April 18, 2014 4:07:20 PM
Fish are just downright strange. A visit to an aquarium is always fun because fish come in so many different shapes and their fixed expressions are often funny or quizzical. Yet the ones you see in aquariums are not the strangest of ocean dwellers. In The Extreme Life of the Sea (Princeton University Press), Professor of Biology Stephen R. Palumbi and his son, science writer Anthony R. Palumbi, have written about some of the most alien creatures you will ever encounter, and for many of them it is far more pleasant to encounter them on these pages than in real life. Yet as strange as they are, many of them are vital to keeping the oceans in balance, or as indicators of oceans out of balance, and so we ought to know them better. Brightly written, with footnotes but without ponderousness, the Palumbis' book succeeds in inspiring what they say they in their preface that they set out to produce: "a sense of guiltless wonder about how wonderful the ocean's life actually is."
Plenty of such life is so hidden we can't know of it directly. Indeed, the first dramatic episode told here, "the world's biggest predator meets its most fearsome prey," describes in exciting, present-tense terms how a sperm whale hunts and takes down a giant squid. Giant squids are not just overgrown versions of the squids you see in fish markets. They have hooks and saw-like suckers that are used to grab and hold prey, but when the whale attacks, they are used as defensive weapons. They tear long, gaping wounds in the flesh of the whale and one tentacle even knocks out one of the whale's teeth. It might be a mismatched battle, but it is a dramatic battle nonetheless. After reading about the fight, and the outcome, it is a surprise to read that no human has ever seen such a thing: "A sperm whale hunting a giant squid has never been directly observed." We would not know that such things happen without the close observation of seagoing natural historians who have looked carefully at sperm whale bodies, counting and measuring the scars on the sperm whale skin and counting the beaks of squids within the sperm whale stomach. The account of this dramatic encounter "is a picture that has been built up over a century of careful cataloging and serendipitous encounters."
There are plenty of other predation battles described here, and they don't all involve giants. One was a puzzle to Charles Darwin, who with all his other brilliant capabilities, was extremely good at admitting what he did not know. He wrote in 1845 that he knew that microbes abounded in the open ocean, "but on what, in the clear blue water, do these subsist?" He never found out because answers have become clear only in the past fifty years, with astonishing revelations about bacteria, which account for much of the biomass in the ocean. Some of them are eating particles of dissolved carbon, some get minerals out of the seawater, some perform photosynthesis. Any source of carbon, like a fecal pellet from a crab, is swiftly colonized by bacteria. The bacteria themselves are grazed upon by animals like amoebae, and thus their molecules and energy ascend the food chain. Not all bacteria get consumed in this way; viruses, which usually we condemn as a cause of disease, play a huge role in killing off bacteria and returning their organic material to dissolve in the sea. This is the tiniest predator-prey cycle on Earth, and it is astonishingly vital: 30% of the biomass of the ocean cycles in it every day!
The book's first chapter traces the growth of the oceans from their start billions of years ago, the time when they were full only of microbes, and then the poison (poison!) oxygen was loosed by the first microbes to perform photosynthesis. But when oxygen levels became high enough for other types of bacteria to use, oxygen became the start of making higher animals. Some of these "living fossils" are still around, like the horseshoe crab. These aren't really crabs and are closer to spiders. There have been evolutionary changes in them, but the changes have little affected the crabs' appearance, which is almost identical to their forebears whose fossils come from 445 million years ago. Evolution experimented with varying the body form slightly, but those experiments failed and are only fossils, whereas the forms we have now have proved sturdy and practical for eons. Why exactly they should have lasted when, for instance, trilobites should be long gone, is not known, but horseshoe crabs have larvae like the trilobites had, the only vestige of trilobites we have left. Sharks might also qualify as living fossils, but they have had plenty of changes and speciation. Shark teeth, even the fossilized ones, have to be handled with care, because they are among the sharpest things nature makes. 400 million years ago, growing something sharp was a new idea, and the sharks hit on this idea and improved it. The complicated process of growing a cutting edge is described here, and because sharper teeth are such an advantage, sharks grow them in rows, a new set every ten days or so.
Repeatedly the authors describe environmental pressures that drive adaptations. These are most clearly seen at the edge of the sea where there are layers of life. Creatures who live in the intertidal regions but closer to land are at risk for overheating or drying out, but they don't have many animals that will eat them. Creatures who live deeper can count on a more consistent, less threatening environment, but are at risk for dangerous neighbors. There are striations at every shoreline of these extremes, and animals who fit in the striations between them. Barnacles show their striation plainly. Everyone who has seen rocks at any ocean has seen a band of barnacles in between the drying-out high level and the eaten-up lower level. Periwinkle snails live in salt marshes and slide up grasses to retreat from tides, but they do not want to go so high that the birds can pick them off. If, however, a particular parasitic worm called Gynaecotyla infects a snail, it invades the snail's brain so that the snail happily climbs higher, and can get picked off by a bird. The worm has to hijack the snail to be eaten by the bird in this way in order to continue its reproductive cycle.
The book is at its best with that sort of bizarre story from specializations wrought by evolution. Microbes do well by reproducing rapidly and living short lives. Whales and turtles live a long while, but whales take a long time to produce single offspring. Turtles take another tack, producing scads of eggs at one time, eggs that will hatch into helpless babies that will mostly be picked off by birds as they head back to the sea, or by fish once they get there. This is what turtles have done for 200 million years, and it is hard to argue with such success. There is a jellyfish that is essentially immortal. If it is in trouble or stressed, it reverts back to its larval form, and when the stress is gone, it can turn adult again. There was gross oversimplification in the movie Finding Nemo. A real clownfish father who lost a mate would simply turn into Nemo's new mother. Then Nemo would grow into a mature male, and the former father and Nemo would mate incestuously and produce new Nemos. ("In retrospect," reflect the authors, "the producers at Disney probably made the right call.") The hideous-looking anglerfish has a sex life that is as weird as its appearance. For a century, anglerfish were caught and identified, but no one ever found any males. Then someone investigated the fleshy parasites on the females, and found out that's where the males were. The tiny, helpless male has one mission in life, to bite onto a female, and after he does, he dissolves away and his circulatory system fuses into hers, and all that is left is his testes. The female even controls those, chemically signalling when it is time for whatever is left of him to release sperm.
Specialized adaptations come from specialized environments. The examples of extreme life given here show that a successful species inhabits a sea-niche and flourishes. As is necessary in a book like this, the final pages reflect on what humans are doing to the oceans, and the take-away lesson is that it is very easy for us to tamper, deliberately or not, with the specialized environments and ruin them for the specialized links that are essential in the oceanic chains of life. There are examples of treating the ocean well and having it spring back, like making a protected area in the Monterey Bay of California and thereby restoring sea otters who in turn restored a whole ecosystem. We can make the huge oceans thrive for the benefit of all the things that swim in them, and incidentally for our benefit, too. No matter what we do (and we are not very good at changing our ways), there is cause for long term optimism, however ironic: "In a few million years, conditions will improve." That's the way all the ecological catastrophes of the past, like the meteor that took away the dinosaurs, ended up eventually. The oceans are always going to be there. The authors remind us: "Over the long term, the oceans don't need saving. People need saving."