Sea Beast

Sea Beast The Natural History of Earth’s Biggest Monsters Introduction Horrors lurk beneath the surface of the deep, ancient horrors. From the most tranquil, tropical lagoon to the stormy surface of the polar ocean, to the duckweed-covered face of a Louisiana bayou, to the prehistoric seaways that once crisscrossed North America, the Earth has always saved its best horrors for the watery depths. Some of the reasons for this are pure geography, some are history, and some are rooted in physics and community ecology. The geography is easy. On Earth, there is much more aquatic habitat than land area, its surface being more than two-thirds ocean. In addition, much of the continental land masses are covered in lakes, rivers, and wetlands. More area equals more habitat for monsters. As for the community ecology, it is all about energy. Plants require water for photosynthesis, and the interplay between sunlight, nutrients, and water in aquatic habitats, especially the marine sort, makes for long food chains. The mechanics of eating being what they are, body sizes get progressively larger as one climbs the links of a trophic ladder. This, long food chains make for creatures at the top which are huge, and built for killing. Long food chains make for more horror. As for history, the horrors of the ocean are inevitable, considering that life began in the seas, and most of its biodiversity still resides beneath the waves. To the human mind, otherness equals horror. A garden centipede, so utterly harmless to a person that a creeping swarm of millions could do nothing more than cause a person the inconvenience of calling an exterminator, seems horrible by virtue of its very otherness. Crawling over the bathroom ceiling, its arrangement of appendages, and its strange simusoidal motion bring us back to a place where we, the vertebrates, were lower on the food chain, while strange and terrible arthropods dined on our ancestors. Aquatic life forms have an astounding capacity to produce this feeling of otherness, because so many of them originate from branches on the tree of life remote from our own, and have means of locomotion and prey capture so strange as to give us the creeps. A bushier tree of life means more horror. Finally, there is the matter of physics. For a creature to be a true sea beast, it must have the power to drag us beneath the waves. Being large, as creatures go, to drag a human being to its doom is no common feat. Most organisms of the deep are very small compared to us, and though uncanny to our eye, they pose no threat to our well-being whatsoever. Indeed, as the history of life on the planet Earth unfolds, it becomes increasingly obvious that our threat to the Earth’s other denizens will be the undoing of us all. Still, there are a few true giants out there. Being buoyant in water, there is no need for the skeleton of a sea creature to support its weight. On land, this is a major constraint on large organisms, because as body size grows, the stresses on the skeleton of increase exponentially. In water, supported by its own buoyancy, there is no engineering constraint on the size of a sea beast. The only thing stopping a sea creature from growing to the size of a city block, or a mountain for that matter, is energy. Always, it comes back to energy. Sooner later, every monster has to eat. The fear of sea monsters runs deep within us. Our prehuman ancestors no doubt knew that the watering holes of our ancient homelands teemed with Nile crocodiles. The first archaic Homo sapiens to push their skin and stick boat, bravely, and perhaps stupidly, onto the clear surface of an African rift-valley lake, no doubt waited for the moment when a reptilian horror would rise up from beneath the water’s glassy surface and devour them. Perhaps they did not have long to wait. Nile crocodiles, which can grow to as long as 20 feet and will prey upon humans even to this day, must have haunted us. Still greater horrors awaited men at sea. Krakens and sea serpents, easily large enough to pull a ship beneath the waves, prowled the icy oceans, waiting for an opportunity to destroy a vessel and feast upon its crew. That these creatures lived only in the lurid imaginations of sailors is beside the point. Things have always been living down there-strange and alien things. The mighty girth of the ocean gives them room to spread out and grow, feeds them with plankton and herring, till at least some of them grow to gargantuan size. In his 1555 work History of the Northern Peoples, Olaus Magnus describes the sea serpent: Those who sail up along the coast of Norway to trade or to fish, all tell the remarkable story of how a serpent of fearsome size, 200 feet long and 20 feet wide, resides in rifts and caves outside Bergen. On bright summer nights this serpent leaves the caves to eat calves, lambs and pigs, or it fares out to the sea and feeds on sea nettles, crabs and similar marine animals. It has ell-long hair hanging from its neck, sharp black scales and flaming red eyes. It attacks vessels, grabs and swallows people, as it lifts itself up like a column from the water. In his 1781 work, Min son pa galejan (My son on the galley), Jacob Wallejan describes the kraken: Kraken, also called the Crab-fish, which [according to the pilots of Norway] is not that huge, for heads and tails counted, he is no larger than our Öland is wide...Kraken ascends to the surface, and when he is at ten to twelve fathoms, the boats had better move out of his vicinity, as he will shortly thereafter burst up, like a floating island, spurting water from his dreadful nostrils and making ring waves around him, which can reach many miles. Could one doubt that this is the Leviathan of Job? Or do they? In this particular era of the Earth’s history, we do indeed sport hundred foot long killing machines, lurking beneath the waves. Fleet, intelligent, and very large, the rorqual whales stack up nicely against the fictional monsters described above. A fin whale can grow to 80 feet long, a bowhead whale can weigh as much as 75 tons and could easily outrun any ship built before the age of steam. A Blue Whale can top both these figures at perhaps 100 feet long and 160 tons. There are giant sharks out there as well. The whale shark can reach 40 feet long and the basking shark can grow 30 feet long. There is a caveat here, of course. The real leviathans feed not on a few large