The Secret Life of Lobsters (16 page)

 

Rick Wahle and Bob Steneck pulled on their dry suits and checked their scuba equipment. They were seventy miles south of Mount Desert Rock, and seventy miles due east of the New Hampshire coast. That put them near the middle of the Gulf of Maine, which was much farther from land than any sane lobster scientist should go.

Rick and Bob were preparing to dive on an underwater mountain range called Cashes Ledge. The slopes on either side dropped six hundred feet and, like Mount Desert Rock, the bottom nearby was littered with live artillery shells from military tests. Ten-foot blue sharks infested the waters, and ocean swells blew like gales across the ridge.

On the deck of the research ship Rick took a couple of deep breaths to calm his nerves. He wasn't sure which was worse, sweating his balls off on the surface in his dry suit or thinking about the frigid temperatures he'd hit a hundred feet down. The jagged undersea summit they were planning to land on was called Ammen Rock. Rick checked his tank, pulled down his mask, and said a prayer.

Carrying steel bolts two inches thick, balls of epoxy, and bundles of rope, Rick, Bob, and two dive buddies splashed overboard and swam straight for the bottom. Despite the danger of the dive, Bob had to wonder if getting underwater wouldn't turn out to be safer than staying aboard the ship. The cook, the proverbial drunk, had passed out while baking a turkey and had set fire to the galley—he'd doused the bird with
a fire extinguisher and served it anyway. Then Bob's female research assistant had discovered a member of the ship's crew stealing underwear from her laundry basket.

Rick, however, was already feeling nostalgic for the antics back aboard the ship. Halfway to the bottom, he could feel his face going numb from the cold and a chill seeping into his arms and legs. The divers had undergone intense training and physical exams, and were breathing a carefully monitored gas mixture called nitrox, which extended their total dive time to about half an hour. But their return ascent would have to be slow so their bodies could reacclimatize, and that left only thirteen minutes of working time on the bottom. Any longer and so much compressed gas would have seeped into their blood that returning to the surface would fill their veins with bubbles, a condition called the bends. Worse, if they waited too long and came up too quickly, the gas could blow holes in their lungs. The former would cause a slow death; the latter a more rapid one. Both were extremely painful.

Rick forgot his fear when he saw the fish. The slopes of Ammen Rock were an undersea park of waving kelp and sea anemones, and over them swarmed vast schools of cod. The scientists felt as though they had dived not just into the sea but into the past, and in a sense they had. Cod continued to thrive on Cashes Ledge because the abrupt rise was murder on commercial fishing nets, which snagged on the sharp peaks. Bob and Rick had come to Cashes Ledge for its resemblance to what the bottom of the entire Gulf of Maine must have looked like before the arrival of modern fishermen—an ocean floor teeming with large predators.

In his predation tests near shore, Rick had been surprised at how soon baby lobsters seemed to outgrow their predators. Lobsters that had reached a body length of about two and a half inches were all but immune to attacks by small fish such as sculpins and cunners. But during most of the American lobster's existence in the Gulf of Maine, the bottom had swarmed with huge codfish. With these large predators in the sea, the risk to young lobsters must have been severe. With its schools
of cod, Cashes Ledge gave Rick and Bob the perfect natural laboratory for reconstructing the past. Whether the lobsters they'd brought with them were quite so eager to undergo time travel was another question.

When the divers reached the ridge they went to work molding their balls of epoxy to fit cracks in the rock. Before the glue set, they jammed in a bolt, then tied in a section of rope. Rick and Bob knew that most scuba-diving deaths resulted not from drowning on the bottom but from separation of the diver from the boat. When swells rolled in from the Atlantic and hit the topographical bump of Cashes Ledge, water surged over Ammen Rock at speeds that could drag a person several hundred yards in a few minutes. By installing ropes along the bottom the divers would be within grabbing distance of a handhold while working. A vertical line connected them to the surface so they could raise and lower themselves through the treacherous winds of water, like human flags on a hundred-foot pole.

Soon Rick, Bob, and their assistants had arranged the patio tiles on the bottom. Again, the lobsters were divided into three size classes. But unlike Rick's predation experiments near shore, out here the scientists would be offering up more than just baby lobsters as fish food. The lobsters in the largest category were big enough for a human dinner. Rick and Bob tied the animals to the patio tiles and returned up the rope to the boat.

