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| An image of two fish in the family Gonostomatidae: the Elongated bristlemouth, Gonostoma elongatum (top) and Bonapartia pedaliota (bottom). From Oceanic Ichthyology by G. Brown Goode and Tarleton H. Bean, published 1896. (Photo credit: Wikipedia) |
Habitats on land-rain forests, steppes, woodlands, deserts, alpine meadows, all well explored over the centuries-make up less than 1 percent of the planet’s biosphere. Why so little? The band of life is narrow. Fertile soil goes down only about a meter, and even the tallest trees stretch up only about 90 meters.
Water, however, is a different story. It covers more than 70 percent of the earth’s surface and goes down kilometers. Scientists put the ocean’s share of the biosphere at more than 99 percent. Fishermen know its surface waters and explorers its depths. But in general, compared with land, the ocean is unfamiliar.
Which helps explain why scientists have only recently come to realize that the bristlemouth, a fish of the middle depths that glows in the dark and can open its mouth extraordinarily wide, baring needlelike fangs, is the most numerous vertebrate on the earth.
“They’re everywhere,” Bruce H.Robison, a senior marine biologists at the Monterey Bay Aquarium Research Institute in California, said of the bony little fish. “Everybody agrees. It’s the most abundant on the planet.”
By human standards, the brute is tiny, smaller than a finger. But this strange little fish makes up for its diminutive size with staggering numbers, as well as a behavioral trick or two.
It starts life as a male and, in some cases, switches to a female. Scientists call it protandrous, a male-first hermaphrodite.
John C. Avise, the author of “Hermaphroditism, “said the adult male bristlemouth tended to be smaller than the female and had a better developed sense of smell, apparently to find mates in the darkness.
“They occupy an environment that’s hard to access,” Dr. Avise said of the fish, so there is “precious little information” about their behavior.
Though the portrait of the bristlemouth is incomplete, scientists know enough to assert that it far outstrips all other contenders for the title of most common vertebrate on the planet. Ichthyologists put the likely figure for bristlemouths at hundreds of trillions –and perhaps quadrillions, or thousands of trillions.
“No other animal gets close,” said Peter C. Davison, a fish scientist at the Farallon Institute for Advanced Ecosystem Research, in Petaluma, Calif. “There are as much as a dozen per square meter of ocean.”
The bristlemouths are a rapacious family of fishes that include the wildly successful genus Cyclothone-Greek for “circular,” in apparent reference to the creature’s gaping mouth. They are also known as roundmouths.
The genus has 13 species, such as the shadow bristlemouth. The main distinguishing features are subtle differences in the fins and luminous organs. All members wield bristlelike teeth. Over all, the fish are 2.5 to 7.5 centimeters in length, tan to black in color, and at times display a kind of ghostly translucence.
The first hints of the fish’s ubiquity came during the voyage of the H.M.S. Challenger, a British ship that sailed the globe from 1872 to 1876 and helped lay the foundations of oceanography. It lowered nets at dozens of sites and hauled up the creatures from as deep as five kilometers.
The first scientist to view the animals in their dark habitat was William Beebe. In the early 1930s, Mr. Beebe, a senior explorer of what is now the Wildlife Conservation Society, plunged into the depths off Bermuda in a spherical submersible, gazed through its porthole- and saw aliens.
“Numberless little creatures “raced through his light beam, he wrote in his 1934 book, “Half Mile Down.” They turned out to be bristlemouths. A color plate in the book shows a group with jaws wide open while chasing a school of copepods, tiny crustaceans with long antennas.
Oceans textbooks from the 1970s to the 1990s said little about Cyclothones. Then came a new wave of research, centering on careful trawls of the deep ocean with a new generation of nets in which the mesh was much finer. No matter how far the nets plunged, up came vast numbers of bristlemouths.
Dr. Robison said bristlemouths have very small eyes that in the dim habitat seemed to play little or no role in finding prey. Instead, the fish apparently relies on sense organs that can detect movement and vibration in the surrounding water.
And the rows of glowing dots on the bristlemouth’s abdomen? Dr. Robison said they appeared to be camouflage that helped the creature hide from predators by matching the surrounding light.
It has taken roughly a century and a half, but science has finally come to know the bristlemouth fairly well, even if questions remain. Not so other creatures of the deep. If the tortuous route to identifying the dominant fish is any indication, it will take longer still to learn about the uncommon forms of life that roam the depths.
“We keep seeing lots of different critters we haven’t seen before,” Dr. Robison said of voyages in the Monterey Canyon, a deep gorge in California’s coastal seabed, and beyond. He added, “The deeper you go, the stranger things get.”
Taken from TODAY Saturday Edition, The New York Times International Weekly, July 11, 2015
