Deep-Sea Gigantism

The domain of nematodes, the ocean’s cold, abyssal reaches also host a surprising selection of formidable “sea monsters.”

On January 23, 1960, Jacques Piccard and Navy Lieutenant Don Walsh, on board the Trieste (a specially engineered bathyscaphe), came to rest at the bottom of Challenger Deep, the deepest part of the Mariana Trench. Challenger Deep is 35,797 feet below the Pacific Ocean’s wave-tossed surface and is the deepest spot in any ocean in the world.

Piccard and Walsh’s descent into this lightless abyss took nearly five hours; they spent only 20 minutes roving about the ooze-covered sea floor, and the vessel’s outer Plexiglas viewing window cracked from the intense pressure (up to 11,000 pounds per square inch). The duo remained crammed into a 7-foot-diameter “pressure sphere,” situated on the bottom of the Trieste, for their 8-hour and 38-minute round trip.

While crushing pressure, a total absence of light and near-freezing water temperatures were to be expected; what was news to scientists were the presence of sole and flounder that Piccard and Walsh viewed as they swam past the Trieste’s viewing portal, thus proving that some higher vertebrates could indeed survive with of a column of sea water 6.78 miles high stacked on top of them. Ever carried a large water-filled bucket while doing a water change? Imagine how heavy a 6-mile-tall bucket of seawater would be.  

Virtually Unexplored
Twelve men have walked on the surface of the moon, or exactly 10 more than have visited the deepest spot in our oceans. In fact, most of the deep-ocean sea floor has never been explored by either manned DSVs (deep submergence vehicles) or unmanned ROVs (remotely operated vehicles).

Neil Armstrong and Buzz Aldrin (Apollo 11), Charles Conrad and Alan Bean (12), Alan Shepard and Edgar Mitchell (14), David Scott and James Irwin (15), John Young and Charles Duke (16), Gene Cernan and Harrison Schmitt (17) represent the 12 men who have walked on the surface of the moon; Piccard and Walsh are the only two humans to have visited the bottom of the Mariana Trench. In fact, we know more about near celestial bodies like asteroids, the moon and Mars than we know about the bathyal (3,300 to 12,999 feet), abyssal (13,000 plus) and hadal (deep-sea trenches, many with endemic species of their own) zones of our own oceans, all of which, incidentally, comprise the largest marine biome.

Deeper and Sometimes Bigger
Dark, cold, aluminum-can crushing pressure and occasional table scraps from higher pelagic zones would seem like the perfect recipe for dwarfism among species found in such an environment. In fact, much of the sea life in the deep ocean is meiofauna by nature, with worms being a major contingent of the life forms found in sea floor ooze. And what isn’t a worm is likely to be a holothurian (i.e., sea cucumber); these make up more than 70 percent of the biomass below 26,000 feet.

Given the extremes, a preponderance of smallish, soft-bodied scavengers makes sense. What doesn’t make sense is the existence at the deepest realms of giant “sci-fi” creatures – the washed-up carcasses of which have lent themselves to legends of “sea monsters.”
Deep-sea gigantism is when some animals become much larger than their shallow-water or terrestrial cousins, bona fide sea monsters.

Scientists postulate as to why some of these animals are the exceptions to the rule at great depths, but no one knows for sure. Perhaps, it is the scarcity of food and the lack of competitors that contribute to the gargantuan sizes of at least some of the animals in deep-sea pelagic zones. These animals are poorly studied at best. Until recently, some such as the giant squid had only been observed as dead or dying specimens washed-up on beaches or brought to the surface by deep-sea fishing nets.

Giant isopod (Bathynomus giganteus). Children are fascinated with pillbugs (aka roly-polys); adults not so much. How do you think you’d react if your workday alarm went off and you tromped downstairs on your way to the kitchen to fix your morning cup-o-Joe, only to find a 20-inch-long, 2-pound “pillbug” attempting to down your Chihuahua Big Louie? Short of plugging it with a .22 or stomping it while clad in hip waders, I’d wrestling away my dog and head for the hills. Well, 1.5-foot versions of 18-millimeter terrestrial roly polys do exist. A distant cousin of terrestrial pillbugs lives at the bottom of the ocean, thousands of feet down, the giant isopod may have even been the inspiration for the rock-and-miner-eating Horta in one of the original “Star Trek” episodes.