Twenty-four hours later they dove again. The cod had barely bothered with the babies. Instead, the fish had gone straight for the big lobsters, and they'd obliterated them.

 

The phylum of “jointed-leg” creatures called Arthropoda includes, among other subphyla, the Insecta and the Crustacea. The subphylum of Crustacea is home to fifty-two thousand species of lobsters, crabs, shrimps, crayfish, and their close relatives, but also includes barnacles, sea fleas, pill bugs, and wood lice. The ancestor of the lobster, a shrimplike animal, appears in the fossil record in Ohio and upstate New York as
early as the Devonian period, about 400 million years ago. By the time of the Jurassic period, 150 million years ago, clawed lobsters were so similar to today's specimens that if one could be boiled up and served in a restaurant, few diners would notice the difference.

Beginning in the Jurassic, clawed lobsters experienced a hundred-million-year heyday. In the depths of the Tethys Sea, precursor of the Mediterranean and Caribbean Seas, they diversified into at least fifty-three species and rapidly colonized the world's oceans. The lobsters spread west and north along the shores of northern Europe, past Greenland to the continental shelf off Labrador, on to Nova Scotia, and into the Gulf of Maine.

But the lobsters' foray into shallow water exposed them to new risks. Sixty-five million years ago a cataclysm enveloped the earth, obliterating the kingdom of dinosaurs and exterminating many marine species. The clawed lobsters suffered too, and in shallow water their numbers declined. But mass extinctions were soon the least of their worries.

The clawed lobsters rebounded in shallow water until about thirty million years ago, when the fossil record reveals another drastic loss of clawed-lobster species from the continental shelves. This time, however, the eclipse of the lobsters was the result of a family feud. From the basic lobster body plan a new crustacean had evolved that was faster, smarter, meaner, and far more adaptable to the challenges of shallow-water life. Lobsters had given rise to their own toughest competitor—the crabs.

The lobster's armor and weaponry would seem to make the animal impervious. In the seventeenth century, Hungarian warriors wore a type of headgear called the
rakfarkas sisak
—“crayfish-tailed helmet”—because it had overlapping steel plates that curved down to protect the neck, resembling the tail of a crayfish. Soldiers throughout Europe adopted the helmet. Among English cavalrymen it was known as the lobster-tail burgonet. If these warriors had been up on their evolutionary biology, however, they might have chosen a different name.

Compared with a crab, a lobster was vulnerable, and its tail was its greatest liability.

To a bottom-dwelling fish with strong bony jaws, the meaty lobster tail and its crunchy, calcium-rich shell made the perfect meal. At the approach of one of these ferocious fish—perhaps the precursors of the cod—a crab could bury itself in the sediment in a puff of sand. Although a lobster's powerful tail did give it the ability to escape in backward spurts, the fast-fiber muscle tissues of the tail tired quickly, and for a lobster to bulldoze itself a burrow could take several hours. As a result, while crabs ranged widely, lobsters generally limited themselves to neighborhoods with complex, stone-and boulder-filled bottoms, where a few flips of their tails could help speed them into nearby shelter. While the number of crab species exploded into the hundreds and then thousands, the number of lobster species in shallow water declined. Most of the clawed lobsters still living today—about fifty species—returned to their refuges in the deep. Only twelve species of clawed lobster have managed to survive near shore, and the American lobster is the only one to have achieved much success. Given the damage that the codfish, long the most abundant predator in the Gulf of Maine, can inflict on a lobster, that success is exceptional.

 

Bob Steneck was eight minutes into another dive on Cashes Ledge when he lost sight of his dive buddy. Bob crawled forward but didn't see anyone, so he turned around and swam back through the kelp to his rope handhold. Except he couldn't find it. He pushed on, then came to the edge of the kelp and realized he'd gone too far. He was lost on Ammen Rock in a jungle of seaweed.

Bob had logged more than fifteen hundred dives in his career. He'd endured saturation dives as an aquanaut aboard the undersea equivalent of the international space station, the Hydrolab, where researchers lived for a week at a time. But he'd never been this scared before. Surfacing without a lifeline would leave him exposed to the swells that washed over the
ridge. He could be dragged so far that his ship would never find him, even if he reached the surface. But he also had less than four minutes of bottom time left before he risked death from the bends. Bob decided to stay low in the seaweed and crawl forward, staying alert to his direction and distance. If he didn't find one of the rope tethers, he could retrace his progress and try another direction. If a swell rolled through, he could grab onto the base of a kelp frond and hope it would hold.

