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. Last Updated: 07/27/2016

How Fast Can Worms Grow on the Sea Bottom?




Location, location, location is a rule that applies well beyond real estate. Scientists report that ultra-exotic tube worms living on the sea floor grow with enormous speed, or with glacial slowness, depending on location.


In fact, scientists now believe some tube worms grow so slowly they rank as the longest-living sea invertebrates known, some being 250 years old or more.


Others face a life that is so iffy they must live fast and die young, or risk missing out on reproduction altogether. The hot water vents they depend on for life can disappear in just a few years, so there's no time to lose.


Remarkably, both species belong to the same family. Both kinds grow near places in the sea floor where water comes spewing out. The tube worms are sessile creatures, anchored to the sea floor. Both live on the same chemistry. And both have no mouth, gut or anus of their own; they live by absorbing sulfur compounds metabolized by bacteria.


Despite these similarities, the two types of tube worms also differ significantly. Those living near hot vents grow rapidly, and are capable of extending their length by about 1.5 meters in two years, becoming as much as 2.4 meters long. In contrast, the tube worms sitting in chilly water near sea-floor seeps may not grow at all from one year to the next. On average, cool ones may extend by just a centimeter per year. But they can grow to as much as 2.7 meters long.


In a report on the worms published last week in the journal Nature, biologists Derk Bergquist, Frederick Williams and Charles Fisher at Pennsylvania State University noted the large difference between growth rates in such worms.


"The evolution of a very long life span is particularly intriguing when considered alongside the remarkably rapid growth of vestimentiferens [tube worms] adapted to living around hydrothermal vents," they wrote.


Some of the worms were as much as 3 meters long, and finding them at the vents, which were discovered in 1977, was a major surprise. Not only do they live under extraordinary conditions - deep, dark and hot - but they also live off geothermal energy, rather than photosynthesis driven by light from the sun.


Tiny bacteria living in the worms' tissues consume hydrogen sulfide from the scalding hot water that squirts up through sea-floor fissures, and contribute their own metabolic products to sustain the worm.


In contrast, several cold-water seeps were found a few years later in the Gulf of Mexico. Here, researchers found tube worms that tend to be thinner, but equally tall.


Now, the Penn State team has measured the growth rate of the cold-seep tube worms and has found that they are the seas' champions for lethargic growth.


"At the cold seeps, they can grow as fast as 10 centimeters per year," Bergquist said, or as slowly as zero centimeters per year.


Unlike the very hot vents, he said, "the seep environments might be around for hundreds or thousands of years, so they can afford to hang out and take their time. It's life in the slow lane."