One of the primary food sources for B. giganteus is whale carcasses that have sunk to the sea floor. These crustaceans are purported to max out at 30 inches and more than 3.5 pounds, but they are more likely to be in the range of 7.5 to 14 inches. In contrast, most of their shallow-water and terrestrial cousins run about four tenths of an inch to 2 inches in size. Giant isopods are most often found at depths between 2,000 and 2,400 feet, but can be found down to more than 7,000 feet.

These animals have been found at locations around the world and are little changed from 160-million-old fossils. It is theorized that low-light levels in their chosen environment have resulted in a virtual absence of divergent evolution, as specimens from far-flung locations seem to be carbon copies of one another.

Japanese spider crab (Macrocheira kaempferi). This is the largest arthropod in the world, weighing up to 40 pounds and possessing a leg span of more than 12.5 feet. Or 2.5 feet above an NBA regulation basketball rim if their other longest leg remains touching the court.

Some public aquaria have live specimens. A small-scale fishery in Japan has put pressure on near-shore populations, forcing fishermen to go after these majestic arthropods in deeper waters. Adults can often be found at depths of up to 2,000 feet.

Giant squid (Architeuthis dux). The original sea monster and poster animal of the deep – the giant squid is so secretive that a living specimen had never been photographed or filmed as recently as 2003. But this all changed in 2004 when Japanese scientists were the first to photograph a living giant squid in the wild; they captured one on film in 2006.

Giant squids are found at depths exceeding 10,000 feet, but are more often found between 1,000 and 3,800 feet. The species exhibits reverse sexual dimorphism, where the female A. dux is much larger than the male. Giant squids typically do not exceed 42 feet in total length. The longest on record is 59 feet. These animals also have some of the largest eyes in the animal kingdom, with a diameter of almost a foot.

They are amazing swimmers that rely on jet propulsion to get about. A giant squid will take a voluminous amount of water into its mantle and quickly emit a jet of water to propel itself. Their suction cups look like circular serrated saw blades and are used to help grip prey.

The colossal squid (Mesonychoteuthis hamiltoni) is purported to reach longer lengths than A. dux, but this may be more conjecture than fact. And while the colossal squid may or may not be longer than A. dux, it certainly beats out its giant cousin in terms of mantle length and girth as well as overall weight. One trawled 2003 specimen weighed in at more than 1,000 pounds. Colossal squid also possess evil-looking hooks on their tentacles that are used to capture and secure prey.

These giants seem to have a circumpolar oceanic distribution around Antarctica. Specimens have been trawled from depths of more than 7,000 feet.

Oarfish (Regalecus glesne). Another possible candidate for original sea monster is the ribbonlike oarfish; in fact, one of its common monikers is that of ribbonfish. With a maximum length that can exceed 50 feet, R. glesne is the longest bony fish in the world. It has a scaleless silvery blue body with a red dorsal fin extending its full length. 

Giant tube worm (Riftia pachyptila). In 1977, scientists in the DSV Alvin discovered black smokers (hydrothermal vents that look similar to the video of the Deepwater Horizon gusher) off the Galapagos Islands. But what really made the scientific and nonscientific world sit up and take note was the existence of entire deep-sea ecosystems of heretofore unknown animals, including 8-foot-long wine-colored tube worms, living in and around these black smokers at a depth exceeding 6,500 feet. But on what were these tube worms and myriad other creatures surviving?

The answer would surprise scientists the world over, as it was determined that these complex ecological hydrothermal communities were chemosynthetic rather than photosynthetic.

Hydrogen sulfide emitted from the hydrothermal vents is synthesized into organic compounds (carbohydrates) by vent bacteria. Similar to plants in photosynthetic food webs, bacteria form the base of the food web in hydrothermal vent communities and support other higher life forms.

Besides being the primary food producers, other bacteria are food-producing symbionts to other hydrothermal vent animals, with the most famous example being the giant tube worms. Lacking eyes, a mouth and stomach, giant tube worms are fed by the billions of bacteria that live inside them. (Did you know that the typical human has more than 50 species of bacteria – “gut fauna” – living within their digestive tract enabling them to process food?)

Other unusual vent denizens include Pompeii worms, which are among the most heat-tolerant animals on Earth – able to withstand water temperatures of 176 degrees Fahrenheit. They sport a gray fluff on their back, which is actually a species of bacteria they feed on. Vent mussels rely on symbiotic bacteria to convert methane into a never-ending food supply, provided the home vent continues pumping out its life-giving elixir.       

If you want to learn more about the amazing creatures of the deep, check out the fun website and click on the left-hand tab “Deep Sea Creatures” for species profiles.


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