chapter explains how each change with depth and—the more fascinating part in my opinion—provides some examples of how organisms have adapted to these changes. I found the subsequent two chapters on motion and food to be the most fascinating. The reason being that this probably itched the part of my brain that loves to categorize creatures—a penchant for many paleontologists—as these chapters break down several methods of moving or capturing prey. Finally, the last two chapters on family and community were more aspirational of what scientists want to know as opposed to what we already do. The author points out that these aspects of open marine life are particularly difficult—again bulldozer analogy—to study, and in all honesty, may be a long way from being known. It was both refreshing and disheartening to hear a researcher so passionate about a topic admit the gaps in their knowledge.
If I had to highlight a positive about this work, it would be the descriptions of the organisms. I had always considered deep-sea creatures to be the true weirdos of the ocean, but it turns out when trying to balance the never-ending descent into darkening depths while still finding a meal, evolution can cook up some real oddballs. One worth highlighting, primarily because I had never heard of them, are larvaceans. If you have never heard of them before, picture two inflatable inner tubes—one inside of the other—holding a party streamer. I think I found my new screensaver.
One drawback to this work is that I did find myself wanting more detail and clarity on the scientific explanations of the physical parameters. As an instructor of an introductory oceanography class, I was hoping for some insight into how marine ecologists measure, study, quantify, or express physical characteristics of the ocean. Something I could use when teaching my students. In general, I think that those who already have a solid science background will not take away a lot of new information from this work. A counter-example to this is the chapter on pressure, in which the author does explain in some more detail how organisms are affected by pressure changes. But overall, I found myself wanting more.
Into the Great Wide Ocean by Sönke Johnsen was an easy read about a little-understood topic. It did provide me with some new perspective on the field and primed my Google search algorithms with some fascinating new topics. In the words of the author “I thought I knew the ocean,” but there is still much more to discover.