On his first pass Bob became disoriented. He tried to double back, but he could easily have been going farther in the same direction. His heart was pounding. The seaweed was so thick it was hard to see his hands in front of him. He checked his timer. Two minutes remained before he had to begin his ascent.

Bob emerged into an abrupt clearing, but it wasn't a place he recognized. In it lay a ship's anchor, by the look of it abandoned more than a century ago, back in the days when cod had been caught with hook and line. Perhaps the crew, like many of the men of Little Cranberry Island, had died in their quest for cod, and perhaps Bob was the first man to see the anchor in a hundred years. It was encrusted in coral, and its graceful flukes curved toward him like arms beckoning. Perhaps Bob too would die on Cashes Ledge, in his own weird quest for cod.

Mankind's pursuit of the codfish has always been deadly, but it has been under way in the Gulf of Maine for much longer than a few hundred years. The first fishermen in Maine didn't catch cod from schooners equipped with iron anchors—they used dugout canoes and hooks carved from deer bone, as early as 3000 BC. Most of the bones in the rubbish heaps, or middens, of ancient Native Americans are from three-and four-foot-long cod. Maine's natives hauled up a respectable catch of the fish for the next five thousand years.

Strangely, the ancient middens contain no lobster shells. The chitin in crustacean armor decomposes more quickly than bone, but the thick ridges of a decent-sized lobster's claw might have been preserved. Thinner clam shells have lasted. The absence of lobsters is striking because early English settlers
found lobsters two and three feet long along the Maine coast and witnessed Native Americans eating them.

What's also striking is that at least some of those English settlers found large codfish hard to come by near shore. In the early 1600s, propaganda aimed at prospective settlers lauded the abundance of large cod in New England, and certainly the fish were plentiful on the offshore banks, where professional fishermen dropped their lines. And yet when settlers had tried to establish a village called Trelawny on the coast of western Maine in 1633, within a decade they were unable to catch enough cod near shore to feed themselves.

On Cashes Ledge, Bob Steneck had seen what a three-foot cod could do to a lobster, and if three-foot cod had been common enough along the coast to be hooked from canoes five thousand years ago, the reason ancient middens didn't contain lobsters might simply be that there hadn't been very many lobsters worth catching—the cod ate them first. Bob guessed that for much of the Gulf of Maine's history, while crabs and other small bottom-dwellers might have flourished, Maine's emblematic crustacean, the lobster, had probably been a marginal resident, struggling to survive the gauntlet of cod mouths. The lucky lobsters that made it through the gauntlet did so because they outgrew their predators.

In those days, the demographic bottleneck that controlled the size of the lobster population might not have been limited to the nurseries. Another bottleneck would have occurred later, when young lobsters became a meaty-enough meal to attract the attention of a sizable cod. The patterns, processes, and mechanisms of lobster ecology would have been different, and the demographic shape of the lobster population unrecognizable. If Bob and Rick could have donned their scuba gear five thousand years ago, what they might have found was some tiny baby lobsters and some huge old lobsters. But lobsters in between, the young adults that today wander freely and supply a vibrant fishery, would have been attacked by cod the instant they were exposed in the open.

By the time European settlers arrived in the middle of the
second millennium, however, cod populations near shore could have been thinned somewhat by thousands of years of Native American fishing. Indeed, recent scholarship suggests that Native American civilizations had a greater impact on the environment than was previously realized. What's more, many scientists believe that beginning around the year 1400 the Northern Hemisphere was chilled by the Little Ice Age, which lasted nearly half a millennium, and could have pushed some of the cod in shallow waters away from the coast, perhaps accounting for the scarcity at Trelawny. If so, more lobsters might have grown to the proportions of invincibility, accounting for the large specimens commonly noted by early explorers. That these monstrous lobsters could be found in shallow water fit with Bob's understanding of how lobsters competed for shelters. Without younger lobsters filling up coastal habitat, the big animals didn't feel pressured to leave for deeper water, as they seemed to today.