prey, but millions of small ones. The creatures I just listed are all effectively filter-feeders. They eat crustaceans, and are not dangerous to humans at all, unless you count the dangers inherent in speeding by their tail flukes in a rubber boat as they dive. Of course, the Earth does support one truly gigantic carnivore. Owen Chase, harpooner from the whaling ship Essex, records the following: "I turned around and saw him about one hundred rods (550 yards) directly ahead of us, coming down with twice his ordinary speed (around 24 knots or 44kph), and it appeared with tenfold fury and vengeance in his aspect. The surf flew in all directions about him with the continual violent thrashing of his tail. His head about half out of the water, and in that way he came upon us, and again struck the ship." The sperm whale is an awesome sea beast. Growing to lengths of 85 feet and topping out at 63 tons, they are true monsters of the deep. Our prehuman ancestors no doubt knew that the watering holes of our ancient homelands teemed with Nile crocodiles. Dining almost exclusively on very large squid, they are too ecologically specialized to be a threat to some lone Polynesian in an outrigger canoe. Nonetheless, they are real monsters. Here we have a real rarity; a sea beast that dines on other sea beasts. At this writing, they still exist. I suppose the real question here is this: why don’t we have monsters ten times the size of blue whales, scooping up sperm whales the way a seal hunts herring. Certainly, there is enough space in the ocean for them. A goldfish, even a hundred goldfish, can swim comfortably in a bathtub. The abyssal plain of the Atlantic Ocean is, on the average, two miles deep. Imagine we were to take a bathtub, with eighteen inches of water, and scale up its contents so that it was the depth of the Atlantic. This leaves us with goldfish six hundred feet long. Our monster goldfish could swim comfortably in their scaled-up world. Clearly, the issue is not space. The earth lacks six hundred foot long leviathans not for lack of space, but for lack of energy. Nearly all organisms on the planet are powered by energy emitted from the sun. Ninety three million miles away, this orb of superheated plasma emits 3.8 x 1026 joules of energy per second. A flux of 173 petawatts falls on the surface of the Earth. Much of this is reflected. Only the small fraction that actually falls on the leaves of plants has any chance of powering the biosphere, and green plants use only a fraction of it, absorbing particular wavelengths at 680 and 700 nanometers respectively. Subtract from this the inherent inefficiencies of photosynthesis, and what is left has entered the biosphere. Ecologists call this gross primary productivity (GPP)-the amount of solar energy fixed by green plants and converted to biological energy. Plants use most of this GPP for themselves. Much as our primary school education has given the impression otherwise, plants are not altruists. They are not in the business of fixing solar energy so that animals can feed devour their bodies and steal it. Just like animals, plants respire and require oxygen. Since they are usually in the business of producing oxygen by photosynthesis, however, you never hear much about oxygen-starved plants asphyxiating (though this can happen-root rot is an everyday case of this, because most plants require air spaces in the soil to bring oxygen to their roots). Plants are net producers of oxygen, and the magnificent green citizens of our biosphere produce a net surplus of oxygen. The importance of this is hard to overstate-you are tapping into it as you read this passage. The difference between the amount of energy plants capture from the sun and the amount they use for themselves is called net primary productivity, NPP, and it is what fuels the rest of the biosphere. NPP flows through food webs, going ever upward. At every transfer, a large fraction is lost. Typical energy transfer efficiencies are ten percent or so, often much less. This is because creatures do not just assimilate energy and store it, obligingly waiting to be devoured and meet their destiny. Animals use energy to swim, copulate, dig burrows, and go about the business of living. In fact, they do everything they can to escape being passed up the food chain, by running, fighting, or making themselves as toxic as possible. Upward the transfer goes, however. Copepod crustaceans eat photosynthetic algae, and as some of them are eaten by herring, some of the energy in their tiny bodies becomes herring flesh. Herring flesh becomes seal flesh, but once again, ten percent or less of what made herring go is passed up the food chain. This makes it much easier for a patch of land, or an ocean basin, to support tons of filter feeding copepods, who dine on the green algae at the bottom, than to support a single killer whale. Oceanic food webs actually run more efficiently than terrestrial ones. Marine denizens are usually ectotherms, assimilating to the temperature of the surrounding water and thus saving countless calories. The longest food chains are only about five or six links from bottom to top, however, and at the top, it becomes lonely. Though large in body size, the creatures at the top are spread wide and far across a huge area. Nearly all migrate from abundant food source to abundant food source, because their appetites quickly exhaust whatever prey is available locally. To add another trophic level, perhaps a superpredator that eats adult sperm whales, would require a creature much less common than sperm whales, and a very large creature at that. This hypothetical dreadnaught would move from place to place devouring whales. Though possible, no such creature exists, currently. In the past, such monsters have, in fact, existed. Beasts like this are the first to go when mass extinctions occur. Small in numbers and spread out, often requiring just the right conditions to complete their life cycle, the megamonster is a very special phenomenon. The last beast like this, and perhaps the greatest of all, left us a few million years ago, a victim of the ice ages. What follows is a very personal account of Earth’s superpredators-the conditions that produced them and allowed them to exist, the story of how they were discovered, the details of how they must have functioned, if we know these at all, and finally, the story of their demise.